Stellite和NiCrSiB合金激光送粉熔覆裂纹倾向的比较研究

Comparative Research on Cracking Tendency in Powder Feeding Laser Cladding Stellite and NiCrSiB Alloys

高功率CO_2激光送粉熔覆Stellite和NiCrSiB合金对比实验表明:NiCrSiB合金激光熔覆具有很大的裂纹倾向,NiCrSiB+50％Ni不出现裂纹,前者微观组织特征为少量的韧性相和大量不规则杂乱分布的粗大硬质相,后者为典型枝晶结构。Stellite 6合金激光熔覆不出现裂纹,Stellite 6+18％以上WC出现裂纹,前者微观组织特征为先共晶枝晶和枝晶间共晶,后者枝晶间共晶增多、共晶内碳化物析出物增多并出现多种复杂形状的碳化物无规沉淀析出。激光熔覆层裂纹形成的根本原因是由于熔覆过程产生的很大拉应力,裂纹形成的主导原因是由于激光熔覆层本身的韧性太低而脆性太大,难以承受大的拉应力。降低裂纹倾向的思路是改变熔覆层内强化相的形态,使其以颗粒形式均匀弥散地析出,同时使强化相颗粒由底部至表面呈梯度分布。

The comparative experimental researches demonstrated that laser cladding NiCrSiB alloy was of great tendency to cracking, with its microstructure mainly composed of small amount tough phases and a great deal of brittle disorder-distributed coarse hard phases. Laser cladding NiCrSiB + 50% Ni was a dendrite microstructure without cracks. Laser cladding Stellite 6 alloy was not sensitive to cracking, its microstructure consisted of tough dendrites and inter-dendrite eutectics. Cracks appeared in laser cladding layers of Stellite 6 plus over 18% of WC, their microstructures changed to be more brittle with more eutectics, more precipitated carbides and more complex shaped carbide precipitates. The basic reason for cracking is the big tensile stress induced in the cladding process, and the principal reason for cracking was attributed to the high brittleness of the as-clad layers due to the random shapes and disorder distribution of the hard phases in the microstructure. The method to decrease the cracking tendency was proposed to change the morphology of the strengthening phases, in which the hard phases precipitated dispersively within the microstructure and gradient distributed in the clad layers, in such a way the clad layer will be strong enough with good toughness and the tensile stress in the interface will be dramatically decreased at the same time.