Simulation-assisted investigation on the formation of layer bands and the microstructural evolution in directed energy deposition of Ti6Al4V blocks
Simulation-assisted investigation on the formation of layer bands and the microstructural evolution in directed energy deposition of Ti6Al4V blocks
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Ti6Al4V块体定向能量沉积层带形成和微观结构演化的模拟辅助研究
DOI：
10.1080/17452759.2021.1942077
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发表时间：
2021-07
影响因子：
10.6
通讯作者：
Huang Weidong
中科院分区：
文献类型：
--
作者：
Lu Xufei;Zhang Guohao;Li Junjie;Cervera Miguel;Chiumenti Michele;Chen Jing;Lin Xin;Huang Weidong
钛合金增材制造（AM）过程中由于热历史的不同，导致了严重的显微组织不均匀性和层带。虽然已经报道了AM中的热-微观结构关系，但复杂的热历史如何影响微观结构演变的细节尚未得到解决，并且多层多道次构建中的层带形成仍然不清楚。为了进行这样的研究，首先使用在不同尺寸的基板上制造的两个部分尺寸块来校准热模型，然后用于研究关键微观结构特征与所涉及的热循环之间的关系。结果表明：打印路径控制的β-横切温度（T β）下温度范围的不同演变是导致块体中心和角落不同波段分布的原因。当温度在T β和α溶解温度之间波动时，正常区域的α尺寸与热曲线的积分面积密切相关，这有助于将AM变量与冶金联系起来。这进一步证明了热循环过程中α粗化主要是由多溶蚀和沉淀转变驱动的，而不是由奥斯特瓦尔德成熟驱动的。最后，建立了定量的热-显微组织-显微硬度关系，为显微组织设计提供了依据。
ABSTRACT Additive manufacturing (AM) of titanium alloy entails severe microstructural heterogeneity and layer bands due to diverse thermal histories. While the thermal-microstructure relationship in AM has been reported, the details on how complex thermal histories influence the microstructural evolution have not been so addressed, and the formation of layer bands in multi-layer multi-pass builds is still unclear. To undertake such investigation, a thermal model is firstly calibrated using two part-scale blocks fabricated on differently sized substrates, and then used to study the relationship between key microstructural characteristics and the thermal cycling involved. Results show that the different evolutions of the temperature ranges just underneath the β-transus temperature (T β ) controlled by the printing path are responsible for the different band distributions at the centre and corner of the blocks. Also, the α sizes in the normal region are closely linked to the integral area obtained from the thermal curve as temperature fluctuates between T β and α dissolution temperature, which helps linking AM variables to metallurgy. This further demonstrates that the α coarsening during thermal cycles is primarily driven by multi dissolution and precipation transformations instead of Ostwald ripening. Finally, the quantitative thermal-microstructure-microhardness relationship is established, helpful for the microstructural design.
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