Erosive Wear Testing of Laser Clad and HVOF Coatings for Drilling in Mining

Abstract

Drilling is a major cost factor to mining operations (exploration, drill and blast operations), and wear of components is a significant driver of drilling costs. For drilling, the so-called Down-the-Hole (DTH) hammers or Reverse Circulation (RC) hammers are used. These drills break the rock through repetitive impact. Cuttings are removed via a high-velocity air stream. The main wear mechanism for these hammers was found to be erosion. To combat erosive wear, laser clad coatings with a Nimatrix and different-sized fused tungsten carbides FTC (WC/W2C) (angular and spherical) and monocrystalline WC were developed. In addition, hard Fe-based HVOF coatings were investigated. Wear-resistant steel, WCCoCr HVOF, electroplated chrome and a high-chrome cast iron as bulk served as references. An erosion-testing apparatus which follows ASTM G76 was developed. Testing was carried out at incident angles from 15-90°. Coating performance was assessed via volume loss, obtained using 3D profilometry. At low angles, the WCCoCr coating lost the least volume, and at high angles a Ni/WC laser clad coating with spherical FTC provided the best erosion resistance. Imperfections like cracks, pores and voids serve as weak points where material loss out of the surface commences.