Characterization of Al2O3 composites with Mo particulates, II. Densification and mechanical properties
Journal
Nanostructured Materials
Journal Volume
10
Journal Issue
6
Pages
983-1000
Date Issued
1998
Author(s)
Wang, Sheng-Chang, Wei, Wen-Cheng J.
Abstract
Three processes were employed to mix MoO3 or Mo powder with submicrometric Al2O3 powder in the preparation of the Mo/Al2O3 precursors. The first two processes employed a dissolution route which dissolved MoO3 powder in ammonia solution, followed by spray-drying or hot-plate-drying to obtain ammonium molybdate/Al2O3 granules. Then, the granulated powders were reduced in H2 atmosphere and hot-pressed to obtain Mo/Al2O3 composites. The third process involved mechanically mixing metallic Mo particles with Al2O3. The composites normally can achieve 99% relative density after hot-pressing. Microstructural results of hot-pressed composites reveal that intergranular Mo grains of micrometer size dispersed at the grain boundaries of dense Al2O3 matrix, and some fine grain Mo grains of nanometric size were entrapped within the Al2O3 grains in the composite. The four-point bending strength and the toughness of the dense composites increases 26% and 32% respectively, with the addition of Mo content, but are controlled by the uniformity of the microstructure of the composites. The hardness of the composites basically obeys the prediction of the rule of mixture. The strengthening and toughening mechanisms of the composites with respect to the microstructure are analyzed.
Type
journal article