CN115786850A

CN115786850A - Gradient coating material, preparation method and application thereof

Info

Publication number: CN115786850A
Application number: CN202211602055.0A
Authority: CN
Inventors: 王梦超; 陈辉; 刘艳; 王丽君; 胡登文; 张振林; 吴影
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2022-12-13
Filing date: 2022-12-13
Publication date: 2023-03-14
Anticipated expiration: 2042-12-13
Also published as: CN115786850B

Abstract

The invention discloses a gradient coating material, a preparation method and application thereof, and relates to the technical field of coating materials. The gradient coating material comprises a bonding layer, a middle transition layer and a top wear-resistant layer which are sequentially deposited on a hard alloy substrate, wherein the middle transition layer and the top wear-resistant layer both contain Ti, N and doping elements, the doping elements are silicon or silicon-aluminum mixture, other functional elements can be additionally added for achieving specific functions, and the content of the doping elements in the middle transition layer is gradually increased from the bottom to the top. Amorphous a-Si similar to honeycomb can be formed on the top layer ₃ N ₄ The composite structure wrapped with nano TiN crystal increases the hardness of the coating through fine crystal strengthening, and the softer amorphous a-Si ₃ N ₄ The energy of the crack is absorbed and the direction of the crack is deflected to prolong the propagation of the crack, so that the toughness of the coating is improved. Can realize the preparation of the gradient coating with high wear resistance and strong combination, and can meet the requirements of the on-line milling and the addition of steel railsThe requirements of workers.

Description

Gradient coating material, preparation method and application thereof

Technical Field

The invention relates to the technical field of coating materials, in particular to a gradient coating material, and a preparation method and application thereof.

Background

The steel rail is an important component of rail traffic such as ordinary iron, heavy load, subway, high-speed railway and the like, can provide a continuous and smooth rolling surface for wheels of carrying equipment, and is a foundation for guaranteeing the safe operation of the carrying equipment. The load of the carrying equipment is transferred to the steel rail through the wheels, the steel rail bears huge pressure, and particularly under the running conditions of high speed and heavy load, severe working conditions such as high load, strong impact, strong vibration and the like exist between the wheel rails; the tread of the steel rail is continuously and repeatedly rolled for a long time by the wheel, so that the tread generates diseases such as fatigue cracks, stripping and dropping blocks, crushing deformation, wave abrasion and the like; in a bend, the strong extrusion of wheels and steel rails can cause side grinding, edge fat and other diseases at the position of a gauge angle, the normal matching relationship of the wheels and the rails is changed, the problems of vibration, high noise and the like occur in the running process of high-speed carrying equipment, the abnormal abrasion of the wheels and the steel rails is accelerated, the running quality of a train is greatly reduced, the service life of the steel rails is greatly prolonged, and even the operation safety is endangered.

In order to prevent and cure the rail diseases, prolong the service life of the rail, improve the running quality of the train and overcome the problems of high cost and long construction period caused by rail replacement, the rail needs to be repaired on line. At present, the damaged steel rail is repaired in two ways: one is rail grinding and the other is rail milling. The steel rail grinding depends on a steel rail grinding vehicle, a plurality of grinding wheels are adopted for grinding for multiple times and multiple times, the damage of a superficial layer on the surface is removed, and the profile of the steel rail is repaired; the grinding wagon is only suitable for treating the steel rail with light damage, generates a large amount of dust in the operation process, and is not suitable for tunnel and underground construction. The steel rail milling and grinding depends on a steel rail milling and grinding vehicle, a single-side group or two groups of milling cutter discs (matched with mounted milling cutter blades) are adopted to carry out profile milling on the damaged steel rail, and the damage of 0.3-1.5 mm of the surface layer of the rail surface, 0.3-3.0 mm of the rail side and the largest 5mm of the gauge angle can be removed through one-time milling; the milling and grinding vehicle is suitable for eliminating serious diseases such as rail surface stripping, poor rail profile, rail corrugation and the like, has high operation efficiency, no spark and dust, automatically collects dust of scrap iron, has small influence on the environment, has wide application range and is the development direction of future rail maintenance.

The milling cutter blade is a key part of a steel rail milling and grinding vehicle and is the core for ensuring milling safety, precision and efficiency. The milling cutter blade of the rail milling and grinding vehicle takes hard alloy as a substrate, and a hard coating with the thickness of several microns is deposited on the surface of the substrate so as to increase the wear resistance of the blade and prolong the service life of the blade. At present, a coating used for a steel rail milling, grinding, turning and milling blade is mainly a TiAlN coating with uniform components and a single structure, the aluminum content is low aluminum (the atomic ratio is Ti: al = 7:3) or medium aluminum (the atomic ratio is Ti: al = 5:5), the coating is prepared on a blade substrate based on a Physical Vapor Deposition (PVD) technology, and the whole film layer presents a columnar crystal structure along the thickness direction. The steel rail milling is under the severe working conditions of dynamic movement, strong vibration and the like, the coating with the columnar crystal structure is easy to crack under the action of impact load in the milling process, the crack is promoted to expand and be connected into a net shape in the dynamic milling process, so that the coating is stripped in a blocking manner, and the blade fails prematurely; the steel rail materials widely used on railways in China are U71Mn and U75V, the structure of the steel rail materials contains more pearlite, the dispersity is higher, the steel rail materials have higher hardness, toughness, plasticity and fatigue performance, and under the milling working condition of high-speed, dry and large-feed-amount milling of a milling blade, the plastic deformation of the steel rail materials generates a large amount of heat, so that the temperature of the surface of the cutting edge of the blade is increased, and the oxidation and the abrasion of a coating are aggravated by high temperature. In conclusion, the existing coating has insufficient toughness, poor oxidation resistance and poor wear resistance in the using process, and the main failure modes are the reticular cracking and peeling, the edge chipping and the oxidation wear of the surface of the coating.

The coating used by the milling blade for the rail milling and grinding machine at present is a TiAlN coating system, the oxidation resistance and the wear resistance of the coating are related to the content of Al in the coating, the AlTiN coating with high Al content has higher hardness, and a thin layer of Al is easily generated on the surface of the AlTiN coating at high temperature generated by rail milling ₂ O ₃ ，Al ₂ O ₃ With heat shieldsThe wear-resisting and wear-reducing effects can slow down the wear rate of the coating, protect the blade substrate and have better performance than low-aluminum and medium-aluminum TiAlN coatings. However, on one hand, the TiAlN coating with high Al content has large lattice distortion due to solid solution of Al element, and can generate higher stress and reduce the film-substrate binding force; on the other hand, the film has larger modulus difference with the hard alloy substrate (the elastic modulus of the TiAlN coating is reduced along with the increase of the Al content), and the deformation of the coating and the substrate is inconsistent under the action of load, so that the film-substrate interface is easy to crack, the coating is peeled off, and the blade fails; also, too high Al content causes the coating crystals to change from a Face Centered Cubic (FCC) structure to a Hexagonal (HCP) structure, deteriorating the properties of the coating, so that the maximum Al content in the coating should be strictly controlled.

In order to adapt to the working conditions of strong vibration and high impact in the online milling of the steel rail, the improvement of the toughness of the hard coating and the inhibition of the formation and the expansion of surface cracks are of great importance. The coating for the milling blade is mostly prepared by a PVD (physical vapor deposition) technology, the special technical characteristics of PVD and the layered growth characteristics of a film enable most of the section structure of the coating prepared by the technology to be in a columnar structure, and a columnar grain boundary is a weak part in the coating and can become a channel for rapid propagation of cracks and oxygen atoms. In order to improve the columnar structure of the coating, on one hand, one or more trace elements (such as Al, V, si, Y, zr and the like) can be added into the traditional binary coating (such as TiN, crN) to change the microstructure of the coating through solid solution strengthening, fine crystal strengthening or forming a second phase and strengthen the performance of the coating; on the other hand, a multilayer structure (TiN/TiAlN) can be formed by the alternate deposition of two coatings (such as TiN and TiAlN) with different components, and the continuous growth of columnar crystals is interrupted by a multi-interface structure to improve the sensitivity of the coatings to cracks. However, the former element doping can distort the coating lattice structure and deteriorate the stress state of the coating, and the excessive element doping can cause the imbalance of the film-based modulus matching; the latter multi-interface structure can still keep the continuous growth of columnar crystals due to the template effect when the modulation period is small, and the interface stress accumulation and the interlayer bonding are not firm due to improper material matching between layers.

Therefore, aiming at the current situations of insufficient toughness, poor durability and low adaptability of the existing milling blade coating for online milling of steel rails, the problem to be solved by the technical personnel in the field is how to provide a blade coating for online milling of steel rails, which has high hardness, high toughness, high wear resistance and oxidation resistance, under the condition of ensuring the film-substrate binding force.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a gradient coating material, a preparation method and application thereof, and aims to prepare a gradient coating with high wear resistance and strong bonding, so as to meet the requirement of on-line milling of a steel rail.

The invention is realized by the following steps:

in a first aspect, the present invention provides a gradient coating material, including an adhesion layer, a middle transition layer and a top wear layer deposited on a cemented carbide substrate in sequence, wherein the middle transition layer and the top wear layer both contain Ti, N and doping elements, the doping elements are silicon or a silicon-aluminum mixture, and other functional elements Mo, V, Y, nb, ta, C, etc. may also be additionally added for achieving specific functions (for example, mo, V, C elements may reduce friction coefficients), the content of the doping elements in the middle transition layer gradually increases from bottom to top, and the content of the doping elements in the top wear layer is greater than or equal to the content of the doping elements in the topmost middle transition layer.

In an alternative embodiment, the adhesion layer is selected from at least one of TiN, crN, zrN, and VN; preferably a TiN coating;

preferably, the thickness of the bonding layer is 20 nm-200 nm, the thickness of the middle transition layer is 1 μm-6 μm, and the thickness of the top wear-resistant layer is 1 μm-3 μm;

preferably, the thickness of the bonding layer is 100 nm-200 nm, the thickness of the middle transition layer is 1.5 mu m-4 mu m, and the thickness of the top wear-resistant layer is 1 mu m-2 mu m;

preferably, in the deposition process of the intermediate transition layer, the content of doping elements in the coating is gradually increased, the thickness of a single layer is regulated and controlled through the deposition time of each single layer, and the thickness between layers is controlled to be 5 nm-20 nm;

preferably, the hard alloy substrate is submicron hard alloy with Co content of 8-12% and WC grain size not more than 0.6 μm.

In an optional embodiment, the middle transition layer is a TiSiN coating with gradually increased Si content, and the top wear-resistant layer is a TiSiN coating;

from the bottom to the top of the intermediate transition layer, the atomic percent of Ti is gradually reduced from 45-60% to 30-50%, the atomic percent of Si is gradually increased from 0-5% to 5-20%, and the atomic percent of N is kept at 40-50%;

in the top wear-resistant layer, the atomic percent of Ti is 30-50%, the atomic percent of Si is 5-20%, and the atomic percent of N is 40-50%.

In an optional embodiment, the middle transition layer is a TiAlSiN coating with gradually increased Si and Al contents, and the top wear-resistant layer is a TiAlSiN coating;

from the bottom to the top of the intermediate transition layer, the atomic percent of Ti is gradually reduced from 46-60% to 20-30%, the atomic percent of Al is gradually increased from 0-2% to 10-30%, the atomic percent of Si is gradually increased from 0-2% to 3-10%, and the atomic percent of N is kept at 40-50%;

in the top wear-resistant layer, the atomic percent of Ti is 20-30%, the atomic percent of Al is 10-30%, the atomic percent of Si is 3-10%, and the atomic percent of N is 40-50%.

In an alternative embodiment, a buffer layer is further arranged between the bonding layer and the hard alloy substrate;

preferably, the buffer layer is a Ti metal layer with the thickness of 10-100 nm; more preferably 10 to 20nm.

In a second aspect, the present invention provides a method of making a gradient coating material according to any one of the preceding embodiments, comprising: and depositing an adhesive layer, a middle transition layer and a top wear-resistant layer on the hard alloy substrate in sequence.

In an alternative embodiment, the method of preparation comprises:

depositing an adhesive layer: introducing nitrogen into the furnace chamber, starting the Ti target material, and depositing a bonding layer on the hard alloy substrate;

depositing an intermediate transition layer: continuously introducing nitrogen into the furnace chamber, simultaneously starting the Ti target material and the Ti alloy target material, keeping the current of the Ti target material unchanged, and gradually increasing the current of the Ti alloy target material; then keeping the current of the Ti alloy target unchanged, and gradually reducing the current of the Ti target;

depositing a top wear-resistant layer: continuously introducing nitrogen into the furnace chamber, and starting the Ti alloy target material for deposition;

wherein the Ti alloy target is a TiSi alloy target or a TiAlSi alloy target, and the atomic mass of Si in the TiSi alloy target accounts for 20-25%; in the TiAlSi alloy target material, the atomic mass ratio of Al is 35-45%, and the atomic mass ratio of Si is 5-15%;

preferably, before depositing the bonding layer, the cemented carbide substrate is pretreated to remove the surface oxide film and pollutants, then the cemented carbide substrate is fixed in a furnace chamber to be vacuumized and heated to 400-500 ℃, then inert gas is introduced into the furnace chamber, the substrate is bombarded and etched under the condition of negative bias, and the surface is cleaned.

In an alternative embodiment, the pressure in the furnace is controlled to be 0.5 × 10 during deposition of the adhesive layer ^-2 mbar～1.5×10 ^-2 Setting the current of the Ti target material at 110-130A, and applying 70-90V negative bias voltage;

preferably, the pressure in the furnace is controlled to be 5.0X 10 when the intermediate transition layer is deposited ^-2 mbar～7.0×10 ^-2 mbar, applying negative bias voltage of 50-70V, simultaneously opening the Ti target material and the Ti alloy target material, keeping the current of the Ti target material unchanged at 110-130A, gradually increasing the current of the Ti alloy target material from 80-100A, increasing the step length to 1-3A, and adjusting the time interval to 1-5 min; when the current of the Ti alloy target is increased to be the same as that of the Ti target, keeping the current of the Ti alloy target unchanged, gradually reducing the current of the Ti target, wherein the reduced step length is 1A-3A, and the adjusted time interval is 1 min-5 min until the current of the Ti target is reduced to be consistent with the initial current of the Ti alloy target, and closing the Ti target;

preferably, the pressure in the furnace is controlled to be 5.0X 10 when the top wear-resistant layer is deposited ^-2 mbar～7.0×10 ^-2 And mbar, applying 40-60V negative bias, setting the current of the Ti alloy target material to be 110-130A, setting the deposition time to be 15-25 min, closing the Ti alloy target material, stopping introducing nitrogen and closing the negative bias.

In an alternative embodiment, a Ti metal buffer layer is deposited before the adhesion layer is deposited;

preferably, during the deposition of the Ti metal buffer layer, inert gas is introduced into the furnace chamber, and the gas pressure is maintained at 0.5X 10 ^- ² mbar～1.5×10 ^-2 mbar, starting the Ti target, setting the current of the Ti target to be 110-130A, and applying negative bias of 70-90V on the workpiece rack.

In a third aspect, the present invention provides a use of the gradient coating material according to any one of the preceding embodiments or the gradient coating material prepared by the preparation method according to any one of the preceding embodiments for preparing a blade.

The invention has the following beneficial effects: the bonding layer, the middle transition layer and the top wear-resistant layer are sequentially deposited on the hard alloy substrate, the middle transition layer and the top wear-resistant layer contain Ti, N and doping elements, the content of the doping elements in the middle transition layer is controlled to gradually increase from the bottom to the top by optimizing the types of the doping elements, and the content of the doping elements in the top wear-resistant layer is enabled to be at a higher level. The technical scheme of the invention can form amorphous a-Si similar to honeycomb on the top layer ₃ N ₄ The composite structure wrapped with nano TiN crystal increases the hardness of the coating through fine crystal strengthening, and the softer amorphous a-Si ₃ N ₄ The energy of the crack is absorbed and the direction of the crack is deflected to prolong the propagation of the crack, so that the toughness of the coating is improved. Based on the design principle, the preparation of the gradient coating with high wear resistance and strong combination can be realized, and the requirements of the online milling of the steel rail can be further met.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.

Fig. 1 is a microstructure of mussels;

FIG. 2 is a schematic view of a gradient coating structure;

FIG. 3 shows the coherent interface formed by the adhesion layer and the WC phase of the substrate;

FIG. 4 is a schematic view of a gradient coating preparation apparatus;

FIG. 5 is a scanning electron microscope test chart of the cross section of the coating material prepared in example 1;

FIG. 6 is a transmission electron microscope test chart of the cross section of the coating material prepared in example 1;

FIG. 7 is a graph of the response of a single structure coating to nanoindentation with the gradient structure coating of example 1;

FIG. 8 is a scanning electron microscope test chart of the cross section of the coating material prepared in example 1 after oxidation at 850 ℃ for 1 hour;

FIG. 9 is a scanning electron microscope test chart of the cross section of the coating material prepared in example 2;

FIG. 10 is a nano indentation hardness profile of a gradient TiAlSiN coating tested using a continuous stiffness method;

FIG. 11 shows that the TiAlSiN gradient coating is not peeled off under a 60Kg load indentation;

FIG. 12 is a scanning electron microscope test chart of the cross section of the coating material prepared in example 2 after oxidation at 850 ℃ for 1 h;

FIG. 13 is a scanning electron microscope test chart of the cross section of the coating material prepared in comparative example 1;

FIG. 14 is a nano-indentation hardness profile of a gradient AlTiN coating tested using a continuous stiffness method;

FIG. 15 is a scanning electron microscope test chart of the cross section of the coating material prepared in comparative example 1 after oxidation at 850 ℃ for 1 h;

FIG. 16 is a scanning electron microscope test chart of the cross section of the coating material prepared in comparative example 2;

FIG. 17 is a transmission electron microscope test chart of the cross section of the coating material prepared in comparative example 2.

Icon: 1, mounting a target material; 2-lower target material; 3-upper target axis; 4-lower target axis; 5, installing a target material power supply; 6-lower target power supply; 7-gas draft tube; 8-three-axis rotating the workpiece holder; 9-workpiece holder bias power supply; 10-the revolving schematic direction (first axis) of the workpiece holder; 11-the revolution direction of the workpiece carrier (second axis); 12-workpiece holder rotation direction (third axis); 13-a flow of target particles; 14-a substrate or workpiece; 15-mixed plasma zone; 16-a heater; 17-furnace chamber; 18-vacuum system.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

In nature, mussels have high hardness and toughness, and have good protection and high impact resistance to the internal soft structure. The mussel is a composite gradient material (as shown in figure 1), the outermost layer is a cuticle composed of scleroprotein, the middle layer is a prismatic layer, the innermost layer is a pearl layer, and the tissue structure of the mussel is gradually changed from inside to outside. The inventor creatively uses the bionic structure construction components of the mussels and the coating structure with gradient change of the crystal structure for reference, and achieves the purposes of slowly releasing the stress of the coating, improving the film-substrate binding force, increasing the toughness of the coating and improving the high-temperature oxidation resistance.

As shown in fig. 2, an embodiment of the present invention provides a gradient coating material having a multi-layer structure, which can be divided into three different functional layers, including a bond layer, an intermediate transition layer and a top wear layer, which are sequentially deposited on a cemented carbide substrate. The middle transition layer and the top wear-resistant layer both contain Ti, N and doping elements, the doping elements are silicon or silicon-aluminum mixture, other functional elements such as Mo, V, Y, nb, ta and C can be additionally added for achieving specific functions (for example, the Mo, V and C elements can reduce friction coefficients), the content of the doping elements in the middle transition layer is gradually increased from the bottom to the top, and the content of the doping elements in the top wear-resistant layer is larger than or equal to that in the topmost middle transition layer.

It should be noted that, the content of the doping element (Si or Al — Si) is continuously increased in a gradient manner layer by layer in the intermediate transition layer, so that the lattice distortion caused by element doping in the coating is gradually changed, and the stress of the coating accumulated due to high doping amount in a single-layer structure can be relieved. The elastic modulus and hardness of the coating material are changed in a gradient manner as a result of the gradient change of the components, and the interlayer interface has higher compatibility due to the coordinated deformation and the gradual change of the components, so that the cracking risk of the interlayer interface can be reduced. The top layer structure with high doping elements can provide better performance for the coating, the TiSiN top layer with high Si content provides higher hardness and high-temperature oxidation resistance, and when the doping amount of the Si element reaches a certain degree, the existence form of the Si element can be changed from a solid solution state to form a second phase, particularly amorphous a-Si with the thickness of a few atomic layers ₃ N ₄ The top layer is formed into amorphous a-Si like honeycomb ₃ N ₄ The composite structure wrapped with nano TiN crystal increases the hardness of the coating through fine crystal strengthening, and the softer amorphous a-Si ₃ N ₄ The energy of the crack is absorbed and the direction of the crack is deflected to prolong the propagation of the crack, so that the toughness of the coating is improved.

Specifically, the kind of the cemented carbide substrate is not limited, and may be a conventional cemented carbide. In some embodiments, the hard alloy substrate is a submicron hard alloy with Co content of 8-12% and WC grain size less than or equal to 0.6 μm, and has high strength, toughness and impact resistance. In some embodiments, the cemented carbide substrate may be a cemented carbide insert blank having the same shape as a rail milling and grinding vehicle mating insert, which may be prepared as a rail milling and grinding vehicle mating gradient coated insert.

Specifically, the bonding layer is selected from at least one of TiN, crN, zrN and VN; preferably a TiN coating. The TiN coating has higher elastic modulus, can be matched with a hard alloy substrate with high elastic modulus, can keep the complete structure of a film-substrate interface through synergistic deformation under the action of load, and reduces the cracking tendency of the film-substrate interface; in addition, tiN crystals can form coherent interfaces in specific orientations of WC grains of the cemented carbide substrate (as shown in fig. 3), improving the strength and toughness of the interfaces.

In the deposition process of the intermediate transition layer, the content of the doping elements in the coating is gradually increased, the thickness of a single layer is regulated and controlled according to the deposition time of each single layer, the thickness between the layers is controlled to be 5 nm-20 nm, and the content of the doping elements is increased layer by layer to form a product with gradient change of the doping elements. According to different doping elements, the middle transition layer and the top wear-resistant layer have the following two realization forms:

in some embodiments, the intermediate transition layer is a TiSiN coating with gradually increasing Si content and the top wear layer is a TiSiN coating. To further ensure the performance of the gradient coating material, the inventor optimizes the content of each atom in the middle transition layer to the top wear-resistant layer: from the bottom to the top of the intermediate transition layer, the atomic percent of Ti is gradually reduced from 45-60% to 30-50%, the atomic percent of Si is gradually increased from 0-5% to 5-20%, and the atomic percent of N is kept at 40-50%; in the top wear-resistant layer, the atomic percent of Ti is 30-50%, the atomic percent of Si is 5-20%, and the atomic percent of N is 40-50%.

In another embodiment, the intermediate transition layer is a TiAlSiN coating with gradually increased Si and Al contents, and the top wear-resistant layer is a TiAlSiN coating. To further ensure the performance of the gradient coating material, the inventor optimizes the content of each atom in the middle transition layer to the top wear-resistant layer: from the bottom to the top of the intermediate transition layer, the atomic percent of Ti is gradually reduced from 46-60% to 20-30%, the atomic percent of Al is gradually increased from 0-2% to 10-30%, the atomic percent of Si is gradually increased from 0-2% to 3-10%, and the atomic percent of N is kept at 40-50%; in the top wear-resistant layer, the atomic percent of Ti is 20-30%, the atomic percent of Al is 10-30%, the atomic percent of Si is 3-10%, and the atomic percent of N is 40-50%.

It should be noted that for ease of control, the composition of the elements in the top wear layer may be the same as the composition of the elements at the top of the intermediate transition layer.

The inventor optimizes the thickness of each layer to further improve the comprehensive performance of the material: the thickness of the bonding layer is 20 nm-200 nm, the thickness of the middle transition layer is 1 mu m-6 mu m, and the thickness of the top wear-resistant layer is 1 mu m-3 mu m; preferably, the thickness of the bonding layer is 100 nm-200 nm, the thickness of the middle transition layer is 1.5 μm-4 μm, and the thickness of the top wear-resistant layer is 1 μm-2 μm.

It should be noted that the adhesive layer, the middle transition layer and the top wear-resistant layer can be designed as required, the transition layer starts to be deposited after the deposition of the adhesive layer is finished, the content of doping elements in the coating is gradually increased (realized by changing the current of a corresponding target in actual operation), a layered structure with gradually changed components is formed in a microscopic view, the interface between the layers is difficult to distinguish in morphology observation, and the layers have good compatibility. On top of the intermediate transition layer, the content of doping elements (Si content) in the coating reaches the highest value of the design. The top wear-resistant layer is the layer with the highest content of doped elements, has better mechanical and tribological properties, and effectively relieves accumulated stress due to the design of the bonding layer and the transition layer, thereby ensuring the film-substrate binding force of the coating.

Specifically, the thickness of the adhesive layer may be 20nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, or the like, or any value between the above adjacent values; the thickness of the intermediate transition layer can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm and the like, and can also be any value between the adjacent values; the thickness of the top wear-resistant layer can be 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm and the like, and can also be any value between the adjacent values.

In some embodiments, a buffer layer is further arranged between the bonding layer and the hard alloy substrate, and the stress of the coating can be further relieved through the buffer layer. The buffer layer can be a Ti metal layer with a thickness of 10-100 nm (such as 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc.); more preferably 10 to 20nm.

The embodiment of the invention also provides a preparation method of the gradient coating material, which adopts the multi-arc ion plating technology to sequentially deposit the bonding layer, the middle transition layer and the top wear-resistant layer on the hard alloy substrate and also can deposit the buffer layer before depositing the bonding layer, and specifically comprises the following steps:

s1, pretreatment of a substrate

Through pretreatment, on one hand, an oxide film and pollutants on the surface can be removed, on the other hand, the surface is etched, the surface is microscopically roughened, and the specific surface area of the substrate is increased.

Specifically, the method for removing the surface oxide film and the contaminants is not limited, and the following steps may be adopted: and (3) grinding, polishing or wet blasting and ultrasonic cleaning the hard alloy substrate or the blade with the corresponding combined structure to remove an oxide film and pollutants on the surface, and drying for later use.

In some embodiments, the step of etching the substrate surface comprises: fixing the hard alloy substrate on a workpiece frame in a furnace cavity, and closing a furnace door of the coating equipment; starting mechanical pump and molecular pump step by step to vacuumize the furnace chamber to 3.0 × 10 ^- ⁵ mba～5.0×10 ^-5 mba (e.g. 4.0X 10) ^-5 mbar) or less; turning on the heater to heat the substrate to about 400 deg.C to 500 deg.C (e.g., 450 deg.C); introducing Ar gas into the furnace chamber, and keeping the gas pressure at 0.5X 10 ^-2 mbar～1.5×10 ^-2 mbar (e.g. 1.0X 10) ^-2 mbar), applying a negative bias of 280V to 320V (e.g. 300V) to the workpiece holder, passing Ar ⁺ Bombard and etch the substrate for 20-40min (such as 30 min), further clean the surface, and microscopically roughen the surface to increase the specific surface area of the substrate.

S2, depositing a buffer layer

To further improve the stress state of the coating, a Ti metal buffer layer is deposited prior to the deposition of the adhesion layer.

In practical operation, during the deposition of the Ti metal buffer layer, inert gas (such as argon) is introduced into the furnace chamber, and the pressure is maintained at 0.5 × 10 ^-2 mbar～1.5×10 ^-2 mbar (e.g. 1.0X 10) ^-2 mbar), the Ti target is started, the current of the Ti target is set to be 110A-130A (such as 120A), a negative bias voltage (such as 80V) of 70V-90V is applied on the workpiece holder, and the deposition thickness of the buffer layer refers to the description in the other parts of the specification.

S3, depositing an adhesive layer

Introducing nitrogen into the furnace chamber, starting the Ti target material, and depositing a bonding layer on the hard alloy substrate, wherein the thickness of the bonding layer can refer to the description in other parts of the specification.

In the actual operation process, N is introduced into the furnace chamber when the bonding layer is deposited ₂ Controlling the pressure in the furnace to be 0.5 multiplied by 10 ^-2 mbar～1.5×10 ^-2 mbar (e.g. 1.0X 10) ^-2 mbar), the current of the Ti target is set to be 110A-130A (such as 120V), and 70V-90V negative bias voltage (such as 80V) is applied.

S4, depositing an intermediate transition layer

Continuously introducing nitrogen into the furnace chamber, simultaneously starting the Ti target material and the Ti alloy target material, keeping the current of the Ti target material unchanged, and gradually increasing the current of the Ti alloy target material; and then keeping the current of the Ti alloy target unchanged, and gradually reducing the current of the Ti target. The gradient change of the doping elements is realized by controlling the current of the Ti alloy target and the Ti target.

Specifically, the adopted Ti alloy target is a TiSi alloy target or a TiAlSi alloy target, and the atomic mass of Si in the TiSi alloy target accounts for 20-25%; in the TiAlSi alloy target material, the atomic mass ratio of Al is 35-45%, and the atomic mass ratio of Si is 5-15%. And selecting a proper target material according to the composition of the prepared intermediate transition layer for preparation, wherein the target material can be a TiSi alloy target material and also can be a TiAlSi alloy target material.

In the actual operation process, N is continuously introduced into the furnace chamber when the intermediate transition layer is deposited ₂ Controlling the pressure in the furnace to be 5.0 x 10 ^-2 mbar～7.0×10 ^-2 mbar (e.g. 6.0X 10) ^-2 mbar), applying a negative bias of 50-70V (such as 60V), and simultaneously opening the Ti target material and the Ti alloy target material, wherein the current of the Ti target material is kept unchanged at 110-130A (such as 120A), the current of the Ti alloy target material is gradually increased from 80-100A (such as 90A), the increasing step length is 1A-3A, and the adjusting time interval is 1-5 min; when the current of the Ti alloy target is increased to be the same as that of the Ti target, the current of the Ti alloy target is kept unchanged, the current of the Ti target is gradually reduced, the step length is reduced to be 1A-3A, the time interval is adjusted to be 1 min-5 min until the current of the Ti target is reduced to be the initial current of the Ti alloy targetAnd closing the Ti target material when the current is consistent. Specifically, in the deposition process of the intermediate transition layer, the thickness of a single layer is regulated and controlled through the deposition time of each single layer, the thickness between layers is controlled to be 5 nm-20 nm, and the content of doping elements is increased layer by layer to form a product with the doping elements changing in a gradient manner.

It should be noted that, the current of the Ti alloy target is gradually increased while the current of the Ti target is kept unchanged, so that the concentration of particles (such as Si and Al) generated by the Ti alloy target in the mixed plasma region can be increased, and the Si content in the coating is gradually increased; and the current of the Ti alloy target is kept unchanged, the current of the Ti target is gradually reduced, the concentration of Ti particles generated by the Ti target in a mixed plasma region can be reduced, and the content of the doping element in the coating is gradually increased, so that the gradient change of the content of the doping element is realized.

S5, depositing a top wear-resistant layer

And continuously introducing nitrogen into the furnace chamber, starting the Ti alloy target material for deposition, wherein the used Ti alloy target material can be the same as S4.

In the actual operation process, N is continuously introduced into the furnace chamber ₂ Controlling the pressure in the furnace to be 5.0 x 10 ^-2 mbar～7.0×10 ^-2 mbar (e.g. 6.0X 10) ^-2 mbar), applying a negative bias voltage of 40-60V (such as 50V), setting the current of the Ti alloy target material to be 110-130A (such as 120A), setting the deposition time to be 15-25 min (such as 20 min), closing the Ti alloy target material, stopping introducing nitrogen and closing the negative bias voltage.

It is necessary to supplement that after the deposition is finished, N is charged into the furnace chamber after the furnace chamber is cooled to below 100 DEG C ₂ And (4) opening the furnace door to atmospheric pressure, and taking out the substrate sample to obtain a product of the gradient coating material.

The gradient coating material provided by the embodiment of the invention can be expanded and applied to processing blades of other key parts in the high-speed rail field, such as processing blades of wheels, axles, bogies and the like of high-speed trains.

In order to better realize the preparation of the gradient coating, the embodiment of the invention also provides a device for preparing the gradient coating, as shown in fig. 4. The device comprises a furnace chamber 17, an upper target 1, a lower target 2, an upper target power supply 5, a lower target power supply 6, a gas guide pipe 7, a three-axis rotating work rest 8, a work rest bias power supply 9, a heater 16 and a vacuum system 18.

Specifically, the upper target 1 and the lower target 2 are obliquely installed in a furnace chamber 17, the upper target 1 and the lower target 2 are powered by an upper target power supply 5 and a lower target power supply 6 respectively, air (such as nitrogen) is introduced into the furnace chamber 17 through a gas flow guide pipe 7, the furnace chamber 17 is heated by a heater 16, and the furnace chamber 17 is vacuumized by a vacuum system 18. When the three-shaft rotating workpiece holder 8 works, a substrate or a workpiece 14 is arranged on the three-shaft rotating workpiece holder 8, a workpiece holder bias power supply 9 is used for providing bias voltage, the three-shaft rotating workpiece holder 8 has a three-shaft rotating mode, namely a workpiece holder revolution indicating direction (a first shaft) 10, a workpiece holder revolution indicating direction (a second shaft) 11 and a workpiece holder rotation indicating direction (a third shaft) 12, and the optional mounting of the workpiece holder can also generate a physical stirring effect on a mixed plasma region of a target material; the target particle flow 13 generated by the upper target 1 and the lower target 2 is deposited on a substrate or a workpiece.

The upper target 1 and the lower target 2 are two targets distributed in different height directions of the furnace chamber wall, and in order to better realize the preparation of the gradient coating, the installation height of the hard alloy substrate should be in the middle height of the two targets, so that the matrix can be positioned in a mixed plasma zone 15 formed by two target particles. In order to make the mixed plasma region 15 of the two targets more uniform, the two targets should be arranged obliquely so that the axes of the two targets (i.e., the upper target axis 3 and the lower target axis 4) intersect within the radius of rotation of the substrate revolution.

In some embodiments, multiple rows of targets may be provided around the circumference of the chamber wall of the apparatus in order to enrich the functionality and increase the deposition rate of the coating, and the multiple rows of targets may be independently or cooperatively controlled during the coating process.

In addition, the gradient coating can be directly realized on the traditional equipment or realized after slightly modifying the traditional equipment, and the popularization and application cost is low.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The embodiment provides a preparation method of a gradient coating material, which comprises a TiN bonding layer, a TiSiN intermediate transition layer and a TiSiN top wear-resistant layer, wherein the content of Si in the TiSiN intermediate transition layer is gradually increased along the thickness direction of a coating. The preparation process comprises the following steps:

(1) Pretreatment of substrates

Grinding, polishing or wet sand blasting and ultrasonic cleaning a hard alloy matrix with the Co content of 12%, the WC content of 87%, the TaC content of 1% and the average transversal grain size of 500nm to remove an oxide film and pollutants on the surface, and drying for later use; fixing the hard alloy on a workpiece frame, and closing a furnace door of the coating equipment; starting mechanical pump and molecular pump step by step to vacuumize the furnace chamber to 4.0 × 10 ^-5 Background vacuum degree below mbar; turning on a heater to heat the substrate to about 450 ℃; introducing Ar gas into the furnace chamber, and maintaining the gas pressure at 1.0 × 10 ^-2 mbar, applying a negative bias of 300V on the workpiece holder, passing Ar ⁺ Bombarding and etching the substrate for 30min.

(2) Depositing an adhesion layer

Introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 1.0X 10 ^-2 And mbar, starting the Ti target material, setting the current of the Ti target material to be 120A, applying 80V negative bias on the workpiece frame, depositing a TiN bonding layer, wherein the thickness of the bonding layer is 150nm, and the atomic ratio of Ti atoms to N atoms is close to 1:1, the crystal structure is a single-phase FCC structure.

(3) Depositing an intermediate transition layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 And mbar, applying a negative bias of 60V on the workpiece holder, simultaneously opening the Ti target and the TiSi alloy target (the atomic ratio of the TiSi alloy target is Ti: si =75 25), keeping the current of the Ti target at 120A, setting the current of the TiSi alloy target to be 90A and gradually increasing, wherein the increasing step size is 2A, and the adjusting time interval is 3min. When the current of the TiSi alloy target material is increased to 120A, the current of the TiSi alloy target material is kept unchanged, the current of the Ti target material is gradually reduced, the step length is reduced to 2A, the time interval is adjusted to be 3min, and the Ti target material is closed until the current of the Ti target material is reduced to 90A.

The TiSiN intermediate transition layer has Si content gradually increasing along the thickness direction of the coating layer, and the thickness of the intermediate transition layer is 3 μm.

(4) Depositing a top wear layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 mbar, applying 50V negative bias on the workpiece holder, maintaining the current of TiSi alloy target at 120A, depositing for 20min (top wear layer thickness is 1 μm), closing TiSi alloy target, and stopping introducing N into the furnace chamber ₂ And turning off the negative bias power supply on the workpiece frame. The top wear layer has 10 atomic percent of Si, 44 atomic percent of Ti and 46 atomic percent of N.

After the furnace chamber is cooled to below 100 deg.C, N is charged into the furnace chamber ₂ To atmospheric pressure, the oven door was opened and the substrate sample was removed.

Referring to fig. 5, in this embodiment, the content gradient of Si is increased by the coordination of the Ti target and the current of the TiSi alloy target which gradually changes in the process of depositing the intermediate transition layer, the atomic percentage of Ti in the coating is gradually decreased from 50% to 40% along the thickness direction of the coating, the atomic percentage of Si is gradually increased from 0% to 10%, and the atomic percentage of N is maintained at 40% to 50%; when the content of Si atoms is lower (7 percent, depending on a deposition process), the Si atoms exist in the TiN crystal in a solid solution mode, the mechanical property is improved through grain refinement and solid solution strengthening, and the coating structure at the stage still keeps the FCC structure of TiN; as the Si content continues to rise, the Si element will form several atomic layer thick Si around TiN grains ₃ N ₄ Amorphous phase to form amorphous a-Si ₃ N ₄ The phase is wrapped by a nano TiN crystal structure (see figure 6), on one hand, the amorphous phase can break the growth of columnar structure grains and refine the grains, on the other hand, the structure of the long columnar crystal is changed into a nano composite structure which is used as a channel for absorbing crack energy, and the generation and the propagation of cracks are retarded by closing and deflecting the cracks.

As shown in figure 7, the hardness of the coating can reach more than 37GPa when the nano indentation test is adopted, in addition, the film-substrate binding force of the coating is more than or equal to 93N when the scratch method test is adopted, the residual stress of the coating is measured based on the substrate curvature method, wherein the residual stress of the coating with a single structure is-4.03 +/-0.03 GPa, and the gradient is adoptedThe residual stress of the structural coating is-2.7 +/-0.02 GPa, and the residual stress is reduced by about 33%; under the nano indentation load of 200mN, the surface of the gradient coating has better capability of inhibiting cracks; the Si element of the surface layer is oxidized at high temperature to form compact SiO ₂ Can prevent O atoms from diffusing into the coating to a certain extent, improves the oxidation resistance of the coating, and in addition, siO ₂ The lubricating and antifriction functions can be realized; after oxidation at 850 ℃ for 1h in an air atmosphere, the thickness of the oxide layer was only 140nm (see FIG. 8).

Note: the single coating in fig. 7 refers to a TiSiN coating of uniform composition, with 44 atomic percent Ti, 48 atomic percent N and 8 atomic percent Si.

Example 2

The embodiment provides a preparation method of a gradient coating material, which comprises a TiN bonding layer, a TiAlSiN intermediate transition layer and a TiAlSiN top wear-resistant layer, wherein the content of Si and Al in the TiAlSiN intermediate transition layer is gradually increased along the coating thickness direction. The preparation process comprises the following steps:

(1) Pretreatment of substrates

Grinding, polishing or wet sand blasting and ultrasonic cleaning a hard alloy flat plate substrate with the Co content of 10%, the WC content of 88.5%, the TaC content of 1.5% and the average transversal grain size of 600nm to remove an oxide film and pollutants on the surface, and drying for later use; fixing the hard alloy on a workpiece frame, and closing a furnace door of the coating equipment; starting mechanical pump and molecular pump step by step to vacuumize the furnace chamber to 4.0 × 10 ^-5 Background vacuum degree below mbar; turning on a heater to heat the substrate to about 450 ℃; introducing Ar gas into the furnace chamber, and maintaining the gas pressure at 1.0 × 10 ^-2 mbar, applying a negative bias of 300V on the workpiece holder, passing Ar ⁺ And (4) bombarding and etching the substrate for 30min.

(2) Depositing a buffer layer

Introducing Ar gas into the oven chamber, and maintaining the pressure at 1.0 × 10 ^-2 mbar, starting the Ti target material, setting the current of the Ti target material to be 120A, applying negative bias of 80V on the workpiece frame, and depositing a Ti metal buffer layer with the thickness of 50nm.

(3) Depositing an adhesion layer

Introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 1.0X 10 ^-2 And mbar, starting the Ti target material, setting the current of the Ti target material to be 120A, applying 80V negative bias on the workpiece frame, depositing a TiN bonding layer, wherein the thickness of the bonding layer is 200nm, and the atomic ratio of Ti atoms to N atoms is close to 1:1, the crystal structure is a single-phase FCC structure.

(4) Depositing an intermediate transition layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 And mbar, applying a negative bias of 60V on the workpiece holder, simultaneously opening the Ti target and the TiAlSi alloy target (the atomic ratio of Ti to Al to Si =50 in the TiAlSi alloy target is 10), keeping the current of the Ti target at 120A, setting the current of the TiAlSi alloy target at 90A, gradually increasing the current, increasing the step size to 1A, and adjusting the time interval to 2min. When the current of the TiAlSi alloy target material is increased to 120A, the current of the TiAlSi alloy target material is kept unchanged, the current of the Ti target material is gradually reduced, the step length is reduced to 1A, the time interval is adjusted to be 2min, and the Ti target material is closed until the current of the Ti target material is reduced to 90A.

The content of the TiAlSiN intermediate transition layer is gradually increased along the thickness direction of the coating layer, and the thickness of the TiAlSiN intermediate transition layer is 2.5 mu m.

(5) Depositing a top wear layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 mbar, applying 50V negative bias on the workpiece holder, keeping the current of the TiAlSi alloy target at 120A, depositing for 20min, closing the TiAlSi alloy target, and stopping introducing N into the furnace chamber ₂ And turning off the negative bias power supply on the workpiece frame. The top wear-resistant layer is formed by depositing a TiAlSiN wear-resistant layer with high Al and Si content doped elements by adopting a single TiAlSi alloy target (atomic ratio is Ti: al: si = 50.

Referring to fig. 9, in the present embodiment, the atomic percent of Ti in the intermediate transition layer coating is gradually decreased from 50% to 25%, the atomic percent of Al is gradually increased from 0% to 20%, the atomic percent of Si is gradually increased from 0% to 4%, and the atomic percent of N is maintained at 40% to 50%; the solid solubility of TiN with an FCC structure can be reduced by simultaneously doping Al and Si atoms, so that the microstructure of the coating can be changed by trace doping of the Al and Si atoms, the columnar structure of the coating is gradually transited to a glassy state morphology without obvious characteristics, crystal grains are refined, and the hardness of the coating is improved.

Referring to fig. 10 and 11, the hardness of the coating can reach over 39GPa by adopting nano indentation test, and the film-substrate binding force of the coating is more than or equal to 90N; the coating did not flake off under the 60Kg load indentation. The Al and Si elements of the surface layer of the top wear-resistant layer at high temperature act synergistically to form compact Al ₂ O ₃ And SiO ₂ A layer which can further improve the high temperature oxidation resistance and red hardness of the coating; after oxidation is carried out for 1h in an air environment at 850 ℃, the thickness of the oxide layer is only 120nm (see figure 12), and the high-temperature oxidation resistance of the coating is effectively improved.

Comparative example 1

The comparative example provides a preparation method of a gradient coating material, which comprises a TiN bonding layer, an AlTiN intermediate transition layer and an AlTiN top wear-resistant layer, wherein the Al content of the AlTiN intermediate transition layer is gradually increased along the coating thickness direction. The preparation process comprises the following steps:

(1) Pretreatment of substrates

The operation steps are the same as those of the embodiment 1.

(2) Depositing an adhesion layer

(3) Depositing an intermediate transition layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 mbar, applying 60V negative bias on the workpiece holder, and simultaneously opening Ti target material and TiAl alloy targetThe current of the Ti target material is kept at 120A, the current of the TiAl alloy target material is set to be 90A and gradually increased, the increasing step size is 2A, and the adjusting time interval is 3min. When the current of the TiAl alloy target material is increased to 120A, the current of the TiAl alloy target material is kept unchanged, the current of the Ti target material is gradually reduced, the step length is reduced to 2A, the time interval is adjusted to be 3min, and the Ti target material is closed until the current of the Ti target material is reduced to 90A.

The content of Al in the TiAlN intermediate transition layer is gradually increased along the thickness direction of the coating, and the thickness of the TiAlN intermediate transition layer is 3 mu m.

(4) Depositing a top wear layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 mbar, applying 50V negative bias on the work rest, maintaining the current of the TiAl alloy target at 120A, depositing for 20min (the thickness of the top wear-resistant layer is 1 μm), closing the TiAl alloy target, and stopping introducing N into the furnace chamber ₂ And turning off the negative bias power supply on the workpiece frame. The wear-resistant layer on the top layer is formed by depositing an AlTiN wear-resistant layer with high aluminum content by adopting a TiAl alloy target material (the atomic ratio is Ti: al =33 = 67), and the thickness of the AlTiN wear-resistant layer is 2 mu m, wherein the atomic percent of Al is 32%, the atomic percent of Ti is 21%, and the atomic percent of N is 47%.

Referring to fig. 13, in the present comparative example, the Al content gradient is increased under the coordination of the gradually changing TiAl target current and Ti target, the atomic percent of Ti in the coating is gradually decreased from 50% to 15%, the atomic percent of Al is gradually increased from 0% to 35%, and the atomic percent of N is maintained at 40% to 50%; due to the precise control of the coating process and the Al content, the crystal structure of the coating still keeps a single-phase FCC structure along with the increase of the Al content, the coating phase structure is a solid solution of Al in TiN crystals, and a hexagonal phase structure with deteriorated performance does not appear.

Referring to fig. 14, the hardness of the coating can reach 31GPa by nanoindentation test, the film-substrate bonding force of the coating is about 80N, and although the Al gradient coating prepared by the method of the present invention also has good hardness and bonding force, no second-phase amorphous phase is formed, and the coating is oxidized for 1 hour in an air environment at 850 ℃ and is completely oxidized (see fig. 15), which is not suitable for high-temperature applications.

Comparative example 2

The only difference from example 2 is: the comparative example incorporates excessive amounts of doping elements Al and Si, resulting in excessive amorphous phase in the coating, poor crystallinity of the coating, and softening of the coating. The preparation process comprises the following steps:

(1) Pretreatment of substrates

The same procedure as in example 2 was followed.

(2) Depositing a buffer layer

The operation steps are the same as those of the example 2

(3) Depositing an adhesion layer

(4) Depositing an intermediate transition layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 And mbar, applying a negative bias of 60V on the workpiece holder, simultaneously opening the Ti target material and the TiAlSi alloy target material (the atomic ratio of Ti to Al to Si =30: 10 in the TiAlSi alloy target material), keeping the current of the Ti target material at 120A, setting the current of the TiAlSi alloy target material at 90A, gradually increasing the current with the increasing step length of 1A, and adjusting the time interval at 2min. When the current of the TiAl alloy target material is increased to 120A, the current of the TiAl alloy target material is kept unchanged, the current of the Ti target material is gradually reduced, the step length is reduced to 1A, the time interval is adjusted to be 2min, and the Ti target material is closed until the current of the Ti target material is reduced to 90A.

(5) Depositing a top wear layer

Continuously introducing N into the furnace chamber ₂ Gas, keeping the gas pressure at 6.0X 10 ^-2 mbar, applying 50V negative bias on the work rest, maintaining the current of the TiAlSi alloy target at 120A, depositing for 20min (the top wear-resistant layer thickness is 1 μm), closing the TiAlSi alloy target, and stopping introducing N into the furnace chamber ₂ And turning off the negative bias power supply on the workpiece frame. The wear-resistant layer on the top layer is a TiAlSi alloy target (atomic ratio is Ti: al: si =30 = 60.

Referring to fig. 16, in the present comparative example, under the coordination of the gradually changing TiAlSi target current and the Ti target, the content gradient of Al and Si is increased, the atomic percent of Ti in the coating layer is gradually decreased from 50% to 20%, the atomic percent of Al is gradually increased from 0% to 33%, and the atomic percent of N is maintained at 40% to 50%; the solid solubility of TiN with an FCC structure can be reduced by doping Al and Si simultaneously, so that with the increase of the content of doping elements, the columnar structure of the coating is gradually transited to a glassy state morphology without obvious characteristics, a large amount of amorphous is presented in a microscopic morphology, a small amount of crystals are wrapped by a large amount of amorphous (see figure 17), the hardness of the coating is only 24GPa due to the large amount of amorphous, the wear resistance is reduced, and the requirement on the wear resistance under the high-speed cutting condition cannot be met.

In conclusion, the traditional coating is easy to generate cracks and deteriorate the service performance due to the fact that the traditional coating is single in structure and mostly has a columnar crystal structure; when the content of the doping element is large, the residual stress is large and the bonding force of the film base is poor. The invention provides a gradient coating material, a preparation method and application thereof, and the gradient coating material is a mussel-like structure and functional gradient coating and has the following effects:

(1) The coherent connection of the coating and the interface of the hard alloy substrate is realized through the design of the bonding layer structure, and the modulus of the film substrate is matched, so that the bottom layer of the coating and the substrate deform cooperatively under load, and the cracking tendency of the film-substrate interface is reduced.

(2) The stress can be further slowly released flexibly by adding the stress buffer layer, and the high-strength and high-toughness connection of the film-substrate interface is realized; the content of doping elements is continuously increased in a gradient manner layer by layer, so that the lattice distortion caused by element doping in the coating is gradually changed, and the stress of the coating accumulated by high doping amount in a single-layer structure can be relieved.

(3) The elastic modulus and hardness of the coating material are changed in a gradient manner as a result of the gradient change of the components, and the interlayer interface has higher compatibility due to the coordinated deformation and gradual change of the components, so that the cracking risk of the interlayer interface is reduced.

(4) The top layer structure with high doping elements can provide better performance for the coating, and simultaneously, the design of the gradient structure also ensures that the coating has better film-substrate binding force and higher hardness, and can realize the preparation of the hard coating with large thickness and high hardness.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The gradient coating material is characterized by comprising a bonding layer, a middle transition layer and a top wear-resistant layer which are sequentially deposited on a hard alloy substrate, wherein the middle transition layer and the top wear-resistant layer both contain Ti, N and doping elements, the doping elements are silicon or silicon-aluminum mixture, the content of the doping elements in the middle transition layer is gradually increased from the bottom to the top, and the content of the doping elements in the top wear-resistant layer is greater than or equal to that in the topmost middle transition layer.

2. A gradient coating material according to claim 1, wherein the bond coat is selected from at least one of TiN, crN, zrN and VN; preferably a TiN coating;

preferably, the thickness of the bonding layer is 20nm to 200nm, the thickness of the middle transition layer is 1 μm to 6 μm, and the thickness of the top wear-resistant layer is 1 μm to 3 μm;

preferably, the thickness of the bonding layer is 100 nm-200 nm, the thickness of the middle transition layer is 1.5 μm-4 μm, and the thickness of the top wear-resistant layer is 1 μm-2 μm;

preferably, the hard alloy substrate is a submicron hard alloy with the Co content of 8-12% and the WC grain size of less than or equal to 0.6 μm.

3. The gradient coating material according to claim 1 or 2, wherein the intermediate transition layer is a TiSiN coating with gradually increasing Si content, and the top wear layer is a TiSiN coating;

4. The gradient coating material according to claim 1 or 2, wherein the intermediate transition layer is a TiAlSiN coating with gradually increased Si and Al contents, and the top wear-resistant layer is a TiAlSiN coating;

5. The gradient coating material according to claim 1 or 2, wherein a buffer layer is further provided between the bonding layer and the cemented carbide substrate;

6. A method for preparing a gradient coating material according to any one of claims 1 to 5, comprising: and depositing the bonding layer, the intermediate transition layer and the top wear-resistant layer on the hard alloy substrate in sequence.

7. The method of claim 6, comprising:

depositing an adhesive layer: introducing nitrogen into the furnace chamber, starting the Ti target material, and depositing the bonding layer on the hard alloy substrate;

depositing an intermediate transition layer: continuously introducing nitrogen into the furnace chamber, and simultaneously starting the Ti target material and the Ti alloy target material, wherein the current of the Ti target material is kept unchanged, and the current of the Ti alloy target material is gradually increased; then keeping the current of the Ti alloy target unchanged, and gradually reducing the current of the Ti alloy target;

preferably, before depositing the bonding layer, the cemented carbide substrate is pretreated to remove a surface oxide film and pollutants, then the cemented carbide substrate is fixed in a furnace chamber to be vacuumized, the cemented carbide substrate is heated to 400-500 ℃, then inert gas is introduced into the furnace chamber, the substrate is bombarded and etched under the condition of negative bias, and the surface is cleaned.

8. The method according to claim 7, wherein the pressure in the furnace is controlled to be 0.5X 10 at the time of depositing the adhesive layer ^-2 mbar～1.5×10 ^-2 mbar, setting the current of the Ti target material to be 110A-130A, and applying negative bias voltage of 70V-90V;

preferably, the gas pressure in the furnace is controlled to be 5.0X 10 when the intermediate transition layer is deposited ^-2 mbar～7.0×10 ^-2 mbar, applying negative bias voltage of 50-70V, simultaneously opening the Ti target material and the Ti alloy target material, keeping the current of the Ti target material unchanged at 110-130A, gradually increasing the current of the Ti alloy target material from 80-100A, wherein the increasing step length is 1-3A, and the adjusting time interval is 1-5 min; when the current of the Ti alloy target is increased to be the same as that of the Ti target, keeping the current of the Ti alloy target unchanged, gradually reducing the current of the Ti target, wherein the reduced step length is 1A-3A, and the adjusted time interval is 1 min-5 min until the current of the Ti target is reduced to be consistent with the initial current of the Ti alloy target, and closing the Ti target;

preferably, the pressure in the furnace is controlled to be 5.0X 10 when the top wear-resistant layer is deposited ^-2 mbar～7.0×10 ^-2 And mbar, applying negative bias of 40-60V, setting the current of the Ti alloy target material to be 110-130A, setting the deposition time to be 15-25 min, closing the Ti alloy target material, stopping introducing nitrogen and closing the negative bias.

9. The method according to claim 7 or 8, wherein a buffer layer of Ti metal is deposited before the adhesion layer is deposited;

preferably, during the deposition of the Ti metal buffer layer, inert gas is introduced into the furnace chamber, and the gas pressure is kept at 0.5X 10 ^- ² mbar～1.5×10 ^-2 mbar, starting the Ti target, setting the current of the Ti target to be 110-130A, and applying negative bias of 70-90V on the workpiece rack.

10. Use of a gradient coating material according to any one of claims 1 to 5 or a gradient coating material prepared by a preparation method according to any one of claims 6 to 9 for the preparation of a blade.