粉末粒度对镍合金熔覆薄层组织及成分的影响

针对在钢基体表面熔覆镍合金薄层时稀释率高的问题,采用304不锈钢基体和两种不同粒度的Ni Cr Fe BSi合金粉末,在较高的扫描速度、较低的热输入下制备熔覆薄层,研究了粉末粒度及熔覆工艺参数对熔覆过程冶金反应及熔覆层微观组织与成分分布的影响。结果表明,在较低的热输入下即可将粉末完全熔化并加热至发生自钎反应的温度,熔覆合金在基体表面铺展,得到表面平整的熔覆层,无裂纹出现。采用厚度200μm,粒度范围70~100μm的镍合金粉末层,制备的熔覆层厚约170μm,稀释率较高;采用相同厚度的粒度约50μm的镍合金粉末层,获得了厚约130μm的熔覆层,稀释率低且熔覆界面更平整。由于更细的合金粉对激光能吸收率更高,在较低的热输入下即可熔化,传导至基体的热量显著降低,基体熔化少,热影响小。该方法可用于制备防护薄层及精密修复。

Effects of particle size on microstructure and composition of thin Ni alloy cladding layers

Since the dilution rate in laser cladding of thin Ni alloy layers is too high,in this study thin Ni alloy cladding layers were prepared on 304 stainless steel using two NiCrFeBSi powders with different particle sizes at low heat input and high scanning speed,and the effects of particle size and cladding parameters on cladding metallurgy reaction,microstructure and composition of the cladding layer were investigated.The results reveal that the thin powder bed can be fully melted and heated to a temperature high enough to complete the self-fluxing reaction with the low heat input,the alloy spreads adequately on the substrate,forming a flat cladding layer with little cracking.Using a Ni alloy powder bed of about 200μm thick consisted of particles with the size of 70~100μm,the thickness of the obtained cladding layer is about 170μm and the dilution rate is relative high.Using the Ni alloy powder bed of the same thickness consisted of particles with the size of 50μm,a cladding layer with a thickness of 130μm was obtained,the dilution rate is lower and the cladding layer/substrate interface is more flat.Since the absorption rate of finer powder to laser energy is higher,it can be melted at lower heat input,the heat transfer to the substrate is restrained,thus melting and heat effect of the substrate is less serious.This method can be used in preparation of thin protective layer and precise repairing.