1998 Volume 45 Issue 2 Pages 182-188
Three kinds of mullite, termed CP, HK and HP mullite (in order of increasing purity) containing 30 mass% zirconia were rapidly solidified to obtain amorphous ceramic powder. The rapidly solidified (RS) amorphous powder was hot-pressed exhibiting a very fine microstructure. High temperature deformation behaviour was assessed using 3 point bending and tensile tests. It was found that (1) The RS specimens exhibited greater ductility than the non RS specimens in the bending test at elevated temperature. (2) The bending force at elevated temperature was dependant on the bending rate. A bending rate sensitivity index (m') of approximately 0.5 was derived from a bending rate (ν) of 10-3 mm s-1 for both HK-RS and HK-non RS materials. The bending force for the RS material was lower than that of the non RS material. (3) The tensile stress at elevated temperature was dependant on strain rate. The strain rate sensitivity index (m) was approximately 0.5 at an initial strain rate (ε) of 2.5×10-4 s-1 for both HK-RS and non RS materials. The flow stress for the RS material was lower than that of the non RS material. A fracture strain of 80% was achieved at the same strain rate for RS material. (4) The ductility exhibited by the RS materials increased at elevated temperature. This was attributed to the ultrafine microstructure which was thought likely to encourage superplastic behaviour.
