Understanding the thermal history of a metal part during additive manufacturing (AM) is essential for process design and microstructural control. In this study, detailed thermal history simulation was carried out for laser metal deposition (LMD) of Ti-6Al-4V (wt%) using the Directed Energy Deposition (DED) module in Simufact Welding. The simulation identified necessary LMD conditions for in-situ decomposition of α′-martensite in Ti-6Al-4V with respect to build height. On this basis, rectangular Ti-6Al-4V coupons were fabricated and systematic microstructural characterisation confirmed in-situ decomposition of α′ into ultrafine α-β lamellae in the as-built samples. In addition, the approximate in-situ transition time from α′ → α + β (lamellar) during the LMD process was determined to be 30–40 s, which is two orders of magnitude faster than conventional isothermal decomposition of α′. The underlying reasons were analysed and attributed to precursor (clusters) development within the α′-martensite laths as well as at the α′-lath boundaries due to being frequently and rapidly heated to temperatures well above the β transus, supported by recent literature. The as-built lamellar α-β Ti-6Al-4V achieved yield strength of 951 ± 10 MPa and tensile ductility of 8.18 ± 1.8%. Other insights obtained from this simulation-based experimental study were discussed including microstructural control of tall titanium alloy components through in-situ decomposition of α′-martensite.

了解增材制造 (AM) 过程中金属零件的热历史对于工艺设计和微观结构控制至关重要。在本研究中，使用Simufact Welding 中的定向能量沉积(DED) 模块对 Ti-6Al-4V (wt%) 的激光金属沉积 (LMD) 进行了详细的热历史模拟. 模拟确定了在 Ti-6Al-4V 中原位分解 α'-马氏体的必要 LMD 条件，与构建高度有关。在此基础上，制备了矩形 Ti-6Al-4V 试样，系统的微观结构表征证实了 α' 原位分解为竣工样品中的超细 α-β 薄片。此外，LMD 过程中从 α' → α + β（层状）的近似原位转变时间被确定为 30-40 秒，这比 α' 的常规等温分解快两个数量级。分析了根本原因并将其归因于 α'-马氏体板条内以及 α'-板条边界处的前体（簇）发展，这是由于频繁且快速地加热到远高于 β 转变的温度，最近的文献支持。竣工的层状 α-β Ti-6Al-4V 的屈服强度为 951 ± 10 MPa，拉伸延展性为 8.18 ± 1.8%。讨论了从这项基于模拟的实验研究中获得的其他见解，包括通过 α'-马氏体的原位分解对高钛合金部件的微观结构控制。