On the role of thermal exposure on the stress controlled fatigue behaviour of a high strength titanium-aluminum alloy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:615

Article

Huang, Z. W.^1,2  Sun, C.¹ 

[1] Southwest Jiaotong Univ, Sch Mat Sci & Engn, Chengdu 610031, Sichuan, Peoples R China

[2] Univ Birmingham, Sch Met & Mat, Birmingham B15 2TT, W Midlands, England

关键词: Gamma titanium aluminides;    Thermodynamic stability;    High cycle fatigue;    Surface damage;    Notch sensitivity;    Scanning electron microscopy;   

DOI  :  10.1016/j.msea.2014.07.063

来源: Elsevier

【 摘 要 】

Fatigue specimens with four types of surface were assessed under three exposure conditions (no exposure, block exposure, individual exposure-oxidation at 700 degrees C for 10,000 h) to quantify the effects of surface roughness, stress concentration, oxidation and inner microstructural embrittlement on fatigue strength of a near lamellar gamma-TiAl alloy Ti-44Al-4Nb-4Zr-0.2Si-1B. With the yield strength of sigma(0.1)=621 MPa, S-N fatigue is found to be always conducted under a loading condition of sigma(max) < sigma(0.1). Local plastic deformation is difficult to occur on the maximum-stressed surface. The surface quality with or without defects and residual stresses therefore becomes critical for fatigue performance. Introducing compressive-stressed layer by shot peening and removing tensile-stressed layer and defects by grinding-electropolishing can improve the fatigue strength significantly, and the latter is more capable than the former for the high strength alloy. It is found that the fatigue performances of all types of surface are deteriorated to some degree when subjected to block exposure, owing to exposure-induced embrittlement. On the other hand, exposure-induced fatigue strengthening occurs after individual exposure oxidation. The relaxation of residual tensile stress and dissipation of bulk stress in warm-air environment are found to outweigh the negative effects of oxidation layer at surface and exposure-induced embrittlement inside specimen. (C) 2014 Elsevier B.V. All rights reserved.

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