The Effect of an Ultrasonic Field on the Microstructure and Tribological Behavior of ZrB2/ZrC+Ni60A/WC Composite Coating Applied by Laser Cladding

Abstract

Ni60A/WC composite coating reinforced with ZrB2/ZrC was layered on GTD-111 superalloy by laser cladding. The effect of an ultrasonic field on coating formation, microstructure, microhardness, and wear was investigated and analyzed. The results showed that the resulting coating had pores and microcracks, which were removed when using an ultrasonic field. Ultrasonic fields increased the heat input and increased the dimensions of the coating pool by creating a cavitation effect. The dendrites of the coating microstructure were mainly composed of Zr(B, C) and ZrC blocks and small α-Zr dendrites. The mechanical vibrations resulting from the application of ultrasonic fields caused the crushing of the growing dendrites, and as a result, the grains and dendrites crumbled. By decreasing the grain size, the average hardness increases from 312 HV for coating without an ultrasonic field to 617 HV for coating with 300 W ultrasonic power. The results of the wear test also showed that the sample coated with 300 W of ultrasonic power, with a coefficient of friction of 0.41 and scar wear of 6.8 µm, has the highest wear resistance due to the removal of porosity and the presence of equiaxed grains on the top and bottom of the clad zone.