CN108385085B

CN108385085B - Low-stress CVD diamond composite coating and preparation method thereof

Info

Publication number: CN108385085B
Application number: CN201810127560.1A
Authority: CN
Inventors: 张建国; 原一高
Original assignee: Donghua University
Current assignee: Ningbo Elken Coating Technology Co., Ltd
Priority date: 2018-02-08
Filing date: 2018-02-08
Publication date: 2020-05-29
Anticipated expiration: 2038-02-08
Also published as: CN108385085A

Abstract

The invention relates to a low-stress CVD diamond composite coating and a preparation method thereof. The preparation method comprises the following steps: and (3) depositing a micro diamond coating and a nano diamond coating on the surface of the pretreated hard alloy substrate by adopting a time mode method and sequentially and alternately carrying out hot wire CVD. According to the invention, the loading flow and time of the reaction gas methane are controlled by a time mode method to realize the self-release of the thermal stress in the deposition process of the hot wire CVD diamond coating, reduce the thermal stress accumulation in the coating, improve the binding force between the coating and the hard alloy substrate as well as the binding force between the coating and the interior of the composite coating, and finally obtain the high-performance composite coating. The method of the invention is simple and convenient to control and is suitable for industrial production.

Description

Low-stress CVD diamond composite coating and preparation method thereof

Technical Field

The invention belongs to the technical field of coatings, and particularly relates to a low-stress CVD diamond composite coating and a preparation method thereof.

Background

Chemical Vapor Deposition (CVD) diamond coatings have excellent properties, such as high hardness, high wear resistance, high thermal conductivity, low coefficient of friction, and good Chemical inertness, that approach natural diamond. The diamond coating is deposited on the surface of the widely applied hard alloy cutter, so that the service life of the cutter can be greatly prolonged, the cutting condition is improved, and the processing quality of a workpiece is improved.

CVD Diamond coatings are divided into micro Diamond (MCD) coatings and nano Diamond (NCD) coatings. The MCD coating formed by the columnar growth micron-sized diamond grains has high hardness and elastic modulus and good surface wear resistance, can reduce the wear rate of the cutter and prolong the service life of the cutter; however, the surface of the coating is rough, the toughness and crack propagation resistance of the coating are poor, and surface cracks are easy to propagate along a grain boundary area to cause the coating to fall off. The NCD coating formed by the nano-scale diamond grains distributed in the cluster shape has good surface smoothness, can obviously reduce cutting force and heat, improves the cutting working condition and prolongs the service life of the cutter. The NCD coating of the continuous growth structure has good crack propagation resistance, but the coating has low bonding strength with the substrate. In order to meet the harsh requirements of machining of high-performance materials on the performance of the cutter, the cutter coating develops from a single-layer structure to a composite coating. By adopting the composite coating technology and utilizing the complementary performance advantages of MCD and NCD, the mechanical and physical properties of the diamond composite coating, such as crack expansion resistance, impact toughness, film-base bonding strength and the like, are enhanced, and the method is an effective method for solving the defects of a single type of diamond coating.

The low film-based adhesion is a major technical bottleneck in the preparation of diamond coatings on the surfaces of hard alloy cutters. The main reasons for the low film-based adhesion are: 1. the difference of the thermal expansion coefficients of the hard alloy and the diamond material is large; excessive coating stress due to heat build-up during CVD. The thermal stress of the coating is reduced, and the method is one of effective methods for improving the adhesion strength of the coating.

Through the patent search of the prior art, Chinese patent application No. 201610027985.6 describes a multilayer diamond coating and a main coating tool of the preparation method thereof, and the technical problem of low hardness of the existing multilayer diamond coating is solved by depositing a composite diamond coating structure, but the problem of thermal stress inside the coating still exists when the multilayer diamond coating is prepared by adopting a hot wire chemical vapor deposition method.

Disclosure of Invention

The invention aims to provide a low-stress CVD diamond composite coating and a preparation method thereof, which solve the defects of a single type of micron diamond or nano diamond coating and provide a more excellent composite diamond coating by utilizing a composite coating technology. In the preparation process of the composite coating, a low-stress CVD diamond composite coating deposition preparation process method is provided.

The invention discloses a low-stress CVD diamond composite coating, which comprises a plurality of layers of micro diamond coatings and nano diamond coatings which are sequentially and alternately deposited.

The grain size of the micron diamond coating is 2-5 mu m, and the grain size of the nano diamond coating is 20-80 nm.

The single-layer thickness of the micro diamond coating is 1-3 mu m, and the single-layer thickness of the nano diamond coating is 200 nm-1 mu m.

The invention discloses a preparation method of a low-stress CVD diamond composite coating, which comprises the following steps:

on the surface of the pretreated hard alloy substrate, a time mode method is adopted to alternately deposit a micron diamond coating and a nanometer diamond coating in turn by hot wire CVD, so that stress release in the coating deposition process can be realized, secondary nucleation of a film is promoted, and gaps among micron diamond particles are filled; the bonding strength between the coating and the substrate and between the coating is improved.

The process of depositing the micro-diamond coating comprises the following steps: methane and hydrogen are used as reaction gases, the hydrogen flow is ensured to be constant, the loading flow and time of the methane are adjusted by adopting a time mode method, and the cyclic deposition process of 'film growth-hydrogen reduction' of the micron diamond is realized.

The flow ratio of hydrogen to methane in the film growth process is 800-1200: 10-20; the flow ratio of hydrogen to methane in the hydrogen reduction process is 800-1200: 1-5; the time ratio of the film growth process to the hydrogen reduction process is 1-2: 1.

The process for depositing the nano-diamond coating comprises the following steps: methane, hydrogen and argon are used as reaction gases, the flow of the hydrogen and the argon is ensured to be unchanged, the loading flow and time of the methane are adjusted by adopting a time mode method, and the cyclic deposition process of 'film growth-argon etching and hydrogen reduction' of the nano-diamond is realized.

The flow ratio of hydrogen, argon and methane in the film growth process is 800-1200: 600-1000: 10-20; the flow ratio of hydrogen, argon and methane in the processes of argon etching and hydrogen reduction is 800-1200: 600-1000: 1-5; the time ratio of the film growth process to the argon etching and hydrogen reduction process is 1-2: 1.

The structure of the composite diamond coating is formed by alternately depositing the micro-diamond coating and the nano-diamond coating, and the heat stress accumulation in the coating is more and more serious along with the progress of a film growth reaction along with the increase of the deposition time. The invention realizes the 'intermittent' growth of the film by controlling the input flow and time of methane as the source gas for reacting the diamond coating. Under the condition of low methane flow, the growth reaction of the diamond film does not occur, no thermal stress is generated in the stage, and meanwhile, the stress release in the grown film can be realized. The thermal stress is reduced, and the interlayer bonding strength of the composite coating is improved.

And (3) depositing micron diamond on the surface of the pretreated hard alloy substrate, and controlling the time of the loading flow of methane as a reaction source gas by adopting a time mode method. Under the condition of normal methane flow, a micron diamond film is deposited on the surface of the substrate; under the condition of low methane flow, the diamond film stops growing, and the stress of the grown film is gradually reduced under the action of aging due to the reduction action of hydrogen, so that the bonding strength of the coating and the substrate is improved. Meanwhile, under the condition of low-flow methane, due to the existence of the carbon source gas, the nucleation process of the diamond film at the early stage of growth is realized, the growth of the diamond film at the next stage under the condition of normal methane flow is promoted, and the quality of the diamond film is improved. The high-density nucleation reaction is beneficial to filling gaps among single-layer micron diamond particles and improving the compactness and uniformity of the coating.

And loading argon gas on the surface of the grown micron diamond coating, adjusting the reaction pressure, and carrying out the deposition preparation of the nano diamond film. Similarly, under the condition of normal methane flow, a nano-diamond film is deposited on the surface of the substrate, and the thickness of the nano-diamond coating is continuously increased after micro-diamond gaps are filled and leveled; under the condition of low methane flow, the diamond film stops growing, and the film stress is gradually reduced under the aging effect due to the reduction effect of hydrogen and the etching effect of argon ions.

Advantageous effects

Compared with the prior art, the invention has the advantages of realizing the release and reduction of thermal stress in the deposition process of the diamond coating and improving the bonding strength between the coating and the base and composite coatings. Under the condition of low methane flow, the growth of the diamond film is stopped, the nucleation of the diamond is promoted, a good nucleation foundation is provided for the growth stage of the film, and the problem of film production defects caused by too low nucleation density is solved. The growth of the diamond film at the stage is stopped, no thermal stress accumulation is generated, and simultaneously, due to the aging effect in the deposited diamond film, the accumulated thermal stress is reduced, and the bonding strength between the coatings is improved.

Drawings

FIG. 1 is a graph showing the control of source gas flow and time during the deposition of the micro-diamond coating in examples 1-2.

FIG. 2 is a control chart showing the flow rate and time of the source gases for the reaction in the process of depositing the nano-diamond coating in examples 1 to 2.

Fig. 3 is a graph showing the wear of the diamond coated milling cutter manufactured in example 1.

Fig. 4 is a graph showing the wear of the diamond coated milling cutter manufactured by the conventional method of comparative example 1.

Fig. 5 is an indentation topography of the surface of a diamond coated cutting insert made in example 2.

Fig. 6 is an indentation topography of the surface of a diamond coated cutting insert made by the conventional method of comparative example 2.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

And preparing the low-stress CVD diamond composite coating on the surface of the integral hard alloy milling cutter. The specification of the cutter is as follows: an integral four-edged ball-end mill having a diameter of 8mm, a blade length (coating portion) of 30mm and a number of 40.

(1) Cleaning the surface of the cutter: immersing the whole cutter in a detergent solution, and carrying out ultrasonic treatment for 10 minutes; and (5) washing with clear water and drying.

(2) Chemical pretreatment of the edge surface: the blade of the milling cutter is put in an alkali solution (potassium ferricyanide: potassium hydroxide: water: 1: 10) for ultrasonic treatment for 30 minutes, and the milling cutter is washed and dried. And then placing the blade part subjected to alkali treatment in an acid solution (hydrochloric acid: hydrogen peroxide: 3: 7) for natural reaction for 1 minute, washing and drying.

(3) Tool before coating: and (3) placing the pretreated cutter in a special fixture of CVD diamond coating equipment, arranging a hot wire, and preparing for coating.

(4) Deposition preparation of the composite coating: starting the coating equipment, and when the vacuum reaction chamber reaches 5Pa, firstly carrying out micron diamond coating deposition: inputting methane and hydrogen, setting the flow rates to be 10sccm and 800sccm respectively, loading the power of the hot wire to a set target value, and performing normal micron diamond film growth for 10 min; then keeping the hydrogen flow unchanged, adjusting the methane flow to 2sccm, and keeping for 20 min; and sequentially circulating the normal flow methane (10sccm, 10min) -low flow methane (2sccm, 20min) until the set time of the coating growth is finished by 1h, thereby realizing the cyclic deposition process of 'film growth-hydrogen reduction-film growth-hydrogen reduction' of the micron diamond.

Then, nano-diamond coating deposition is carried out: inputting methane, argon and hydrogen, setting the flow rates to be 10sccm, 600sccm and 800sccm respectively, loading the hot wire power to a set target value, and performing normal nano-diamond film growth for 10 min; then keeping the flow of argon and hydrogen unchanged, adjusting the flow of methane to 2sccm, and keeping for 20 min; and sequentially circulating the normal flow methane (10sccm, 10min) -low flow methane (2sccm, 20min) until the set time of the growth of the coating is finished by 1h, thereby realizing the cyclic deposition process of 'thin film growth-argon etching, hydrogen reduction-thin film growth-argon etching and hydrogen reduction' of the micron diamond.

The above process was repeated 5 times, the deposition time of the coating was accumulated for 10 hours, the preparation was completed, and the cutter was taken out, wherein the flow rate and time control of the source gases for the deposition process of the micro-diamond coating and the nano-diamond coating are shown in fig. 1 and 2, respectively.

Example 2

And preparing the low-stress CVD diamond composite coating on the surface of the flat-sheet type hard alloy turning blade. The specification of the cutter is as follows: flat sheet type turning blade, specification 15mm 5mm, quantity is 50.

(2) Chemical pretreatment of the blade surface: the whole blade is put into an alkali solution (potassium ferricyanide: potassium hydroxide: water: 1: 10) for ultrasonic treatment for 30 minutes, taken out, washed and dried. And placing the blade subjected to the alkali treatment in an acid solution (hydrochloric acid: hydrogen peroxide: 3: 7) for natural reaction for 1 minute, taking out, washing and drying.

(3) Tool before coating: and (3) placing the pretreated blade in a special fixture of CVD diamond coating equipment, arranging a hot wire, and preparing for coating.

Comparative example 1

And preparing the diamond coating on the surface of the integral hard alloy milling cutter by a conventional method.

The diamond-coated milling cutter prepared in example 1 and the diamond-coated milling cutter prepared by the conventional method in the comparative example were subjected to a graphite milling comparative experiment, and after milling for 30min, the wear conditions of the cutter were respectively shown in fig. 3 and 4, which shows that the coating on the blade portion in fig. 3 slightly falls off and the coating on the blade portion in fig. 4 seriously falls off, indicating that the preparation method of the present invention can effectively reduce the thermal stress of the coating and further improve the bonding force between the coating and the substrate.

Comparative example 2

And preparing the diamond coating on the surface of the flat-sheet type hard alloy turning blade by a conventional method.

The diamond coated cutting blade prepared in example 2 and the cutting blade prepared in the conventional method of the comparative example were respectively inspected by an indentation method, and the shapes of indentations on the surfaces of the cutting blades are respectively shown in fig. 5 and 6, and it can be seen that only the coating layer is peeled off around the indenter in fig. 5; and the result shows that the coating prepared by the method has better adhesive force than the coating prepared by the conventional method.

Claims

1. A low stress CVD diamond composite coating is characterized in that: the coating is a multilayer micron diamond coating and a nanometer diamond coating which are sequentially and alternately deposited; wherein the micron diamond is a cyclic deposition process of 'film growth-hydrogen reduction'; the nano diamond is a cyclic deposition process of 'film growth-argon etching and hydrogen reduction';

wherein the depositing a micro-diamond coating process comprises: methane and hydrogen are used as reaction gases, the hydrogen flow is ensured to be constant, the loading flow and time of the methane are adjusted by adopting a time mode method, and the cyclic deposition process of 'film growth-hydrogen reduction' of the micron diamond is realized; the flow ratio of hydrogen to methane in the film growth process is 800-1200: 10-20; the flow ratio of hydrogen to methane in the hydrogen reduction process is 800-1200: 1-5; the time ratio of the film growth process to the hydrogen reduction process is 1-2: 1;

the process for depositing the nano-diamond coating comprises the following steps: methane, hydrogen and argon are used as reaction gases to ensure that the flow rates of the hydrogen and the argon are unchanged, and a time mode method is adopted to adjust the loading flow rate and time of the methane, so that the cyclic deposition process of 'film growth-argon etching and hydrogen reduction' of the nano-diamond is realized; the flow ratio of hydrogen, argon and methane in the film growth process is 800-1200: 600-1000: 10-20; the flow ratio of hydrogen, argon and methane in the processes of argon etching and hydrogen reduction is 800-1200: 600-1000: 1-5; the time ratio of the film growth process to the argon etching and hydrogen reduction process is 1-2: 1.

2. A low stress CVD diamond composite coating according to claim 1, wherein: the grain size of the micron diamond coating is 2-5 mu m, and the grain size of the nano diamond coating is 20-80 nm.

3. A low stress CVD diamond composite coating according to claim 1, wherein: the single-layer thickness of the micro diamond coating is 1-3 mu m, and the single-layer thickness of the nano diamond coating is 200 nm-1 mu m.

4. A method of producing a low stress CVD diamond composite coating according to claim 1, comprising:

sequentially and alternately depositing a micro diamond coating and a nano diamond coating on the surface of the pretreated hard alloy substrate by adopting a time mode method through hot wire CVD; wherein the depositing a micro-diamond coating process comprises: methane and hydrogen are used as reaction gases, the hydrogen flow is ensured to be constant, the loading flow and time of the methane are adjusted by adopting a time mode method, and the cyclic deposition process of 'film growth-hydrogen reduction' of the micron diamond is realized; the flow ratio of hydrogen to methane in the film growth process is 800-1200: 10-20; the flow ratio of hydrogen to methane in the hydrogen reduction process is 800-1200: 1-5; the time ratio of the film growth process to the hydrogen reduction process is 1-2: 1;