基于DMNR模型建立EB炉熔炼TC4钛合金的双重多元非线性回归本构方程

通过热模拟压缩实验研究EB炉熔炼TC4钛合金在应变速率为0.01 s_^-1-10 s_^-1,变形温度为800 ℃-1100℃条件下的热变形行为,计算合金在不同变形条件下的应变速率敏感性指数m,并基于DMNR模型建立EB炉熔炼TC4钛合金的双重多元非线性回归本构方程。结果表明：在变形开始阶段,加工硬化占主导作用,流动应力随着应变的增加而增加,当达到峰值应力时,软化作用比较明显,位错开始发生滑移和攀移,流动应力随着应变的增加而降低。在低温小应变速率下m值较大,在高温大应变速率下m值较小,m值越大,对应的显微组织越均匀。采用所建立的非线性回归本构方程能够较好地预测EB炉熔炼TC4钛合金的流动应力,预测值与实测值之间的平均绝对相对误差为5.83% ,相关系数为0.98。     

非真空熔铸Cu-Cr-Zr合金的热变形行为及动态再结晶临界条件

采用Gleeble-1500热模拟实验机对Cu-0.90Cr-0.18Zr合金在变形温度为500~800℃、应变速率为0.01~1 s-1变形条件下进行热压缩变形实验,研究该合金的流变应力、本构方程及动态再结晶临界条件。结果表明:Cu-Cr-Zr合金的流变应力随变形温度的升高而降低,随应变速率的增加而增加,计算出该合金的热变形激活能为584.87 kJ/mol并构建本构方程;利用合金的lnθ-ε曲线出现拐点及-(lnθ)ε-ε曲线出现最小值来研究动态再结晶临界应变。     

SP700钛合金热变形行为及物理本构关系研究

采用Gleeble-3800型热模拟试验机在变形温度为700～850℃、应变速率为0.001～1 s^-1条件下对SP700钛合金进行等温恒应变速率压缩试验,分析SP700钛合金的热变形行为。首次探讨了该合金考虑变形温度对杨氏模量和自扩散系数影响的传统物理本构关系以及考虑晶界扩散和晶格扩散耦合的修正物理本构关系。结果表明,SP700钛合金的流动应力曲线为典型的动态再结晶型曲线,其流动应力随应变速率的降低和变形温度的升高而减小;传统物理本构关系和修正的物理本构关系相关系数R分别为0.986和0.965,平均相对误差AARE分别为14.4%和13.1%,说明建立的两个物理本构关系都能较好地表征该合金的流动应力行为。另外,确定了该合金在700～800℃热变形时主要扩散机制是晶界扩散,在850℃热变形时主要是晶格扩散。     

Incoloy825高温合金热变形行为及动态再结晶模型

采用Gleeble-3800热模拟试验机，对Incoloy825高温合金在应变为0.92、温度为950～1150℃和应变速率为0.001～1 s^-1条件下进行单道次压缩试验。依据真应力-真应变曲线建立了动态再结晶临界方程和动态再结晶动力学模型。结果表明，Incoloy825高温合金热变形对温度和应变速率较为敏感，真应力-真应变曲线整体满足硬化-软化-稳态的流变过程，动态再结晶是Incoloy 825高温合金材料的主要软化机制。在热变形过程中，动态再结晶临界应变随变形温度的升高和应变速率的降低呈减小趋势。对动态再结晶动力学模型进行分析发现，动态再结晶百分含量随变形温度的升高和应变速率的降低而增大，表明高变形温度和低应变速率对动态再结晶具有促进作用。     

Fe-13Cr-4Al合金的高温流变行为

在Gleeble-1500热模拟实验机上对Fe-13Cr-4Al合金进行了等温压缩实验,研究了该材料在变形温度800～1000℃、应变速率0.01～10 s~(-1)条件下的高温流变行为;构建了包含Arrhenius项同时考虑应变、应变速率及温度影响的高温热变形本构方程。结果表明,Fe-13Cr-4Al合金的高温流变应力状态主要受温度和应变速率的影响,并且在较低变形温度和低应变速率(800～900℃、0.01～0.1 s~(-1))的变形条件下呈现出动态再结晶;而在较高温度(950～1000℃)的变形条件下呈现出动态回复。材料常数Q、α、n和ln A均是应变ε的函数,采用五次多项式可拟合两者之间的关系。同时应用包含应变补偿的本构方程可预测Fe-13Cr-4Al合金在实验温度和应变速率条件下的流变应力。     

基于物理参数和响应面法的S280超高强度不锈钢本构模型

采用Thermecmaster-Z型热模拟试验机在变形温度为800～1000℃、应变速率为0.001～10 s^-1条件下对S280超高强度不锈钢进行了等温恒应变速率压缩实验，分析了S280超高强度不锈钢的热变形行为，计算了热变形激活能。考虑变形温度对自扩散系数和杨氏模量的影响，建立了S280超高强度不锈钢基于应变补偿的物理本构模型。以变形温度、应变速率和应变为输入变量，流动应力为响应目标，建立了S280超高强度不锈钢的响应面本构模型。结果表明，S280超高强度不锈钢为正应变速率负温度敏感型材料，其流动应力随应变速率的增加和变形温度的降低而增大。热变形激活能对变形条件敏感，其随变形温度、应变速率和应变的增加而减小。基于应变补偿的物理本构模型具有一定的物理意义和良好的预测精度，其相关系数R和平均相对误差e_AARE分别为0.971和7.8%。响应面本构模型的响应曲面和等高线图能反映变形条件之间的相互作用对流动应力的影响。建立的两个本构模型都能够用于表征S280超高强度不锈钢在热变形过程中的流动应力行为。     

Cu-Ni-Si-P合金的动态再结晶

在Gleeble-1500D热模拟实验机上,在应变速率为0.01～5 /s、变形温度为600～800 ℃条件下,采用高温等温压缩实验对Cu-2.0Ni-0.5Si-0.03P合金的流变应力行为进行研究。结果表明：热模拟实验中,应变速率和变形温度的变化强烈地影响合金流变应力的大小,流变应力随变形温度升高而降低,随应变速率提高而增大;在应变温度为750和800 ℃时,合金热压缩变形流变应力出现明显的峰值应力,表现为连续动态再结晶特征。从流变应力、应变速率和温度的相关性,得出该合金热压缩变形时的热变形激活能和本构方程。     

镁合金Mg-Zn-Y-Zr的高温变形及本构方程

采用Gleeble-1500热模拟试验机对铸态镁合金Mg-Zn-Y-Zr在变形温度为250～450℃,应变速率为0.001～1s-1条件下的高温压缩变形行为进行研究,利用双曲正弦关系描述了该合金的本构方程。结果表明,Mg-Zn-Y-Zr合金的高温流动应力-应变曲线主要以动态回复和动态再结晶软化机制为特征,峰值应力随变形温度的降低或应变速率的升高而增加;在真实应力-应变曲线基础上,建立的Mg-Zn-Y-Zr合金高温变形的本构模型较好地表征了其高温流变特性。     

耐热镍铬铁合金高温流变应力的模拟研究

以耐热镍铬铁合金800H为研究对象,通过热压缩实验获得了流变应力和变形温度、应变速率的变化关系。结果表明,在高温压缩变形过程中,镍铬铁合金800H在变形温度不变时,随着应变速率的增加,流变应力逐渐增大;应变速率不变时,随着变形温度的升高,流变应力逐渐降低。通过镍铬铁合金本构关系模型确定了应变量和材料常数的关系,运用六次多项式拟合得到了具有代表性的函数关系式。     

Incoloy901合金的热加工图与热变形行为

利用Gleeble-3800热模拟机研究Incoloy901高温合金在变形温度950～1150℃,应变速率0.005～1 s^-1,真应变0.6下的热变形行为。结果表明:变形温度大于1000℃,应变速率大于0.01 s^-1时,Incoloy901合金真应力-应变曲线呈现动态再结晶特征。根据应力-应变曲线构建Incoloy901合金的本构方程与热加工图,得出形变激活能Q=439.401 k J/mol,最佳热加工工艺为:变形温度1050～1150℃,应变速率0.005～0.1 s^-1,在此工艺范围内合金的高温变形功率耗散系数η较高,可达37%,能获得较好的动态再结晶组织。     

轧制态ME20M镁合金热拉伸变形行为及加工图

在变形温度为623～773 K,应变速率为0.001～0.1 s~(-1)的条件下,通过INSPEKT Table 100 kN电子万能高温试验机对轧制态ME20M镁合金进行了热拉伸实验,分析了变形温度和应变速率对材料流动应力的影响,建立了热变形条件下的本构模型及加工图。结果表明:随着变形温度的降低和应变速率的升高,轧制态ME20M镁合金的流动应力增加;建立的本构模型预测峰值应力与实验结果吻合较好,平均相对误差为5.19%;考虑应变对本构模型中材料常数影响后的预测应力值与实验值的相关度较高,平均相对误差为6.00%;最佳热加工范围为673～773 K、应变速率0.001～0.01 s~(-1)。     

30CrNi3MoV钢的热变形行为及热加工图

采用Gleeble-3500热模拟试验机对30CrNi3MoV钢进行单向热压缩试验,研究了其在变形温度950~1150 ℃、应变速率0.01~10 s^-1的热变形行为,构建了应变补偿型流变应力本构方程,并绘制出该钢的热加工图。结果表明,30CrNi3MoV钢真应力-真应变曲线有3种不同特征:高温小应变速率时,表现为典型的动态再结晶过程;低温小应变速率时,曲线为动态回复特征;应变速率较大时,应力随应变的增大而增大,无明显的峰值应力。采用5次多项式拟合构建的应变耦合流变应力本构方程具有高的精确度,采用该方程获得的预测值与试验值的平均相对误差为3.2%,相关性系数R值为0.993。从热加工图中得到试验钢最佳的热加工工艺参数范围是:变形温度为1020~1150 ℃、应变速率为0.03~0.35 s^-1。     

Modeling the High Temperature Flow Behavior and Dynamic Recrystallization Kinetics of a Medium Carbon Microalloyed Steel

In this study, the hot deformation behavior of a medium carbon microalloyed steel was investigated. The hot compression test was conducted in the temperature range of 1000-1200 °C under strain rates of 0.01, 0.1 and 1 s^?1. It has been observed that the flow stress increases with a decrease in temperature and/or an increase in strain rate. Furthermore, dynamic recrystallization (DRX) is found to be the main flow softening mechanism in almost all deformation conditions. Material parameters of the constitutive equations are found to be strain dependent. Their relationship with strain is identified by a fourth order polynomial fit. Then, a constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect. The accuracy of the proposed model for the flow stress is evaluated by applying the absolute average error method. The result of 6.08% indicates a good agreement between predicted and experimental data. Moreover, the critical characteristics of DRX are extracted from the stress-strain curves at different deformation conditions. It is found that by increasing the strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate, the recrystallization curve shifts to the higher strains. The kinetics of DRX increases with increasing deformation temperature or strain rate.     

基于BP神经网络的GH5188高温合金本构模型

采用Gleeble-3500热模拟试验机对GH5188高温合金试样进行热压缩试验,研究其在应变速率为0.001~0.1s^-1和变形温度在1000~1150℃时的热变形行为;建立了基于BP神经网络的本构模型,并验证了所建本构模型的可靠性,最后基于误差计算分析了BP神经网络本构模型的精度。结果表明,温度和应变速率对GH5188合金流变应力的影响明显,随着压缩温度升高和应变速率降低,GH5188合金流变应力明显减小。经定量误差计算分析,BP神经网络本构模型应力预测偏差值在10%以内的数据点占97.92%,BP神经网络模型能准确地预测GH5188高温合金的高温流变应力。     

The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s⁻¹. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s⁻¹. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.     

Hot Deformation Behavior and Processing Maps of a High Al-low Si Transformation-Induced Plasticity Steel: Microstructural Evolution and Flow Stress Behavior

Hot deformation behavior of a high Al-low Si transformation-induced plasticity(TRIP) steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s~(-1). The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves(dynamic recrystallization and dynamic recovery) were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s~(-1) and deformation temperature of 1200℃ as compared to other deformation conditions.     

Zr-1.0Ti-0.35Nb合金热变形行为研究

乏燃料后处理强酸、强氧化性、强放射性的工作环境,对后处理溶解器选材、加工工艺提出了严苛要求。本论文研究了自主设计Zr-1.0Ti-0.35Nb合金在670 ~ 750 ℃温度范围、三种不同应变速率0.01、0.1和1 s_-1^条件下的热压缩变形行为,分析了热压缩过程中该合金的微观组织特征,并基于峰值应力构建了其热变形本构模型。结果表明,应变速率和变形温度对Zr-1.0Ti-0.35Nb合金热变形过程具有显著影响,流变应力随应变速率增加而增大,随变形温度的增加而减小,达到峰值应力后流变曲线呈现明显动态再结晶特征;提高变形温度有助于发生动态再结晶和晶粒长大;基于Arrhenius本构方程计算得到Zr-1.0Ti-0.35Nb合金的热变形激活能为225.8 kJ/mol,硬化指数为5.62,说明合金元素Ti使锆合金的热变形激活能升高;实验值与预测值之间的相关系数为0.97,平均相对误差为6.15%,证实此本构方程预测Zr-1.0Ti-0.35Nb合金流变应力的准确性,能够为新型锆合金热加工工艺优化提供理论指导。     

The Strain-Compensated Constitutive Equation for High Temperature Flow Behavior of an Al-Zn-Mg-Cu Alloy

In order to study flow stress behavior for hot working of a typical Al-Zn-Mg-Cu alloy, experimental stress-strain data obtained from isothermal hot compression tests at strain rates of 0.004, 0.04, and 0.4 s^?1 and deformation temperatures of 400, 450, 500, and 520 °C were used to develop the constitutive equation. The peak stress decreased with increasing deformation temperature and decreasing strain rate. The effects of temperature and strain rate on deformation behavior were represented by Zener-Hollomon parameter in an exponent-type equation. Employing an Arrhenius-type constitutive equation, the influence of strain has been incorporated by considering the related material constants as functions of strain. The accuracy of the developed constitutive equations has been evaluated using standard statistical parameters such as correlation coefficient and average absolute relative error. The results indicate that the proposed strain-dependent constitutive equation gives an accurate and precise estimate of the flow stress in the relevant temperature range.     

Hot Deformation Behavior and Dynamic Recrystallization Characteristics in a Low-Alloy High-Strength Ni–Cr–Mo–V Steel

This study presented a quantitative investigation of deformation behavior and dynamic recrystallization of low-alloy highstrength Ni–Cr–Mo–V steels during hot deformation.A series of isothermal compression experiments were performed at temperatures ranging from 800 to 1200°C and strain rates from 0.01 to 10 s~(-1)with a height reduction of 60%.A complete Arrhenius constitutive model and processing maps were developed.The results showed that the constitutive model had the ability to predict the flow stress with an average absolute relative error of\5.7%.The processing maps constructed at strains of 0.2,0.4,and 0.8 showed that flow instability was prone to occur at higher strain.Dynamic recrystallization tended to take place at higher temperatures(900–1200°C)and lower strain rates(0.01–1 s~(-1)).The critical strain for the onset of dynamic recrystallization was determined,and a kinetics model was developed.The predicted results for recrystallization volume fraction and flow stress were compared with the experimental data,which indicated that the model was accurate and reliable.     

纯铂的热塑性变形行为及微观结构演变规律研究

用热模拟试验机研究了纯铂在真应变量为0.9、变形温度为550℃～950℃和应变速率为0.01～1 s~(-1)的热塑性变形行为,并对热压缩后的样品进行了金相观察和显微硬度测量。结果表明,纯铂的流变应力随变形温度的升高和应变速率的降低而降低;其热压缩变形过程中软化行为由变形温度和变形速率共同作用决定,一般以动态回复为主,而在低应变速率和高形变温度下以动态再结晶为主,动态再结晶发生造成的软化使纯铂样品的硬度迅速下降。利用Zener-Hollomon参数方程获得了热塑性变形流变应力本构方程,得到纯铂的热变形激活能为208.51 kJ/mol,流变应力拟合公式计算值与实验值的平均误差为5.9%。