Effect of wall thickness and casting defects on microstructure and properties of ZTA15 titanium alloy
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摘要: 利用熔模精密铸造技术,制备了圆柱形和哑铃形的ZTA15钛合金试棒(铸态),然后进行热等静压处理(HIP态),采用室温拉伸、显微组织观察、晶粒度评定、X射线探伤、扫描电镜(SEM)及能谱分析等方法,研究了壁厚和铸造缺陷对ZTA15钛合金组织及性能的影响。结果表明:铸态ZTA15钛合金存在残余应力和缩松类铸造缺陷,影响其力学性能,对工程化应用不利;壁厚影响ZTA15钛合金力学性能,壁薄位置晶粒度级别较高,铸态残余应力较大,力学性能反而较低,经热等静压后残余应力得到消除,力学性能稍有提高,为较佳使用状态;缩松类缺陷经热等静压后压实闭合,扩散结合成致密、均匀组织,提高了力学性能,且数据分布集中;夹杂类缺陷对ZTA15钛合金的力学性能不利,尤其是塑性。Abstract: In this paper, cylindrical and dumbbell shaped ZTA15 titanium alloy test bars (as cast) were prepared by investment casting technology, and then treated by hot isostatic pressing (HIP). The effects of wall thickness and casting defects on the microstructure and properties of ZTA15 titanium alloy were studied by means of room temperature tensile test, microstructure observation, grain size evaluation, X-ray flaw detection, scanning electron microscope (SEM) and energy spectrum analysis. The results show that as-cast ZTA15 titanium alloy has residual stress and shrinkage casting defects, which affect its mechanical properties and are detrimental to its engineering application. The wall thickness affects the mechanical properties of ZTA15 titanium alloy. The grain size at the thin wall position is finer, but the as-cast residual stress is larger, leading to the lower mechanical properties. After hot isostatic pressing, the residual stress is eliminated, and the mechanical properties are slightly improved, which enable the alloy at better use state. The shrinkage defects are compacted and closed after hot isostatic pressing, and the dense and uniform structure is formed by diffusion bonding, which improves the mechanical properties, and the data distribution is centralized. Inclusion defects are detrimental to the mechanical properties of ZTA15 titanium alloy, especially the plasticity.
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Key words:
- ZTA15 titanium alloy /
- investment casting /
- wall thickness /
- casting defect /
- microstructure /
- mechanical property /
- grain size
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表 1 ZTA15钛合金化学成分
Table 1. The chemical compositions of ZTA15 titanium alloy
% 主要成分 杂质含量 Ti Al V Zr Mo Fe Si C N H O 标准要求 基 5.5~6.8 0.8~2.5 1.5~2.5 0.5~2.0 0.25 0.15 0.13 0.05 0.01 0.16 实测值 基 6.49 2.02 1.60 1.82 0.048 0.018 0.012 0.0066 0.0024 0.093 表 2 铸态试样室温拉伸力学性能
Table 2. Tensile mechanical properties of as-cast samples at room temperature
试棒
形状Rm/MPa Rp0.2/MPa A/% Z/% 标准要求 ≥885 ≥785 ≥5 ≥12 圆柱形 917~992 788~813 4~9.5 11~19 哑铃形 934~987 774~798 3.5~11.5 9~15 表 3 HIP态试样室温拉伸力学性能
Table 3. Tensile mechanical properties of HIP state samples at room temperature
试棒
形状抗拉强度Rm/
MPa规定非比例延伸强度Rp0.2/
MPa断后伸长率A/
%断面收缩率Z/
%标准要求 ≥885 ≥785 ≥5 ≥12 圆柱形 932~942 813~825 9.5~12.5 17~21 哑铃形 936~947 816~841 4~12 9~22 -
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