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（1533 K）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。

Thermal stress caused by oversized temperature gradient in the process of laser cladding ceramic coating on metal substrate usually makes the coating cracked. Reducing the temperature gradient of the laser cladding process can reduce the thermal stress to a certain degree to suppress the generation of cracks. Through numerical simulation of temperature distribution during laser cladding Al2O3 coating on Ti6Al4V substrate, a method of providing preheating and slow-cooling using top hat laser beam is proposed. Temperature distribution and temperature gradient of the coating with preheating and slow-cooling are discussed by changing the spot size and power density of the top hat assistant laser beam. The results show that there is a significant feature of preheating and slow-cooling during the cladding process, the top hat assistant laser beam can reduce the temperature gradient effectively. The temperature gradient of the plastic point (1533 K) of Al2O3 reduces while the preheating and slow-cooling temperature raises. But the temperature gradient of the plastic point will rebound when the preheating and slow-cooling temperature is near the plastic point. Higher preheating and slow-cooling temperature make the cladding process better, but temperature around the plastic point should be avoided.