Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing
Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing
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DOI：
10.3390/met9080843
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发表时间：
2019-07
期刊：
影响因子：
2.9
通讯作者：
A. Reck;A. Zeuner;M. Zimmermann
中科院分区：
文献类型：
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作者：
A. Reck;A. Zeuner;M. Zimmermann
研究了激光切割加工的（α+β） Ti-6Al-4V-ELI钛合金在机械后处理和不机械后处理条件下的疲劳强度。对未优化的中间切削参数所导致的表面质量和可能的缺口效应进行了表征和评价。详细记录了热影响区（HAZ）的显微组织变化，并与机械后处理（桶形磨削、机械抛光）表面条件的样品进行了比较。结果表明，与未优化激光切割的表面质量相比，机械后处理与表面粗糙度降低和缺口效应最小化相关，使疲劳强度显著提高（≈50%）。与初始等轴α+β组织相比，在HAZ区检测到马氏体α′相，形成了不同的区域。通过桶形研磨可以去除50%的HAZ，通过机械抛光可以去除100%的HAZ。断口分析表明，在未切割的表面状态下，疲劳裂纹总是在激光切割边缘处萌生，可归因于不规则的宏观和微观缺口。然而，非优化激光切割工艺的典型特征（熔滴和明显较高的表面粗糙度）导致了早期疲劳失效。疲劳裂纹完全是从表面浮雕的微缺口开始的，而不是从渣渣开始的。因此，与机械加工和表面质量较好的表面条件相比，这些缺口会导致明显的散射，并且疲劳强度降低，从而控制了疲劳性能。优化激光切割条件后，热影响区最小，表面粗糙度显著降低，疲劳强度显著提高。
The study presented investigates the fatigue strength of the (α+β) Ti-6Al-4V-ELI titanium alloy processed by laser cutting with and without mechanical post-processing. The surface quality and possible notch effects as a consequence of non-optimized intermediate cutting parameters are characterized and evaluated. The microstructural changes in the heat-affected zone (HAZ) are documented in detail and compared to samples with a mechanically post-processed (barrel grinding, mechanical polishing) surface condition. The obtained results show a significant increase (≈50%) in fatigue strength due to mechanical post-processing correlating with decreased surface roughness and minimized notch effects when compared to the surface quality of the non-optimized laser cutting. The martensitic α’-phase is detected in the HAZ with the formation of distinctive zones compared to the initial equiaxial α+β microstructure. The HAZ could be removed up to 50% by means of barrel grinding and up to 100% through mechanical polishing. A fracture analysis revealed that the fatigue cracks always initiate on the laser-cut edges in the as-cut surface condition, which could be assigned to an irregular macro and micro-notch relief. However, the typical characteristics of the non-optimized laser cutting process (melting drops and significant higher surface roughness) lead to early fatigue failure. The fatigue cracks solely started from the micro-notches of the surface relief and not from the dross. As a consequence, the fatigue properties are dominated by these notches, which lead to significant scatter, as well as decreased fatigue strength compared to the surface conditions with mechanical finishing and better surface quality. With optimized laser-cutting conditions, HAZ will be minimized, and surface roughness strongly decreased, which will lead to significantly improved fatigue strength.