Laser shock peening and deposited film compounded inner hole surface strengthening method

Abstract

The invention relates to the technical field of surface strengthening, in particular to a laser shock strengthening and film deposition compounded inner hole surface strengthening method which comprises the following steps: carrying out laser shock strengthening on the surface of an inner hole of a part by adopting strip rectangular light spots so as to realize full-coverage deformation strengthening on the surface of the inner hole of the part, periodically distributed strip-shaped grooves are formed in the surface of the inner hole of the part; and preparing a deposited film on the surface of the inner hole of the part subjected to laser shock peening to form a laser shock peening and deposited film composite peening surface. The laser shock peening and film deposition compounded inner hole surface peening method aims at solving the problem that the wear-resisting property is poor after the inner hole surface of a part is treated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface strengthening, in particular to a method for surface strengthening of an inner hole by combining laser shock peening and deposition of a film. BACKGROUND

[0002] A connecting hole on a metal or metal-based part is a typical concentrated load transmission channel. Through contact and cooperation with other parts via the connecting hole, micro relative sliding occurs between the hole wall of the connecting hole and the cooperating structure under alternating load combination, which causes micro-motion fatigue cracks on the hole wall of the connecting hole, and further evolves into conventional cracks to cause fatigue fracture. In order to improve the performance of the connecting hole, surface treatment is performed on the inner hole surface of the connecting hole. Laser shock peening and deposition of a film are currently the most promising inner hole surface treatment technologies. Laser shock peening is a surface strengthening technology that uses nanosecond pulse laser to act on the surface of a material to generate plasma shock wave effects, thereby generating a surface residual compressive stress layer on the surface of the material (the depth can exceed 1 mm), which can significantly reduce the propagation rate of micro-motion cracks, thereby improving the micro-motion fatigue resistance of the inner hole. After deposition of a film, the deposited film on the inner hole surface can significantly improve the wear resistance. Generally, the diameter of the inner hole increases after laser shock peening, and the diameter of the inner hole decreases after deposition of a film.

[0003] After laser shock peening of the inner hole, the micro-motion fatigue performance of the connecting hole is significantly improved, but the inner hole surface is severely worn during the micro-motion fatigue process, the size of the inner hole changes, and the micro-motion sliding distance increases, which further accelerates the wear. After deposition of a film on the inner diameter, the micro-motion wear performance of the connecting hole is significantly improved, but the film is easily detached under the abrasive wear mechanism during the micro-motion process.

[0004] Therefore, the present application provides a method for surface strengthening of an inner hole by combining laser shock peening and deposition of a film. SUMMARY

[0005] (1) Technical problem to be solved The present application provides a method for surface strengthening of an inner hole by combining laser shock peening and deposition of a film, which solves the technical problem of poor wear resistance after surface treatment of the inner hole of a part.

[0006] (2) Technical solution The present application provides a method for surface strengthening of an inner hole by combining laser shock peening and deposition of a film, which includes the following steps: The laser shock peening is performed on the inner hole surface of the part by using strip rectangular light spots, so that the inner hole surface of the part is fully covered by deformation strengthening, and periodic strip grooves are formed on the inner hole surface of the part. The inner hole surface of the part after the laser shock peening is deposited with a film, so as to form a laser shock peening and film deposition composite strengthening surface.

[0007] Further, the strip rectangular light spot has high-power density strip areas and low-power density strip areas which are alternately and parallelly distributed.

[0008] Further, the width of the high-power density strip area is 10-500 microns, and the width of the low-power density strip area is at least 5 times of the width of the high-power density strip area.

[0009] Further, the width of the edge high-power density strip area in the strip rectangular light spot is 60-70% of the width of the center high-power density strip area.

[0010] Further, the strip direction of each strip rectangular light spot is parallel to the inner hole generatrix, and the boundaries of two adjacent strip rectangular light spots are aligned.

[0011] Further, the laser power density of each low-power density strip area is the same and higher than the laser power density threshold value of the plastic deformation of the inner hole material, and the laser power density of the high-power density strip areas presents a distribution feature that the power density is the highest at the center of the strip and gradually decreases to both sides.

[0012] Further, the strip rectangular light spots are regularly overlapped, and the high-power density strip areas correspond to the strip grooves.

[0013] Further, the width of the strip groove is positively correlated with the high-power density strip area, and the cross-sectional profile of the strip groove presents a distribution feature that the depth of the concave is the largest at the center of the strip and continuously decreases to both sides.

[0014] Further, the pulse width of the strip rectangular light spot is 8-40 ns.

[0015] Further, the wavelength of the strip rectangular light spot is 320-1064 nm.

[0016] (3) Beneficial effects In conclusion, the inner hole surface of the part is prepared to form a strengthening surface with a residual compressive stress layer, a wear-resistant or self-lubricating film, and periodic strip grooves. The wear-resistant or self-lubricating film can reduce the fretting wear of the inner hole, the periodic strip grooves can store abrasive particles to weaken the fretting wear, and the residual compressive stress layer is beneficial to the fretting fatigue performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0018] Figure 1 is a flowchart of a method for laser shock peening and depositing thin film to strengthen the inner hole surface provided by the embodiments of the present application; Figure 2 is a structural schematic diagram of a laser shock peening device provided by the embodiment 1 of the present application; Figure 3 is a schematic diagram of a strip rectangular light spot provided by the embodiment 1 of the present application; Figure 4 is Figure 3 is the A-A sectional view in Figure 5 is a schematic diagram of a concave strip surface provided by the embodiment 1 of the present application; Figure 6 is a structural schematic diagram of a strip-shaped groove provided by the embodiment 1 of the present application; Figure 7 is a structural schematic diagram of a depositing thin film preparation device provided by the embodiment 1 of the present application; Figure 8 is a structural schematic diagram of a surface groove provided by the embodiment 1 of the present application; Figure 9 is a schematic diagram of a uniform light spot provided by the embodiment 1 of the present application; Figure 10 is a schematic diagram of a spaced strip light spot provided by the embodiment 1 of the present application.

[0019] In the drawings: 1 - part; 2 - inner hole; 3 - rotary table; 4 - aluminum foil tape; 5 - deionized water; 6 - nanosecond pulse laser beam; 7 - strip rectangular light spot; 8 - high power density strip area; 9 - low power density strip area; 10 - strip strengthening surface; 11 - strip-shaped groove; 12 - concave strip surface; 13 - vacuum chamber; 14 - rotary table; 15 - first magnetron sputtering target; 16 - second magnetron sputtering target; 17 - deposited thin film; 18 - surface groove. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be further described in details below with reference to the accompanying drawings and embodiments. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, i.e., the present application is not limited to the described embodiments.

[0021] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in details below with reference to the accompanying drawings and embodiments.

[0022] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", etc. indicate the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the product of the present application is used, or the orientation or positional relationship commonly understood by those skilled in the art, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0023] The embodiment of the present application provides a laser shock peening and deposited film combined inner hole surface strengthening method, referring to Figure 1 The method can include the following steps: S100, laser shock peening is performed on the inner hole surface of the part by using a strip rectangular light spot to realize full coverage deformation strengthening of the inner hole surface of the part, and periodic distribution of strip-shaped grooves is formed on the inner hole surface of the part.

[0024] Specifically, the strip rectangular light spot has high power density strip areas and low power density strip areas which are parallel and alternating. It should be noted that each material will correspond to a laser power density threshold value I for generating plastic deformation. The power density of the high power density strip area is 1.5I-2.0I, and the power density of the low power density strip area is 1.0I-1.5I. The width of the high power density strip area is 10-500 microns, and the width of the low power density strip area is at least 5 times the width of the high power density strip area. The width of the edge high power density strip area in the strip rectangular light spot is 60%-70% of the width of the center high power density strip area. The strip direction of each strip rectangular light spot is parallel to the inner hole generatrix, and the boundaries of the two adjacent strip rectangular light spots are aligned.

[0025] Further, the laser power density of all the low-power density strip areas is the same and higher than the laser power density threshold value at which the inner hole material produces plastic deformation, and the laser power density of all the high-power density strip areas presents a distribution feature that the power density is the highest at the center of the strip and gradually decreases to both sides. Under certain conditions, a uniform rectangular spot with the same size as the above-mentioned strip rectangular spot and the same low-power density and a discrete strip spot with the same size as the above-mentioned strip rectangular spot and the same high-power density can be used to perform laser shock peening in sequence, and the same laser shock peening effect as the strip rectangular spot can be produced.

[0026] Further, the plurality of strip rectangular spots are regularly overlapped, and the high-power density strip areas correspond to the strip-shaped grooves. The width of the strip-shaped grooves is positively correlated with the high-power density strip areas, and the cross-sectional profile of the plurality of strip-shaped grooves presents a distribution feature that the depth of the concave is the largest at the center of the strip and continuously decreases to both sides. The distribution feature of the strip-shaped grooves is designed to make the surface of the grooves smoother to enhance the bonding stability with the deposited film and to avoid the surface stress of the strip-shaped grooves from being too concentrated to produce fatigue strength.

[0027] As an optional embodiment, the spot size of the strip rectangular spot is in the order of millimeter, the pulse width of the strip rectangular spot is 8 ns to 40 ns, and the wavelength of the strip rectangular spot is 320 nm to 1064 nm.

[0028] S200, depositing a film on the inner hole surface of the part after laser shock peening to form a laser shock peening and deposited film composite strengthening surface.

[0029] Specifically, the preparation process of the deposited film is to sequentially perform plasma cleaning, metal adhesive layer deposition, and surface layer DLC (Diamond Like Carbon) film deposition. The types of the deposited film include but are not limited to diamond-like carbon film, TiN film, etc., and the preparation methods include but are not limited to physical vapor deposition, chemical vapor deposition, etc. The deposited film is mainly composed of a metal adhesive film layer and a diamond-like carbon or TiN surface layer. The deposition temperature of the diamond-like carbon film should not exceed 200°C, the maximum temperature of the adhesive layer and the TiN film should not exceed 90% of the annealing temperature of the inner hole material, and the thickness of the deposited film is 1 μm to 6 μm.

[0030] Embodiment 1 Part 1 is a TB6 titanium alloy material with an inner hole 2, the diameter of the inner hole 2 is 20 mm, and the depth is 18 mm. A nanosecond pulsed laser beam 6 is used to irradiate the inner hole 2 for laser shock peening, and then the preparation of a deposited film 17 is performed on the surface of the inner hole 2. The specific process flow is as follows: 1. Laser shock peening As shown in Figure 2 , the part 1 is fixed on the rotary table 3, and the center axis of the inner hole 2 is coaxial with the rotation center axis of the rotary table 3.

[0031] Before laser shock peening, the aluminum foil tape 4 with a thickness of 120 μm and the deionized water 5 with a thickness of 1 mm are sequentially pasted on the hole wall surface of the inner hole 2. The included angle between the center axis of the nanosecond pulse laser beam 6 and the generatrix of the inner hole 2 is 60°, as shown in Figure 3 , the size of the strip rectangular spot 7 formed on the hole wall surface is 5.0 mm×5.0 mm, and the strip rectangular spot 7 has the high-power density strip area 8 and the low-power density strip area 9 which are alternately and parallelly distributed. The width of the high-power density strip area 8 inside the strip rectangular spot 7 is 100 μm, the width of the low-power density strip area 9 is 900 μm, and the width of the high-power density strip area at the edge of the strip rectangular spot 7 is 70 μm. The laser wavelength of the nanosecond pulse laser beam 6 is 1064 nm, and the pulse width is 18 ns.

[0032] The laser power density distribution curve of the strip rectangular spot 7 is shown in Figure 4 , the laser power density of the low-power density strip area 9 is 6 GW / cm 2 , and the laser power density is uniformly distributed. The laser power density at the center of the high-power density strip area 8 is 12 GW / cm 2 , and continuously decreases to 6 GW / cm 2 on both sides.

[0033] The laser is started to perform laser shock peening. The inner hole 2 is driven to rotate around the center axis by the rotary table 3. After one circle of the inner hole is strengthened, the strip rectangular spot 7 is moved along the center axis direction to perform the next circle of the inner hole strengthening. Until the strip strengthening spot is overlapped regularly and completely covers the hole wall surface of the inner hole 2, the boundaries of the adjacent strip rectangular spots 7 are aligned, and the corresponding high-power density strip areas 8 are aligned. The strip direction is parallel to the generatrix of the inner hole.

[0034] As shown in Figure 5 , the concave strip periodic distribution strengthening surface is formed on the hole wall of the inner hole 2 after laser shock peening. The multiple strip strengthening surfaces 10 form the concave strip surface 12 on the hole wall of the inner hole 2. The inner part of the single strip strengthening surface 10 has multiple strip-shaped grooves 11 which are uniformly distributed and regularly jointed by the strip strengthening spots (the dashed box in Figure 5 is the strengthening area of the single strip strengthening spot). The cross-sectional profile of the strip-shaped groove 11 of the hole wall of the inner hole 2 is shown in Figure 6 . The depth of the strip-shaped groove 11 is about 10 μm, and the width is about 100 μm. After laser shock peening, the aluminum foil tape 4 is removed, and the inner hole surface is cleaned.

[0035] 2, deposition film preparation seeFigure 7 After the strip-shaped light spot laser shock peening of the inner hole 2 is completed, the inner hole 2 is prepared by depositing a thin film, and plasma cleaning, metal bonding layer deposition and surface layer DLC film deposition are sequentially performed. Specifically, each process is as follows: ① Plasma cleaning: the part 1 is placed in the vacuum chamber 13, and is pumped to 2x10 -3 Pa, then argon gas 100sccm is introduced, the radio frequency ion source is turned on, the power is set to 300W, the substrate bias is turned on to -300V, the rotation speed of the rotation table 14 is set to 3r / min, and the cleaning time is 30min; ② Metal bonding layer deposition: the radio frequency ion source is turned off, the substrate bias is adjusted to -100V, the first (Cr) magnetron sputtering target 15 is turned on, the target current is set to 12A, the rotation speed of the rotation table 14 remains unchanged, and the deposition time is 30min; ③ Surface layer DLC film deposition: the second (Cr) magnetron sputtering target 16 is adjusted to 1A, the argon gas flow is adjusted to 80sccm, C2H2 gas is introduced, the gas flow is adjusted to 100sccm, the C target current is turned on to 4A, the substrate bias is adjusted to -800V, the rotation speed of the rotation table 14 remains unchanged, and the deposition time is 200min.

[0036] After the deposition of the thin film 17 is completed, the part 1 is taken out, and the laser shock peening and DLC thin film composite surface strengthening of the inner hole 2 are completed, as shown in Figure 8 The deposition thin film 17 uniformly covers the strip-shaped groove 11 to form a surface groove 18. During the micro-attrition process, the surface groove 18 can be used to store abrasive particles, reduce abrasive particle wear, and overall improve the micro-attrition damage resistance of the inner hole 2.

[0037] In addition, in the above embodiment 1, the strip-shaped rectangular light spot can be replaced by a uniform light spot 19 (see Figure 9 ) with a size of 5.0mmx5.0mm and a laser power density of 6GW / cm 2 , and a spaced strip-shaped light spot 20 (see Figure 10 ) with a strip size of 5.0mmx100μm, a strip spacing of 900μm and a laser power density of 12GW / cm 2 . The uniform light spot 19 and the spaced strip-shaped light spot 20 are used for laser shock peening in turn to produce the same laser shock peening effect as the strip-shaped rectangular light spot 7.

[0038] It should be clear that each embodiment in the specification is described in a progressive manner, and the same or similar parts between each embodiment can be referred to each other. Each embodiment focuses on the differences from other embodiments. The present application is not limited to the specific steps and structures described above and shown in the drawings. Moreover, for the sake of brevity, detailed descriptions of known methods and techniques are omitted.

[0039] The above merely provides an example of the present application, and is not limited to the present application. Various changes and modifications can be made to the present application without departing from the scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of claims of the present application.

Claims

1. A method for strengthening the surface of internal holes using a combination of laser shock peening and thin film deposition, characterized in that, The method includes the following steps: A strip-shaped rectangular laser spot is used to perform laser shock strengthening on the surface of the inner hole of the part, so as to achieve full coverage deformation strengthening of the surface of the inner hole of the part and form periodically distributed strip-shaped grooves on the surface of the inner hole of the part. A thin film is deposited on the inner hole surface of the laser-shock-strengthened part to form a composite strengthened surface of laser-shock-strengthened and deposited thin film.

2. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 1, characterized in that, The striped rectangular light spot has parallel alternating high-power density strip regions and low-power density strip regions.

3. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 2, characterized in that, The width of the high power density strip region is 10μm to 500μm, and the width of the low power density strip region is at least 5 times that of the high power density strip region.

4. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 3, characterized in that, The width of the edge high-power density strip area within the strip rectangular spot is 60% to 70% of that of the central high-power density strip area.

5. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 1, characterized in that, The strip direction of each of the striped rectangular light spots is parallel to the generatrix of the inner hole, and the boundaries of two adjacent striped rectangular light spots are aligned.

6. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 1, characterized in that, The laser power density of each of the low power density strip regions is the same and higher than the laser power density threshold for plastic deformation of the inner hole material. The laser power density of the multiple high power density strip regions exhibits a distribution characteristic where the power density is highest at the center of the strip and gradually decreases towards both sides.

7. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 2, characterized in that, Multiple rectangular light spots are neatly and regularly overlapped, and the high power density strip area corresponds to the strip-shaped groove.

8. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 7, characterized in that, The width of the strip-shaped groove is positively correlated with the high power density strip area, and the cross-sectional profile of the multiple strip-shaped grooves shows a distribution characteristic in which the depth of the groove is the greatest at the center of the strip and the depth of the groove continuously decreases to both sides.

9. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 1, characterized in that, The pulse width of the striped rectangular light spot is 8ns to 40ns.

10. The method for strengthening the surface of internal holes by combining laser shock peening and thin film deposition according to claim 1, characterized in that, The wavelength of the striped rectangular light spot is 320nm to 1064nm.

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