EVALUATION OF Nb SOLID SOLUTIONS AS MATRIX OF COMPOSITES FOR VERY HIGH TEMPERATURE STRUCTURAL APPLICATIONS

采用Nb固溶体单晶材料研究了高温变形行为，为开发超高温结构用Nb基自生复合材料提供了基础数据。选择Nb-Ta和Nb-Mo合金来满足该目标，因为Ta与Nb具有非常小的尺寸失配和剪切模量差异，而Mo与Nb具有显著的尺寸失配和剪切模量差异。Nb固溶体Nb-Ta和Nb-Mo在低温和中温下的固溶强化可以用尺寸错配和i-s（替代-替代）相互作用来解释。TEM观察表明，Nb-Ta-O合金的变形组织由长而直的螺旋位错组成，表明螺旋位错与Ta-O和Mo-O之间存在强烈的相互作用，这种相互作用可以从Nb-Ta-O合金的屈服应力和滑移面随氧含量的取向关系中出现明显的各向异性得到证实。Nb-Mo-O的高温形变组织主要由刃位错组成，表明刃位错与Mo-O的相互作用。内耗测量表明，在低和中温下，螺旋位错与Ta-O和Mo-O产生的Snoek气氛相互作用。在高温下，刃位错与Mo-O产生的Cottrell气氛相互作用。

High temperature deformation behavior was investigated by using Nb solid solution single crystals in order to obtain fundamental data for development of Nb base in-situ composites for very high temperature structural applications. Nb-Ta and Nb-Mo alloys were se1ected to meet this objective, because Ta has a very small size misfit and shear modulus difference to Nb, while Mo has a significant size misfit and shear modulus difference to Nb. hi addition, both Ta and Mo have no scavenging effect in alloying with Nb, which means that the addition of these elements reveals the intrinsic nature of solid solution strengthening.Solid solution strengthening of Nb solid solutions, Nb-Ta and Nb-Mo, at low and intermediate temperatures can be interpreted in terms of size misfit and i-s (interstitial-substitutional) interaction. TEM observations indicate that deformation microstructures consist of long, straight screw dislocations, suggesting that screw dislocations interact strongly with Ta-O and Mo-O.This interaction is confirmed by the fact that marked anisotropy appears in the orientation dependence of yield stress and slip plane depending on oxygen content.At high temperatures yield stress of Nb-Ta-O decreases rapidly with increasing temperature, while that of Nb-Mo-O keep a high stress level up to about 1500K.Deformation microstructures of Nb-Mo-O at high temperatures consist dominantly of edge dislocations, suggesting the interaction of edge dislocations with Mo-O.Internal friction measurements reveal that at low and intermediate temperatures screw dislocations interact with Snoek atmosphere generated by Ta-O and Mo-O which receive the i-s effect, whereas at high temperatures edge dislocations interact with Cottrell atmosphere generated by Mo-O.