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在金属表面激光熔覆陶瓷材料过程中,过大的温度梯度产生的热应力易使熔覆层开裂。降低激光熔覆陶瓷材料过程中的温度梯度,一定程度上能够降低热应力,抑制裂纹缺陷产生。通过模拟计算Ti6Al4V基板上双激光束熔覆Al2O3涂层过程温度场的分布规律,提出采用能量均匀的平顶辅助激光束为熔覆过程提供预热缓冷的方法,通过改变平顶辅助光束光斑大小及功率密度,研究平顶辅助光束预热缓冷对熔覆层温度分布及温度梯度大小的影响。计算结果表明,平顶辅助激光束使熔覆过程出现明显的预热缓冷特征,能够有效降低熔覆层温度梯度。熔覆过程中Al2O3陶瓷塑性点(1533K)温度梯度随预热缓冷温度的升高而降低,但在预热缓冷温度升至塑性点附近温度时会引起塑性点温度梯度回升。实际加工中预热缓冷温度越高对加工过程越有利,但应避开塑性点附近温度。
In the process of laser cladding ceramic materials on metal surfaces, the thermal stress generated by the excessive temperature gradient can easily crack the cladding layer. Reducing the temperature gradient in the process of laser cladding ceramic materials can reduce the thermal stress to a certain degree and restrain the occurrence of crack defects. By simulating the distribution law of the temperature field of Al2O3 coating on the Ti6Al4V substrate, the method of providing preheating and slow cooling for the cladding process with the uniform energy of the top-level auxiliary laser beam is proposed. By changing the flat-top auxiliary beam spot Size and power density, study the influence of the flat-topped auxiliary beam preheating and slow cooling on the temperature distribution and temperature gradient of cladding layer. The calculation results show that the flattened auxiliary laser beam makes the cladding process have obvious preheating and slow cooling characteristics, which can effectively reduce the temperature gradient of the cladding layer. During the cladding process, the temperature gradient of Al2O3 ceramic plastic point (1533K) decreases with the slow cooling temperature of preheating, but it will cause the temperature gradient of plastic point to rise when the slow cooling temperature rises to near the plastic point. The actual processing slow warm-up temperature higher the higher the temperature for the processing, but should avoid the temperature near the plastic point.