INFLUENCE OF RESIDUAL-STRESSES ON THE EVOLUTION OF MICROSTRUCTURE DURING THE PARTIAL REDUCTION OF NIAL2O4

Metal-ceramic microstructures were formed in situ by the partial reduc tion (i.e. the reduction of only one of the metallic elements) of the spinel compound NiAl2O4. Depending on reduction conditions, these micr ostructures consist of Ni particles embedded in an alpha-Al2O3 or a mu ltiphase matrix called 'defect spinel'. The volume shrinkage that acco mpanies the reaction generates residual stresses which profoundly affe ct the microstructure evolution. Conversely, formation of metastable, intermediate phases, generation of porosity and cracking are all obser ved and may act to relax the residual stresses. Electron microscopy ob servations as well as both neutron and X-ray diffraction residual stre ss measurements are used to study the influence of residual stresses o n the microstructure evolution during the reduction process. (C) 1997 Elsevier Science S.A.