Study on the hot-deformation behavior and hot processing map of Ti551 alloy
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摘要: 针对Ti551钛合金热变形行为，开展了800～950 ℃、应变速率0.01～1 s-1条件下的热压缩试验，基于真实应力–应变曲线分析了温度与应变速率对流变应力特征的影响。结果表明，Ti551钛合金流变应力对温度、应变速率变化比较敏感。基于Arrhenius型本构关系建立了考虑应变补偿的Ti551热变形本构模型，并对模型预测能力进行了评价。进一步采用Prasad判据构建热加工图，得到功率耗散效率与失稳区随温度—应变速率变化的分布特征，提出Ti551钛合金的优选热加工参数窗口（高温、低—中应变速率区域）并识别潜在失稳加工区（低温、高应变速率区域），进而研究揭示了不同变形条件下初生α相形貌与α/β两相比例变化趋势。上述结果可为Ti551钛合金热加工工艺参数设计与组织性能调控提供依据。Abstract: To investigate the hot deformation behavior of Ti551 titanium alloy, isothermal compression tests were conducted at temperatures ranging from 800 ℃ to 950 ℃ and strain rates between 0.01–1 s−1. Based on the true stress–true strain data, the hot deformation characteristics of Ti551 titanium alloy were systematically analyzed. The results indicate that the flow stress of the Ti551 titanium alloy is highly sensitive to variations in temperature and strain rate. An Arrhenius-type constitutive model incorporating strain compensation was established to describe the hot deformation behavior of the alloy, and the predictive capability of the model was evaluated. Furthermore, processing maps were constructed using the Prasad instability criterion, revealing the distribution characteristics of power dissipation efficiency and instability domains as functions of temperature and strain rate. The optimal hot processing window for the Ti551 titanium alloy was identified as the high-temperature and low-to-medium strain rate region, while potential flow instability regions were located in the low-temperature and high strain rate domain. In addition, the evolution of primary α-phase morphology and the variation in the α/β phase fraction under different deformation conditions were investigated. These results provide a theoretical basis for the design of hot working process parameters and the microstructure–property optimization of Ti551 titanium alloy.
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图 3 不同试验温度下Ti551钛合金的应力-应变行为
Figure 3. Stress-strain behaviors of Ti551 titanium alloy under different thermal deformation temperatures
(a)800 ℃；(b)850 ℃；(c)900 ℃；(d)950 ℃
图 4 Ti551钛合金流变应力随变形温度与应变速率的变化特征
(a)变形温度；(b)应变速率
Figure 4. Flow stress dependence of Ti551 alloy on deformation temperature and strain rate
图 5 Ti551 钛合金的Arrhenius本构模型的拟合特征
Figure 5. Arrhenius constitutive model fitting outputs for Ti551 titanium alloy
(a)$ \ln \dot{\varepsilon }-\ln \sigma $；(b)$ \mathrm{ln}\dot{\varepsilon}-\sigma $；(c)$ \mathrm{ln}\dot{\varepsilon}-\mathrm{ln}[\mathrm{sinh}(\alpha\sigma)] $；(d)$ 1/T-\mathrm{ln}[\mathrm{sinh}(\alpha\sigma)] $
图 6 不同应变下对应的材料常数
Figure 6. Material constants corresponding to different strains
(a)α；(b)n；(c)Q；(d)lnA
图 7 试验真实值与本构预测值对比
Figure 7. Comparison of experimental actual values and constitutive model predicted values
(a)800 ℃；(b)850 ℃；(c)900 ℃；(d)950 ℃
图 8 Ti551钛合金功率耗散系数的分布特征
Figure 8. Distribution map of power dissipation coefficients for Ti551 titanium alloy
图 9 Ti551钛合金失稳系数的分布特征
Figure 9. Distribution map of instability efficiency for Ti551 titanium alloy
图 10 Ti551钛合金热加工窗口特征
Figure 10. Thermomechanical processing map of Ti551 titanium alloy
图 11 温度为800 ℃、应变速率0.1 s−1下Ti551钛合金的微观组织（失稳）
Figure 11. Microstructure of Ti551 titanium alloy at 800 °C and strain rates of 0.1–1 s−1 (instability region)
图 12 温度为850 ℃、应变速率0.1 s−1下Ti551钛合金的微观组织（未失稳）
Figure 12. Microstructural characteristics of Ti551 titanium alloy at 850 ℃ with strain rates of 0.1–1 s−1 (stable deformation zone)
表 1 五次多项式拟合α、Q、n及lnA的对应参数
Table 1. Corresponding parameters of the 5th degree polynomial fit for α, Q, n, and lnA
Coefficient α Coefficient n Coefficient Q Coefficient lnA a0 0.01231 b0 3.15245 c0 661.94334 d0 63.32248 a1 0.00744 b1 − 3.94584 c1 − 1011.22463 d1 − 63.77881 a2 − 0.02762 b2 10.72476 c2 3763.02358 d2 83.73715 a3 0.1163 b3 − 17.87755 c3 − 9192.60619 d3 13.10599 a4 − 0.17656 b4 18.00658 c4 11173.51223 d4 − 152.96576 a5 0.08551 b5 − 7.60918 c5 − 5073.22552 d5 107.70056 
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表 2 不同变形工况下60%形变量的功率耗散系数
Table 2. Power dissipation coefficients of 60% deformation amount in distinct deformation conditions
$ \dot{\varepsilon } $/s−1 η 800 ℃ 850 ℃ 900 ℃ 950 ℃ 0.01 0.41719599 0.686709565 0.548743679 0.419549678 0.1 0.248480364 0.480180821 0.402200109 0.348700255 1 0.039505638 0.196572932 0.222737388 0.271200544
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表 3 不同变形工况下60%形变量的失稳系数
Table 3. Instability coefficients of 60% deformation amount in distinct deformation conditions
$ \dot{\varepsilon } $/s−1 η 800 ℃ 850 ℃ 900 ℃ 950 ℃ 0.01 0.038532271 0.367524096 0.243188959 0.185130984 0.1 − 0.369974932 0.04432133 0.055932998 0.116420729 1 − 0.778482134 − 0.278881437 − 0.131322964 0.047710474
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