Characteristics of the laser clad metal made with powder mixture of Co-based alloy and vanadium carbide

A powder mixture of Co-based alloy (Stellite-6) and vanadium carbide (VC) was deposited to substrates of SM400B mild steel and SUS304 stainless steel using a 2.4 kW cw CO2 laser. The mechanism of crack for clad metal was investigated by changing the VC weight fraction in the range of 0%–56%. The microstructures of the clad layer for matrix of Co-based alloy can be classified into two types—hypoeutectic structure (0–12 wt % VC) and hypereutectic structure (13–56 wt % VC). The wear resistance and Vickers hardness of the clad layer increased with increase of VC weight fraction. The cracks of the clad metal that occurred below 573 K depend on measurement results of a temperature sensor. The fractography of the clad metal belonged to a quasicleavage fracture due to the brittle microstructures by an increase of the VC weight fraction. The crack sensitivity increased with the increase of the VC weight fraction. On the other hand, compared with substrate SM400B, substrate SUS304 showed lower crack sensitivity due to the larger thermal expansion coefficient and a lower residual stress generated on the clad metal. Namely, with substrate SUS304 shifts the critical amount of VC at which cracking appears to the higher level.