Characterization of laser clad yttria partially-stabilized ZrO 2 ceramic layers on steel 16MnCr5

Abstract

One-step laser cladding technique was used to melt 7 wt.% yttria partially stabilized zirconia (YPSZ) powder particles to produce single tracks of ZrO 2 ceramic layers on steel 16MnCr5. The ceramic layers were analyzed using optical microscope, scanning electron microscope (SEM), X-ray diffractometer (XRD) and microhardness testing techniques for the study of microstructure, topography, cracking formation and hardness. This laser cladding process involved a continuous feeding of ZrO 2 powder into the melt pool as the metal substrate was moved under laser beam at various traverse speeds. The optimum parameters for laser cladding were: 1.6–2.0 kW laser power, 300–500 mm/min traverse speed, 3 mm beam diameter and 5–7 g/min feed rate. Under these conditions, the clad ceramic layers consisted mainly of non-transformable t′ phase and the retained c phase. Cross-sections of the clad layers showed three distinct microstructural regions which consisted of planar crystals at the bottom, columnar grains in the intermediate, and equiaxed grains at the upper. Two kinds of different combination modes were observed to be straight interface combination and diffusion fusion connection. In the latter combination, Fe and Cr elements diffused preferably along the grain boundaries into the ceramic layer.