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首页> 外文期刊>Materials Science and Engineering >Dynamic mechanical properties and failure characteristics of electron beam melted Ti-6Al-4V under high strain rate impact loadings
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Dynamic mechanical properties and failure characteristics of electron beam melted Ti-6Al-4V under high strain rate impact loadings

机译：高应变率冲击载荷下电子束熔化Ti-6Al-4V的动态力学性能和故障特性

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摘要

This study presents an investigation on the effects of building direction on microstructure, dynamic mechanical properties, and deformation mechanisms of electron beam melted Ti-6Al-4V (EBM-Ti64) cylindrical rods. Microstructural features were characterized using optical microscopy (OM) and scanning electron microscopy (SEM). The initial microstructure in both directions consists of transformed α+β phases and grain boundary-α (α_GB))along prior β-grain boundaries. The vertically built cylindrical specimens have a finer grain structure, including lower interlamellar spacing and finer α-laths compared to the horizontally built ones. Dynamic impact tests using Split-Hopkinson Pressure Bar (SHPB) were conducted on both horizontally and vertically built samples at strain rates ranging between 1150 and 2700 s~(-1). Dynamic mechanical properties are strain-rate sensitive; the maximum flow stress of 1960 MPa (at 2100 s~(-1)) and 2160 MPa (1650 s~(-1)) were obtained for horizontal and vertical specimens, respectively. Horizontal specimens fragmented when deformed at 2700 s~(-1), whereas the vertical specimens failed at a much lower strain rate (1900 s~(-1)). At a given strain rate, vertical specimens exhibited better dynamic strength and lower strain (total strain) due to their finer microstructure. The temperature rise during deformation primarily governs flow softening at all conditions, which led to the formation of adiabatic shear bands (ASBs). Microstructures of deformed specimens revealed thermal softening features such as voids formation. These voids coalesced and grew, leading to crack initiation and propagation along ASBs. Fractographic examination of the fragmented specimens under impact loading revealed ductile dimples and smoother surfaces, which indicate a combination of both ductile and brittle fracture. The contribution of twinning and pyramidal slip systems is the primary deformation mechanism during high strain rate impact loading of EBM-Ti64. The experimentally obtained flow curves are in good agreement with the Chang-Asaro equation-based constitutive modeling results.
机译：该研究提出了对电子束熔化Ti-6Al-4V（EBM-Ti64）圆柱形杆的构建方向对构建方向对微观结构，动态力学性能和变形机制的影响。使用光学显微镜（OM）和扫描电子显微镜（SEM）的微观结构特征。两个方向上的初始组织包括沿预先β-晶界的转化的α+β相和晶界-α（α_GB）组成。垂直构建的圆柱形样品具有更精细的晶粒结构，包括与水平构建的颗粒间距和更细的α-Laths。使用分流霍普金森压力棒（SHPB）的动态冲击试验在1150和2700S〜（-1）之间的应变率下水平和垂直构建的样品。动态力学性能是应变率敏感;为水平和垂直标本分别获得了1960MPa的最大流量应力（在2100S〜（-1））和2160MPa（1650 s〜（-1））中。在2700 s〜（-1）变形时，横向样品片段化，而垂直标本以低得多的应变速率（1900 s〜（-1））失效。在给定的应变速率下，由于它们的微观结构细胞，垂直试样表现出更好的动态强度和更低的应变（总菌株）。变形过程中的温度升高主要控制所有条件的流动软化，这导致了绝热剪切带（ASB）的形成。变形样品的微观结构显示了空白软化特征，例如空隙形成。这些空隙合并并增长，导致沿ASBB的开发和传播。冲击载荷下碎片样本的碎片检测显示延性凹槽和更平滑的表面，表明延性和脆性骨折的组合。孪晶和金字塔的贡献滑移系统是EBM-Ti64高应变率冲击载荷期间的主要变形机制。实验获得的流动曲线与基于Chang-Asaro公式的本构型建模结果吻合良好。

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