深过冷Cu-30Ni合金单向凝固组织的力学性能

研究了过冷0～210K的Cu－30Ni（原子百分数）合金的组织演化规律．在105～155K的过冷范围内实现了自由生长枝晶的单向凝固，获得了单向凝固的单晶组织.深过冷熔体的微观净化和单向快速凝固，有效地去除了合金中的微细夹杂物，减少了宏观偏析和校晶偏析，显著改善了材料的均匀性，在拉应力作用下材料从沿晶断裂转变为穿晶断裂与常规铸态组织相比，其延伸率、极限抗拉强度和0．2％屈服强度分别提高到原组织的25倍、3倍和1．3倍

MECHANICAL PROPERTIES OF THE UNIDIRECTIONALLY SOLIDIFIED STRUCTURE OF THE HIGHLY UNDERCOOLED Cu-30Ni ALLOY

On the basis of investigating the structure evolution of Cu-30Ni alloy with variousundercoolings, the feasibility of unidirectional solidification in the undercooled alloy melt was evaluated, and the mechanical properties were tested. With undercooling increasing, there were two processes of grain refinements in the alloy. One took place in the undercooling range of 45~ 75K, and the other beyond the critical undercooling 190K. A unidirectionally solidified single crystal comprised of the dendrite substructures was gained in the undercooling range of 105~155K. The experimental results indicated that the inclusions could be excluded from the alloy melt during the purification. The rapid solidification at such high undercoolings as 105~155K suppressed the macrosegregation and the microsegregation, and led to the notable improvement of chemical uniformity. The achievement of the unidirectionally solidified single crystal structure also eradicated the pernicious effect of macro grain boundary on the mechanical properties, and made the breaking of the material transfer from intergranular fracture into transgranular. As a result, the elongation, ultimate tensile strength and 0.2% yield strength of the alloy with the unidirectionally solidified structure were 25, 3 and l.3 times, respectively, as high as those with the conventional as--cast structure.