Method for improving impact energy absorption capability of sapphire single crystal

Abstract

The invention discloses a method for improving the impact energy absorption capacity of sapphire single crystals. The method specifically comprises the following steps: inputting a sapphire single crystal into a polishing machine, carrying out mechanical polishing by using an aluminum oxide polishing solution, processing the sapphire single crystal by using a femtosecond laser, flatly laying a sapphire sample into a refractive index matching solution, keeping the liquid level height of sapphire to be 0.5-1mm, setting the plane processing point interval to be 0.5-3mm and the depth processing point interval to be 0.5-1mm, and then annealing, and precisely processing the obtained sample to obtain the sapphire single crystal bullet-facing surface material with high impact energy. According to the method, femtosecond laser is adopted for carrying out internal hidden lattice inscribing on the sapphire single crystal, nano defects are introduced, sapphire is induced to form small-size splashes, the mechanical and optical performance of the sapphire single crystal is not affected, the damage capacity of sapphire to projectiles is not reduced, and the impact energy absorption capacity of sapphire is improved; therefore, the protective performance of the sapphire type transparent protective material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sapphire single crystal processing, and in particular to a method for improving the impact energy absorption capacity of a sapphire single crystal. Background Art

[0002] Armor is a key protective material used to improve the battlefield combat capability and survivability of weapons and equipment under modern high-tech combat conditions. It has high strength, high hardness, high toughness and low density application requirements and is widely used in various military platforms such as individual soldier protection, vehicle protection, ship protection, engineering protection, etc. Therefore, improving the lightweight degree and anti-precision strike capability of optical observation components such as portholes, observation windows, infrared sighting systems, etc. has become the most cost-effective way to improve the combat capability of armored equipment.

[0003] Sapphire (Al2O3) single crystal has the characteristics of high optical quality, high hardness, high strength, high modulus, etc. It is the most ideal material for the projectile surface of transparent armor. Although its relative dissipation coefficient of projectile energy is only 2.42, the technical maturity of sapphire single crystal in preparation, production, and processing is far superior to that of magnesium aluminum spinel and aluminum oxynitride transparent ceramics. At present, the US Air Force and Navy have completed the installation of sapphire transparent armor on military platforms such as Apache, F-35, F-22 Joint Strike Fighter, and C-130 Hercules Transporter. However, since sapphire is a single crystal structure of directional growth, its internal stress is large during its growth process, the lack of slip system in the lattice, and the high dislocation slip barrier lead to poor plasticity and high brittleness of sapphire single crystal, and it is easy to form irregular brittle cracking and cleavage cracks, which affects its actual application as a material for the projectile surface of transparent armor.

[0004] In order to solve the above problems, a sapphire strengthening method disclosed in Chinese patent application (CN104451890A) is a strengthening mechanism for eliminating microcracks on the surface of sapphire and releasing the mechanical stress generated after sapphire processing. However, although this method can improve the strength of sapphire, the sapphire itself has a weakened ability to absorb impact energy. The reason for this phenomenon is that the sapphire defects are eliminated, resulting in a lack of impact energy release area inside it, thereby forming large pieces of splashes, which reduces the ability to absorb impact energy. A laser high-precision processing method for sapphire submicron-level facets disclosed in Chinese patent application (CN106891098A) uses laser non-ablative cutting of hard and brittle transparent materials to achieve high-precision processing of sapphire submicron-level facets, overcoming the high-precision cutting of sapphire with near-zero taper and no heat-affected zone limited by the Gaussian focusing mode of the beam. However, this technical solution is a fine processing of sapphire, and it is impossible to achieve the morphological transformation of sapphire from single crystal to quasi-"polycrystalline", and it is impossible to improve the impact energy absorption capacity of sapphire. Therefore, without sacrificing the optical properties of sapphire, it is of certain scientific significance to improve the impact energy absorption capacity of sapphire and thus improve the protective performance of sapphire-type transparent protective materials. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the impact energy absorption capacity of sapphire single crystal, changing the sapphire single crystal from a single crystal state to a quasi "polycrystalline" state, realizing that the sapphire is transformed from large splashes after impact fragmentation into small pieces without sacrificing the surface hardness and optical properties of the sapphire, thereby improving the impact energy absorption capacity of the sapphire and thus improving the protective performance of sapphire-type transparent protective materials.

[0006] To achieve the above object, the present invention provides a method for improving the impact energy absorption capacity of a sapphire single crystal, which specifically comprises the following steps:

[0007] (1) Sample surface treatment: The sapphire single crystal is mechanically polished. For mechanical polishing, nano-alumina powder of 50 to 500 nm is used, and a polishing liquid is prepared with water, a dispersant, and a suspending agent at a solid content ratio of 10% to 15%, and then input into a polishing machine for polishing;

[0008] (2) Femtosecond laser processing system settings: adjust the laser to titanium sapphire laser, the laser wavelength is 800nm, the pulse width is 130-200fs, the repetition frequency is 500-800Hz, the average power is 1-3W, the displacement platform moving speed is 400-500mm / s, the moving range is 500mm, and the moving accuracy is 500nm;

[0009] (3) Femtosecond processing parameter setting: Spread the sapphire sample flat in the refractive index matching liquid, keep the height of the sapphire to the liquid surface at 0.5-1 mm, set the plane processing point interval to 0.5-3 mm, and the depth processing point interval to 0.5-1 mm;

[0010] (4) Post-processing of sapphire: The sapphire sample is annealed at a temperature of 1850-1900°C for 10-15 hours, and then the obtained sample is precision-processed to obtain a sapphire single crystal bullet-facing surface material with high impact energy.

[0011] Preferably, the alumina polishing liquid described in step (1) is prepared from 10% to 15% of nano alumina powder, 3 to 5% of dispersant, 3 to 5% of suspending agent and the balance of water, wherein the particle size of the nano alumina powder is 50 to 500 nm.

[0012] Preferably, the femtosecond laser processing system described in step (2) is equipped with a long focal length lens system, an effective spot size of 0.8 to 1.2 μm, and a single pulse energy of 100 to 130 μJ.

[0013] Preferably, the laser wavelength described in step (2) is 800nm, the pulse width is 130-200fs, the repetition frequency is 500-800Hz, the average power is 1-3W, the displacement platform moving speed is 400-500mm / s, the moving range is 500mm, and the moving accuracy is 500nm.

[0014] Preferably, the refractive index matching liquid described in step (3) has a refractive index of 1.72 and is cooled by an air cooling system to a constant temperature of 20 to 25°C.

[0015] Preferably, in the sapphire annealing process described in step (4), the annealing environment is a hydrogen atmosphere, the annealing temperature is 1850-1900°C, the insulation time is 10-15h, and the annealing cooling rate is 3-5°C / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention uses a femtosecond laser to perform internal hidden grid engraving on a sapphire single crystal, which does not affect the mechanical and optical properties of the sapphire single crystal itself; does not reduce the destructive ability of sapphire to projectiles; the hidden grid patterns after engraving do not affect the field of view, and the haze of the sapphire single crystal is not increased.

[0018] 2. The present invention uses a femtosecond laser to perform internal hidden grid writing on a sapphire single crystal, and artificially introduces defect points through physical and chemical means, so that the anisotropic sapphire single crystal becomes "isotropic" in a local area; the sapphire single crystal is provided with an energy release area (artificially introduced defect points). Under a strong impact, splashing will occur in a local area of ​​the sapphire single crystal, thereby improving the impact energy absorption capacity of the sapphire single crystal.

[0019] 3. The "quasi-polycrystalline" sapphire impact surface structure designed by the present invention induces directional extension of sapphire cracks through artificially introduced defect points, converts the uncontrollable through-body cleavage fracture into directional crack extension of different dimensions, and then through the splashing of fragments, thereby improving the impact energy absorption capacity of sapphire. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a perspective schematic diagram of sapphire single crystal femtosecond processing.

[0021] Figure 2 This is a physical picture of a gridded sapphire single crystal.

[0022] Figure 3 A side view of a gridded sapphire single crystal. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] In the following examples, the sample surface mechanical polishing treatment uses an alumina polishing liquid composed of 10% to 15% nano-alumina powder, 3 to 5% dispersant, 3 to 5% suspending agent and the remainder of water, wherein the particle size of the nano-alumina powder is 50 to 500 nm; the dispersant is ethylene glycol, glycerol, ethanol, etc., and the suspending agent is fumed silica, organic bentonite, acrylic copolymer, xanthan gum, etc.

[0025] Example 1: Gridding of Sapphire Single Crystal Using 0.5mm Pitch

[0026] Sample surface treatment: mechanically polish the sapphire single crystal. For mechanical polishing, 100nm nano-alumina powder is used. The polishing liquid is prepared with deionized water, dispersant and suspending agent at a solid content of 15%, and then input into the polishing machine for polishing.

[0027] Femtosecond laser processing system settings: adjust the laser to titanium sapphire laser, laser wavelength is 800nm, pulse width is 150fs, repetition frequency is 500Hz, average power is 1W, displacement platform moving speed is 400mm / s, moving range is 50mm, moving accuracy is 500nm; effective spot size is 0.8μm, single pulse energy is 100μJ;

[0028] Femtosecond processing parameter setting: Spread the sapphire sample flat in the refractive index matching liquid, the refractive index of the refractive index matching liquid is 1.72, and use an air cooling system to cool it down, and the temperature is constant at 20°C; keep the height of the sapphire to the liquid surface at 0.5mm, set the plane processing point interval to 0.5mm, and the depth processing point interval to 0.5mm;

[0029] Sapphire post-processing: The above sapphire samples are annealed at a temperature of 1850°C for 15 hours in a hydrogen atmosphere at a cooling rate of 3°C / min. The obtained samples are then precision machined to obtain sapphire single crystal anti-bullet surface materials with high impact energy.

[0030] Example 2: Gridding of Sapphire Single Crystal Using 3mm Pitch

[0031] Sample surface treatment: mechanically polish the sapphire single crystal. For mechanical polishing, 500nm nano-alumina powder is used. The polishing liquid is prepared with deionized water, dispersant and suspending agent at a solid content of 10%, and then input into the polishing machine for polishing.

[0032] Femtosecond laser processing system settings: adjust the laser to titanium sapphire laser, laser wavelength is 800nm, pulse width is 200fs, repetition frequency is 800Hz, average power is 2W, displacement platform moving speed is 450mm / s, moving range is 50mm, moving accuracy is 500nm; effective spot size is 1.2μm, single pulse energy is 130μJ;

[0033] Femtosecond processing parameter setting: Spread the sapphire sample flat in the refractive index matching liquid, the refractive index of the refractive index matching liquid is 1.72, and use an air cooling system to cool it down at a constant temperature of 25°C; keep the height of the sapphire to the liquid surface at 1.0mm, set the plane processing point interval to 3.0mm, and the depth processing point interval to 1.0mm;

[0034] Sapphire post-processing: The above sapphire samples are annealed at 1900°C for 10 hours in a hydrogen atmosphere at a cooling rate of 5°C / min. The obtained samples are then precision machined to obtain high impact energy sapphire single crystal bullet-facing materials.

[0035] Figure 1 This is a perspective schematic diagram of femtosecond processing of sapphire single crystal. The processed area is a dot-shaped area with no linear damage, indicating that the sapphire has good hidden grid.

[0036] Figure 2 This is a real picture of the gridded sapphire single crystal. No damaged femtosecond processing points are observed in the picture, indicating that the gridded sapphire does not affect the field of view observation.

[0037] Figure 3 This is a side view of a gridded sapphire single crystal, showing a slight processing damage area.

[0038] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for improving the impact energy absorption capacity of a sapphire single crystal, characterized in that: The steps include: (1) Sample surface treatment: The sapphire single crystal is input into a polishing machine and mechanically polished using an alumina polishing liquid; (2) Femtosecond laser processing system settings: adjust the laser to titanium sapphire laser; (3) Femtosecond processing parameter setting: Spread the sapphire sample flat in the refractive index matching liquid, keep the height of the sapphire to the liquid surface at 0.5-1 mm, set the plane processing point interval to 0.5-3 mm, and the depth processing point interval to 0.5-1 mm; (4) Post-processing of sapphire: The sapphire sample is annealed, and then the obtained sample is precision-processed to obtain a sapphire single crystal impact surface material with high impact energy.

2. The method for improving the impact energy absorption capacity of a sapphire single crystal according to claim 1, characterized in that: The alumina polishing liquid described in step (1) is prepared from 10% to 15% of nano alumina powder, 3 to 5% of dispersant, 3 to 5% of suspending agent and the balance of water, wherein the particle size of the nano alumina powder is 50 to 500 nm.

3. The method for improving the impact energy absorption capacity of a sapphire single crystal according to claim 1, characterized in that: The femtosecond laser processing system described in step (2) is equipped with a long focal length lens system, an effective spot size of 0.8 to 1.2 μm, and a single pulse energy of 100 to 130 μJ.

4. The method for improving the impact energy absorption capacity of a sapphire single crystal according to claim 1, characterized in that: The laser wavelength described in step (2) is 800nm, the pulse width is 130-200fs, the repetition frequency is 500-800Hz, the average power is 1-3W, the displacement platform moving speed is 400-500mm / s, the moving range is 500mm, and the moving accuracy is 500nm.

5. The method for improving the impact energy absorption capacity of a sapphire single crystal according to claim 1, characterized in that: The refractive index matching liquid described in step (3) has a refractive index of 1.72 and is cooled by an air cooling system to a constant temperature of 20 to 25°C.

6. The method for improving the impact energy absorption capacity of a sapphire single crystal according to claim 1, characterized in that: In the sapphire annealing process described in step (4), the annealing environment is a hydrogen atmosphere, the annealing temperature is 1850-1900°C, the insulation time is 10-15h, and the annealing cooling rate is 3-5°C / min.

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