(1.西北工业大学 工程力学系，西安 710072；
2.西安交通大学 焊接研究所，西安 710049)
摘 要: 采用单轴拉伸对LY12粗晶材料进行超塑性研究， 温度一定时， 在较高和较低的应变速率下都得到了大延伸率， 而处于中间应变速率的试样延伸率较低。SEM断口分析表明, 晶界上产生的粘性物质对粗晶超塑性行为有决定性影响。在高应变速率下，晶界上粘性层很薄，被粘性层包围着的晶粒和亚结构在相互挤压和相对转动中容易细化，有利于超塑性变形能力的提高且不易产生孔洞，室温性能良好；低应变速率下，大多晶界上都有粘性物质包围且粘性层厚度增大，粘性物质的增多使超塑性变形能力增强，但易产生孔洞，使室温性能恶化；而中间应变速率区间，晶粒细化程度不够，晶界上未产生较多粘性物质，有少量孔洞产生且变形能力较差。
关键字: LY12合金； 粗晶； 超塑性变形； 晶界； 粘性物质
mechanisms of coarse-grained LY12
（1. Department of Engineering Mechanics,
Northwestern Polytechnical University,
Xian 710072, China;
2. Welding Institute, Xian Jiaotong University,
Xian 710049, China）
Abstract:Superplastic uniaxial tensile tests of coarse-grained LY12 are conducted. Large elongation to fracture is obtained at 10-4 s-1 and 10-1 s-1 strain rates, while elongation to fracture is low at intermediate strain rates. Analysis of the SEM fracture surface shows that amorphous matter at the grain boundary plays a dominant role in coarse-grained superplastic behaviors. At higher strain rates, the amorphous matter layer is thin and the grains and sub-structure size decrease during the grains extruding and turning around among each other so that exhibit good superplastic characteristics. In this case, few cavities form and mechanical properties at room temperature are good. At lower strain rates, nearly all grains are covered with thick amorphous matter layer which makes grain boundary sliding more easily and enhances superplastic deforming ability, but many cavities tend to form and mechanical properties at room temperature deteriorate. At intermediate strain rates, grains cant become very fine and amorphous matter layer at the grain boundary is not very thick, hence a samll quantity of cavities forms and the specimens exhibit a decrease in superplastic characteristics.
Key words: LY12 alloy; coarse grains; superplastic deformation; grain boundary; amorphous matter
