Ohsaku Matsuda

Mechanical properties of strontium ferrites with duplex structure

Abstract The microstructures and the mechanical properties of the strontium ferrites (Sr-ferrites) with duplex structure were examined. As-received Sr-ferrites had a homogeneous microstructure and their average grain size was 1.58 μm. Some grains increased up to 106 μm and 228 μm in size after annealing at 1250 °C for 1 h and 6 h, respectively. The volume fractions of the large grains were 4% after 1 h-annealing and 45% after 6 h-annealing. According to the microstructural evolution, the bending strength decreased from 148 MPa (as-received) to 140 MPa (3 h-annealing) and 93 MPa (6 h-annealing), but the fracture toughness increased from 2.14 MPa · m 1/2 (as-received) to 2.20 MPa · m 1/2 (3 h-annealing) and 2.36 MPa · m 1/2 (6 h-annealing). These results indicated that the large grains in the duplex structure acted as both fracture origins and reinforcements. The Weibull modulus of materials was improved from 7 (as-received materials) to 17 (material after 3 h-annealing) and 9.5 (material after 6 h-annealing).

Preparation of Al2O3/metal composites using aluminum metal

By the oxidation of Al powder compacts adjacent porous Al2O3-mullite-SiO2 bodies (AMS), Al2O3/metal composites were grown into the pores of AMS, forming new Al2O3/metal composites. The composite grew between 1100 and 1250°, and the growth rate of the composite had the maximum value at 1150°. The composite grew in O2, N2, and Ar atmospheres. The growth rate of the composite was faster than that in the directed metal oxidation process. Mullite and SiO2 phases of AMS reacted with molten Al, forming Al2O3 and Si phases. The bending strength and the fracture toughness of an Al2O3/metal composite were 244MPa and 4.3MPa. m1/2, respectively.