Titanium alloy cutting hard coating, method for preparing same, and use thereof

Abstract

The present application belongs to the technical field of cutting tool surface coating, and discloses a hard coating for titanium alloy cutting and a preparation method and application thereof. The hard coating comprises a bottom layer and a top layer. The bottom layer is a W bottom layer or a W-N bottom layer, and the top layer is a W top layer or a W-N top layer. The thickness of the hard coating is 2.0-2.5 μm, wherein the thickness of the bottom layer is 0.3-0.6 μm, and the thickness of the top layer is 1.5-2.0 μm. The elements in the hard coating are tungsten 80-100 at. % and nitrogen 0-20 at. %. The coating is deposited by high-power pulsed magnetron sputtering. The coating has good hardness and good oxidation resistance, prolongs the service life of the coated tool in titanium alloy machining, and still shows excellent titanium alloy cutting performance under dry machining conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tool protective coating for metal cutting, more particularly, relates to a hard coating for titanium alloy cutting and a preparation method and application thereof. BACKGROUND

[0002] Titanium alloy has the advantages of high strength, strong corrosion resistance and high temperature resistance, and is widely used in the fields of aviation, navigation and biomedical engineering. However, when machining titanium alloy, the cutting force is large, which easily causes chip accumulation, affecting the reliability of the coated tool. At present, the machining efficiency of titanium alloy is low (the cutting speed is less than 80 m / min), and the cutting is difficult. Titanium alloy is prone to diffusion reaction with tool materials, and has high requirements for tool surface protective coating. Therefore, when machining titanium alloy, the performance of the tool surface coating material is very critical. Developing high wear-resistant and temperature-resistant coating material with good performance is the premise of obtaining excellent cutting performance of coated tools. SUMMARY

[0003] In order to solve the above-mentioned shortcomings and deficiencies in the prior art, and to make the tool and the machined material have lower chemical reactivity when machining titanium alloy, the primary purpose of the present application is to provide a hard coating for titanium alloy cutting, which has good mechanical properties, film base bonding force and higher oxidation resistance.

[0004] Another purpose of the present application is to provide a preparation method of the above-mentioned hard coating for titanium alloy cutting. The method uses high-power pulsed magnetron sputtering technology to prepare W and W-N coatings. Since the W and W-N coatings prepared by physical vapor deposition technology are sensitive to changes in deposition atmosphere, the growth morphology and microstructure of the hard coating are changed by adjusting the preparation process of the hard coating. Under the premise of maintaining good mechanical properties and oxidation resistance, the service life of the coated tool for machining titanium alloy is prolonged, and the tool exhibits better titanium alloy cutting performance.

[0005] Still another purpose of the present application is to provide the application of the above-mentioned hard coating. The tool with the hard coating has a significantly improved cutting life when cutting titanium alloy compared with other common coated tools for machining titanium alloy, and exhibits better titanium alloy cutting performance.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A hard coating for titanium alloy cutting, the hard coating comprises a bottom layer and a top layer, the bottom layer is a W bottom layer or a W-N bottom layer, the top layer is a W top layer or a W-N top layer, the thickness of the hard coating is 2.0-2.5 μm, wherein the thickness of the bottom layer is 0.3-0.6 μm, and the thickness of the top layer is 1.5-2.0 μm; the elements in the hard coating are as follows in terms of atomic percentage: tungsten 80-100 at.% and nitrogen 0-20 at.%.

[0008] The preparation method of the hard coating for cutting titanium alloy comprises the following steps:

[0009] S1. Pre-treating the hard alloy substrate;

[0010] S2. Adjusting the flow rates of argon and nitrogen to maintain the pressure ratio of the coating chamber at P N2 / (P Ar +P N2 ) = 0-30%, maintaining the total gas pressure at 0.4-1.6 Pa, turning on the high-power pulsed magnetron tungsten target, adjusting the average power density of the tungsten target to 12-14 W / cm 2 , the duty cycle to 2.5-10%, the frequency to 50-1000 Hz, adjusting the bias voltage of the hard alloy substrate to -40--60 V, the deposition temperature to 250-500 DEG C, depositing a bottom layer with a thickness of 0.3-0.6 mu m on the hard alloy substrate; then adjusting the bias voltage of the hard alloy substrate to -80--120 V, the deposition temperature to 250-500 DEG C, depositing a top layer with a thickness of 1.5-2.0 mu m on the bottom layer;

[0011] S3. After the deposition is completed, the target power supply and the bias voltage power supply are turned off, the argon and nitrogen gas flow valves are closed, and after the chamber temperature is reduced to room temperature, the furnace door can be opened to take out the sample, thereby obtaining the hard coating for cutting titanium alloy.

[0012] Preferably, the pre-treatment in step S1 is to fix the cleaned hard alloy substrate on the workpiece turntable in the coating chamber, make the substrate face the tungsten target material, turn on the heater to heat to 500 DEG C, pre-extract the base vacuum to 3.0-5.0 x 10 - 3 Pa, introduce argon into the vacuum chamber, maintain the argon pressure at 1.5-3.0 Pa, maintain the substrate bias voltage at -800--1000 V, and perform glow discharge sputtering cleaning on the chamber for 10-30 min.

[0013] Preferably, the hard alloy is YG6 brand hard alloy.

[0014] The application of the hard coating in the field of cutting processing of titanium alloy.

[0015] Compared with the prior art, the application has the following beneficial effects:

[0016] 1. The hard coating has good mechanical properties, film-substrate adhesion and oxidation resistance. The prepared coating has a nitrogen content of (0-20 at.%) and a high specific gravity tungsten element has a very small diffusion rate, thereby reducing the chemical reaction tendency during the processing of titanium alloy, reducing the adhesive wear between the tool surface and the processed material, and ultimately prolonging the service life of the coated tool.

[0017] 2. The present application uses high-energy pulsed magnetron sputtering of pure tungsten target to prepare W and W-N hard coatings in nitrogen and argon atmosphere, which has lower chemical reactivity when machining titanium alloy, reducing the adhesive wear of titanium alloy during machining.

[0018] 3. The coating prepared by the present application using high-power pulsed magnetron sputtering technology has the characteristics of smooth surface and higher coating density, which is beneficial to resist the reaction diffusion when machining titanium alloy, and can further improve the cutting performance when machining titanium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM cross-sectional morphology of the hard coating for machining titanium alloy prepared for Examples 1-2 and Comparative Examples 1-2.

[0020] Figure 2 Hardness and elastic modulus results of the hard coating for machining titanium alloy prepared for Examples 1-2 and Comparative Examples 1-2.

[0021] Figure 3 TEM micrograph of the W-N hard coating prepared for Example 2.

[0022] Figure 4 Oxidation cross-section of the hard coating for machining titanium alloy prepared for Examples 1-2 and Comparative Examples 1-2 oxidized at 500°C for 5h.

[0023] Figure 5 Rake face wear curve of the hard coating for machining titanium alloy prepared for Examples 1-2 and Comparative Examples 1-2 at an online speed v c = 80 m / min.

[0024] Figure 6 Rake face wear curve of the hard coating for machining titanium alloy prepared for Examples 1-2 and Comparative Examples 1-2 at an online speed v c = 100 m / min. DETAILED DESCRIPTION

[0025] The present application will be further described in conjunction with specific examples, but should not be construed as a limitation of the present application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art. Unless specifically indicated, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0026] Example 1

[0027] The W hard coating for machining titanium alloy contains elements in atomic percentage: tungsten is 100 at.%, and the preparation method is according to the following steps:

[0028] (1) The cleaned YG6 cemented carbide tool substrate was fixed on the workpiece turntable in the coating chamber, with the substrate facing the tungsten target. The rotation rate of the substrate turntable was 3.0 rpm, the heater was turned on to heat to 500°C, and the base vacuum was pre-pumped to 3.0x10 –3 Pa:

[0029] (2) Argon was introduced into the vacuum chamber, the gas pressure in the chamber was maintained at 3 Pa, the substrate bias was maintained at -800 V, and the chamber was glow sputter cleaned for 30 min;

[0030] (3) The substrate bias was reduced to -60 V; the argon flow rate was adjusted to maintain the total gas pressure in the chamber at 0.8 Pa; the high-power pulsed magnetron tungsten target was turned on, the average power density of the tungsten target was adjusted to 12 W / cm 2 , the duty cycle was 2.5%, and the frequency was 50 Hz; a W bottom layer with a thickness of 0.5 μm was deposited on the tool substrate;

[0031] (4) The deposition conditions of step (3) were maintained, the bias was increased to -120 V; a W top layer with a thickness of 2.0 μm was obtained on the W bottom layer;

[0032] (5) After the deposition was completed, the target power supply and the bias power supply were turned off, the argon and nitrogen flow valves were closed, and after the chamber temperature decreased to room temperature, the furnace door was opened to take out the sample, obtaining a W hard coating for titanium alloy cutting, which has a structure of a 2.0 μm W top layer and a 0.5 μm W bottom layer.

[0033] Example 2

[0034] The W-N hard coating for titanium alloy cutting contains elements in atomic percentages of 81.5 at.% tungsten and 18.5 at.% nitrogen, and the preparation method comprises the following steps:

[0035] (1) The cleaned YG6 cemented carbide tool substrate was fixed on the workpiece turntable in the coating chamber, with the substrate facing the tungsten target. The rotation rate of the substrate turntable was 3.0 rpm, the heater was turned on to heat to 500°C, and the base vacuum was pre-pumped to 3.0x10 –3 Pa:

[0036] (2) Argon was introduced into the vacuum chamber, the argon gas pressure was maintained at 3 Pa, the substrate bias was maintained at -800 V, and the chamber was glow sputter cleaned for 30 min;

[0037] (3) The substrate bias was reduced to -60 V; the argon and nitrogen flow rates were adjusted to maintain the pressure ratio P N2 / (P Ar +P N2 ) = 30%; the high-power pulsed magnetron tungsten target was turned on, and the average power density of the tungsten target was adjusted to 12 W / cm 2, duty cycle 2.5%, frequency 50Hz; W-N bottom layer with thickness of 0.5μm is deposited;

[0038] (4) The deposition conditions of step (3) are kept unchanged, and the bias voltage is increased to -120V; a W-N top layer with thickness of 1.7μm is obtained;

[0039] (5) After the deposition is completed, the target power supply and the bias voltage power supply are turned off, the argon and nitrogen flow valves are turned off, and the furnace door is opened to take out the sample after the chamber temperature is reduced to room temperature, thereby obtaining the W-N hard coating for titanium alloy cutting, which has a structure of a 1.7μm W-N top layer and a 0.5μm W-N bottom layer.

[0040] Figure 3 A TEM micrograph of the W-N hard coating prepared in Example 2 is shown in FIG. 1. Figure 3 As can be seen from FIG. 1, the W-N hard coating for titanium alloy cutting prepared by the process mainly has a nanocrystalline body-centered cubic pure tungsten phase structure, and a small amount of tungsten nitride amorphous phase.

[0041] Comparative Example 1

[0042] The W-N hard coating for titanium alloy cutting contains elements in atomic percentage of 65.6at.% tungsten and 35.4at.% nitrogen, and is prepared according to the following steps:

[0043] (1) The cleaned YG6 hard alloy cutter substrate is fixed on the workpiece turret in the coating chamber, so that the substrate faces the tungsten target, the rotation rate of the substrate turret is 3.0rpm, the heater is turned on to heat to 500℃, and the base vacuum is pre-extracted to 3.0×10 –3 Pa:

[0044] (2) Argon is introduced into the vacuum chamber, the argon pressure is maintained at 3Pa, the substrate bias voltage is maintained at -800V, and the chamber is glow discharge sputtered for 30min;

[0045] (3) The substrate bias voltage is reduced to -60V; the argon and nitrogen flow rates are adjusted so that the pressure ratio is maintained at P N2 / (P Ar +P N2 ) = 50%; the high-power pulsed magnetron tungsten target is turned on, the average power density of the tungsten target is adjusted to 12W / cm 2 , duty cycle 2.5%, frequency 50Hz; W-N bottom layer with thickness of 0.5μm is deposited;

[0046] (4) The deposition conditions of step (3) are kept unchanged, and the bias voltage is increased to -120V; a W-N top layer with thickness of 1.6μm is obtained;

[0047] (5) After the deposition, the target power supply and the bias power supply are turned off, the argon and nitrogen flow valves are closed, and the chamber temperature is reduced to room temperature before the furnace door is opened to remove the sample, thereby obtaining the W-N hard coating for cutting titanium alloy, which has a structure of a 1.6-μm-thick W-N top layer and a 0.5-μm-thick W-N bottom layer.

[0048] Comparative Example 2

[0049] The W-N hard coating for cutting titanium alloy contains, in atomic percentage, 56.4 at.% tungsten and 43.6 at.% nitrogen; and is prepared according to the following steps:

[0050] (1) The cleaned YG6 hard alloy cutter substrate is fixed on the workpiece turret in the plating chamber, with the substrate facing the tungsten target, the rotation rate of the substrate turret is 3.0 rpm, the heater is turned on to heat to 500°C, and the base vacuum is pre-pumped to 3.0×10 –3 Pa:

[0051] (2) Argon is introduced into the vacuum chamber, the argon pressure is maintained at 3 Pa, the substrate bias is maintained at -800 V, and the chamber is glow discharge sputtered for 30 min;

[0052] (3) The substrate bias is reduced to -60 V; the argon and nitrogen flow rates are adjusted so that the pressure ratio is maintained at P N2 / (P Ar +P N2 ) = 66%; the high-power pulsed tungsten target is turned on, the average power density of the tungsten target is adjusted to 12 W / cm 2 , the duty cycle is 2.5%, and the frequency is 50 Hz; and a 0.5-μm-thick W-N bottom layer is deposited;

[0053] (4) The deposition conditions of step (3) are maintained, and the bias is increased to -120 V; thereby obtaining a 1.5-μm-thick W-N top layer;

[0054] (5) After the deposition, the target power supply and the bias power supply are turned off, the argon and nitrogen flow valves are closed, and the chamber temperature is reduced to room temperature before the furnace door is opened to remove the sample, thereby obtaining the W-N hard coating for cutting titanium alloy, which has a structure of a 1.5-μm-thick W-N top layer and a 0.5-μm-thick W-N bottom layer.

[0055] Figure 1SEM cross-sectional morphology of the hard coating for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2. Wherein, (a) is 2.0 μιη of W top layer and 0.5 μιη of W bottom layer for Example 1, (b) is 1.7 μιη of W-N top layer and 0.5 μιη of W-N bottom layer for Example 2, (c) is 1.6 μιη of W-N top layer and 0.5 μιη of W-N bottom layer for Comparative Example 1, (d) is 1.5 μιη of W-N top layer and 0.5 μιη of W-N bottom layer for Comparative Example 2. From the figures, it can be seen that the hard coatings for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2 all present obvious columnar crystal growth morphology, but the W-N coating of Example 2 prepared under low nitrogen atmosphere has similar amorphous phase or two-phase competitive growth morphology. Figure 1 From the figures, it can be seen that the hard coatings for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2 all present obvious columnar crystal growth morphology, but the W-N coating of Example 2 prepared under low nitrogen atmosphere has similar amorphous phase or two-phase competitive growth morphology.

[0056] Nanoindentation test was performed on the hard coating samples, Figure 2 Hardness and elastic modulus results of the hard coating for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2. Wherein, (a) is W hard coating for Example 1, (b) is W-N hard coating for Example 2, (c) is W-N hard coating for Comparative Example 1, (d) is W-N hard coating for Comparative Example 2. From the figures, it can be seen that the W hard coating of Example 1 has lower hardness compared with the W-N coatings of Examples 2 and Comparative Examples 1-2, but maintains close elastic modulus, and the mechanical properties of the W-N coatings of Examples 2 and Comparative Examples 1-2 are close. Figure 2 From the figures, it can be seen that the W hard coating of Example 1 has lower hardness compared with the W-N coatings of Examples 2 and Comparative Examples 1-2, but maintains close elastic modulus, and the mechanical properties of the W-N coatings of Examples 2 and Comparative Examples 1-2 are close.

[0057] Figure 4 Cross-sectional images of the hard coating for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2 oxidized at 500°C for 5h. Wherein, (a) is W hard coating for Example 1, (b) is W-N hard coating for Example 2, (c) is W-N hard coating for Comparative Example 1, (d) is W-N hard coating for Comparative Example 2. From the figures, it can be seen that the thickness of the oxidation layer of Example 1 is 1.0 μιη, the thickness of the oxidation layer of Example 2 is 1.6 μιη, the thickness of the oxidation layer of Comparative Example 1 is 1.8 μιη, and the thickness of the oxidation layer of Comparative Example 2 is 3.3 μιη. The oxidation rate of the coating increases with the increase of nitrogen content in the coating, and in comparison, the W hard coating of Example 1 has lower oxidation rate. Figure 4 From the figures, it can be seen that the thickness of the oxidation layer of Example 1 is 1.0 μιη, the thickness of the oxidation layer of Example 2 is 1.6 μιη, the thickness of the oxidation layer of Comparative Example 1 is 1.8 μιη, and the thickness of the oxidation layer of Comparative Example 2 is 3.3 μιη. The oxidation rate of the coating increases with the increase of nitrogen content in the coating, and in comparison, the W hard coating of Example 1 has lower oxidation rate.

[0058] Dry cutting test of titanium alloy was performed at different machining line speeds. The machining parameters were: v c = 80 and 100 m / min, a p = 0.5 mm, f = 0.15 mm / r, and TC4 titanium alloy was cut. Figure 5 Cross-sectional images of the hard coating for titanium alloy cutting prepared for Examples 1-2 and Comparative Examples 1-2 at machining line speed v c= 80 m / min flank wear curve. From Figure 5 It can be seen that the comparative example 2 reached the failure criterion at about 950 m of cutting length, the comparative example 1 and the example 2 both reached the failure criterion at about 1300 m of cutting length, and the example 1 reached the failure criterion at about 1770 m of cutting length. Figure 6 The on-line speed v of the hard coating for cutting titanium alloy prepared for the examples 1-2 and the comparative examples 1-2 is shown in Table 1. c = 100 m / min flank wear curve. From Figure 6 It can be seen that the comparative example 2 reached the failure criterion at about 370 m of cutting length, the comparative example 1 reached the failure criterion at about 520 m of cutting length, the example 2 reached the failure criterion at about 730 m of cutting length, and the example 1 reached the failure criterion at about 860 m of cutting length. Figure 5 and Figure 6 It can be seen from the results of the examples 1-2 and the comparative examples 1-2 that the W hard coating of the example 1 has a longer cutting life when cutting TC4 at two cutting speeds, which is due to the lower oxidation rate of the W hard coating of the example 1 under the premise of maintaining certain mechanical properties, resulting in the reduction of oxidation wear during machining.

[0059] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods, which are all included in the protection scope of the present application.

Claims

1. The application of a hard coating in the machining of titanium alloys, characterized in that, The hard coating comprises a base layer and a top layer. The base layer is a W-type base layer or a W-N-type base layer, and the top layer is a W-type top layer or a W-N-type top layer. The thickness of the hard coating is 2.0~2.5 μm, wherein the thickness of the base layer is 0.3~0.6 μm, and the thickness of the top layer is 1.5~2.0 μm. The elemental composition of the hard coating, in atomic percentage, is: tungsten 80~100 at.% and nitrogen 0~20 at.%. The method for preparing the hard coating for titanium alloy cutting includes the following steps: S1. Pre-treat the YG6 grade cemented carbide matrix; S2. Adjust the flow rates of argon and nitrogen to maintain the pressure ratio in the coating chamber at P. N2 / (P) Ar +P N2 With the pressure set at 0-30%, maintain a total gas pressure of 0.4-1.6 Pa, turn on the high-power pulsed magnetron sputtering tungsten target, and adjust the average power density of the tungsten target to 12-14 W / cm³. 2 The duty cycle is 2.5 ~ 10%, and the frequency is 50 ~ 1000 Hz. The cemented carbide substrate bias voltage is adjusted to −40 ~ −60 V, and the deposition temperature is 250 ~ 500 °C to deposit a bottom layer with a thickness of 0.3 ~ 0.6 μm on the cemented carbide substrate. Then, the cemented carbide substrate bias voltage is adjusted to −80 ~ −120 V, and the deposition temperature is 250 ~ 500 °C to deposit a top layer with a thickness of 1.5 ~ 2.0 μm on the bottom layer. S3. After deposition, turn off the target power supply and bias power supply, and turn off the argon and nitrogen gas flow valves. After the chamber temperature drops to room temperature, open the furnace door and take out the sample to obtain a hard coating for titanium alloy cutting.

2. The application of the hard coating according to claim 1 in the field of titanium alloy machining, characterized in that, The pretreatment described in step S1 involves fixing the cleaned cemented carbide onto the workpiece holder inside the coating chamber, ensuring the substrate faces the tungsten target, turning on the heater to raise the temperature to 50°C, and pre-evacuating the base vacuum to 3.0~5.0×10⁻⁶. -3 Pa; Argon gas is introduced into the vacuum chamber, and the Ar gas pressure is maintained at 1.5~3.0 Pa. The substrate bias voltage is maintained at −800~−1000 V. The chamber is cleaned by glow discharge sputtering for 10~30 min.

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