TC4钛合金在慢速率形变下的银脆行为

Investigation of Silver Embrittlement Behavior of Titanium Alloy TC4 by Slow Strain Rate Tests

利用慢应变速率拉伸试验（ＳＳＲＴ）并结合断口分析，研究了镀银方式、镍阻挡层、表面压应力和温度等因素对ＴＣ４钛合金固态银致脆（ＳＳＩＥ）行为的影响，并对ＳＳＩＥ机制进行了理论分析。结果表明，在２８×１０－６·ｓ－１慢速率提伸条件下，ＴＣ４于３５０℃以上表现出较显著的ＳＳＩＥ敏感性，ＳＳＩＥ下限温度约为２８０℃。银与ＴＣ４表面紧密结合是产生ＳＳＩＥ的必要条件。电镀（ＥＰ）银可引起ＴＣ４氢脆（ＨＥ）和ＳＳＩＥ双重破坏作用。镍阻挡层对ＴＣ４的ＳＳＩＥ裂纹萌生有一定抑制作用。ＴＣ４合金ＳＳＩＥ过程速率由银在裂纹表面自扩散速率与裂尖氧化膜破裂速率的相对大小决定。

The efect of silver state, nickel barrier, contact pressure and test temperature on the solid silverinduced embrittlement (SSIE) of TC4 alloy was investigated by using slow strain rate tests (SSRT) and fractographic technique. The mechanism of SSIE is discussed in the light of test observation and thermodynamic analysis. TC4 alloy manifests severe embrittlement at temperature above 350℃ when loaded at a tensile strain rate of 2.8×10-6 s-1. The lover limit of embrittlement is about 280℃. Intimate contact between solid silver and TC4 alloy is one of the prequisites for SSIE. Electroplating silver causes both hydrogen embrittlement and silver embritllement. Crack initiation can be repressed in some degree by prior plating a thin layer of nickel onto the surface of TC4 alloy to act as a barrier to silver. The SSIE susceptibility of TC4 alloy depends mainly on the transport rate of silver atoms to the crack tip by surface selfdiffusion of silver on the fracture surface and the cracking rate of oxide film at crack tip.