Fabrication of Graded Nickel–Alumina Composites with a Thermal-Behavior-Matching Process

Composites of nickel and Al₂O₃ with compositionally graded microstructures were fabricated from powders through an empirically determined thermal-behavior-matching process that was designed to minimize processing-induced stresses. Compositions ranged from pure Al₂O₃ to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5–25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al₂O₃ comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack-free, graded composites to be produced.