Processing of Ceramic Based Nanocomposite Using α-Al_2O_3 Powder and FeCl_2 Solution as Starting Materials

摘要

Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al_2O_3-FeCl_2 powder mixture was formed by mixing α-Al_2O_3 powders with FeCl_2 solution followed by drying. In the second step, the FeCl_2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750℃ for 15 min in dry H_2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl_2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al_2O_3 nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400℃ and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al_2O_3/Fe interface bonding and mechanical properties of the composite, the second batch was heat treated in air at 700℃ for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe micro analysis (EPMA). The suggested processing route (mixing, reduction and hot pressing) produces ceramic-metal nanocomposite much tougher than the pure Al_2O_3. The fracture strength of the produced Al_2O_3/Fe nanocomposite is nearly twice that of the pure Al_2O_3. The presence of spinel phase, FeAl_2O_4, as thick layer around the Fe particles in the Al_2O_3 rnatrix has a detrimental effect on interfacial bonding between Fe and Al_2O_3 and the fracture properties of the composite.