Laser-processed composite metal cladding for slurry erosion resistance

Abstract

Processes based on the fusion of applied powder particles to metal baseplates using a continuous CO 2 laser beam as the heat source can produce a variety of novel clad overlayers. In particular, the simultaneous cladding of a matrix alloy powder and hard-phase particles yields a composite surface microstructure in which the hard-phase particles can retain their integrity in a ductile matrix. These structures are potentially valuable as wear-resistant materials. This paper concerns the evaluation of mixed-particle laser-clad overlays for wear resistance in critical components of coal slurry pipelines. Emphasis has been placed on the microstructural factors influencing surface erosion by the slurry particles. Varying mixtures of hard particles (WC, TiC or MoSi 2) and cobalt-base alloy powders were employed. While the number of process variables was large, two parameters exhibited a major influence on the wear properties of the coating. These parameters were (1) the hard particle species and (2) the volume fraction of hard phase in the starting powder. The loading of hard-phase particles was limited to a practical maximum of about 65 vol.%. Hence the laser-clad overlays were generally intermediate in hard particle fraction between conventional hardfacing alloys on the low side and cemented carbides at the other extreme. The slurry erosion rates of laser-processed coatings was consistent with the particle loading, being higher than those of commercial sintered carbides but significantly less than those of precipitation-hardened alloys.