Anomalous Plasticity in MoSi_2 Single Crystals and its utilization

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IN 1995 we first reported that plastic flow is possible even at temperatures as low as room temperature for single crystals of MoSi_2 wirh orientations away from[001], while single crystals with orientations near [001] can be plastically deformed on a macroscopic scale only at temperatures above 1300ﾟC.In this study, we first examined whether such anomalous plasticity oberved in MoSi_2 single crystals with orientations away from [001] is observed in other transition metal disilisides with the C11_b structure such as WSi_2 and (Mo, W) Si_2, those with the C40 structure such as Mo(Al, Si)_2, VSi_2, NbSi_2, TaSi_2 and CrSi_2, TiSi_2 with the C54 structure. Secondly, we investigated possible ways to utilize the anomalous plasticity for structural spplications of MoSi_2.Deformation experiments of four different C40 disilicides result in the following findings : (1) plastic flow of VSi_2, NbSi_2 and TaSi_2 is possible only when slip along <1210> on (0001) is operative and no other slip systems are observed in the whole temperature range investigates, (2) basal slip in VSi_2, NbSi_2 and TaSi_2 occurs in a conventional manner unlike in CrSi_2 and Mo (Si, Al)_2 in which the corresponding slip occurs through a synchroshear mechanism, (3) while the onset temperature for plastic flow in NbSi_2 is 500ﾟC for as-grown crystals, it is lowered by 300ﾟC when the crystal is prestrained at 1400ﾟC and then re-deformed at low temperatures, (4) the critical resolved shear stress (CRSS) for basal slip in NbSi_2 decreases with increasing temperature, but exhibits a moderate peak around 1300ﾟC.One way to utilize the anomalous plasticity of MoSi_2 is to form MoSi_2-base composites with NbSi_2 and TaSi_2 forming interfaces perpendicular to cleavage planes in MoSi_2.