【摘要】 用X-射线分析和拉伸实验研究了Nb-Zr和Nb-Ti超导合金的临界电流密度J_c与其组织结构之间的关系。研究结果表明:当合金中没有第二相粒子时,热处理提高变形合金的J_c是由于位错重排后形成位错胞结构,位错胞壁成为磁通线的有效钉扎中心。当合金中含有第二相粒子时,则能在第二相粒子析出过程中因共格畸变应力场松弛而形成新的位错,这些新形成的位错进一步提高了变形合金的位错胞壁中的位错密度,从而因提高位错胞壁对磁通线的钉扎能力而使J_c进一步提高。因此在Nb-Zr和Nb-Ti合金中,析出相提高合金载流能力的作用实质是和冷加工变形的作用实质相同的。更多还原

【Abstract】 The pinning effect in Nb-Zr and Nb-Ti alloys was studied by means of X-ray analysis and tensile test. It was found that both dislocations and! precipitates are effective pinning centres which had also been mentioned by other investigators. As to the mechanism of the pinning effect of the second phase, there exist three models in the literature, namely K pinning, pinning due to the interface between the matrix and the second phase, and pinning resulting from the suitable size and distribution of the second phase. Attempts were made by us to explain our experimental results with these three models but they were unsuccessful. Another model was therefore suggested which may be used to explain all of our experimental results satisfactorily. It may be stated as follows. Before the precipitation of the second phase take place, there exists a stage of segregation of the solute atoms. As the solute atoms segregate, a coherent stress field is produced arround the aggregate. This stress field will become stronger and stronger as the segregation of the solute atoms proceeds, and dislocations will be formed finally so that the stress field is relieved. The dislocations so produced can arrange themselves into cell structures after a suitable heat treatment. The dislocation cell wall is an effective pinning center, and the higher the density of dislocations in the wall, the stronger the pinning effect. The density of dislocation in the cell walls is increased as a result of the precipitation of the second phase after annealing, so that the precipitates increase Jc of the superconductor. It was concluded that the pinning mechanism due to second phase particles in Nb-Zr and Nb-Ti alloys is just the same as that of the dislocations.更多还原