Laser engineered net shaping of WC-9.2wt%Ni alloys: A feasibility study

A design of experiment matrix was successfully applied to the LENS technology to produce a series of WC-9.2wt %Ni (Monel) thin walls and cubes. The alloys were characterised using scanning electron microscopy, energy dispersive spectroscopy, electron probe micro-analysis, Vickers hardness, X-ray diffraction and porosity. ANOVA regression and multiple parameter refinements allowed for the production of some high-density depositions. The lowest porosity of 2.5% was obtained using a laser beam power of 220 W, traverse speed of 4.5 mm/s, powder feed rate of 11.9 g/min, hatch overlap of 50% and a z-increment of 0.4 mm, with the 2.5% porosity contribution being attributed due to lack of fusion and oxygen entrapment during deposition. An increase in the laser beam diameter resulted in severe cracking and indicated that depositions retained better geometric and material properties when the laser beam was kept at a reduced diameter. The tungsten carbide microstructure varied from the base-plate-alloy interface to the final deposited layer, with a higher density of spheroids at the interface region and the formation of a bimodal microstructure near the surface regions. This was attributed to increasing fracture of the carbides as each new layer is deposited. This variation in microstructure resulted in a hardness gradient which increased from the base-plate-alloy interface to the surface due to the grain refinement and microstructural alterations as successive layers were deposited.