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首页> 外文期刊>International Journal of Plasticity >The role of dwell hold on the dislocation mechanisms of fatigue in a near alpha titanium alloy
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The role of dwell hold on the dislocation mechanisms of fatigue in a near alpha titanium alloy

机译：居住持有对近α钛合金疲劳脱位机制的作用

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摘要

The dislocation structures appearing in highly mis-oriented soft/hard grain pairs in near-alpha titanium alloy Ti6242Si were examined with and without the application of load holds (dwell) during fatigue. Dislocation pile-up in a soft grain resulted in internal stresses in an adjacent hard grain which could be relaxed by dislocation multiplication at localised Frank-Read sources, a process assisted by the provision of a relaxation time during a load hold. The rate of this process is suggested to be controlled by < c + a > pyramidal cross-slip and < a > basal junction formation. A high density of < a > prism pile-ups was observed with dual slip on two prism planes, together with edge dislocations on the third prism plane in the soft grain of a highly mis-oriented grain pair, increasing the pile-up stress. The stress concentration developed by such pile-ups is found to be higher in dwell fatigue (single-ended pile-ups) than in LCF (double ended). Analytical modelling shows that the maximum normal stress produced on the hard grain in dwell fatigue by this pile-up would be near-basal, approximate to 2.5 degrees to (0002). This provides support for the dominant hypothesis for the rationalisation of dwell fatigue crack nucleation in Ti alloys, which derives from the Stroh pile-up model, and elaboration of the underlying dislocation phenomena that result from load shedding and lead to basal faceting.
机译：用疲劳期间检查近乎α钛合金Ti6242SI中高度错误定向的软/硬粒对的脱位结构，在疲劳期间，不应用载荷（居住）。软谷物中的位错堆积导致相邻的硬颗粒中的内部应力，其可以通过局部坦率读取源的位错倍增，通过在负载保持期间提供弛豫时间来辅助的过程。建议该过程的速率由金字塔滑槽和基底结形成来控制。观察到高密度棱镜堆积，在两个棱镜平面上观察到双滑平面，以及在高度错误定向的谷物对的软粒中的第三棱镜平面上的边缘位错，增加了堆积应力。由于LCF（双端），这种堆积产生的应力浓度被发现比在LCF（双端）中的疲劳（单端桩）更高。分析模型表明，这种堆积的疲劳疲劳中硬粒的最大正常应力将接近基础，近似为2.5度至（0002）。这提供了对Ti合金中患者疲劳裂纹成核的合理化的主导假设的支持，其源于STROH堆积模型，并阐述由负载脱落和导致基座的潜在脱位现象。

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