Subsurface facets-induced crack nucleation behavior and microstructure-based strength evaluation of titanium alloys in ultra-long life regime

IF 7 2区材料科学 Q1 MATERIALS SCIENCE, MULTIDISCIPLINARY Materials Science and Engineering: A Pub Date : 2019-07-22 DOI:10.1016/j.msea.2019.138055

Wei Li , Xinxin Xing , Ning Gao , Meng Li , Rui Sun , Siqi Zhou , Tatsuo Sakai

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引用次数: 14

Abstract

Ultra-long life fatigue tests of 10⁶-10⁹ cycles under asymmetrical loading were conducted to elucidate the subsurface facets-induced crack nucleation behavior of two alpha-beta titanium alloys, and a theoretical method of describing the microstructure-based strength relationship was proposed. As a result, two titanium alloys all present the continuously descending S–N (stress - number of cycles) curve characteristics with subsurface non-defect induced failure. A bright convergence zone with facets becomes the remarkable feature of failure. By means of the milling of focused ion beam system, the coalescence and growth of subsurface micro-cracks crossing several grains along the 45° angle, controlled by the maximum shear stress, can be observable. Based on this, a subsurface facets-induced crack nucleation and growth mechanisms for titanium alloys was proposed in combination with the discussion of small crack fracture mechanics. In view of the good consistency between the evaluated nucleation life of crack at the size of convergence zone with facets and the total life, the microstructure-based modelling method for evaluating fatigue strength of titanium alloys with subsurface failure in ultra-long life regime can be acceptable.

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钛合金超长寿命亚表面裂纹形核行为及基于显微组织的强度评价

通过非对称载荷下106 ~ 109次的超长寿命疲劳试验，研究了两种α - β钛合金的亚表面裂纹形核行为，提出了一种描述基于微观组织的强度关系的理论方法。结果表明，两种钛合金均呈现连续下降的S-N(应力-循环次数)曲线特征，并伴有亚表面非缺陷诱发失效。带有切面的明亮辐合带成为失效的显著特征。通过聚焦离子束系统的铣削，可以观察到在最大剪切应力控制下，沿45°角沿多个晶粒相交的亚表面微裂纹的合并和生长。在此基础上，结合对小裂纹断裂力学的讨论，提出了钛合金亚表面裂纹形核扩展机制。考虑到裂纹在带切面的会聚区尺寸处的形核寿命与总寿命具有较好的一致性，基于微观组织的超长寿命下亚表面破坏钛合金疲劳强度评估建模方法是可以接受的。

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来源期刊

Materials Science and Engineering: A 工程技术-材料科学：综合

CiteScore

11.50

自引率

15.60%

发文量

1811

审稿时长

31 days

期刊介绍： Materials Science and Engineering A provides an international medium for the publication of theoretical and experimental studies related to the load-bearing capacity of materials as influenced by their basic properties, processing history, microstructure and operating environment. Appropriate submissions to Materials Science and Engineering A should include scientific and/or engineering factors which affect the microstructure - strength relationships of materials and report the changes to mechanical behavior.