预热温度对激光熔覆镍基碳化钨涂层裂纹的影响机理

Effect mechanism of preheating temperature on crack of laser clad nickel-based tungsten carbide coating

针对在镍基高温合金表面采用激光熔覆制备碳化钨(WC)含量较高的镍基碳化钨金属复合陶瓷涂层易开裂问题,利用自组装熔池温度检测设备探究了不同激光熔覆扫描速度(300、500、700 mm/min)与基材预热温度(室温、300℃、500℃)对熔池升降温过程的影响,并结合涂层显微结构观测等分析涂层内部的开裂机理。结果表明,激光熔覆参数与涂层材料均会对涂层开裂行为产生影响。一方面,激光熔覆过程中熔池内的升温和降温速率与扫描速度呈正相关,而与预热温度呈负相关。较低的扫描速度与较高的预热温度可获得较小的温变速率,更有利于抑制涂层整体开裂;另一方面,由于WC与NiCrSiBC间熔点、热膨胀系数差异较大,在熔池冷却速率过高或过低时,易造成WC开裂或离解。因此,需针对熔池降温速率进行针对性优化,以有效提升涂层整体的成型质量。

In order to solve the problem that the nickel-based tungsten carbide metal composite ceramic coating with high tungsten carbide(WC)content prepared by laser cladding on the surface of nickel-based superalloy is easy to crack,the effects of different laser cladding scanning speeds(300,500,700 mm/min)and substrate preheating temperatures(ambient temperature,300℃,500℃)on the heating and cooling processes of the weld pool were investigated by using self-assembled weld pool temperature detection equipment,and the cracking mechanism of the coating was analyzed by observing the microstructure of the coating.The results show that the laser cladding parameters and coating materials will affect the cracking behavior of the coating.On the one hand,the heating and cooling rates in the molten pool during laser cladding are positively correlated with the scanning speed,but negatively correlated with the preheating temperature.Lower scanning speed and higher preheating temperature can obtain smaller temperature change rate,which is more conducive to inhibiting the overall cracking of the coating.On the other hand,because of the great difference in melting point and thermal expansion coefficient between WC and NiCrSiBC,when the cooling rate of molten pool is too high or too low,it is easy to cause WC to crack or dissociate.Therefore,it is necessary to optimize the cooling rate of the molten pool in order to effectively improve the overall forming quality of the coating.