A method of mitigating the damage to the fatigue performance of a metal by a brittle nitride coating

Abstract

The present application relates to a kind of vacuum PVD coating methods, specifically to a kind of method for relieving the damage of brittle nitride coating to metal fatigue performance.The technical problem that the hard metal nitride coating for existing aero-engine blade can significantly reduce the fatigue performance of metal matrix under the action of alternating load is solved.The present application includes the following steps:1) pretreatment is carried out to the surface of metal matrix;2) metal matrix is installed in the vacuum chamber of cathode vacuum arc, and metal target is arranged in ion implantation target position;3) vacuumizing;4) metal target ion is injected to the surface of metal matrix;5) the nitride coating of doped Ni is deposited on the surface of metal matrix, so that the thickness of nitride coating reaches 4.5-5.5 μm, and the addition amount of Ni in nitride coating is 10.2at.%-10.6at.%.The present application effectively relieves the damage of nitride coating to metal matrix fatigue performance.

Description

TECHNICAL FIELD

[0001] The application relates to a vacuum PVD coating method, in particular to a method for relieving damage of a brittle nitride coating to metal fatigue performance, which can be used for surface protection of a titanium alloy blade material of an aero-engine. BACKGROUND

[0002] An aero-engine serving in a sand-dust environment often suffers from serious sand-dust erosion, which causes serious damage to compressor blades and blisks and affects propulsion efficiency. A metal nitride coating with high hardness can effectively improve the erosion resistance of the blade surface. However, hard metal nitride coatings such as ZrN, CrN and TiN can significantly reduce the fatigue performance of the metal substrate under alternating loads. Studies have shown that the fatigue strength of a Ti6Al4V substrate is 875 MPa, and after being provided with CrN and TiN coatings respectively, the fatigue strength is reduced from 875 MPa to 775 MPa and 450 MPa respectively. This reduction in fatigue strength limits the application of metal nitride coatings in the compressor of an aero-engine. In addition, the structure of a blisk is complex, and there is serious shielding between the blades, so that a multilayer coating structure with alternating soft and hard cannot be realized on the surface of the blisk, and the preparation is difficult. Therefore, it is necessary to develop a coating preparation method which is convenient to prepare and is not limited by the complex shape of the blisk, so as to relieve the damage of hard metal nitride coatings to the fatigue performance of the substrate. SUMMARY

[0003] The application aims to solve the technical problem that the existing hard metal nitride coating for an aero-engine blade can significantly reduce the fatigue performance of the metal substrate under alternating loads, and provides a method for relieving the damage of a brittle nitride coating to metal fatigue performance.

[0004] The application concept is that, when the nitride coating is prepared, a second-phase metal Ni phase which does not form a bond with nitrogen elements is added, so as to relieve the damage of the nitride coating to the fatigue performance of the metal by adding the second phase, and solve the technical problem that the existing hard metal nitride coating for an aero-engine blade can significantly reduce the fatigue performance of the metal substrate under alternating loads.

[0005] To achieve the above application purposes and complete the above application concept, the technical solution of the application is as follows:

[0006] A method for relieving the damage of a brittle nitride coating to metal fatigue performance, which is characterized by comprising the following steps:

[0007] 1) The surface of the metal substrate is pretreated to be clean and dry;

[0008] 2) install the metal substrate in the vacuum chamber of the cathode vacuum arc, and arrange the metal target at the ion implantation target position; the metal target is any one of a Zr metal target, a Cr metal target and a Ti metal target;

[0009] 3) vacuumize the vacuum chamber to 1×10 -4 ~ 5×10 -3 Pa;

[0010] 4) start the ion implantation target, implant the metal target ion to the metal substrate surface, and clean the oxide on the metal substrate surface;

[0011] 5) use three arc sources, two of which use the metal target material in step 2), and the other uses a composite target material combined by Ni and the metal target in step 2), the mass ratio of Ni to the metal in the composite target material is 1:1, deposit a Ni-doped nitride coating on the metal substrate surface, so that the thickness of the nitride coating reaches 4.5-5.5 μm, and the addition amount of Ni in the nitride coating is 10.2 at.% to 10.6 at.%.

[0012] Further, in step 1), the pretreatment is specifically: ultrasonic cleaning the metal substrate with acetone for 5-10 min, then ultrasonic cleaning with deionized water for 5-10 min, and finally cleaning with anhydrous ethanol and drying.

[0013] Further, in step 2), the metal target is a Cr metal target.

[0014] Further, in step 4), the conditions for implanting Cr ions to the metal substrate surface are: the arc pressure is set to 90 V, the high voltage is set to 8 kV, the frequency is set to 8 Hz, the beam intensity is 4-8 mA, and the ion implantation time is 20-40 min.

[0015] Further, in step 5), the deposition conditions of the nitride coating are: the arc source of the two Cr metal target materials is 120 A, the arc source of the composite target material is 100 A, the substrate bias is 280 V, and the N2 flow is 15 sccm.

[0016] Further, in step 3), the vacuum chamber is vacuumized to 5×10 -3 Pa;

[0017] In step 5), the addition amount of Ni in the nitride coating is 10.4 at.%.

[0018] The beneficial effects of the present application are:

[0019] 1. The method for relieving the damage of brittle nitride coating to metal fatigue performance, by adding a second metal soft phase in the nitride coating, reducing the stress concentration caused by the surface defects of the coating, increasing the fracture toughness of the nitride coating, improving the critical cracking stress of the coating under alternating load, and effectively relieving the damage of the nitride coating to the fatigue performance of the metal matrix.

[0020] 2. The method for relieving the damage of brittle nitride coating to metal fatigue performance, the addition amount of Ni in the nitride coating is 10.2at.% to 10.6at.%, at this concentration, Ni will precipitate at the position of the nitride columnar crystal grain boundary, form an independent metal phase, maintain the hardness of the nitride coating, improve the fatigue resistance of the nitride coating, and ensure the erosion resistance and fatigue resistance of the coating. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a morphology diagram of the CrN coating prepared by the method for relieving the damage of brittle nitride coating to metal fatigue performance;

[0022] Figure 2 is a morphology diagram of the CrN coating prepared by the method for relieving the damage of brittle nitride coating to metal fatigue performance, and the addition amount of Ni is 10.4at.%;

[0023] Figure 3 is a phase analysis spectrum of the CrN coating, wherein CrNiN-0 represents the CrN coating without addition, CrNiN-1 represents the CrN coating with the addition amount of Ni being 10.4at.%, Ni PDF represents the standard spectrum of Ni, and CrN PDF represents the standard spectrum of CrN;

[0024] Figure 4 is a curve diagram of the comparison results of the rotary bending fatigue test of the TC4 matrix, the TC4 matrix with the CrN coating (CrNiN-0), and the TC4 matrix with the CrN coating with the addition amount of Ni being 10.4at.% (CrNiN-1). DETAILED DESCRIPTION

[0025] The application will be described in detail below with the drawings and examples.

[0026] The method for relieving the damage of brittle nitride coating to metal fatigue performance comprises the following steps:

[0027] 1) The surface of the metal substrate is pretreated to make the surface clean and dry. In this embodiment, the metal substrate is TC4 substrate, and the pretreatment is as follows: the TC4 substrate is ultrasonically cleaned with acetone for 6 min, then ultrasonically cleaned with deionized water for 7 min, and finally cleaned with anhydrous ethanol and dried. In other embodiments, the ultrasonic cleaning time with acetone can be controlled within 5-10 min, and the ultrasonic cleaning time with deionized water can be controlled within 5-10 min.

[0028] 2) The TC4 substrate is installed in the vacuum chamber of the cathode vacuum arc, and the metal target is placed in the ion implantation target position. The metal element in the metal target is the metal element in the hard metal nitride coating to be prepared. The hard metal nitride coating mainly includes ZrN, CrN and TiN coatings, and the corresponding metal targets are Zr metal target, Cr metal target and Ti metal target, respectively. In this embodiment, the CrN coating is taken as an example, and the metal target in the ion implantation target is a Cr metal target.

[0029] 3) Start the mechanical pump to vacuumize to below 10 Pa, and then start the molecular pump to vacuumize to 5 x 10 -3 Pa. In other embodiments, the vacuum chamber can be vacuumized to 1 x 10 -4 - 5 x 10 -3 Pa.

[0030] 4) Turn on the ion implantation target to implant Cr ions onto the surface of the TC4 substrate to clean the oxide on the surface of the TC4 substrate. The conditions for implanting Cr ions onto the surface of the TC4 substrate are as follows: the arc voltage is set to 90 V, the high voltage is set to 8 kV, the frequency is set to 8 Hz, the beam intensity is 4-8 mA, and the ion implantation time is 30 min. In other embodiments, the ion implantation time can be 20-40 min.

[0031] 5) Three arc sources are used, two of which use pure Cr metal target material, and the other uses NiCr (NiCr mass ratio of 50wt.%:50wt.%) composite target material, to deposit a Ni-doped CrN coating on the surface of the TC4 substrate, so that the thickness of the CrN coating reaches 5 μm, and the addition amount of Ni in the CrN coating is 10.4 at.%. In other embodiments, the thickness of the CrN coating can be controlled within 4.5-5.5 μm, and the addition amount of Ni in the coating can be 10.2 at.%-10.6 at.%.

[0032] The deposition conditions of the nitride coating are as follows: the arc source of the two Cr metal target materials has an arc current of 120 A, the arc source of the composite target material has an arc current of 100 A, the substrate bias is 280 V, and the N2 flow rate is 15 sccm.

[0033] Meanwhile, the present application carries out CrN coating deposition on the TC4 substrate only under the same conditions according to the method of the present application to obtain a TC4 substrate with the same coating thickness, and here the CrN coating has no any addition. The morphology diagrams of the CrN coating without addition (CrNiN-0) and the CrN coating with the addition of 10.4 at.% Ni (CrNiN-1) are respectively shown in Figure 1 and Figure 2 It can be seen that the CrN coating after adding Ni has higher surface flatness. The phase analysis results of the CrN coating without addition (CrNiN-0) and the CrN coating with the addition of 10.4 at.% Ni (CrNiN-1) are shown in Figure 3 .

[0034] The control experiment of the performance test of the TC4 substrate with the CrN coating without addition and the TC4 substrate with the CrN coating with the addition of 10.4 at.% Ni is carried out, and the test results are as follows:

[0035] (1) Coating hardness

[0036] The hardness of the CrN coating with the addition of 10.4 at.% Ni is reduced from 21 GPa of the CrN coating without addition to 18 GPa, about 1800 Hv, which is higher than the hardness of quartz sand SiO2.

[0037] (2) Coating surface roughness

[0038] The roughness of the CrN coating with the addition of 10.4 at.% Ni is reduced from 52.0±8.2 nm of the CrN coating without addition to 42.7±2.4 nm.

[0039] (3) Fracture toughness evaluation

[0040] The fracture toughness of the CrN coating with the addition of 10.4 at.% Ni is increased from 2.92 MPa·m 1 / 2 of the CrN coating without addition to 3.22 MPa·m 1 / 2 .

[0041] (4) Rotary bending fatigue

[0042] The fatigue sample is prepared according to the aviation standard HB5152-1996 (metal room temperature rotary bending fatigue test method), and the test of the influence of the coating on the fatigue strength of the TC4 substrate at room temperature is carried out according to the standard. The fatigue strength is tested by the ascending and descending method, and the obtained test results are as follows: Figure 4As shown, the median fatigue limit at one million cycles for the uncoated TC4 substrate was 531 MPa, for the TC4 substrate with the unalloyed CrN coating was 452 MPa, and for the TC4 substrate with the CrN coating with a 10.4 at. % Ni addition was 505 MPa.

Claims

1. A method for mitigating fatigue performance damage to metals caused by brittle nitride coatings, characterized in that, Includes the following steps: 1) Pre-treat the surface of the metal substrate to ensure it is clean and dry; 2) The metal substrate is installed in the vacuum chamber of the cathode vacuum arc, and the metal target is placed at the ion implantation target site; the metal target is any one of Zr metal target, Cr metal target and Ti metal target; 3) Evacuate the vacuum chamber to 1×10⁻⁶. -4 ~5×10 -3 Pa; 4) Turn on the ion implantation target and inject metal target ions into the surface of the metal substrate to clean the oxides on the surface of the metal substrate; The conditions for implanting Cr ions into the surface of the metal substrate are: arc voltage set to 90V, high voltage set to 8kV, frequency set to 8Hz, beam current intensity set to 4-8mA, and ion implantation time set to 20-40min. 5) Use three arc sources, two of which use the metal target material from step 2), and the other arc source uses Ni combined with the metal target material from step 2) to form a composite target material. The mass ratio of Ni to metal in step 2) in the composite target material is 1:

1. Deposit a Ni-doped nitride coating on the surface of the metal substrate to make the nitride coating thickness reach 4.5 to 5.5 μm, and the amount of Ni added in the nitride coating is 10.2 at.% to 10.6 at.%. The deposition conditions for the nitride coating are as follows: the arc source ignition current of the two Cr metal targets is 120A, the arc source ignition current of the composite target is 100A, the substrate bias voltage is 280V, and the flow rate of N2 is 15sccm.

2. The method for mitigating fatigue performance damage to metals caused by brittle nitride coatings according to claim 1, characterized in that, In step 1), the pretreatment specifically involves: ultrasonically cleaning the metal substrate with acetone for 5-10 minutes, then ultrasonically cleaning it with deionized water for 5-10 minutes, and finally cleaning and drying it with anhydrous ethanol.

3. A method for mitigating fatigue performance damage to metals caused by brittle nitride coatings according to claim 1 or 2, characterized in that: In step 2), the metal target is a Cr metal target.

4. The method for mitigating fatigue performance damage to metals caused by brittle nitride coatings according to claim 1, characterized in that: In step 3), the vacuum chamber is evacuated to a pressure of 5 × 10⁻⁶. -3 Pa; In step 5), the amount of Ni added to the nitride coating is 10.4 at.%.

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