Effect of Sintering Profile and Composition of Ni/Al2O3 Functional Gradient Materials Coating Layers via Pulsed DC Electrophoretic Deposition

Abstract

Ni/Al2O3 functional gradient material (FGM) coating layers with its thickness of 20-25 mu m were fabricated by pulsed direct current (DC) electrophoretic deposition (EPD). The coarsening effect of Ni was studied to control sintering profile with an intermediate step of 1000 degrees C for 3 h. Controlling the sintering conditions through an intermediate step and varying the number of layers played important roles in reducing cracks on the coating surface. The samples were characterized using X-ray diffraction (XRD), back scattered electron microscopy (BSE) and electron probe micro analyzer (EPMA). From these analyses, the effects of sintering step on microstructures of FGM coating layers were studied systematically to minimize crack problems within Ni-rich region by controlling its composition and form gradient through coarsening of Ni particles caused by intermediate step during sintering process. The high hardness was found for two- and three-layered samples by introducing intermediate step during sintering. Hence, pulsed DC EPD method was successfully employed to fabricate crack-free FGM with desirable microstructures.