| Research Abstract |
Transition metal disilicides, in particular those formed with refractory metals of groups IVa 〜 VIa in the Periodic Table have drawn considerable attention for structural applications at high temperatures because of their high melting temperature, intrinsic oxidation resistance, resistance, relatively low density and high thermal conductivity. These transition metal disilicides, except ZrSiィイD22ィエD2 and HfSiィイD22ィエD2 with the C49 structure, crystallize into one of the three structures of the types C11b, C40 and C54, which are all relatively simple and closely akin to each other. The relative phase stability of these three structures is closely related with the nature of directional atomic bonding in these structures. The deformation mechanism of transition metal disilicides with these structures was studied putting stress on the effect of atomic bonding on their deformation.
Transition metal disilicides with the three crystal structures were found to be classified into two *oups, i.e. one group including CrSiィイD22ィエD2 whose plastic flow is observed only above 700℃. The difference in deformability between the two groups of silicides is closely associated with the difference in the core structure of dislocations.
The creep behavior and creep strength of MoSiィイD22ィエD2 alloyed with Nb, W, Re and A1 was also studied in the temperature range from 1200 to 1400℃. The creep strain rate for the [001] orientation, which is the hardest orientation in conventional compression tests, is significantly improved upon alloying with Re, Nb, W and A1. The extent of improvement is significantly large for adding Re and Nb. The creep rate attained for Re-bearing MoSiィイD22ィエD2 is comparable to that obtained for the most advanced SiィイD23ィエD2 NィイD24ィエD2-based composites in tension.
|
