Effect of matrix chemistry and WC types on the performance of Ni-WC based MMC overlays deposited by plasma transferred arc (PTA) welding

Abstract

Ground Engaging Tools (GETs) are subjected to severe abrasion during service in earth moving applications. Ni-based MMC overlays reinforced with tungsten carbides are ideal hardfacing candidates for critical surfaces on GETs. In this work, a combination of two types of Ni matrix (NiBSi/NiCrBSi) and two types of tungsten carbides (macrocrystalline-MWC and cast eutectic WC/W2C-CWC) were produced by Plasma Transferred Arc (PTA) welding. Optical microscopy, scanning electron microscopy (SEM), ASTM G65-A abrasion testing and rotary impact testing have been employed to evaluate the microstructure, hardness, wear resistance and impact resistance of the overlays. Overlays with MWC carbides show better wear resistance under low stress abrasive condition tested by ASTM G65. The matrix chemistry and hardness do not seem to have any significant effect on the wear resistance of Ni-WC MMCs while using the same type of tungsten carbides. Overlays with NiBSi-matrix and CWC carbides show the best high stress wear resistance under the modified ASTM G65 with 20/30 mesh abrasive sands. This could be attributed to the good combination of microhardness and toughness of cast eutectic carbides. In case of impact testing, NiBSi-CWC and NiCrBSi-MWC overlays have shown better resistance than the other two types of MMC. The severe dissolution of cast eutectic carbides in Cr containing matrix has caused the formation of secondary carbides and reduced its impact resistance. Overall, this study provides valuable criteria for materials selections of hardfacing overlays applied onto GETs under different working conditions.