环境断裂研究进展

Progress in Environment Sensitive Fracture Research

本文介绍了环境断裂近年来的研究进展。第一部分是功能材料的环境断裂。研究发现,铁电陶瓷如PZT和Ba- TiO_3在有水或无水环境中,应力能使压痕裂纹发生滞后扩展(即存在应力腐蚀)。恒电场能引起铁电陶瓷的畴变,不协调畴变会产生内应力,电场和应力场对环境断裂存在耦合作用,因此,恒电场下环境断裂的本质是内应力引起的环境断裂；对磁致伸缩材料如(ThDy)Fe_2,应力和磁场均能引起畴变,卸载压痕裂纹在湿空气中的滞后扩展以及恒磁场引起的滞后畴变及滞后开裂均能发生。第二部分是关于氢压裂纹(白点)的再认识。氢压裂纹形核前是一个内壁光滑的空腔,微裂纹从空腔壁产生,而后连接形成白点。白点断口和含白点试样的断口概念不同,对车轮钢,前者为准解理的穿晶断裂,和氢致滞后开裂断口相同,但后者则依赖断裂方式和试样厚度。钢中白点除了产生二次裂纹外,对各种断口形貌均没有影响。车轮钢的滞后断裂由原子氢引起,与白点无关。

The progresses of recent years in our lab are introduced. First part is about the environment sensitive fracture of functional materials. For ferroelectric ceramics such as PZT and BaTiO3, stress corrosion cracking （SCC） in aqueous and non - aqueous enrichments under constant load, and domain change under sustained electric field can both occur. Internal stress will engender if domain change is disharmony. Thus, combined effect of electric field and mechanical loading on delayed fracture cornea into being. Therefore, the essence of environmental fracture under sustained electric field is the environmental fracture which caused by internal stress. For magnetostrictive alloy such as （ThDy） Fe2, delayed propagation of unloaded indentation crack as well as delayed domain change and delayed cracking induced by constant magnetic filed in humid air can occur. Second part is the further understanding of hydrogen flaking. It is a cavity with smooth wall before the hydrogen flaking forming. Microcracks initiate from the wall and then connect each other resulting in formation of flaking. The fight cracking surface of the flaking is a different idea with the fracture surface of the sample containing flaking. For a wheel steel, the former is quasi- cleavage and transgranular, similar to that of hydrogen - induced delayed cracking, but the later is dependent upon the failure method and the thickness of the sample. There is no effect of flaking on various fracture surface morphologies except secondary cracks. Hydrogen - induced delayed failure is due to atomic hydrogen rather than flaking.