CN109989059B

CN109989059B - TiBw-Ti composite layer and laser in-situ preparation method thereof

Info

Publication number: CN109989059B
Application number: CN201910166080.0A
Authority: CN
Inventors: 林英华; 林振衡; 陈庆堂; 唐群华; 雷永平
Original assignee: Putian University
Current assignee: Putian University
Priority date: 2019-03-06
Filing date: 2019-03-06
Publication date: 2021-01-05
Anticipated expiration: 2039-03-06
Also published as: CN109989059A

Abstract

The invention provides a TiBw-Ti composite layer and a laser in-situ synthesis method of the composite layer. In particular, the amount of the solvent to be used,the composite layer is made of Ti powder and TiB₂The powder is used as a raw material, a melting layer with TiBw/Ti content gradient change is prepared on the surface of a substrate, then the melting layer is remelted, and a cladding layer is prepared on the surface of the remelted layer in a mode of synergistic effect of induction heating and laser quenching. The interface structure of alpha-Ti and TiBw in the cladding layer is in a coherent or semi-coherent combination form, and the toughness, high-temperature oxidation resistance, fretting wear resistance and fretting fatigue resistance of the cladding layer can be obviously improved. The TiBw-Ti composite layer can be widely applied to a modification layer and a repair layer of an auxiliary component of an aircraft engine shell manufactured by titanium alloy materials.

Description

TiBw-Ti composite layer and laser in-situ preparation method thereof

Technical Field

The invention relates to the technical field of composite materials, in particular to a TiBw-Ti composite layer and a method for preparing the TiBw-Ti composite layer by adopting a laser in-situ technology.

Background

TiBw as a reinforcing phase is widely applied to titanium-based composite materials, and can be divided into an external addition method and an in-situ reaction self-generation method according to a reinforcing phase generation method. Due to the difficulty in preparing TiBw powder, the TiBw reinforced titanium-based composite material is prepared by an in-situ reaction self-generation method basically at present. ZrB is a commonly used raw material as the B source₂、B₄C、BN、TiB₂、LaB₆And powder B. The main preparation technology for generating the TiBw reinforced titanium-based composite material by using the in-situ method at present comprises the following steps: powder metallurgy, mechanical alloying, self-propagating high-temperature synthesis processes, exothermic diffusion, melt casting techniques, laser cladding techniques, and a variety of coating techniques.

In the traditional process for preparing the TiBw/Ti composite coating, people always pursue to prepare the composite material with the TiBw uniformly distributed in the Ti matrix in the past, and although the titanium-based composite material with the TiBw uniformly distributed has more excellent performances than the titanium alloy material, the ideal reinforcing effect is difficult to achieve. In recent years, a great deal of research finds that the metal matrix composite material with uniformly distributed reinforcing phases only shows limited reinforcing effect and poor plasticity and toughness level, and the uneven geometric shape, multi-scale, non-uniform component distribution and multi-level coupling structure have the advantages of higher strength, toughness, damage resistance and the like. Meanwhile, with the continuous and deep understanding of people on many natural biomaterials in nature, it is found that natural biomaterials with excellent comprehensive mechanical properties and toughness often have more complex structural element characteristics, such as uneven geometric forms and spatial distribution, multi-scale, multi-phase, uneven component distribution, multi-level coupling structures and the like. For example, the tissue structure of the shell nacre of the haliotis discus hannai with high obdurability and high chemical-mechanical stability has multilevel structure, namely the structure is formed by stacking a stone sheet consisting of multi-scale particles and a multi-level organic matter thin layer by layer; and for another example, the lobster chelate structure with high pressure resistance and high wear resistance has multi-level characteristics and is divided into an upper skin, an outer skin and an inner skin, wherein the outer skin layer and the inner skin layer are formed by spiral clamping plate layers, and obvious mechanical property gradients exist in the lobster chelate structure. The multi-level and multi-scale organization (or phase) construction provides a very valuable clue for developing TiBw/Ti composite materials with high strength, high toughness and damage resistance.

At present, although TiBw/Ti composite materials with non-uniform structures can be prepared by hot-pressing sintering, smelting, powder metallurgy and other technologies, the obtained titanium-based composite materials have the problems of looseness, porosity, reinforcing phase agglomeration and the like, and need to be subjected to subsequent thermal deformation and subsequent thermal treatment. This not only increases the cost due to multiple processes, but also tends to cause structural instability. (2) Part of the layered Ti-TiBw/Ti composite material can be prepared by methods such as reaction hot-pressing sintering, diffusion connection and the like, but the interlayer interface bonding is not complete metallurgical bonding, the interface bonding strength still needs to be further improved, and the layered surface is mainly Ti-based material, which is not beneficial to oxidation resistance and wear resistance. (3) The traditional preparation technology cannot be effectively used as a titanium alloy surface modification and repair technology, and even if the TiBw/Ti composite coating which is non-uniformly distributed can be successfully prepared on the surface of the titanium alloy, the original performance of the titanium alloy base metal can be damaged to a great extent, such as hot-pressing sintering, smelting and powder metallurgy technologies.

Among the numerous surface modification techniques, the laser surface modification technique has gradually become an important tool for modifying and repairing the surface of titanium alloy due to the advantages of compact coating structure, good metallurgical bonding with the base material, small influence on the heat affected zone of the base material, and the like. And the laser is adopted to directly irradiate the cladding material, the melting direction of the material is gradually pushed from the outside along the inner layer under the action of heat transfer, and the solidification direction is pushed from the bottom to the outer layer due to the chilling action of the base material. The opposite characteristic of the melting direction and the solidification direction easily causes the cladding layer to show the characteristic of uneven distribution from the surface and the inner structure.

With the continuous development of advanced national defense equipment such as aviation, aerospace, weapons, ships and the like in the future, the service conditions of titanium alloy parts become more complex, and the titanium alloy surface not only needs to bear fretting wear and impact wear, but also needs to bear oxidation, high-temperature softening and the like, so that higher performance requirements are provided for a titanium alloy surface modification layer and a repair layer. The developed titanium-based composite coating not only has high hardness, high strength and high elastic modulus, but also has high fretting wear resistance, high-temperature oxidation resistance, impact resistance and the like. However, to effectively improve fretting wear resistance and high temperature oxidation resistance, it is only possible to increase the content of the reinforcing phase, so that the surface layer of the composite coating should maintain a high content of TiBw during the material design process. However, the high TiBw content easily causes high brittleness, and the pure Ti with high plasticity is required to be used as a matrix to be filled around the TiBw so as to simultaneously show a certain toughness level. The problem of high brittleness caused by impact resistance and high TiBw content on the surface layer can be solved by adopting an uneven structure, namely, a distribution state that the TiBw content decreases in a gradient manner from the surface to the inside and the Ti matrix content increases in a gradient manner is adopted. Meanwhile, when the surface layer is superhard, the surface layer is more favorable for reaching higher strong plasticity level. Therefore, in the TiBw/Ti gradient structure design, the grain size of the Ti matrix filled around the TiBw in the surface layer is finer, and the yield ratio of the surface layer to the interior is further increased by a fine grain strengthening mode.

In order to prepare a high-quality laser in-situ synthesized TiBw-Ti cladding layer with two-phase gradient structure distribution, the TiBw content and the Ti grain content and size are spatially self-expressed and self-containedThe distribution state of gradient change, namely the TiBw content gradient is reduced from the surface and the inside, and the Ti grain content and size gradient are increased. In the aspect of selection of cladding materials, although the main material capable of providing B element at present is B₄C、BN、TiB₂And B powder etc., but B₄C. BN and B powder can react with Ti powder in situ to generate TiB and also generate TiB in situ₂The production conditions are not easy to control and the repeatability is poor. But only TiB₂Reacts with Ti powder in situ to only generate TiB. Although TiB₂Has a hardness of not BN and B₄C is high, but TiB₂Has high chemical stability and TiB₂The density and the thermal expansion coefficient of the alloy are similar to those of TiB and Ti. These all contribute to obtaining high-stability, high-quality TiB₂And TiB reinforced titanium-based composite coatings provide good conditions.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The first purpose of the invention is to provide a TiBw-Ti composite layer.

The second purpose of the invention is to provide a method for preparing the TiBw-Ti composite layer by adopting a laser in-situ technology.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the invention relates to a TiBw-Ti composite layer, which comprises a cladding layer and a melting layer from top to bottom,

the cladding layer contains alpha-Ti crystal grains and TiBw crystal grains, the alpha-Ti crystal grains and the TiBw crystal grains are in an interface coherent structure, the area fraction of the TiBw crystal grains is 40-60%, the grain size of the alpha-Ti crystal grains is 0.1-1 mu m,

the melting layer contains alpha-Ti grains and TiB₂Grains of said TiB₂The area fraction of the crystal grains is 20-40%, and the grain diameter of the Ti crystal grains is 1-3 mu m.

Preferably, the thickness ratio of the cladding layer to the melting layer is (1-2): 1, preferably 1: 1.

Preferably, in the cladding layer, the TiBw crystal grains are in a fine needle shape and a coarse needle shape, the diameter of the fine needle is 300-600 nm, and the size of the coarse needle is 1-3 μm.

The invention also relates to a laser in-situ preparation method of the TiBw-Ti composite layer, which uses TiB₂Powder and Ti powder are taken as raw materials, the raw materials are sent into a processing chamber through coaxial powder feeding equipment, and a cladding layer, a re-melting layer and a melting layer are sequentially prepared on the surface of a substrate by adopting laser beams;

in the raw material TiB₂The mass ratio of the powder to the Ti powder is (6-3) to 1.

Preferably, the TiB₂The particle size of the powder is 0.5-150 μm, and the particle size of the Ti powder is 1-200 μm.

Preferably, the substrate is made of a titanium alloy.

Preferably, the method comprises the steps of:

(1) mixing the raw material TiB₂Uniformly mixing the powder and Ti powder, placing the powder in a coaxial powder feeder, placing the substrate in a closed processing chamber, and introducing argon, wherein the oxygen content and the nitrogen content in the processing chamber are preferably less than 0.1%;

(2) starting the coaxial powder feeder to convey TiB into the processing chamber₂Mixing the powder with Ti, synchronously starting a laser beam heat source, and preparing a melting layer on the surface of the substrate;

(3) regulating and controlling laser energy density to enable remelting from the top of the melting layer to a position close to the middle, and preparing a remelted layer on the surface of the melting layer;

(4) regulating and controlling laser energy density, and heating the substrate to convert residual beta-Ti in the remelted layer and the melted layer into alpha-Ti so as to obtain a composite layer with an interface coherent structure of alpha-Ti and TiBw.

Preferably, in the step (2), the powder feeding amount is 10-30 g/min, and the dilution rate is 50-150%.

Preferably, in the step (2), the laser beam power is 2.0-2.6 kW, the scanning speed is 5-6 mm/s, the powder feeding rate is 5-25 g/min, and the thickness of the obtained melting layer is 1.6-2.1 mm.

Preferably, in the step (3), the laser beam power is 1.0-1.3 kW, the scanning speed is 8-11 mm/s, and the thickness of the obtained remelted layer is 0.8-1.0 mm.

Preferably, in the step (4), the surface temperature of the remelting layer is controlled to be 250-350 ℃, and laser quenching is carried out after preheating is carried out for 3 min;

the laser quenching process parameters are as follows: the laser beam power is 0.5-0.6 kW, the scanning speed is 7-8 mm/s, and the surface temperature of the cladding layer is 885-1250 ℃ under the synergistic effect of induction heating and laser; the thickness of the obtained cladding layer does not exceed 2/3 of the thickness of the remelting layer.

The invention has the beneficial effects that:

the invention provides a TiBw-Ti composite layer and a laser in-situ synthesis method of the composite layer. Specifically, the composite layer is formed by Ti powder and TiB₂The powder is used as a raw material, a melting layer with TiBw/Ti content gradient change is prepared on the surface of a substrate, then the melting layer is remelted, and a cladding layer is prepared on the surface of the remelted layer in a mode of synergistic effect of induction heating and laser quenching. The interface structure of alpha-Ti and TiBw in the cladding layer is in a coherent or semi-coherent combination form, and the toughness, high-temperature oxidation resistance, fretting wear resistance and fretting fatigue resistance of the cladding layer can be obviously improved. The TiBw-Ti composite layer can be widely applied to a modification layer and a repair layer of an auxiliary component of an aircraft engine shell manufactured by titanium alloy materials.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a Scanning Electron Microscope (SEM) image of a molten layer prepared in example 1;

wherein, FIG. 1a is the macro morphology of the cross section of the melting layer, FIG. 1b is the structure diagram of the surface layer (0.3-0.6 mm from the surface) of the cross section of the melting layer, and FIG. 1c is the structure diagram of the bottom (1.2-1.5 mm) of the cross section of the melting layer.

FIG. 2 is an SEM image of a remelted layer prepared in example 1;

wherein FIG. 2a shows Ti grains in a cross section of a molten layer without remelting; FIG. 2b shows Ti grains in a cross section of the remelted layer.

FIG. 3 is SEM images of the upper and lower portions of the cladding layer prepared in example 1;

wherein, FIG. 3a is the structure of the cross section of the laser remelting layer, and FIG. 3b is the structure of the cross section of the melting layer below the laser remelting layer;

FIG. 4 is a High Resolution Transmission Electron Microscope (HRTEM) image of the coherent structure of the α -Ti and TiBw interface in the cladding layer prepared in example 1;

wherein FIG. 4a is a low power topography under HRTEM and FIG. 4b is a high power topography under HRTEM;

FIG. 5 is a SEM image of the surface topography of a cross-section of a cladding layer of example 3;

FIG. 6 is an SEM image of a cross section of a remelted layer and a melted layer below the remelted layer of example 3;

wherein, FIG. 6a is the structure of the cross section of the laser remelting layer, and FIG. 6b is the structure of the cross section of the melting layer below the laser remelting layer.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.

The embodiment of the invention relates to a TiBw-Ti composite layer which comprises a cladding layer and a melting layer from top to bottom. The thickness of the cladding layer is more than 1.5mm, and excellent performances such as obdurability, high-temperature oxidation resistance, high wear resistance and the like can be provided for the titanium alloy. The composite layer can be widely applied to manufacturing layers and repairing layers of various auxiliary components for manufacturing aeroengine shells by using titanium alloy materials.

The cladding layer of the composite layer contains alpha-Ti grains and TiBw grains, the alpha-Ti grains and the TiBw grains are in an interface coherent structure, the area fraction of the TiBw grains is 40-60%, and the grain size of the alpha-Ti grains is 0.1-1 mu m.

In the melting layer of the composite layer, alpha-Ti crystal grains are containedAnd TiB₂Grains, TiB₂The area fraction of the crystal grains is 20-40%, and the grain diameter of the Ti crystal grains is 1-3 mu m.

Furthermore, TiBw crystal grains in the cladding layer are in a fine needle shape and a coarse needle shape, the diameter of the fine needle is 300-600 nm, and the size of the coarse needle is 1-3 mu m.

Furthermore, in the composite layer prepared by the laser in-situ technology, the thickness ratio of the cladding layer to the melting layer is (1-2): 1, and preferably 1: 1.

The embodiment of the invention also relates to a laser in-situ preparation method of the TiBw-Ti composite layer. The method uses TiB₂Powder and Ti powder are taken as raw materials, the raw materials are sent into a processing chamber through coaxial powder feeding equipment, and a cladding layer, a re-melting layer and a melting layer are sequentially prepared on the surface of a substrate by adopting laser beams;

in the preparation method, the TiB in the raw materials needs to be controlled₂The mass ratio of the powder to the Ti powder is (6-3) to 1. TiB₂If the powder consumption is too large or too small, a cladding layer with an interface coherent structure of alpha-Ti grains and TiBw grains cannot be obtained.

Further, TiB₂The particle size of the powder is 0.5-150 μm, and the particle size of the Ti powder is 1-200 μm. The substrate is made of titanium alloy.

The laser in-situ preparation method can be realized by the following reaction equipment: the apparatus comprises: (A) a laser beam as a heat source; (B) a coaxial powder feeder for inputting raw materials; (C) a closed processing chamber for atmosphere replacement protection; (D) and the induction heating device is used for heating the substrate and monitoring the temperature in real time.

In the method, firstly, the self-surface TiB and the self-surface TiB are obtained by regulating and controlling the component proportion and the laser parameter₂A melting layer with a reduced content gradient and an increased Ti grain size gradient; secondly, inducing remelting from the top of the melting layer to a position close to the middle by selecting lower laser energy density to obtain a remelting layer with an organization structure with increased TiBw content and reduced Ti grain size; finally, the residual beta-Ti in the remelted layer and the melted layer is promoted to be converted into alpha-Ti in a synergistic way of induction heating and laser quenching, and cladding with the interface structure of the alpha-Ti and TiBw in a coherent or semi-coherent combination form is obtainedAnd (3) a layer.

In one embodiment of the invention, the method comprises the steps of:

(1) mixing the raw material TiB₂The powder and Ti powder are uniformly mixed and then placed in a coaxial powder feeder, the substrate is placed in a closed processing chamber, and high-purity argon gas with the purity of 99.9-99.99% is filled until the oxygen content and the nitrogen content in the processing chamber are both less than 0.1%.

(2) Starting the coaxial powder feeder to convey TiB into the processing chamber₂The powder feeding amount of the mixed powder with Ti is 10-30 g/min. And synchronously starting a laser beam heat source to prepare a melting layer on the surface of the substrate.

Further, in the process, the size of a laser beam spot is 4-5 mm, the power of the laser beam is 2.0-2.6 kW, the scanning speed is 5-6 mm/s, the powder feeding rate is 5-25 g/min, the defocusing amount is-1-0 mm, and the dilution rate of the laser melting substrate is 50-150%. The dilution ratio refers to the ratio of the thickness of the melted substrate to the thickness of the melted layer.

The thickness of the obtained melting layer is 1.6-2.1 mm. Wherein TiB is in the melting layer₂And the distribution of Ti crystal grains is changed in a gradient way. Specifically, TiB in the upper surface layer of the melt layer₂The area fraction of the crystal grains is 10-20 percent, and the area fraction of the Ti crystal grains is 50-70 percent; TiB in lower surface of melt layer₂The area fraction of the crystal grains is 5-10%, and the area fraction of the Ti crystal grains is 60-80%.

(3) Regulating and controlling the laser energy density to ensure that the remelting occurs from the top to the position close to the middle part of the melting layer, and preparing a remelting layer on the surface of the melting layer.

Further, in the process, the spot size of the laser beam is 4-5 mm, the power of the laser beam is 1.0-1.3 kW, the scanning speed is 8-11 mm/s, the defocusing amount moves downwards by 1-2 mm, and the thickness of the obtained remelted layer is 0.8-1.0 mm. During remelting only a part of the molten layer is converted into a remelted layer. The TiBw content in the remelted layer is increased and the Ti grain content is reduced compared to the same region before remelting (the melted layer before conversion into the remelted layer).

Furthermore, in the process, an induction heating device is required to be started, the surface temperature of the remelted layer is controlled to be 250-350 ℃, and laser quenching is carried out after preheating is carried out for 3 min.

The laser quenching process parameters are as follows: the laser beam spot size is 4-5 mm, the laser beam power is 0.5-0.6 kW, the scanning speed is 7-8 mm/s, and the defocusing amount is 0-1 mm. Under the synergistic effect of induction heating and laser, the surface temperature of the cladding layer is 885-1250 ℃; the thickness of the obtained cladding layer does not exceed 2/3 of the thickness of the remelting layer.

The cladding layers of examples 1-4 were prepared using a YLS-6000 type fiber laser.

Example 1

(1) Early preparation: ti-6Al-4V alloy is selected as a substrate, and the components of the Ti-6.01Al-3.84V-0.3Fe-0.15S-0.1C-0.1O-0.15Ni in percentage by weight. And putting the titanium alloy substrate into a closed atmosphere controllable processing protection chamber, and placing and fastening the induction heater at the lower part of the substrate.

The pure TiB with the argon atomization size of 75-48 mu m and the purity of 99.9 percent is selected₂And pure Ti powder with the purity of 99 percent as a cladding material, and TiB₂The mass component ratio of the Ti powder to the Ti powder is 6:1, the 2 materials are mixed by a vertical high-energy ball milling device for 120min, and are placed in a drying box to be dried for 60min at 120 ℃, and then are placed in a coaxial powder feeder. High-purity argon with the purity of 99.9 percent is selected as protective gas and powder conveying gas.

(2) Preparing a melting layer: the laser melting process parameters are as follows: the laser beam spot size is 5 multiplied by 5mm (square spot), the laser power is 2.1kW, the scanning speed is 6mm/s, the powder feeding rate is about 10g/min, the defocusing amount is 0, and the thickness of the obtained melting layer is 1.6 mm-1.8 mm.

FIG. 1 is an SEM photograph of the molten layer prepared in example 1, and it can be seen that the molten layer has a self-surface TiB and a self-surface TiB₂The content gradient is reduced, and the content gradient of Ti grains is increased. The specific analysis process is as follows: the melt layer was cut in the transverse and longitudinal directions by wire electro discharge machining, and the thickness of the melt layer was calculated by the additional function of an optical microscope, as shown in FIG. 1 a.Respectively observing the content and the form of TiB and Ti on the surface layer and the middle part of the melting layer by using a Hitachi S-3400 scanning electron microscope, and finding that the grains on the surface layer of the melting layer are mainly TiB₂Particles and TiBw, as shown in fig. 1 b. While the bottom of the molten layer is mainly TiBw and Ti grains, as shown in fig. 1 c.

(3) Preparing a remelted layer: the laser remelting process parameters are as follows: the laser beam spot size is 5 multiplied by 5mm (square spot), the laser power is 1.1kW, the scanning speed is 9mm/s, the defocusing amount moves downwards by 2mm, and the thickness of the remelted layer is about 0.8mm to 0.9mm in a dynamic sealed atmosphere controllable processing protection chamber.

The remelted layer has an organization structure with increased TiBw content gradient and reduced Ti grain gradient. By adopting a contrast difference principle, the area fraction of the TiB grains of the remelted layer is calculated to be 40-60%, the TiBw diameter is 2-5 mu m, and the grain size of the Ti grains of the remelted layer is 0.1-1 mu m by multiple statistics, as shown in figure 2. The area fraction of TiB grains of the melting layer below the remelted layer is 20-40%, and the size of Ti grains is 1-3 μm, as shown in FIG. 3.

(3) Preparing a cladding layer: and starting an induction heating device, monitoring the surface temperature of the remelting layer to reach 300 ℃ by an infrared remote sensing thermometer, and preheating for 3 min. Setting the laser quenching process parameters as follows: the spot size of the laser beam is 5 multiplied by 5mm (square spot), the laser power is 0.6kW, the scanning speed is 8mm/s, the defocusing amount position is unchanged, induction heating and laser cooperate to act on the surface temperature of the remelting layer to be 1000 ℃ in a dynamic sealed atmosphere controllable processing protection chamber, so that residual beta-Ti in the remelting layer and the melting layer is promoted to be converted into alpha-Ti, and the interface structure of the alpha-Ti and TiBw is obtained and is in a coherent combination form, as shown in figure 4. In the figure, the arrows indicate the interface layer, and it can be seen that the thickness of the interface layer is only 2 to 3 nm.

Example 2

(1) Early preparation: the TA2 titanium alloy is selected as a substrate, and the components of the TA2 titanium alloy are Ti-0.03N-0.015H-0.3Fe-0.25O-0.1C in percentage by weight.

The pure TiB with the argon atomization granularity of 70-50 mu m and the purity of 99.9 percent is selected₂And pure Ti powder with the purity of 99.1 percent is taken as a cladding material. Mixing TiB₂The mass component ratio of the Ti powder to the Ti powder is 4:1, and the Ti powder are mixed togetherAfter the 2 materials are mixed by the vertical high-energy ball mill for 150min, the mixture is placed in a drying box to be dried for 90min at 120 ℃, and then the mixture is placed in a coaxial powder feeder. High-purity argon with the purity of 99.99 percent is selected as protective gas and powder conveying gas.

(2) Preparing a melting layer: the laser melting process parameters are as follows: the diameter of a laser beam spot is 4mm (a circular spot), the laser power is 2.5-2.6 kW, the scanning speed is 4mm/s, the powder feeding rate is about 20g/min, the defocusing amount is-1 mm, and the thickness of a melting layer is about 1.9-2.1 mm. The melting layer has a self-surface and a surface of TiB₂The content gradient is reduced, and the content gradient of Ti grains is increased.

(3) Preparing a remelted layer: the laser remelting process parameters are as follows: the laser beam spot size is 4mm (circular spot), the laser power is 1.3kW, the scanning speed is 11mm/s, the defocusing amount moves downwards by 1.5mm, and the thickness of the remelted layer is about 0.9 mm-1.0 mm in a dynamic sealed atmosphere controllable processing protection chamber. The remelted layer has an organization structure with increased TiBw content gradient and reduced Ti grain gradient.

(4) Preparing a cladding layer: the induction heating device is started firstly, the temperature of the surface of the cladding layer is monitored to be stable and reach 350 ℃ by an infrared remote sensing thermometer, and the cladding layer is preheated for 3 min. Setting the laser quenching process parameters as follows: the spot size of a laser beam is 4mm (circular spot), the laser power is 0.45kW, the scanning speed is 8mm/s, the defocusing position moves upwards by 1mm, the surface temperature of a remelted layer is 1150 ℃ under the synergistic action of induction heating and laser in a dynamic sealed atmosphere controllable processing protection chamber, the residual beta-Ti of the remelted layer and a molten layer is promoted to be converted into alpha-Ti, and the coherent combination form of the interface structure of the alpha-Ti and TiBw is obtained.

Example 3

(1) Early preparation: the TC4 titanium alloy is selected as a substrate, and the components of the TC4 titanium alloy are Ti-6Al-4V in percentage by weight. The pure TiB with the argon atomization granularity of 70-50 mu m and the purity of 99.9 percent is selected₂And pure Ti powder with the purity of 99.1 percent is taken as a cladding material. Mixing TiB₂The mass component ratio of the Ti powder to the Ti powder is 1: 3. The subsequent melt layer, remelt layer and cladding layer were prepared in the same manner as in example 2.

FIG. 5 is an SEM image of the surface topography of a cross section of a cladding layer of example 3. FIG. 6 is a drawing showingExample 3 SEM image of the cross section of the remelted layer and the melted layer below the remelted layer, wherein FIG. 6a is the structure of the cross section of the laser remelted layer, and FIG. 6b is the structure of the cross section of the melted layer below the laser remelted layer. As can be seen from FIG. 6, cracks occurred in the molten layer, and TiB did not occur in the molten layer from the surface to the inside₂The content gradient is reduced, and the content gradient of Ti grains is increased. Meanwhile, as can be seen from fig. 5, the subsequent re-melting layer preparation and cladding layer preparation processes with the same parameters as those in example 2 cannot eliminate the cracks in the melting layer. The laser in-situ synthesis TiBw-Ti high-quality cladding layer with two-phase gradient structure distribution cannot be obtained (figure 6).

Example 4

The substrate, raw material composition, melt layer and remelted layer were prepared in the same manner as in example 1. Only the process parameters for preparing the remelted layer are different.

The laser remelting process parameters are as follows: the laser beam spot size is 5X 5mm (square spot), the laser power is 2.5kW, the scanning speed is 6mm/s, and the defocus amount moves downward by 2 mm. The obtained remelted layer has a thickness of about 1.5mm to 1.9mm and a microstructure with increased TiBw content and reduced Ti grain content.

After the preparation process of the remelting layer is finished, residual beta-Ti in the remelting layer and the melting layer is converted into alpha-Ti, and the interface structure of the alpha-Ti and TiBw is in a coherent combination form. However, a high-quality laser in-situ synthesized TiBw-Ti cladding layer with a two-phase gradient structure distribution cannot be obtained.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. A TiBw-Ti composite layer is characterized in that the composite layer comprises a cladding layer and a melting layer from top to bottom,

the melting layer contains alpha-Ti grains and TiB₂Grains of said TiB₂The area fraction of the crystal grains is 20-40%, and the grain size of the Ti crystal grains is 1-3 mu m;

the TiBw-Ti composite layer is prepared by a laser in-situ preparation method, and the method comprises the following steps:

(1) mixing the raw material TiB₂Uniformly mixing the powder and Ti powder, placing the mixture in a coaxial powder feeder, placing a substrate in a closed processing chamber, and introducing argon, wherein TiB is contained in the raw material₂The mass ratio of the powder to the Ti powder is (6-3) to 1;

(2) starting a coaxial powder feeder, wherein the powder feeding amount is 10-30 g/min, the dilution rate is 50% -150%, and conveying TiB into a processing chamber₂Mixing powder with Ti, synchronously starting a laser beam heat source, wherein the power of a laser beam is 2.0-2.6 kW, the scanning speed is 5-6 mm/s, the powder feeding rate is 5-25 g/min, and preparing a melting layer on the surface of the substrate, wherein the thickness of the obtained melting layer is 1.6-2.1 mm;

(3) regulating and controlling laser energy density, wherein the power of a laser beam is 1.0-1.3 kW, the scanning speed is 8-11 mm/s, remelting is carried out from the top of the melting layer to the position close to the middle part, a remelting layer is prepared on the surface of the melting layer, and the thickness of the obtained remelting layer is 0.8-1.0 mm;

(4) regulating and controlling laser energy density, heating the substrate, controlling the surface temperature of the remelting layer to be 250-350 ℃, preheating for 3min, and then carrying out laser quenching to convert residual beta-Ti in the remelting layer and the melting layer into alpha-Ti so as to obtain a composite layer with an interface coherent structure of alpha-Ti and TiBw;

2. The TiBw-Ti composite layer of claim 1, wherein the thickness ratio of the cladding layer to the melting layer is (1-2): 1.

3. The TiBw-Ti composite layer as claimed in claim 2, wherein the thickness ratio of the cladding layer to the melting layer is 1: 1.

4. The TiBw-Ti composite layer as claimed in claim 1, wherein the TiBw grains in the cladding layer are in the form of fine needles and coarse needles, the fine needles have a diameter of 300-600 nm, and the coarse needles have a size of 1-3 μm.

5. The TiBw-Ti composite layer of claim 1, wherein the TiB₂The particle size of the powder is 0.5-150 μm, and the particle size of the Ti powder is 1-200 μm.

6. The TiBw-Ti composite layer of claim 5, wherein the substrate is made of a titanium alloy.