MICROSTRUCTURES AND MECHANICAL-PROPERTIES OF NI-MGO COMPOSITES FORMEDBY DISPLACEMENT AND PARTIAL REDUCTION REACTIONS

Metal-ceramic microstructures were produced by two different approache s: a displacement reaction between Mg and NiO and a partial reduction reaction starting with a solid solution of(Mg,Ni)O. In both cases Ni-r ich particles were embedded in a Mg-rich (Mg,Ni)O ceramic phase. For t he displacement reaction, the two phase structure is produced during h ot pressing. For the partial reduction reaction, individual ceramic gr ains are first reduced to a two phase mixture and then hot pressed to form a monolithic solid. The resultant microstructures contain differe nt distributions of Ni in the MgO matrix. The fracture toughness measu red by the chevron notch technique was related to the morphologies of the different microstructures. The presence of chromium ions as a dopa nt in the partial reduction reaction was found to have a significant b eneficial effect on the bend strength and fracture toughness of the co mposites produced by this method. (C) 1997 Acta Metallurgica Inc.