阅读说明：本技术 一种非均匀热源促熔池对流的金属表面合金化方法 (Metal surface alloying method for promoting molten pool convection by non-uniform heat source ) 是由 石玗 郭晋昌 顾玉芬 朱明� 张刚 李春凯 于 2020-07-16 设计创作，主要内容包括：本发明涉及一种非均匀热源促熔池对流的金属表面合金化方法,包括以下步骤：1)采用第一热源对金属表面进行加热并熔化形成熔池；2)合金化气体进入熔池进行反应生成高熔点的化合物,化合物有凝固形成凝固层的趋势,采用第二热源加热化合物所在区域,保证化合物不发生凝固,促进熔池发生对流,形成成分和组织均匀的合金化层,第一热源和第二热源沿热源的移动方向依次布置,且第二热源的功率密度大于第一热源的功率密度；3)沿热源的移动方向,第一热源和第二热源整体移动,上述熔池凝固形成合金化层。采用上述非均匀热源进行金属表面的激光气体合金化,最后得到具有较佳组织和性能的合金化层。(The invention relates to a metal surface alloying method for promoting molten pool convection by a non-uniform heat source, which comprises the following steps: 1) heating and melting the metal surface by adopting a first heat source to form a molten pool; 2) alloying gas enters a molten pool to react to generate a high-melting-point compound, the compound has a tendency of solidifying to form a solidified layer, a second heat source is adopted to heat the area where the compound is located, the compound is ensured not to solidify, the molten pool is promoted to generate convection, an alloying layer with uniform components and tissues is formed, the first heat source and the second heat source are sequentially arranged along the moving direction of the heat source, and the power density of the second heat source is greater than that of the first heat source; 3) the first heat source and the second heat source are moved integrally in the moving direction of the heat source, and the molten pool is solidified to form an alloyed layer. The laser gas alloying of the metal surface is carried out by adopting the non-uniform heat source, and finally the alloying layer with better structure and performance is obtained.)

1. A metal surface alloying method for promoting the convection of a molten pool by a non-uniform heat source is characterized by comprising the following steps:

1) heating and melting the metal surface by adopting a first heat source to form a molten pool;

2) alloying gas enters a molten pool to react to generate a high-melting-point compound, the compound has a tendency of solidifying to form a solidified layer, a second heat source is adopted to heat the area where the compound is located, the compound is guaranteed not to solidify, the molten pool is promoted to generate convection, the first heat source and the second heat source are sequentially arranged along the moving direction of the heat source, and the power density of the second heat source is greater than that of the first heat source;

3) the first heat source and the second heat source are moved integrally in the moving direction of the heat source, and the molten pool is solidified to form an alloyed layer.

2. The method of metal surface alloying with non-uniform heat source facilitated molten bath convection as set forth in claim 1 wherein: the first heat source is implemented using a first laser beam and the second heat source is implemented using a second laser beam.

3. The method of metal surface alloying with non-uniform heat source facilitated molten bath convection as set forth in claim 2 wherein: the focal plane beam diameter of the first laser beam is 3mm, the focal plane beam diameter of the second laser beam is 3mm, and the front-back distance between the central point of the first laser beam and the central point of the second laser beam is 1.8 mm.

Technical Field

The invention relates to the technical field of metal surface laser gas alloying, in particular to a metal surface gas alloying method for promoting molten pool convection by a non-uniform heat source.

Background

In the melting welding process, a large temperature gradient exists on the surface of the molten pool, so that a large surface tension gradient is formed on the surface of the molten pool, and Marangoni convection is formed in the molten pool. Convection promotes homogenization of components in a molten pool, and optimizes the structure and performance of a weld joint.

Laser gas alloying of metal surfaces can improve metal surface properties. The process engineering is divided into three stages: in the first stage, metal is heated by laser, and the surface of the metal is melted to form a molten pool; in the second stage, alloying gas enters a molten pool, and the molten pool reacts; and in the third stage, the molten pool is solidified to form an alloying layer. It is desirable to optimize alloying layer composition, structure and performance by creating marangoni convection in the weld pool in the second stage similar to the welding process described above. However, the alloying gas in the second stage reacts with the molten pool, compounds are formed on the surface of the molten pool, the melting point of the compounds is high, and the compounds are preferentially solidified, so that a thin solidified layer is formed on the surface of the molten pool, the flowing of the molten pool is hindered or slowed down, the composition segregation is formed in the molten pool, and the structure and the performance of an alloying layer are deteriorated.

In the past, the laser power density of laser gas alloying of metal surface has two kinds: the first and the second laser power density are high, the temperature of the surface of the molten pool is higher, the melting of a 'thin solidified layer' on the surface of the molten pool at the second stage is ensured, and the convection of the molten pool is facilitated. However, the large laser power density causes a large amount of vaporization and strong evaporation on the metal surface in the first stage, pollutes the air of the working environment and deteriorates the surface quality of the alloying layer. Large laser power densities are not the optimal solution. And the second, small laser power density and low surface temperature of the molten pool ensure that the metal surface is melted to form the molten pool in the first stage, but violent evaporation cannot occur, and the surface quality of the alloying layer is ensured. But the 'thin solidified layer' on the surface of the second stage molten pool can not be melted, thereby hindering or slowing down the convection of the molten pool, forming composition segregation in the molten pool and deteriorating the structure and the performance of the alloying layer. Small laser power density is also not an optimal solution.

The following further describes the laser gas nitriding on the titanium surface as an example. The melting point of pure titanium is about 1600 ℃, the boiling point is about 3200 ℃, TiN is formed on the surface of the molten pool in the second stage, and the melting point of TiN is about 3200 ℃. Firstly, the high laser power density is adopted, the surface temperature of a molten pool is higher than 3200 ℃, and in the first stage, a large amount of evaporation occurs on the surface of the titanium alloy, so that the air of the operation environment is polluted, the surface quality of a nitrided layer is deteriorated, and the surface quality of the nitrided layer is deteriorated. Large laser powers are not optimal. And secondly, the small laser power density is adopted, the surface temperature of the molten pool is higher than 1600 ℃ and lower than 3200 ℃, and a large amount of evaporation cannot occur on the surface of the molten pool in the first stage, so that the surface quality of a nitride layer is ensured. But in the second stage, a 'thin solidified layer' is formed on the surface of the molten pool, thereby hindering or slowing down the convection of the molten pool, forming segregation in the molten pool and deteriorating the structure and the performance of the nitride layer. Small laser power density is also not an optimal solution.

Disclosure of Invention

The invention aims to provide a metal surface gas alloying method for promoting molten pool convection by a non-uniform heat source so as to solve the problem of poor metal surface alloying effect in the prior art

In order to realize the aim, the metal surface gas alloying method for promoting the convection of the molten pool by the non-uniform heat source adopts the following technical scheme: a metal surface alloying method for promoting the convection of a molten pool by a non-uniform heat source comprises the following steps:

1) heating and melting the metal surface by adopting a first heat source to form a molten pool;

2) alloying gas enters a molten pool to react to generate a high-melting-point compound, the compound has a tendency of solidifying to form a solidified layer, a second heat source is adopted to heat the area where the compound is located, the compound is guaranteed not to solidify, the molten pool is promoted to generate convection, the first heat source and the second heat source are sequentially arranged along the moving direction of the heat source, and the power density of the second heat source is greater than that of the first heat source;

3) the first heat source and the second heat source are moved integrally in the moving direction of the heat source, and the molten pool is solidified to form an alloyed layer.

The first heat source is implemented using a first laser beam and the second heat source is implemented using a second laser beam.

The focal plane beam diameter of the first laser beam is 3mm, the focal plane beam diameter of the second laser beam is 3mm, and the front-back distance between the central point of the first laser beam and the central point of the second laser beam is 1.8 mm.

The invention has the beneficial effects that: the first heat source adopts a low-power density heat source and has the function of ensuring that the metal surface is melted to form a molten pool in the first stage, but violent evaporation cannot occur, so that the quality of the operation environment is ensured, and the quality of the metal surface is ensured; the gas enters the molten pool to react to generate a high-melting-point compound, and the compound has the tendency of solidifying to form a compound solidified layer on the surface of the molten pool, so that a second heat source with high power density is adopted to melt and heat the compound area, the compound is ensured not to be solidified, the convection inside the molten pool is promoted, the component segregation inside the molten pool is reduced, and the alloy components, the structure and the performance are optimized. The laser gas alloying of the metal surface is carried out by adopting the non-uniform heat source, and finally the alloying layer with better structure and performance is obtained.

Drawings

FIG. 1 is a schematic diagram of an embodiment of a non-uniform heat source molten pool convection enhanced metal surface gas alloying method of the present invention.

Detailed Description

The embodiment of the invention relates to a metal surface alloying method for promoting the convection of a molten pool by a non-uniform heat source, which comprises the following steps:

1) heating and melting the metal surface by adopting a first heat source to form a molten pool;

2) alloying gas enters a molten pool to react to generate a high-melting-point compound, the compound has a tendency of solidifying to form a solidified layer, a second heat source is adopted to heat the area where the compound is located, the compound is guaranteed not to solidify, the molten pool is promoted to generate convection, the first heat source and the second heat source are sequentially arranged along the moving direction of the heat source, and the power density of the second heat source is greater than that of the first heat source;

3) the first heat source and the second heat source are integrated along the moving direction of the heat source, and the molten pool is solidified to form an alloying layer.

The first heat source is implemented using a first laser beam and the second heat source is implemented using a second laser beam. In other embodiments of the present invention, the heat source may not use a laser beam, and may use one of an electron beam, a plasma arc, and a general electric arc. The heat source can also adopt the same laser generator, and the front part of the light spot of the same light spot along the exciting direction of the heat source has high power density and the rear part of the light spot has low power density through laser shaping.

The focal plane beam diameter of the first laser beam was 3mm, the focal plane beam diameter of the second laser beam was 3mm, and the front-to-back distance between the center point of the first laser beam and the center point of the second laser beam was 1.8 mm. I.e. the distance between the spot centre points of the two laser beams is 1.8 mm.

The first laser beam is a low power density laser beam. Laser type: fiber laser, laser output type: continuously outputting laser beams with the wavelength of 1064nm, the defocusing amount of the laser beams being 0mm, and the distance between laser nozzles being 30 mm. The heat source distribution type: a gaussian distribution. Heat source power 1400W, center point maximum power density about: 5.94*10⁴W/cm²The average power density is about: 1.98*10⁴W/cm²。

The second laser beam is a high power density laser beam. Laser type: fiber laser, laser output type: continuous output, laser wavelength: 1064nm, defocusing amount of laser beams of 0mm, and distance between laser touch nozzles of 30 mm. The heat source distribution type: a gaussian distribution. Heat source power 3200W, maximum power density at the center of the beam is about: 1.36*10⁵W/cm²The average power density is about: 4.53*10⁴W/cm²。

The alloying gas flow is 15L/min, the gas purity is 99.99 percent, and the gas supply mode is as follows: the gas is coaxial with the laser beam.

Experimental example:

the test was carried out by laser gas nitriding of pure titanium metal surface. In the test process, the parameters are as follows: the first laser beam is a fiber laser, and the laser generator is a YLS4000 laser generator manufactured by IPG of Germany. Laser wavelength: 1064nm, the diameter of a focal plane beam is 3mm, the defocusing amount of the laser beam is 0mm, and the distance between laser touch nozzles is 30 mm. Moving speed of laser beam: 30mm/s, power 1400W, center point maximum power density about: 5.94*10⁴W/cm²The average power density is about:1.98*10⁴W/cm². The second laser beam is fiber laser, and the laser generator is a YLS4000 laser generator manufactured by IPG of Germany. Laser wavelength: 1064nm, the diameter of a focal plane beam is 3mm, the defocusing amount of the laser beam is 0mm, and the distance between laser touch nozzles is 30 mm. Moving speed of laser beam: 30mm/s, 3200W of power, the maximum power density of the center point of the light beam is about: 1.36*10⁵W/cm²The average power density is about: 4.53*10⁴W/cm². Only by using the first laser beam, the nitrided layer was found to have a non-uniform composition and crack defects inside. Nitridation was performed using only the second laser beam and the surface of the nitrided layer was found to be very rough. By adopting the metal surface alloying method, the metal surface is heated non-uniformly by adopting the first laser beam and the second laser beam, and the front-back distance between the central point of the first laser beam and the central point of the second laser beam is kept to be 1.8mm, namely the front-back overlapping of the light spots of the first laser beam and the second laser beam is 1.2 mm. As a result, the surface of the TiN alloy layer with the pure titanium surface is smooth and flat, has uniform components and has no defects such as air holes and cracks inside.

It should be understood that: the invention is not limited to the above examples, and it will be obvious to a person skilled in the art that modifications and variations are possible in light of the above description, all of which are intended to fall within the scope of the protection claimed in the enclosed area of the business.