Hot workability and microstructure evolution of highly β stabilised Ti–25V–15Cr–0·3Si alloy
Hot workability and microstructure evolution of highly β stabilised Ti–25V–15Cr–0·3Si alloy
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DOI：
10.1179/174328407x185884
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发表时间：
2008-10
影响因子：
1.8
通讯作者：
W. Zeng;Y. Shu;X. Zhang;Y. Zhou;Y. Q. Zhao;H. Wu;Y. Dai;Junliang Yang;L. Zhou
中科院分区：
文献类型：
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作者：
W. Zeng;Y. Shu;X. Zhang;Y. Zhou;Y. Q. Zhao;H. Wu;Y. Dai;Junliang Yang;L. Zhou
在90 0~110 0℃和0·01~10 S−1应变速率范围内，用恒应变率等温压缩试验研究了高度稳定的Ti-25V-15Cr-0·3Si合金的热加工性能和组织演变。结果表明，所有的流动应力曲线都具有初始急剧的不连续屈服，然后是稳态软化和随应变的连续流动软化的特征。该合金在低于950°C的温度下表现出动态回复，但在高于1000°C的温度下表现出动态再结晶。在更高的应变率下(>；1 S−1)，由细小的再结晶颗粒装饰晶界的‘项链’再结晶是有效的。在低应变率(1000°C)下，这是由于元素V的严重氧化造成的自由表面开裂以及圆柱形试件在镦粗过程中鼓起的二次拉应力造成的。从临界应变到断裂ϵf可以评价Ti-25V-15Cr-0.3硅合金的断裂行为，该应变随温度的升高和应变速率的降低而增大。结果表明，断裂的临界应变可以用一个单一的函数来表示，即ϵ-Holloman参数Z，它综合了温度和应变速率的影响。ϵf和Inz服从线性关系。在实验结果的基础上，建立了优化工艺参数和实现热加工组织控制的工艺窗口，该窗口的温度范围为95 0~10 5 0℃，应变速率范围为0·01~0·1 S−1。利用直径为140 mm的合金试件进行了圆柱体顶粗放大试验，验证了加工窗口的有效性。
The hot workability and microstructural evolution of a highly β stabilised Ti–25V–15Cr–0·3Si alloy have been studied using constant strain rate isothermal compression tests in the temperature range 900–1100°C and strain rate range 0·01–10 s−1. It was found that all the flow stress curves were characterised by a sharp initial discontinuous yielding followed by either a steady state or continuous flow softening with strain. This alloy showed dynamic recovery at temperatures less than 950°C but dynamic recrystallisation at temperatures higher than 1000°C. At higher strain rates (>1 s−1), ‘necklace’ recrystallisation, in which grain boundaries were decorated by finely recrystallised grains, was operative. At lower strain rates (1000°C), it was attributed to free surface cracking due to severe oxidation of element V and the secondary tensile stresses caused by bulging of the cylindrical specimen during upsetting. The cracking behaviour of Ti–25V–15Cr–0·3Si alloy can be evaluated from the critical strain to fracture ϵf. This strain increased with increasing temperature and decreasing strain rate. It is demonstrated that the critical strain to fracture ϵf can be expressed by a single function, namely, the Zener–Hollomon parameter Z, which combines the effects of both temperature and strain rate. ϵf and InZ obeyed a linear relationship. Based on the experimental results, a processing window, which consisted of a temperature range 950–1050°C and strain rate range 0·01–0·1 s−1, was established for optimising the process parameters and achieving microstructural control during hot working. The processing window has been validated through scaled up cylinder upsetting experiments using 140 mm diameter alloy specimens.