Influence of high-temperature treatment conditions on the structure and tribological properties of a nickel-based laser clad coating

Abstract

Laser cladding featuring by a minimal thermal impact on the substrate is an advanced method of restoring the working dimensions of parts operated under wear conditions. Ni–Cr–B–Si system coatings can be used in parts operated at high temperatures. The research was aimed to study the influence of heating and subsequent cooling conditions during high-temperature treatment on the structural phase state formation features of the coating obtained by PG-SR2 powder laser cladding (chemical composition, wt.%: 14.8Cr; 2.1B; 2.9Si; 2.6Fe; 0.48C; the rest is Ni), and properties achieved in this process (hardness and tribological properties when sliding on the fixed corundum abrasive). Samples with the clad layer were heated at 1050 °С (holding for 1 h) with subsequent cooling in water (which made it possible to record structural transformations under high-temperature heating), in air, in a muffle furnace and in a vacuum furnace. It was shown that the cooling rate during the high-temperature treatment of the laser clad PG-SR2 coating has a significant effect on the formed structure and properties. High-temperature heating leads to a partial diffusive dissolution of Ni3B nickel borides and Cr23C6 chromium carbides in a solid solution and a corresponding decrease in hardness, an increase in abrasive wear intensity and friction coefficient. Cooling rate deceleration from 1050 °C when samples are cooled in air, muffle and vacuum furnaces leads to the release of CrB chromium borides and Ni3Si nickel silicides that were absent in the clad coating structure. High-strength CrB borides with hardness equal to or even higher than that of the corundum abrasive limit the development of the microcutting mechanism during abrasive wear. Large chromium carbides and borides formed during slow cooling in the furnace form wear-resistant frame-like structures. This leads to an increase in hardness and abrasive wear resistance to levels that exceed the features of the original clad coating.