TiAl金属间化合物损伤机理的研究

【作者】 朱浩；

【导师】 陈剑虹； 曹睿； 王国珍；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 本文通过拉伸卸载实验及原位拉伸SEM观察对全层和双态TiAl基合金损伤机理进行了研究。研究结果表明:在平板拉伸卸载试验中,如果采用位移控制的方式,材料则产生微裂纹从而导致材料发生损伤;随着载荷的增加,原先产生的微裂纹继续扩展,而微裂纹扩展的同时又产生大量新的微裂纹;预损伤加快裂纹产生、扩展,使得损伤程度进一步加强,裂纹面密度增大。通过统计分析发现裂纹面密度可以作为衡量损伤程度的损伤参量;不同程度的预损伤使得材料的弹性模量降低,使材料抵抗裂纹产生、扩展的能力下降,但是对这种材料的最终断裂性能没有影响。在拉伸的过程中如果采用载荷控制的方式,材料则不易产生微裂纹。微裂纹即使产生了,也来不及扩展,这样的结果使得材料的弹性模量、断裂应力、断裂应变、屈服应力等几乎没有变化。另外通过原位拉伸卸载试验发现:带缺口试样和平板试样在拉伸卸载过程中的损伤机理不同,断裂过程也完全不一样。对于缺口(预裂纹)试样,由于缺口根部应力集中的作用,其断裂过程主要是主裂纹首先起裂、扩展并最后断裂的过程。而对于平板拉伸试样,先产生很多微裂纹,随着外加应力的进一步增加,这些微裂纹扩展,当微裂纹和外加应力共同作用足以引起微裂纹进一步贯穿的瞬间,试样整体发生解理断裂。更多还原

【Abstract】 This paper focuses on the studying of damage mechanisms of TiAl-based alloys of fully lamellar and duplex. The damage mechanism of lamellar and duplex TiAl alloys has been investigated in tensile-unload experiments and situ SEM experiments. The studies indicate that, if the displacement-controlled is applied, the fiat tensile process produces microcracks which result in damage of materials. With load increasing, microcracks will propagate and at the same time, a lot of new microcracks will come into being. Pre-damage will increase the initiation and propagation of cracks as well as the degree of damage. Pre-damage at different degrees will decrease the material elastic module and the ability against crack initiation and propagation; but the pre-damage has no effect on the ultimate fracture properties. If the load-controlled is applied, the microcracks will not come into being easily, even if they have, they will have no time to propagate. So the damage has no influence on the elastic module, the stress of fracture, the strain of fracture and yielding stress. In addition, the result of in-situ tensile-unload experiment indicates: during the tensile-unload process, the fracture process is completely different because the damage mechamsm is different to specimens with notch and flat specimens. To the specimens with notch (pre-fracture), the process of causing fracture is the one that is initiated by the main fracture which will propagate and fracture because of the centralization of stress in the root of notch; while, to the flat specimens, it is many microcracks that will fist come into being, and they will propagate with the increasing of stress. At the moment that facture and stress interact with each other and cause the further propagation of microcracks, the specimens will cleavage fracture.更多还原