摘要
基于等温恒应变速率热压缩实验,探究了新型Ti-4Al-5Mo-6Cr-5V-1Nb合金在变形温度700~900℃、应变速率0.001~1.000 s;条件下的热变形行为。通过真应力-真应变曲线分析了变形参数对合金力学性能的影响规律,选用修正的Arrhenuis双曲正弦函数模型推导了耦合应变的本构方程,基于动态材料模型及Prassd流变失稳准则构建了热加工图。结果表明:Ti-45651合金为温度、应变速率敏感型材料,其峰值应力及稳态流变应力随变形温度的增加逐渐降低,随应变速率的增大呈增加趋势。流变曲线在两相区呈动态再结晶型,在β单相区为动态回复型。本构方程计算可得两相区平均热变形激活能为280.023 kJ·mol^(-1),远大于纯钛的自激活能,说明两相区的热变形软化机制以动态再结晶为主。β单相区平均热变形激活能为202.564 kJ·mol^(-1),稍大于纯钛的自激活能,说明其软化机制以动态回复为主。该合金的公共失稳区为700~800℃,0.010~1.000 s;和850~870℃,0.320~1.000 s^(-1),该区域的功率耗散效率(η)低至0.15,且有绝热剪切带等失稳组织出现;其公共峰值变形区为700~770℃,0.001~0.010 s;和790~810℃,0.001~0.0032 s^(-1),该区域η值高达0.57,且因动态再结晶的充分进行,其中心主变形区无剧烈变形晶粒。
With the development of the damage tolerance design concept for long-life structure parts,high strength and high toughness had gradually become the eternal pursuit of titanium alloy materials for main load-bearing structural parts of aircraft.Because of enoughβ-stabilizing elements could reduce its martensite transformation temperature range to below room temperature,metastableβ-titanium alloy was an ideal choice for high-strength and high-toughness titanium alloys,whose mechanical properties could be effectively improved by reasonable heat treatment system.As a new type of high-strength and high-toughness metastableβtitanium alloy,Ti-45651 alloy had a strength as high as 1350 MPa,and it had many advantages such as few kinds of elements,good performance reproducibility and excellent comprehensive mechanical properties etc.It was expected to replace traditional high-strength and hightoughness titanium alloy materials using as the large load-bearing structural parts such as aircraft landing gear.However,metastableβtitanium alloys were sensitive to deformation temperature and strain rate during high-temperature forging,and it was easy to produce microstructure defects such as cracking,un-uniform microstructure,and low forming accuracy due to inappropriate thermal deformation process parameters.At present,there hadn’t seen any research on the high-temperature deformation behavior of Ti-45651 alloy.Therefore,it was necessary to investigate the hot deformation behavior and construct the hot working map of Ti-45651 alloy.The thermal deformation behavior of Ti-4 Al-5 Mo-6 Cr-5 V-1 Nb alloy was investigated based on the isothermal constant strain rate thermal compression test under the condition of deformation temperature from 700 to 900℃and strain rates from 0.001 to 1.000 s;using Gleeble-3800 thermal simulation test machine.The influence of deformation parameters on mechanical properties of this alloy was analyzed by the true stress-true strain curves.The constitutive equation coupled strain was derived through the regression of true stress-strain data using the modified Arrhenuis hyperbolic function.The thermal processing map was constructed based on the dynamic material model and the Prassd instability criterion for the true strain of 10%~50%.The deformation mechanism was described by the microstructure characterization in different region of thermal processing map,while the reasonable thermal processing parameters range of Ti-45651 was determined,which provided reference for the forging forming of its components.The results showed that the Ti-45651 alloy was a material sensitive to both temperature and strain rate,and its temperature sensitivity increased with the increase of strain rate,while the strain rate sensitivity showed a decreasing trend with the increase of temperature.Otherwise,its peak stress and flow stress decreased with the increase of deformation temperature,while rose with the increase of strain rate.Its flow curve was dynamic recrystallization type inα+βphase region whose flow stress increased rapidly to the peak with the increase of strain,and then showed a significant downward trend due to the existence of dynamic recrystallization and dynamic recovery softening mechanism.And the flow curve in theβsingle-phase region was dynamic recovery type,which presented a gentle decrease from peak to steady state,indicating that the rheological softening effect dominated by dynamic recovery mechanism achieved dynamic equilibrium quickly with the work hardening caused by plastic deformation.The average thermal deformation activation energy of theα+βphase region calculated by the constitutive equation was 280.023 kJ·mol;,which was greater than that of the pure titanium,indicating that the softening mechanism was related to dynamic recrystallization.However,it was 202.564 kJ·mol^(-1)inβphase region,which was slightly larger than that of pure titanium,revealing that the softening mechanism was dominated by dynamic recovery mostly.The result was consistent with the true stress-strain curves.This alloy went through the unstable deformation under the condition of 700~800℃,0.001~1.000 s;and 850~870℃,0.32~1.00 s^(-1).The power dissipation efficiency(η)of these regions was as low as 0.15,and there appeared some unstable structures such as adiabatic shear bands.In fact,the deformation of adiabatic shear bands was related to the heat generated during the plastic deformation process.The release of the heat was suppressed by unstable deformation conditions which resulted in a reduction in the local flow stress of Ti-45651 alloy and the adiabatic shear phenomenon occurred.In addition,it reached the best deformation state in the regions of 700~770℃,0.001~0.010 s;and 790~810℃,0.001~0.0032 s^(-1).Its power dissipation efficiencyηincreased to 0.57,and elongated deformed crystals generated by severe plastic deformation weren’t found in the central main deformation zone,which transformed into equiaxed crystal because of absolute dynamic recrystallization and grain growth.Moreover,its grain boundary still presented a serrated shape that was the typical features of dynamic recrystallization.In summary,a comprehensive analysis of thermal processing map and microstructure of the Ti-45651 alloy showed that its typical characteristic of energy dissipation efficiencyηand microstructure conformed to a discipline that the largerηvalue corresponded the more obvious dynamic recrystallization and recovery of metal material during plastic deformation.
作者
周琳
刘运玺
陈玮
付明杰
Zhou Lin;Liu Yunxi;Chen Wei;Fu Mingjie(AVIC Manufacture Technology Institute,Beijing 100024,China;Key Laboratory of Power Beam Processing,Beijing 100024,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2022年第1期27-35,共9页
Chinese Journal of Rare Metals
基金
装备预研领域基金项目(61409230409)资助。
作者简介
周琳(1993-),女,陕西咸阳人,硕士,工程师,研究方向:超高强钛合金,E-mail:linzhounpu@foxmail.com;通信作者:陈玮,研究员,电话:13810258541,E-mail:werner_nju@163.com。
