阅读说明：本技术 一种碳化硼陶瓷的激光冲击强化方法 (Laser shock strengthening method of boron carbide ceramic ) 是由 张帆 陈贝迪 张金咏 王为民 傅正义 于 2021-06-29 设计创作，主要内容包括：本发明公开一种碳化硼陶瓷的激光冲击强化方法,包括如下步骤：提供含有至少一抛光面的碳化硼陶瓷试件；在碳化硼陶瓷试件的一抛光面覆盖吸收层,并在吸收层上施加约束层；将施加约束层的抛光面朝向激光束并对其进行激光冲击强化处理；其中,激光冲击强化处理采用波长为1064nm的激光器,脉冲20-50ns,激光的光斑直径为2-4mm,单脉冲能量2-7J,频率2-5Hz,单脉冲激光光斑搭接率在37.5％-62.5％,冲击次数为2次。本发明提供的碳化硼陶瓷的激光冲击强化方法,能够实现碳化硼陶瓷的高质量冲击强韧化,并避免由于激光冲击强化引起的整体结构变形和破损。(The invention discloses a laser shock strengthening method of boron carbide ceramic, which comprises the following steps: providing a boron carbide ceramic test piece with at least one polished surface; covering a polished surface of the boron carbide ceramic test piece with an absorption layer, and applying a constraint layer on the absorption layer; facing the polished surface applied with the restraint layer to a laser beam and carrying out laser shock strengthening treatment on the polished surface; wherein, the laser shock peening adopts a laser with the wavelength of 1064nm, the pulse is 20-50ns, the spot diameter of the laser is 2-4mm, the single pulse energy is 2-7J, the frequency is 2-5Hz, the single pulse laser spot lap-joint rate is 37.5-62.5%, and the shock frequency is 2 times. The laser shock strengthening method of the boron carbide ceramic provided by the invention can realize high-quality shock strengthening and toughening of the boron carbide ceramic and avoid deformation and damage of the whole structure caused by laser shock strengthening.)

1. A laser shock peening method of boron carbide ceramic is characterized by comprising the following steps:

providing a boron carbide ceramic test piece with at least one polished surface;

covering a polished surface of the boron carbide ceramic test piece with an absorption layer, and applying a constraint layer on the absorption layer;

facing the polished surface applied with the restraint layer to a laser beam and carrying out laser shock strengthening treatment on the polished surface; the laser shock peening treatment adopts a laser with the wavelength of 1064nm, the pulse is 20-50ns, the spot diameter of the laser is 2-4mm, the single-pulse energy is 2-7J, the frequency is 2-5Hz, the single-pulse laser spot lap-joint rate is 37.5-62.5%, and the shock frequency is 2 times.

2. The method for laser shock peening of boron carbide ceramic according to claim 1, wherein the step of providing the boron carbide ceramic test piece having at least one polished surface comprises: and processing the boron carbide ceramic into a long strip shape, and grinding and polishing the boron carbide ceramic to obtain a boron carbide ceramic test piece.

3. The laser shock peening method of boron carbide ceramic according to claim 1, wherein the compactness of the boron carbide ceramic test piece is greater than 98%, and the roughness Ra of the polished surface is less than or equal to 4 μm.

4. The method of laser shock peening of boron carbide ceramic according to claim 1, wherein the absorption layer is black glue.

5. The method for laser shock peening of boron carbide ceramic according to claim 1, wherein the constraining layer is a deionized water layer 1-2 mm thick.

6. The method for laser shock peening of boron carbide ceramic according to claim 1, wherein the laser is an Nd: YAG laser or Yb: YAG laser.

7. The method for laser shock peening of boron carbide ceramic according to claim 1, wherein, in the laser shock peening treatment, a 1064nm Nd: YAG laser with pulse width of 20ns, laser spot diameter of 2-4mm, frequency of 2Hz, single pulse energy of 4-7J and spot overlapping rate of 50-62.5%.

8. The method for laser shock peening of boron carbide ceramic according to claim 7, wherein the spot diameter is 3-4 mm.

9. The method of laser shock peening of boron carbide ceramic according to claim 7, wherein the single pulse energy is 4.8 to 5.6J.

10. The method for laser shock peening of boron carbide ceramic according to claim 1, further comprising, after the laser shock peening treatment, surface cleaning the boron carbide ceramic test piece to remove the absorption layer.

Technical Field

The invention relates to the technical field of laser shock peening, in particular to a laser shock peening method of boron carbide ceramic.

Background

The boron carbide material has the advantages of low density, high strength, good thermal stability and good chemical stability, and is commonly used for light armors of helicopters and bulletproof armors of tanks. Although boron carbide ceramic has excellent penetration resistance, the boron carbide ceramic has low fracture toughness and high brittleness, so that the boron carbide ceramic is easy to break and weak in multiple-strike resistance in practical application, and the application of the boron carbide ceramic is limited to a certain extent, so that the strengthening and toughening of high-performance ceramic becomes a hotspot of the research on the ceramic material at present.

The laser shock peening technology is an advanced surface peening technology. Laser penetrates through the constraint layer to irradiate on the absorption layer, the absorption layer absorbs the laser energy to generate plasma, the plasma continuously absorbs the laser energy to form shock waves, and the shock waves are transmitted to the inside of the part, so that the material surface layer is subjected to strain hardening while a dense and stable dislocation structure is formed on the material surface layer, high-amplitude compressive stress is remained, and the residual compressive stress induced by laser shock strengthening can effectively inhibit crack propagation and improve the bending strength and fracture toughness of the material.

The laser shock strengthening technology has been industrially applied to the strengthening treatment of the surfaces of metal and alloy materials, and becomes a successful metal strengthening technology. However, since most ceramic materials are brittle and have poor thermal shock resistance, the existing metal strengthening technology cannot be directly applied to ceramics. At present, the research on laser shock peening of ceramic materials is less, and no systematic laser-ceramic interaction is reported.

Disclosure of Invention

In view of the above, there is a need for a laser shock peening method of boron carbide ceramic to achieve high quality shock peening of boron carbide ceramic and avoid deformation and breakage of the overall structure due to laser shock peening.

The invention provides a laser shock strengthening method of boron carbide ceramic, which comprises the following steps:

providing a boron carbide ceramic test piece with at least one polished surface;

covering an absorption layer on the polished surface of the boron carbide ceramic test piece, and applying a constraint layer on the absorption layer;

facing the polished surface of the boron carbide ceramic test piece to a laser beam and carrying out laser shock strengthening treatment on the polished surface; wherein, the laser shock peening adopts a laser with the wavelength within 1064nm, the pulse is 20-50ns, the spot diameter of the laser is 2-4mm, the single pulse energy is 2-7J, the frequency is 2-5Hz, the single pulse laser spot lap-joint rate is 37.5-62.5%, and the shock frequency is 2 times.

Compared with the prior art, the invention has the beneficial effects that:

the laser shock strengthening method of the boron carbide ceramic provided by the invention can realize high-quality shock strengthening and toughening of the boron carbide ceramic and avoid deformation and damage of the whole structure caused by laser shock strengthening.

Drawings

FIG. 1 is a process flow diagram of one embodiment of a method for laser shock peening of boron carbide ceramics according to the present invention;

FIG. 2 is a drawing of an apparatus used in the method for laser shock peening of boron carbide ceramics according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1, the present invention provides a method for laser shock peening of boron carbide ceramic, wherein the method for laser shock peening of boron carbide ceramic uses a single pulse beam to perform full-surface covering shock on the surface of boron carbide ceramic, and comprises the following steps:

s1, providing a boron carbide ceramic test piece with at least one polished surface;

s2, covering a polished surface of the boron carbide ceramic test piece with an absorption layer, and applying a constraint layer on the absorption layer;

s3, facing the polished surface with the constraint layer to the laser beam and carrying out laser shock strengthening treatment on the polished surface; wherein, the laser shock peening treatment adopts a laser with the wavelength of 1064nm, the pulse is 20-50ns, the spot diameter of the laser is 2-4mm, the single pulse energy is 2-7J, the frequency is 2-5Hz, the single pulse laser spot lap-joint rate is 37.5-62.5%, and the shock frequency is 2 times; in the invention, it should be noted that the single pulse energy is not too large, when the energy is more than or equal to 8J, the generated shock wave is too strong, which may cause the back of the ceramic to crack, and when the energy is more than or equal to 15J, the ceramic is easy to break.

The invention adopts the laser impact technology to strengthen the ceramic surface for the first time, and the ceramic surface has short pulse (ns level) and high power density (GW/cm)²) After the laser irradiates the black glue, plasma explosion can occur, so that shock waves with the GPa magnitude are formed, and certain dislocation is caused on the surface of the boron carbide. After laser impact, the roughness of the ceramic surface is obviously increased, the plastic deformation of the boron carbide surface is increased along with the impact of the laser, a certain compressive residual stress can be introduced, so that the mechanical property of the boron carbide ceramic surface is obviously improved, the fracture toughness and the bending strength are increased, and a part made of the boron carbide ceramic still has excellent performance under higher cyclic stress.

In this embodiment, step S1 specifically includes: and processing the boron carbide ceramic into a long strip shape, and grinding and polishing the boron carbide ceramic to obtain a boron carbide ceramic test piece. In the invention, the surface of the boron carbide ceramic needs to be ground and polished before laser shock peening, firstly, the surface performance difference of different areas is obvious after the rough surface is processed by single pulse laser, and secondly, the smooth surface is more beneficial to the mechanical property test. Furthermore, the compactness of the boron carbide ceramic test piece is more than 98 percent, and the roughness Ra of the polished surface is less than or equal to 4 mu m.

In this embodiment, the absorption layer is black glue. Furthermore, the black adhesive is a special PVC black adhesive tape for laser shock peening, and the thickness of the black adhesive is 0.1 mm. According to the invention, the black adhesive tape is selected as the absorption layer, so that the ceramic surface can be effectively protected, ablation is prevented, the absorption efficiency of the black adhesive tape on laser is high, the impact strengthening effect is enhanced, and the black adhesive tape is easy to cover and remove.

In this embodiment, the restraint layer is a deionized water layer with a thickness of 1-2 mm. Furthermore, the deionized water needs to be output stably, and the water flow impact direction and the normal direction of the surface of the sample form an angle of 30-60 degrees.

In the present embodiment, the laser beam is applied perpendicularly to the sample surface, and in general, other laser parameters not mentioned are not particularly limited.

In this embodiment, the laser used is Nd: YAG laser or Yb: YAG laser.

In some preferred embodiments of the invention, a 1064nm Nd: YAG laser with pulse width of 20ns, laser spot diameter of 2-4mm, frequency of 2Hz, single pulse energy of 4-7J and spot overlapping rate of 50-62.5%. Within the above parameter range, the laser shock peening effect is more significant. Preferably, the light spot diameter is 3-4mm, and the single pulse energy is 4.8-5.6J.

In the present embodiment, the laser shock peening further includes, after the laser shock peening, cleaning the surface of the boron carbide ceramic test piece to remove the absorption layer.

Example 1

Referring to fig. 2, the laser shock peening method of boron carbide ceramic includes the following steps:

(1) processing the sintered boron carbide ceramic (B4C ceramic) into strips of 140mm multiplied by 20mm multiplied by 8mm, grinding the upper and lower surfaces of the strips on a grinding machine (the grinding surface is 140mm multiplied by 20mm), and polishing one surface of the strips until the surface smoothness Ra is 3.2 mu m;

(2) the polishing surface of the boron carbide ceramic test piece is completely coated with a layer of black glue, the clamp is adjusted on the moving arm to clamp the boron carbide ceramic test piece, the polishing surface of the boron carbide ceramic test piece faces to a laser beam, the ceramic sample is ensured to be fixed, and a laser is adopted as a 1064nm Nd: YAG laser, setting parameters of pulse width of 20ns, spot diameter of 2mm, laser working frequency of 2Hz, single pulse energy of 4J, overlapping rate of 50%, and opening stable water beam after debugging program;

(3) starting the program, and carrying out whole-surface impact on the polished surface of the boron carbide ceramic, wherein the impact frequency is 2 times.

(4) Removing black glue on the surface of the boron carbide ceramic sample subjected to laser shock strengthening, and then carrying out performance test, wherein various performance changes are shown in table 1.

TABLE 1

As can be seen from Table 1, the residual stress of the boron carbide ceramic test piece is changed from tensile stress to compressive stress after the laser shock peening treatment, the bending strength is improved by 71.9%, which indicates that the laser shock peening can effectively inhibit crack propagation and improve the bending strength and fracture toughness of the boron carbide ceramic material.

Example 2

The single pulse energy was changed to 4.4J, 4.8J, 5.2J, 5.6J, 6J, 7J, respectively, with each sample averaged for any three-zone test performance, otherwise as in example 1, with each performance change as shown in table 2.

TABLE 2

As can be seen from Table 2, with a 1064nm Nd: YAG laser, the pulse width is 20ns, the diameter of the facula is 2mm, the laser working frequency is 2Hz, the single pulse energy is 4.8-5.6J, the lap-joint rate is 50%, when the impact frequency is 2 times, the boron carbide ceramic obtained after laser impact strengthening has better performance.

Example 3

The spot diameters were changed to 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, and 5.0mm, respectively, and each sample was averaged for any three-region test performance, otherwise as in example 1, with the changes in performance shown in table 3.

TABLE 3

As can be seen from Table 3, with a 1064nm Nd: YAG laser, the pulse width is 20ns, the diameter of facula is 3-4mm, the laser working frequency is 2Hz, the single pulse energy is 4J, the overlap ratio is 50%, when the impact frequency is 2 times, the boron carbide ceramics obtained after laser impact strengthening has better performance.

Example 4

The single pulse laser spot overlapping rates were changed to 25%, 37.5%, 62.5%, and 75%, respectively, wherein each sample was averaged for any three-region test performance, and otherwise as in example 1, the changes in each performance are shown in table 4.

TABLE 4

Sample (I)	Lap ratio (%)	Mean residual stress (MPa)	Flexural Strength (MPa)
				1	25.0	-118	521
2	37.5	-164	574
				3	62.5	-193	586
4	75.0	-137	543

As can be seen from Table 4, with a 1064nm Nd: YAG laser, the pulse width is 20ns, the spot diameter is 2mm, the laser working frequency is 2Hz, the single pulse energy is 4J, the lap joint rate is 50-62.5%, and when the impact frequency is 2 times, the boron carbide ceramic obtained after laser impact strengthening has better performance.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.