Microstructural Evolution and Phase Transformation in Laser Cladding of Cr and Mo Powder on Grey Cast Iron: Mixture Design of Experiment (DOE)

Laser cladding on grey cast iron at high power processing was investigated for microstructural evolution and phase transformation to enhance surface properties. Cladding was designed using a mixture of DOE with peak power (Pp) and pulse repetition frequency (PRF), and a mixture component of Cr and Mo ratio as factors. Microstructural findings indicated absolute elimination of graphite phase from the clad zone, in conjunction with particles evolution occurrence. Meanwhile, Cr, Mo and Fe phases were detected on the clad surface, along with M-C carbide, retained austenite and MoFe formation. The clad surface with addition of Mo exhibited a high hardness value of 945.5 HV0.1 due to carbide formation. As a result of high peak power penetration into substrate surface, the depth range of clad zone was 53 to 131 µm. From the optimisation, the highest desirability is 82.3 %. Cladding with molybdenum powder addition was found to have produced minimum surface roughness, maximum depth and hardness of 9.14 µm, 110 µm and 891.1 HV0.1, respectively.

本研究针对高功率加工条件下灰铸铁表面的激光熔覆（Laser cladding）工艺展开系统性探究，围绕其微观组织演化与相变行为开展分析，以优化表面性能。本研究采用以峰值功率（Peak Power, Pp）、脉冲重复频率（Pulse Repetition Frequency, PRF）以及铬（Cr）与钼（Mo）的配比为影响因子的实验设计（Design of Experiments, DOE）方法，开展熔覆工艺参数的设计与构建。微观组织分析结果显示，熔覆区（clad zone）内的石墨相已被完全消除，同时伴随颗粒演化现象的产生。与此同时，熔覆表面检测到铬、钼与铁的物相，同时存在M-C碳化物（M-C carbide）、残余奥氏体（retained austenite）以及MoFe相的生成。添加钼的熔覆层表面因碳化物的生成，展现出高达945.5 HV0.1的硬度值。由于峰值功率可穿透至基体表面，熔覆区的深度范围为53至131 µm。经工艺优化后，最高期望度可达82.3%。研究表明，添加钼粉的熔覆工艺可获得最低的表面粗糙度、最大的熔覆深度与最高的硬度，三者分别为9.14 µm、110 µm与891.1 HV0.1。