Liquid impact erosion characteristics of martensitic stainless steel laser clad with Ni-based intermetallic composites and matrix composites

NiAl-Ni3Al intermetallic composites (IC) and intermetallic matrix composites (IMC) with TiC and WC reinforcement were laser clad to increase the liquid impact erosion resistance of AISI 420 Martensitic stainless steel. Laser process parameter optimisation and pre- and post-heat treatment of the laser clad specimens were carried out to minimise porosity and sensitivity to crack formation. The coatings were characterised by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The erosion resistance of the substrate material at a water droplet exit velocity of up to 150 m/s was improved from 116.9 to 838.7 min/mm3 for the nickel aluminide IC coating and from 855 to 1446 min/mm3 for the IMC coating with TiC and WC reinforcement. The pseudo-elasticity combined with the high work hardening ability was attributed to the excellent erosion resistance of nickel aluminide IC coatings. The IMC coatings with ceramic reinforcement extended significantly the initial resistance against liquid impact erosion. However, once damage occurred the erosion accelerated rapidly. No direct correlation could be established between the erosion resistance and the mechanical properties. The influence of hardness, elastic modulus, strain-hardening coefficient and the reversible penetration ratio on the erosion resistance was discussed.