Fabrication of crack-free SUS316L/Al2O3 functionally graded materials by spark plasma sintering

This paper describes the preparation of crack-free stainless steel 316L/alumina functionally graded material (SUS316L/Al2O3 FGM) by spark plasma sintering (SPS). The sintering of individual powders and their composites was first studied to find an optimum SPS condition to get both materials and their mixtures highly dense. Sintering of cylindrical-shaped FGM pellets (ϕ20 mm) with various numbers of interlayers of 1, 2, 3, 4, and 9 was then carried out where the kind of and location of related cracking were carefully examined. The FGMs faced the problem of cracking mainly in the radial direction near the Al2O3-rich layers regardless of the number of layers or the gradient compositional profile. An yttrium-stabilized zirconia (3Y-ZrO2) was added thereafter to the gradient on the expense of Al2O3 content (up to 50 vol.%) and no radial cracking was found. Defects-free FGM pellets were successfully produced by interposing 19 interlayers between the SUS316L and Al2O3 ends. The Vickers hardness profile was determined throughout the cross-section of sintered FGM and it was varying steadily through the gradient from 2.0 GPa at the SUS316L surface to 14.4 GPa at the Al2O3 surface.