阅读说明：本技术 一种控制激光表面合金化过程中wc颗粒与基材扩散界面的方法 (Method for controlling WC (wolfram carbide) particle and base material diffusion interface in laser surface alloying process ) 是由 肖辉 肖文甲 谢盼 洪悦 于 2020-12-23 设计创作，主要内容包括：本发明公开了一种控制激光表面合金化过程中WC颗粒与基材扩散界面的方法。将基材预热至280℃-300℃,获得熔池形貌及温度信息,包括测量出熔池长轴平均值a与短轴平均值b,单道合金化层中部位置点所经历的定点温度变化曲线,熔池定点温度变化曲线与固相线截距t及熔池平均冷却速率ξ,根据1.4≤a/b≤2.2,30ms≤t≤80ms,且5.5×10～3℃/s≤ξ≤1.5×10～5℃/s原则对工艺参数优化；优化的激光表面合金化工艺窗口：激光功率为700-950W,光斑直径为2～2.5mm,扫描速度为15-18mm/s,送粉量为3-5g/min,搭接量65%；获得WC颗粒与基材扩散界面良好且无裂纹的合金化试样。(The invention discloses a method for controlling a WC particle and base material diffusion interface in a laser surface alloying process. Preheating a substrate to 280-300 ℃ to obtain molten pool morphology and temperature information, wherein the molten pool morphology and temperature information comprises a measured molten pool major axis average value a, a measured molten pool minor axis average value b, a fixed point temperature change curve experienced by a middle position point of a single alloying layer, a molten pool fixed point temperature change curve, a solid phase line intercept t and a molten pool average cooling rate xi, and according to the conditions that a/b is more than or equal to 1.4 and less than or equal to 2.2, t is more than or equal to 30ms and less than or equal to 80ms, and t is more 3 ℃/s≤ξ≤1.5×10 5 Optimizing process parameters according to the principle of DEG C/s; the optimized laser surface alloying process window is as follows: the laser power is 700-950W, the diameter of a light spot is 2-2.5 mm, the scanning speed is 15-18mm/s, the powder feeding amount is 3-5g/min, and the lap joint amount is 65%; the obtained alloyed sample has good WC particles and base material diffusion interface and no cracks.)

1. A method for controlling the diffusion interface of WC particles and a substrate in a laser surface alloying process, comprising the steps of:

the method comprises the following steps: preheating the base material to 280-300 ℃;

step two: monitoring a molten pool in the laser surface alloying process by adopting a thermal imager to obtain the morphology and temperature information of the molten pool, calculating a major axis average value a and a minor axis average value b of the molten pool, extracting a fixed point temperature change curve experienced by a middle position point of a single alloying layer, and calculating the average cooling rate xi of the molten pool and the intercept t of the fixed point temperature change curve of the molten pool and a solid phase line;

step three: according to a/b is more than or equal to 1.4 and less than or equal to 2.2, 5.5 multiplied by 10³℃/s≤ξ≤1.5×10⁵Optimizing process parameters according to the principle that t is more than or equal to 30ms and less than or equal to 80 ms;

step four: obtaining an optimized laser surface alloying process window: the laser power is 800-1200W, the spot diameter is 2-2.5 mm, the scanning speed is 16-22mm/s, the powder feeding amount is 4-6g/min, and the lap joint amount is 60%;

step five: and carrying out laser surface alloying according to optimized process parameters to obtain an alloying sample with a good WC particle and base material diffusion interface.

2. The method of claim 1, wherein the WC particles are diffused in the substrate by the substrate during the laser surface alloying process, and the method comprises the steps of: in the second step, the emissivity of the thermal imager is set to 1.08, and the single data acquisition time is 1 ms.

3. The method of claim 1, wherein the WC particles are diffused in the substrate by the substrate during the laser surface alloying process, and the method comprises the steps of: in the fifth step, the alloying powder consists of mixed powder of 95 percent of tungsten carbide powder, 3.5 percent of yttrium oxide powder and 1.5 percent of pure chromium powder by mass ratio, and the particle size of the powder is 15-45 mu m.

4. The method of claim 1, wherein the WC particles are diffused in the substrate by the substrate during the laser surface alloying process, and the method comprises the steps of: in step five, the scanning path is a unidirectional path.

5. The method of claim 1, wherein the WC particles are diffused in the substrate by the substrate during the laser surface alloying process, and the method comprises the steps of: the die steel is cold-work die steel, hot-work die steel or plastic die steel.

Technical Field

The invention relates to the field of laser metal material processing, in particular to a method for controlling a WC (wolfram carbide) particle and base material diffusion interface in a laser surface alloying process.

Background

Laser surface alloying is a surface engineering technique, which uses high-energy laser beam as heat source to quickly heat and melt the base material, and injects reinforcing powder (such as WC) into the molten pool, so as to form a new surface alloying layer based on the original base material. The technology can effectively change the tissue structure, the physical and chemical properties and the mechanical properties of the surface of the material, and endow the cheap base material with more excellent surface properties, thereby replacing expensive integral alloy, saving precious metal materials and greatly reducing the cost. The laser surface alloying with WC grains as reinforcing material is one of the most common surface modification methods for improving the surface performance of metal. After alloying, the surface hardness, the wear resistance and the service life of the metal part are all improved. However, the WC particles are ceramic phase, which has a large difference in thermal properties from the metal substrate, and on the other hand, have a high melting point and hardly form a diffusion interface with the substrate, and thus have poor adhesion to the substrate, are easily peeled off, and even cause cracks. Therefore, it is important to control the diffusion interface between the WC particles and the metal substrate.

The invention provides a method for controlling a WC (wolfram carbide) particle and base material diffusion interface in a laser surface alloying process, which can obtain an alloying sample with a good WC particle and base material diffusion interface under the condition of ensuring the internal quality of an alloying layer, thereby improving the mechanical property of the alloying layer.

Disclosure of Invention

The invention aims to provide a method for controlling a WC particle and base material diffusion interface in a laser surface alloying process.

A method for controlling the diffusion interface of WC particles and a substrate in a laser surface alloying process, comprising the steps of:

the method comprises the following steps: preheating the base material to 280-300 ℃;

step two: the method comprises the steps of monitoring a molten pool in the laser surface alloying process by using a thermal imager to obtain the morphology and temperature information of the molten pool, calculating a major axis average value a and a minor axis average value b of the molten pool, extracting a fixed point temperature change curve experienced by a middle position point of a single alloying layer, and calculating the average cooling rate xi of the molten pool and the intercept t of the fixed point temperature change curve of the molten pool and a solid phase line.

Step three: according to a/b is more than or equal to 1.4 and less than or equal to 2.2, 5.5 multiplied by 10³℃/s≤ξ≤1.5×10⁵The technological parameters are optimized according to the principle that t is more than or equal to 30ms and less than or equal to 80 ms.

Step four: obtaining an optimized laser surface alloying process window: the laser power is 800-1200W, the spot diameter is 2-2.5 mm, the scanning speed is 16-22mm/s, the powder feeding amount is 4-6g/min, and the lap joint amount is 60%.

Step five: and carrying out laser surface alloying according to optimized process parameters to obtain an alloying sample with a good WC particle and base material diffusion interface.

In the second step, the emissivity of the thermal imager is set to be 1.08, and the single data acquisition time is 1 ms;

in the fifth step, the alloying powder consists of mixed powder of 95 percent of tungsten carbide powder, 3.5 percent of yttrium oxide powder and 1.5 percent of pure chromium powder in mass ratio, and the particle size of the powder is 15-45 mu m;

in the fifth step, the scanning path is a unidirectional path;

the die steel includes cold-work die steel (such as Cr12MoV), hot-work die steel (such as H13) and plastic die steel (such as 40 Cr).

A large number of experiments prove that a/b is more than or equal to 1.4 and less than or equal to 2.2 and 5.5 multiplied by 10³℃/s≤ξ≤1.5×10⁵Optimizing and selecting the process parameters according to the principle that t is more than or equal to 30ms and less than or equal to 80ms, wherein the obtained optimized process parameters are as follows: the laser power is 800-1200W, the spot diameter is 2-2.5 mm, the scanning speed is 16-22mm/s, the powder feeding amount is 4-6g/min, and the lap joint amount is 60%; laser surface alloying is carried out according to optimized process parameters, on one hand, enough energy input of a molten pool and the service life of the molten pool in the surface alloying process can be ensured, so that the generation of WC particles and the interface diffusion of a base material is facilitated; on the other hand, the higher cooling rate of the molten pool is ensured, and the solidification microstructure is effectively refined. In addition, 3.5 percent of yttrium oxide powder and 1.5 percent of pure chromium powder are added into the tungsten carbide powder, the particle size of the powder is 15-45 mu m, the yttrium oxide powder is added in the surface modification process to further solidify the structure and reduce the thermal cracks, the yttrium oxide powder and the pure chromium powder generate alumina ceramic particles with high melting point through in-situ reaction with oxygen in a molten pool, the particles with high melting point provide heterogeneous nucleation points for the nucleation of crystal grains or dendrites in the molten pool solidification process, and further the structure is refined and the structure is avoidedThe thermal cracking is avoided, an alloying sample with a good WC particle and base material diffusion interface is obtained, and the thickness of a diffusion layer between the WC particle and a matrix can reach 3-5. According to the invention, by strictly controlling the laser surface alloying process parameters, the diffusion interface of the WC particles and the base material can be effectively controlled under the condition of ensuring the internal quality of the alloying layer, the bonding strength of the WC particles and the matrix is enhanced, and the mechanical property of the sample is further improved.

Drawings

FIG. 1 is a metallographic diagram of a WC-enhanced laser surface alloying sample obtained by a conventional method;

FIG. 2 is a metallographic diagram of a WC-enhanced laser surface alloying sample obtained by the method.

Detailed Description

Example 1

Take H13 die steel as an example.

The method comprises the following steps: the H13 die steel substrate was preheated to 285 ℃.

Step two: the method comprises the steps of monitoring a molten pool in the laser surface alloying process by using a thermal imager to obtain the morphology and temperature information of the molten pool, calculating a major axis average value a and a minor axis average value b of the molten pool, extracting a fixed point temperature change curve experienced by a middle position point of a single alloying layer, and calculating the average cooling rate xi of the molten pool and the intercept t of the fixed point temperature change curve of the molten pool and a solid phase line.

Step three: according to a/b is more than or equal to 1.4 and less than or equal to 2.2, 5.5 multiplied by 10³℃/s≤ξ≤1.5×10⁵The technological parameters are optimized according to the principle that t is more than or equal to 30ms and less than or equal to 80 ms.

Step four: obtaining an optimized laser surface alloying process window: the laser power is 900W, the diameter of a light spot is 2.3mm, the scanning speed is 18mm/s, the powder feeding amount is 5.5g/min, and the lap joint amount is 60 percent; the alloying powder is mixed powder of 95 percent of tungsten carbide powder, 3.5 percent of yttrium oxide powder and 1.5 percent of pure chromium powder, and the particle size of the powder is 15-45 mu m.

Step five: and carrying out laser surface alloying according to optimized process parameters to obtain an alloying sample with a good WC particle and base material diffusion interface, wherein the average diffusion layer thickness is about 4 mu m.

FIG. 1 is a gold phase diagram of a laser surface alloying sample obtained by a conventional method. The existence of a large number of cracks in the WC grains and the few existence of diffusion layers at the boundaries of the WC grains indicate that the WC grains and the base material do not form metallurgical bonding, and the interface bonding capability is poor, which is very unfavorable for the service performance of the sample under the load bearing condition.

FIG. 2 is a gold phase diagram of a laser surface alloying sample obtained in example 1 of the present invention. The obvious diffusion layer exists between the WC particle boundary and the base material, which shows that the WC particles and the base material form metallurgical bonding after the method is adopted, the interface bonding is good, and the mechanical property of the sample is favorably improved. The results show that the method can effectively improve the interface bonding performance of the WC particles and the base material, and further improve the mechanical property of the alloying layer.

Example 2

Take 40Cr die steel as an example.

The method comprises the following steps: preheating the 40Cr die steel substrate to 295 ℃.

Step two: the method comprises the steps of monitoring a molten pool in the laser surface alloying process by using a thermal imager to obtain the morphology and temperature information of the molten pool, calculating a major axis average value a and a minor axis average value b of the molten pool, extracting a fixed point temperature change curve experienced by a middle position point of a single alloying layer, and calculating the average cooling rate xi of the molten pool and the intercept t of the fixed point temperature change curve of the molten pool and a solid phase line.

Step three: according to a/b is more than or equal to 1.4 and less than or equal to 2.2, 5.5 multiplied by 10³℃/s≤ξ≤1.5×10⁵The technological parameters are optimized according to the principle that t is more than or equal to 30ms and less than or equal to 80 ms.

Step four: obtaining an optimized laser surface alloying process window: the laser power is 1000W, the diameter of a light spot is 2.5mm, the scanning speed is 20mm/s, the powder feeding amount is 5.8g/min, and the lapping amount is 60%. The alloying powder is mixed powder of 95 percent of tungsten carbide powder, 3.5 percent of yttrium oxide powder and 1.5 percent of pure chromium powder, and the particle size of the powder is 15-45 mu m.

Step five: and carrying out laser surface alloying according to optimized process parameters to obtain a 40Cr die steel alloying sample with a good WC particle and base material diffusion interface, wherein the average diffusion layer thickness is about 4.5 mu m.