铸态ER8车轮钢的热变形行为及本构模型研究

采用Gleeble-1500D热模拟试验机,在变形温度为900～1250℃、应变速率为0.001～1 s-1的条件下对铸态ER8车轮钢进行热压缩试验,得到真应力-真应变曲线.结果发现:其真应力-真应变曲线符合动态再结晶型软化机制,变形初始阶段,材料发生硬化,真应力快速增加,随着变形的继续,材料发生动态回复,加工硬化速率...     

Al-Mg-Si 合金的高温流变过程动态再结晶研究

采用热力模拟试验机对Al-0.83Mg-0.59Si铝合金进行热压缩实验,研究了变形温度300～500 ℃、变形速率0.001～10 s-1下材料的动态再结晶行为。实验得到Al 0.83Mg 0.59Si合金在300～500 ℃变形时,软化机制以动态再结晶为主;流变应力会随着变形温度的降低和变形速率的升高而升高,较低变形速率下,动态再结晶行为更充分,应力软化现象更明显。统计实验所得流变应力曲线数据,建立了热变形本构方程,确定了合金热变形激活能Q为480.243 kJ/mol 。基于加工硬化率曲线,建立了其动态再结晶临界应变模型。结果表明,Al-0.83Mg-0.59Si铝合金的流变应力随温度的升高和变形速率的降低而降低,动态再结晶是其主要的软化机制。临界应力与峰值应力存在线性关系：σc=0.85σp-5.061 58。引入Zener Hollomon参数来描述变形条件对临界条件的影响,得到临界应变与Z参数的关系为：εc=0.000 134Z0.051 64。     

7075-T6铝合金的高温成形性能和微观组织

采用等温拉伸试验,研究了温度对7075-T6铝合金板材力学性能的影响规律。通过金相观察和断口形貌分析,讨论了7075-T6铝合金板材高温拉伸变形的微观组织变化和断裂失效机制。结果表明,随温度升高,材料强度和硬度逐渐降低,断后伸长率总体上呈上升趋势,但在250 ℃时出现低值。温度低于200 ℃,应力随应变先快速增加后缓慢增加,应变硬化占主导作用,主要的软化机制为动态回复;200 ℃时,应力峰值后保持平稳,应变硬化和回复软化相互平衡;高于200 ℃,应力随应变快速增加到峰值后逐渐减小,动态再结晶软化占主导作用。250 ℃时,由于动态再结晶软化占主导作用,应力下降,塑性显著下降;300 ℃时,再结晶过程完成,且晶粒沿拉伸方向拉长,韧窝深度加深、平均尺寸增大,材料塑性提升。     

7150铝合金高温热压缩变形流变应力行为

在Gleeble-1500热模拟机上对7150铝合金进行高温热压缩实验,研究该合金在变形温度为300~450 ℃和应变速率为0.01～10 s~(-1) 条件下的流变应力行为.结果表明:流变应力在变形初期随着应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随着温度的升高而减小,随着应变速率的增大而增大;可用包含Zener-Hollomon参数的Arrhenius双曲正弦关系来描述合金的热流变行为,其变形激活能为226.698 8 kJ/mol;随着温度的升高和应变速率的降低,合金中拉长的晶粒发生粗化,亚晶尺寸增大,再结晶晶粒在晶界交叉处出现并且晶粒数量逐渐增加;合金热压缩变形的主要软化机制由动态回复逐步转变为动态再结晶.     

120°模具室温ECAP制备工业纯钛的热压缩变形行为

在Gleeble-1500热模拟机上对室温120°模具等径弯曲通道变形(ECAP)制备的平均晶粒尺寸为200nm的工业纯钛(CP-Ti)进行等温变速压缩实验,研究超细晶(UFG)工业纯钛在变形温度为298～673K和应变速率为10-3～100s-1条件下的流变行为。利用透射电子显微镜分析超细晶工业纯钛在不同变形条件下的组织演化规律。结果表明:流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳;峰值应力随温度的升高而减小,随应变速率的增大而增大;随变形温度的升高和应变速率的降低,应变速率敏感性指数m增加,晶粒粗化,亚晶尺寸增大,再结晶晶粒数量逐渐增加;超细晶工业纯钛热压缩变形的主要软化机制随变形温度的升高和应变速率的降低由动态回复逐步转变为动态再结晶。     

工业纯钛TA1的双道次热压缩变形及软化行为

在Gleeble-3500热模拟试验机上对工业纯钛TA1进行单、双道次等温热压缩试验,变形温度为650~850 ℃,道次间隙时间为1~60 s,变形速率为10 s^-1,研究了工业纯钛TA1单、双道次热压缩过程中静态软化和动态软化行为。利用光学显微镜对变形后的微观组织进行观察,研究了工业纯钛TA1在不同变形条件下的微观组织演变。结果表明,工业纯钛TA1在单、双道次热压缩变形过程中表现出明显的硬化和软化行为,峰值应力前表现为加工硬化,峰值应力后表现为加工软化,最终达到动态软化和加工硬化的动态平衡。在道次间隙时间内发生静态软化,静态软化程度随着道次间隙时间的增加和温度的升高而增大。随着道次间隙时间的延长和温度的升高,道次间再结晶更加充分,第二道次变形后晶粒尺寸增加更明显,当发生完全再结晶时,软化程度达到最大。在热压缩变形期间,发生动态软化,650 ℃和750 ℃时以动态再结晶为主,850 ℃时以动态回复为主。     

超高强DP980钢的动态再结晶模型

采用Gleeble-3500热模拟试验机对超高强DP980钢进行热压缩试验,研究其在变形温度为900~1 200℃、应变速率为0.05~30s~(-1)条件下的动态再结晶行为,分析了变形温度和应变速率对真应力-真应变曲线的影响。结果表明:超高强DP980钢在变形过程中,存在动态再结晶和动态回复两种软化机制,且随着温度的升高和应变速率的降低,临界应变越小,动态再结晶越容易发生;同时,得到了发生动态再结晶时的形变激活能,建立了峰值应变模型、动态再结晶临界应力模型和动态再结晶动力学模型。     

Deformation behavior of dispersion-strengthened copper at high temperature

1. Introduction Dispersion-strengthened copper (DSC) is a promising material developed recently. Considerable attention has been focused on it because of its excel- lent high-temperature properties. The metallic mate- rial, which is strengthened by solution strengthening, deformation strengthening, and ageing strengthening, is always low at high temperature, and the strength- ening factor contradicts with the electrical conduc- tivity of the material to a certain extent [1-2]. But DSC has g…     

Constitutive modeling and dynamic softening mechanism during hot deformation of an ultra-pure 17%Cr ferritic stainless steel stabilized with Nb

The hot deformation behavior of an ultra-pure 17%Cr ferritic stainless steel was studied in the temperature range of 750–1000 °C and strain rates of 0.5 to 10 s^?1 using isothermal hot compression tests in a thermomechanical simulator. The microstructural evolution was investigated using electron backscattered diffraction and transmission electron microscopy. A modified constitutive equation considering the effect of strain on material constant was developed, which predicted the flow stress for the deformation conditions studied, except at 950 °C in 1 s^?1 and 900 °C in 10 s^?1. Decreasing deformation temperature and increasing strain was beneficial in refining the microstructure. Decreasing deformation temperature, the in-grain shear bands appeared in the microstructure. It is suggested that the dynamic softening mechanism is closely related to deformation temperature. At low deformation temperature, dynamic recovery was major softening mechanism and no dynamic recrystallization occurred. At high deformation temperature, dynamic softening was explained in terms of efficient dynamic recovery and limited continuous dynamic recrystallization. A drop in the flow stress was not found due to very small fraction of new grains nucleated during dynamic recrystallization.     

高强合金钢50SiMnVB动态再结晶模型研究

通过热模拟压缩试验研究了50SiMnVB合金钢在应变速率为0.01-10s-1、温度为800-1000 ℃条件下的高温热变形行为.利用金相显微镜观察了合金压缩变形后的显微组织,结果表明:50SiMnVB合金钢在高温热变形过程中发生了典型的动态回复和动态再结晶行为,其中,动态再结晶以连续再结晶的形式进行,且应变速率越小、...     

6016铝合金热变形实验模拟热轧显微组织演变(英文)

采用Gleeble-1500热模拟机研究6016铝合金单道次高温压缩变形时的显微组织演变。采用光学显微镜和透射电子显微镜分析合金在不同变形条件下的组织形貌特征。结果表明:在高温压缩变形时,该合金的变形激活能为270.257kJ/mol,硬化指数为8.5254;流变应力双曲正弦的自然对数值与温度补偿Zener-Hollomon参数自然对数值成线性关系;合金低温、低应变速率时的主要变形组织为动态回复组织,而高温变形时产生局部动态再结晶组织;该铝合金高温变形时的主要软化机制为动态回复,只有在高温、高应变速率下发生部分的动态再结晶;合金平均亚晶粒尺寸随温度补偿应变速率Zener-Hollomon参数的升高而减小。     

Modeling the initiation of dynamic recrystallization using a dynamic recovery model

Dynamic recrystallization flow curve was studied in AISI 410 martensitic stainless steel by performing hot compression tests in a temperature range of 900-1150 °C and at strain rates of 0.001-1 s⁻¹. The Estrin and Mecking's equation for dynamic recovery was used to model the work hardening region of the flow curves. The critical strain and stress for the initiation of dynamic recrystallization were determined using the method developed by Poliak and Jonas. The critical dislocation density for starting dynamic recrystallization was estimated using the Estrin and Mecking's dynamic recovery model. A modified Arrhenius-type equation was used to relate the critical dislocation density to strain rate and temperature. The proposed model was also verified by the model proposed by Roberts and Ahlblom and developed to describe the variation of dislocation density and fractional softening due to dynamic recrystallization up to the peak of flow curve.     

Modeling of Work Hardening During Hot Rolling of Vanadium and Niobium Microalloyed Steels in the Low Temperature Austenite Region

This work extends the application of the well-established Estrin and Mecking (EM) work-hardening model in unstable low temperature austenite region. The interaction between work hardening, recovery and softening attributed to recrystallization and transformation to ferrite under dynamic conditions is considered. Experimental parameters were varied to study the effects of strain, strain rate and temperature during hot rolling in the low temperature austenite region. Hot compression tests were performed two microalloyed steels—one containing V and the other Nb—at strain rates between 0.1 and 10 s^?1 over a temperature range of 750-1000 °C. A model is presented that describes the influence of dynamic recovery on flow behavior in the unstable austenite region. The modified work-hardening model incorporates an additional fitting parameter to the EM model and is dependent on the recovery and softening rates. The new model improved prediction in the unstable austenite region, while the original EM model gave better correlation at relatively higher temperatures when dynamic recrystallization is dominant or at relatively lower temperatures when only dynamic recrystallization to ferrite was the softening mechanism.     

Kinetics and critical conditions for initiation of dynamic recrystallization during hot compression deformation of AISI 321 austenitic stainless steel

Dynamic recrystallization behavior of AISI 321 austenitic stainless steel were studied using hot compression tests over the range of temperatures from 900 °C to 1200 °C and strain rates from 0.001 s^-1 to 1 s^-1. The critical strain and stress for initiation of dynamic recrystallization were determined by plotting strain hardening rate vs. stress curves and a constitutive equation describing the flow stress at strains lower than peak strain. Also, the strain at maximum flow softening was obtained and the effect of deformation conditions (Z parameter) on the critical strain and stress were analyzed. Finally, the volume fraction of dynamic recrystallization was calculated at different deformation conditions using these critical values. Results showed that the model used for predicting the kinetics of dynamic recrystallization has a great consistency with the data, in the form of θ-ε curves, directly acquired from experimental flow curves.     

High-strain-rate response of ultra-fine-grained copper

The high-strain-rate response of ultra-fine-grained (UFG) copper processed by equal channel angular pressing (ECAP) was characterized by three different dynamic testing methods: reverse Taylor impact, cylindrical compression specimens, and hat-shaped specimens in Hopkinson bar experiments. Upon recovery after impact, the specimens were found to undergo dynamic recrystallization at a calculated temperature of 360 K, indicating that the UFG copper is thermally unstable. Reverse Taylor tests were conducted on as-received oxygen-free high-conductivity copper rod and ECAP specimens with 2 and 8 sequential deformation passes. The dynamic deformation of the samples was modeled using AUTODYN-2D, and a modified Johnson–Cook constitutive equation was found to closely capture the dynamic response. Both the dynamic experiments and analysis from the reverse Taylor tests indicate enhanced strain-rate sensitivity in comparison with conventional polycrystalline copper, in agreement with predictions of reduced activation volume. The shear band thickness, as obtained in forced localization tests, showed a marked decrease, in comparison to conventional polycrystalline copper; this effect is interpreted as due to an accelerated thermal softening and inherent instability exhibited by the UFG structure.     

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。     

ZK60镁合金热变形过程中的应变强化与动态再结晶行为(英文)

研究ZK60合金的高温流变应力行为。分别采用Kocks-Mecking模型和Avrami方程对合金的应变强化和动态再结晶过程进行模拟,在此基础上,构建一个考虑合金动态再结晶软化的流变应力方程并对流变应力进行预测。结果表明:预测曲线与实验结果具有很高的相关系数,所构建的流变应力方程能准确地描述热变形过程中合金的流变应力行为。微观组织观察表明在变形初期合金组织主要为动态回复组织,随着应变增加,逐渐转变为再结晶组织。     

Modeling the Flow Curve of AISI 410 Martensitic Stainless Steel

In the present study, hot deformation behavior of AISI 410 martensitic stainless steel was investigated and modeled after conducting compression tests at the temperature range of 900-1150?°C and strain rate range of 0.001-1?s^?1. At the studied temperature and strain rates, the flow curves were typical of dynamic recrystallization (DRX) showing a hardening peak followed by a softening one, and a steady state. The flow curves up to the peaks were modeled using the Estrin and Mecking equation. The softening due to DRX was also considered to increase the consistency of the developed model. The experimental equation proposed by Cingara and McQueen was also used to model the work hardening region. The results showed that the phenomenological model based on the Estrin and Mecking equation resulted in a better model for the work hardening region. Based on the Avrami equation, a model was developed to estimate the flow softening due to DRX between the peak and the starting point of steady state. The average value of the Avrami exponent was determined as 2.2, and it decreased with the increasing Zener-Hollomon parameter.     

AerMet100超高强度钢热变形行为

在热模拟机上对AerMet100超高强度钢进行了恒温和恒应变速率的热压缩实验,温度范围是900℃～1100℃,应变速率范围是0.01s-1～10s-1。实测了高温下应力-应变关系曲线,观察了变形后的显微组织,计算了材料的激活能,并建立了峰值应力与变形温度和应变速率的关系。结果表明,材料的流动应力随着变形温度的升高而降低,随应变速率的增大而增大;材料在不同变形条件下其软化机制分别受动态回复和动态再结晶控制;在实验条件范围内,AerMet100超高强度钢的再结晶温度在1000℃～1050℃之间,材料的热变形激活能为261.2kJ/mol。     

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%。