arXiv 2006.082882020-06cond-mat.mtrl-sci

料床温度对选择性laser熔炼Ti-6Al-4V合金溶质偏析和力学性能的影响

Effect of bed temperature on solute segregation and mechanical properties in Ti-6Al-4V produced by selective laser melting

S. Pedrazzini, M. E. Pek, A. K. Ackerman, Q. Cheng, H. Ali, H. Ghadbeigi, K. Mumtaz, T. Dessolier, T. B. Britton, P. Bajaj, E. Jägle, B. Gault, A. J. London, E. Galindo-Nava

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摘要：

先进的表征技术用于在加热基板上生产的LPBF Ti-6Al-4V样品。当基体温度为100°C时，延伸率为6%，在570°C时，延伸率增加并达到峰值10%，然后在770°C时，延伸率急剧下降至零。在100°C下，观察到主要由α+ α '组成的严重应变和孪晶显微组织，并且其与通过常规LPBF方法获得的预制显微组织相当。在更高的温度下，孪晶不再存在，而是在α'和α内观察到纳米级β沉淀物，以及位错网络（570°C）和缠结（770°C）。在所有的预热条件下，观察到在晶体缺陷处的溶质偏析。在100°C的样品中观察到微孪晶处的Al和V偏析，首次报告了在相邻孪晶中形成的“选择性”和相互排斥的富Al和富V区域。在570°C和770°C样品中观察到位错处的V偏析，这与较高的预热温度一致。在所有样品中测得高O含量，但具有明显的相反效果。在100°C和570°C下，估计低于O脆化的临界阈值，并通过固溶体强化局部帮助保持高强度，而在770°C下，它高于阈值，因此以脆性方式失效。基于这些观察结果，从100°C到570°C的延展性的初始增加归因于微孪晶和位错网络的减少，所述位错网络在较粗糙的微观结构中充当滑移的“软屏障”。在770°C下缺乏延展性归因于该样品中局部溶质再分布导致位错钉扎和O含量增加。

英文摘要：

Advanced characterisation techniques were used on LPBF Ti-6Al-4V samples produced on a heated base plate. When the substrate temperature is 100°C the elongation is 6\%, which increases and peaks at 10\% at 570°C, then sharply decreases to zero ductility at 770°C. At 100°C, a heavily strained and twinned microstructure, primarily composed of α+α', was observed and it was comparable to asbuilt microstructures obtained by conventional LPBF methods. At higher temperatures, twins are no longer present and instead nano-scale β precipitates are observed within α' and α, as well as dislocation networks (570°C) and tangles (770°C). Solute segregation at crystal defects was observed in all pre-heating conditions. Al and V segregation at microtwins was observed in the 100°C sample, reporting for the first time `selective' and mutually exclusive Al- and V-rich regions forming in adjacent twins. V segregation at dislocations was observed in the 570°C and 770°C samples, consistent with the higher preheating temperatures. High O contents were measured in all samples but with apparent opposing effects. At 100°C and 570°C was estimated to be below the critical threshold for O embrittlement and locally aids in maintaining a strength high by solid solution strengthening, whereas at 770°C it was above the threshold, therefore failing in a brittle fashion. Based on these observations, the initial increase in ductility from 100°C to 570°C is attributed to a reduction in microtwins and the dislocation networks acting as `soft barriers' for slip within a coarser microstructure. The lack of ductility at 770°C was attributed to local solute redistribution causing dislocation pinning and an increase of O content in this sample.

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