The development of nickel-tungsten carbide functionally graded materials by a laser-based direct metal deposition process for industrial slurry erosion applications

Functionally graded materials (FGMs) consisting of Ni-tung (nickel-tungsten carbide) powders with different concentrations of tungsten carbide particles are successfully deposited by a laser-based direct metal deposition (LBDMD) process on 4140 steel substrates. The slurry erosion behaviour of the Ni-tung FGMs is studied at different impingement angles. The slurry erosion tests are performed at Southern Methodist University's Center for Laser-Aided Manufacturing using a centrifugal-force-driven erosion-testing machine. For the purpose of comparison, Ni-tung 40 depositions and 4140 steel samples are also tested. The results indicate that the LBDMD process is able to deposit defect-free Ni-tung FGMs with uniform distribution of tungsten carbide particles in a nickel-based matrix. The slurry erosion resistance of Ni-tung FGMs as observed to be much better than that of the Ni-tung 40 and 4140 steels. The superior slurry erosion resistance of Ni-tung FGMs is attributed to the presence of large amounts of very hard tungsten carbide particles. The material removal rate (MRR) values by erosion decrease with a decrease in the impingement angle, except at a 45 degrees impingement angle on 4140 steel. The relationship among the MRRs, the craters' depth of penetration, the areas of the craters formed, the average surface roughness values, and the impingement angles are established for Ni-tung FGMs, Ni-tung 40, and 4140 steels. The surface profiles of the eroded samples are analysed by measuring the depth of penetration of the craters formed by the slurry jet using a needle-shaped probe and a linear scale with a digital readout. The damaged surfaces are characterized by scanning electron microscopy to investigate the possible application of a material failure model, called damage initiation and damage propagation, to the case of the impingement of a mixture of solid and liquid particles on the Ni-tung FGMs, Ni-tung 40, and 4140 steels. The potentiodynamic polarization curves are generated for the three tested materials and to discover the susceptibility of the material in an erosive environment.