钛合金Ti-6Al-4V两种微观结构的裂纹扩展行为研究

介绍对两种均匀锻造的片晶结构的钛合金Ti-6Al-4V的疲劳裂纹扩展性能的研究情况。在材料准备时，注意避免材料的方向性等对性能的影响。采用标准试验方法进行各项力学性能试验，试验数据表明，两种片晶微观结构的钛合金的拉伸强度相差约5％，拉伸塑性相关13％，疲劳行为有较大不同，微观组织细密的钛合金材料的性能比较好。两种片晶的小裂纹扩展速率与长裂纹扩展速率相比有明显增加，但对于本研究的试验条件，在应力比R＝0和R＝－1的情况下，两种状态之间的裂纹扩展行为差别不大。试验数据说明，裂纹闭合是小裂纹效应的主要原因之一。

CRACK PROPAGATION BEHAVIOR IN Ti-6Al-4V TITANIUM ALLOY WITH DIFFERENT MICROSTRUCTURES

The research is focused on the crack propagation behavior of Ti 6Al 4V alloy with two kinds of Widmansttten lath microstructures. Amongst these two microstructures, one of them has thinner and more mixed lath crystals than the other. Attention is paid to the material preparation to avoid the orientation effect. All the tests are under the guidance of standards. From the experimental results, it is found that the difference of tensile strength between these two microstructures is about 5%. The difference of their ductility is bigger, about 13%. The better property is obtained from the thinner lath microstructure. Its fatigue life is longer than the other one in the lower stress level. However the crack propagation behaviors, either long or small, are similar for these two microstructures. It is found obviously that, for stress ratio R =0 and R =-1, the small crack propagation rate of both microstructures are much higher than the long crack propagation rate in the lower stress intensity factor range. The test data support that the crack closure is one of the main reasons of small crack effects.