Investigation of laser surface alloying of copper on high nickel austenitic ductile iron

Laser surface alloying (LSA) of pure copper on high nickel austenitic ductile iron was carried out using a 2 kW continuous wave (CW) CO2 laser with two processing conditions: laser beam spot size D=5 mm, scanning speed V=2 mm s−1, power density E=1.02×104 W cm−2 (condition 1) and D=2 mm, V=9 mm s−1, 6.37×104 W cm−2 (condition 2). Microstructure in the alloyed zone was found to consist mainly of primary γ-austenite dendrites and an interdendritic eutectic of γ-austenite and M7C3 carbides with copper wetting the dendritic boundaries. Distribution of the copper in the alloyed zone is fairly uniform across the depth of the pool and the concentration of copper in the alloyed zone highly depends on the power density. Copper spheroidal particles can be observed at the interdendritic boundaries under condition 1, indicating that the melt could be near the metastable miscibility gap and liquid phase separation (LPS) takes place due to rapid solidification. After LSA, hardness of the alloyed zone is considerably higher than before, which is attributed to both precipitation hardening and work hardening caused by the thermal stress.