Anomalous Plasticity in MoSi_2 Single Crystals and its utilization

1995年，我们首次报道了远离[001]取向的MoSi_2单晶即使在室温下也可以塑性流动，而接近[001]取向的单晶只有在1300ﾟC以上的温度下才能在宏观尺度上塑性变形。在这项研究中，我们首先考察了在远离[001]取向的MoSi_2单晶中观察到的这种异常塑性是否在其他具有C11_b结构的过渡金属晶相中观察到，如WSi_2和(Mo，W)Si_2，具有C40结构的单晶如Mo(Al，Si)_2，VSi_2，具有C54结构的NbSi2、TaSi2和CrSi2、TiSi2。其次，我们研究了利用MoSi_2的反常塑性作为结构材料的可能途径。四种不同的C_(40)二硅化物的变形实验结果表明：(1)VSi_2、NbSi_2和TaSi_2只有在沿-lt；1210&gt；(2)VSi_2、NbSi_2和TaSi_2中的基面滑移以常规方式发生，不同于CrSi_2和Mo(Si，Al)_2中相应的滑移是通过同步剪切机制发生的；(3)对于生长的晶体，当NbSi_2中塑性流动的起始温度为500ﾟC时，当晶体在1400ﾟC预应变时，塑性流动的起始温度降低300ﾟC，然后在低温下再变形，(4)NbSi_2基面滑移的临界分辨剪应力随温度的升高而降低，但在1300ﾟc附近出现一个中等的峰值。利用MoSi_2的反常塑性的一种方法是形成MoSi_2基复合材料，其中NbSi_2和TaSi_2形成垂直于MoSi_2解理面的界面。

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.