Oxidation of Metals ( IF 2.1 ) Pub Date : 2021-07-31 , DOI: 10.1007/s11085-021-10079-y Pranad Seth 1 , Jyoti S. Jha 1 , Alankar Alankar 1 , Sushil K. Mishra 1
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\(\alpha + \beta\) titanium alloy is known for its high strength to low weight ratio, excellent mechanical properties and superior corrosion resistance, which make it a favorable material for aerospace and biomedical applications. However, on exposure to oxygen and nitrogen at elevated temperatures, a hard and brittle \(\alpha\)-layer develops on the titanium alloy surface, which is referred to as ‘\(\alpha\)-casing.’ In the present study, Ti–6Al–4 V was heat treated above the \(\beta\)-transition temperature and cooled at different rates in water, air and furnace to obtain lamellar morphologies of different \(\alpha\)-lath thicknesses. Tensile and compact tension (CT) specimens with three different lamellar morphologies were obtained by heat treatment in such a way that one set (A) had ‘\(\alpha\)-case’ and other set (B) was devoid of such casing. Water quenched (WQ) samples formed a very thick \(\alpha\)-case with numerous micro-cracks compared to the air and furnace cooled samples. On tensile loading, the WQ sample with \(\alpha\)-case failed in fully brittle mode and the ductility of the air-cooled (AC) and furnace cooled (FC) samples with \(\alpha\)-case was reduced significantly. It was also observed that the fatigue crack growth rate (FCGR) increased considerably as the apparent effective crack front area was reduced due to \(\alpha\)-case formation.
Graphical abstract
中文翻译：
不同氧化环境下 Ti-6Al-4V 中 α-壳的形成及其对拉伸和疲劳裂纹扩展行为的影响
\(\alpha + \beta\)钛合金以其高强度与低重量比、优异的机械性能和优异的耐腐蚀性而闻名，这使其成为航空航天和生物医学应用的有利材料。然而，在高温下暴露于氧气和氮气时，钛合金表面会形成硬而脆的\(\alpha\) -层，称为“ \(\alpha\) -外壳”。在本研究中，Ti-6Al-4 V 在\(\beta\)转变温度以上进行热处理，并在水、空气和炉中以不同的速率冷却，以获得不同\(\alpha\)- 板条厚度。通过热处理获得具有三种不同层状形态的拉伸和致密张力 (CT) 试样，其中一组 (A) 具有“ \(\alpha\) -case”，另一组 (B) 没有这种外壳. 与空冷和炉冷样品相比，水淬 (WQ) 样品形成了非常厚的\(\alpha\)外壳，具有许多微裂纹。上拉伸载荷时，WQ样品与\（\阿尔法\） -案例未能完全脆性模式和空冷（AC）的延展性和炉内冷却（FC）样品\（\阿尔法\） -案例减少显着地。还观察到疲劳裂纹扩展速率 (FCGR) 显着增加，因为表观有效裂纹前沿面积由于以下原因减少了\(\alpha\) -案例形成。
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