热等静压态FGH96合金的热变形行为及热加工图

采用Gleeble-3800热模拟压缩试验机对热等静压态FGH96合金进行了不同温度和应变速率的等温热压缩试验,研究了FGH96合金在变形温度分别为1040、1070、1100、1130 ℃,应变速率为0.001、0.01、0.1和1 s^-1,最大真应变为0.7条件下的高温热变形行为,分析了真应力-真应变曲线,建立了本构方程,并利用Origin软件构建了热加工图,结合变形温度和应变速率对组织的影响确定了FGH96合金合适的热加工参数。结果表明,热等静压态FGH96合金的真应力-真应变曲线呈现典型的动态再结晶特征,其峰值应力随变形温度的降低和应变速率的增加而增加,结合本构方程、热加工图以及微观组织确定了FGH96合金合适的热加工区域为变形温度1060~1080 ℃,应变速率0.0001~0.004 s^-1。     

Cu-0.23Be-0.84Co合金热变形行为

为实现Cu-Be-Co合金连续挤压的数值模拟和制定合理的热成形工艺参数,采用Gleeble-1500D热模拟机对Cu-Be-Co合金在变形温度为450℃~850℃和应变速率为0.1s-1~10s-1条件下的热变形行为进行研究;分析热压缩对合金组织的影响;根据Arrhenius方程对实验数据进行分析,建立Cu-Be-Co合金热变形本构方程。结果表明,Cu-Be-Co合金热变形的流变应力随应变速率的降低和变形温度的升高而减小,并且Cu-Be-Co合金在高温变形条件下发生动态再结晶。     

Cu-Ni-Si-P合金热变形行为及热加工图

采用高温等温压缩试验,对Cu?Ni?Si?P合金在应变速率0.01~5?1、变形温度600~800°C条件下的高温变形行为进行了研究,得出了该合金热压缩变形时的热变形激活能Q和本构方程。根据实验数据与热加工工艺参数构建了该合金的热加工图,利用热加工图对该合金在热变形过程中的热变形工艺参数进行了优化,并利用热加工图分析了该合金的高温组织变化。热变形过程中Cu?Ni?Si?P合金的流变应力随着变形温度的升高而降低,随着应变速率的提高而增大,该合金的动态再结晶温度为700°C。该合金热变形过程中的热变形激活能Q为485.6 kJ/mol。通过分析合金在应变为0.3和0.5时的热加工图得出该合金的安全加工区域的温度为750~800°C,应变速率为0.01~0.1 s?1。通过合金热变形过程中高温显微组织的观察,其组织规律很好地符合热加工图所预测的组织规律。     

Al-Zn-Mg-0.25Sc-Zr合金的热压缩变形行为和微观组织演化(英文)

采用等温轴对称热压缩实验对Al-Zn-Mg-0.25Sc-Zr合金的热变形行为和微观组织演化进行研究。变形温度为340~500°C,应变速率为0.001~10 s-1。结果表明:稳态流变应力随着应变速率的增加和变形温度的降低而增大,该合金的流变应力行为可用双曲正弦形式的本构方程来描述,其变形激活能为150.25 kJ/mol。在变形温度较高和应变速率较低(即Z参数较低)的条件下,动态再结晶更容易发生。随着Z参数的变小,合金的主要软化机制由动态回复转变为动态再结晶,合金中的位错密度降低,亚晶尺寸增大。     

Ti6Al4V钛合金的变形组织及织构

在温度850~930°C、应变速率0.01~1 s-1的条件下,对初始组织为等轴组织的Ti6Al4V钛合金进行变形程度为70%的热压缩变形实验,研究合金的变形组织及织构。结果表明,当温度低于900°C、应变速率高于0.1 s-1时,合金的组织主要是拉长的α晶粒;而在高于900°C以及低应变速率下,则会发生动态再结晶。电子背散射衍射（EBSD）结果显示,合金在再结晶过程中亚晶界吸收位错,最终形成大角晶界。在930°C时动态再结晶已基本完成,水冷至室温时形成针状α相。与原始组织相比,合金在930°C变形时织构得到增强,低于930°C变形时织构变弱。     

热挤压态FGH95合金的动态再结晶机制研究

针对热挤压态FGH95合金进行变形温度为1050~1120 ℃、变形量为50%和70%、应变速率为10?4~1 s?1的热压缩试验,研究该合金动态再结晶（DRX）的组织演变和形核机制。结果表明:提高变形温度和降低应变速率可以促进小角度晶界向大角度晶界迁移,有利于动态再结晶晶粒的长大;变形温度和变形量对热挤压态FGH95合金的动态再结晶机理的影响不明显,而应变速率对动态再结晶机制影响较大;随着应变速率的增加,热挤压态FGH95合金由不连续动态再结晶机制逐渐转变为连续动态再结晶机制;热挤压态FGH95合金的动态再结晶以不连续动态再结晶形核机制为主,以连续动态再结晶形核机制为辅;在1050 ℃、1 s?1变形条件下,热挤压态FGH95合金发生连续动态再结晶形核。     

Mg-6Zn-1Al-0.3Mn 镁合金的热压缩变形行为及变形组织

采用Gleeble热模拟方法研究Mg?6Zn?1Al?0.3Mn 变形镁合金在温度为200~400°C,应变速率为0.01~7 s?1条件下的热压缩变形行为。结果表明,变形温度和应变速率显著影响其热变形行为。通过计算获得了热变形激活能及应力指数分别为Q=166 kJ/mol,n=5.99,且其本构方程为ε&=3.16×1013[sinh(0.010σ)]5.99exp [?1.66×105/(RT)]。热压缩显微组织观察表明：在应变速率为0.01~1 s?1的条件下,在250°C热压缩变形时初始晶粒晶界及孪晶处发生了部分动态再结晶,而在高温(350~400°C)条件下,发生了完全动态再结晶且再结晶晶粒尺寸随着应变速率的增加而减小。获得的较优的变形条件为温度330~400°C、应变速率为0.01~0.03 s?1以及350°C、应变速率为1 s?1。     

FGH4096/GH4133B双合金高温变形的动态软化行为

FGH4096/GH4133B双合金在变形温度1020~1140℃、应变速率0.001~1.0s-1条件下进行50%变形量的热模拟压缩试验。根据应力-应变曲线,基于传统Arrhenius型方程建立双合金高温变形过程中的本构关系。结合应力-应变曲线与Poliak-Jonas准则分析不同变形参数对双合金组织软化机制的影响。结果表明:FGH4096/GH4133B双合金变形时,升高温度和降低应变速率可有效诱导该双合金的软化机制由动态回复转变为动态再结晶。     

新型耐热合金TG700C热变形及动态再结晶行为

利用等温热压缩实验,研究了TG700C合金变形温度为1050~1250℃、应变速率为1~20 s-1、变形量为60%变形条件下的热变形及动态再结晶行为。对材料高应变速率下的变形热效应进行了温升修正,获得了该合金的流变曲线和热变形本构方程,热变形过程的表观激活能为Q=624.762 k J/mol。该合金经过温升修正后的流变曲线呈现稳态的流变应力,不同变形温度和应变速率下合金的流变应力存在差异。合金的动态再结晶形核方式为应变诱导晶界迁移形核,在高温低应变速率下,动态再结晶形核容易发生,再结晶的比例随着温度的升高和应变速率的降低而提高。     

铸态Mg-Zn-Zr-Gd合金的热压缩变形行为

为了研究Mg-Zn-Zr-Gd合金的热压缩变形行为,采用Gleeble-3500型热模拟试验机,在变形温度为300～400℃,变形速率为0.001～1 s^-1条件下对合金进行热压缩实验。分析了在不同的热压缩条件下合金的真应力-真应变曲线,通过引入Z参数建立了相关流变应力本构方程,同时观察了合金的微观组织演变。结果表明：合金在热压缩变形过程中主要发生了动态再结晶,且合金的流变应力随着应变速率降低和温度升高而减小。在低变形温度或高应变速率下进行热压缩变形时,再结晶晶粒比较细小,但是动态再结晶进行不充分,动态再结晶仅仅发生在晶界处且分布不均匀,仍然存在原始大晶粒。随着变形温度的升高和应变速率的降低,再结晶区域明显增加,再结晶晶粒也逐渐长大。根据热加工图分析得到合金最佳的热加工成形工艺区域为：温度为350～400℃,应变速率为0.1～1 s^-1。     

Flow Behavior and Microstructures of Inconel 625 Superalloy at the Elevated Temperature

The deformation behavior of Inconel 625 superalloy was investigated by means of hot compression tests. The flow stress curves were obtained in the temperature and strain rate ranges of 950-1200 ℃ and 0.01-10 s-1, respectively. Optical microscopy was used to evaluate the microstructural evolution of the alloy under different conditions examined. The results show that the flow stress decreases with decreasing strain rate and increasing temperature, and the activation energy is about 654.502 kJ/mol. Microstructure observations show that with increasing temperature, the sizes and volume fraction of dynamic recrystallization (DRX) grains increase. The strain has no remarkably effect on the sizes of DRX grains, but with increasing strain the volume fraction of DRX grains increases. During hot compression of Inconel 625 superalloy at elevated temperature, the occurrence of DRX was the main softening mechanism. The DRX mechanism of Inconel 625 superalloy can be mainly attributed to the discontinuous dynamic recrystallization (DDRX).     

Constitutive Modeling of Dynamic Recrystallization Kinetics and Processing Maps of Solution and Aging FGH96 Superalloy

The hot deformation behavior of solution and aging FGH96 superalloy were investigated in the deformation temperature range of 1000-1175 °C and strain rate range of 0.001-5.0/s on a Gleeble-1500 thermo-mechanical simulator. The results show that the true stress-strain curves are typical of the occurrence of dynamic recrystallization (DRX). The value of the activation energy and materials constants of A and n was obtained through the hyperbolic sine function between the peak stress and Zener-Hollomon parameter. Optical microscopy observations of the grains showed that Zener-Hollomon parameter affected the DRX grain size obviously. In addition, the constitutive equations and DRX kinetics model were also built. The processing maps with the strain of 0.3 and 0.6 were obtained on the basis of dynamic materials model. The results predicted that there existed instability regions at around 1050 °C when the strain rate exceeds 0.01/s.     

Deformation Mechanism and Hot Workability of Extruded Magnesium Alloy AZ31

Using the flow stress curves obtained by Gleeble thermo-mechanical testing, the processing map of extruded magnesium alloy AZ31 was established to analyze the hot workability. Stress exponent and activation energy were calculated to characterize the deformation mechanism. Then, the effects of hot deformation parameters on deformation mechanism,microstructure evolution and hot workability of AZ31 alloy were discussed. With increasing deformation temperature, the operation of non-basal slip systems and full development of dynamic recrystallization(DRX) contribute to effective improvement in hot workability of AZ31 alloy. The influences of strain rate and strain are complex. When temperature exceeds 350 °C, the deformation mechanism is slightly dependent of the strain rate or strain. The dominant mechanism is dislocation cross-slip, which favors DRX nucleation and grain growth and thus leads to good plasticity. At low temperature(below 350 °C), the deformation mechanism is sensitive to strain and strain rate. Both the dominant deformation mechanism and inadequate development of DRX deteriorate the ductility of AZ31 alloy. The flow instability mainly occurs in the vicinity of 250 °C and 1 s-1.     

Dynamic Recrystallization Mechanism of Inconel 690 Superalloy During Hot deformation at High Strain Rate

The hot deformation characteristics of Inconel 690 superalloy were investigated on the Gleeble-3800 thermal-mechanical simulator. The testing temperatures were in the range of 1000-1200 °C, the strain rate was 10 s^?1, and the maximum true strain was 0.9. Optical microscopy, transmission electron microscopy, and electron backscatter diffraction techniques were employed to analyze the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). The results show that multiple-cycle discontinuous dynamic recrystallization (DDRX) occurs in the process of hot deformation under the conditions above. DRX grain size decreases with decreasing temperature and increasing strain. DDRX with sub-grains directly transforming into grains is the dominating nucleation mechanism of DRX. And, the nucleation mechanism of bulging of the original grain boundaries can only be considered as an assistant nucleation mechanism of DRX, which mainly occurs in the beginning of the deformation.     

Optimization of deformation parameters of dynamic recrystallization for 7055 aluminum alloy by cellular automaton

In order to simulate the microstructure evolution during hot compressive deformation, models of dynamic recrystallization (DRX) by cellular automaton (CA) method for 7055 aluminum alloy were established. The hot compression tests were conducted to obtain material constants, and models of dislocation density, nucleation rate and recrystallized grain growth were fitted by least square method. The effects of strain, strain rate, deformation temperature and initial grain size on microstructure variation were studied. The results show that the DRX plays a vital role in grain refinement in hot deformation. Large strain, high temperature and small strain rate are beneficial to grain refinement. The stable size of recrystallized grain is not concerned with initial grain size, but depends on strain rate and temperature. Kinetic characteristic of DRX process was analyzed. By comparison of simulated and experimental flow stress–strain curves and metallographs, it is found that the established CA models can accurately predict the microstructure evolution of 7055 aluminum alloy during hot compressive deformation.     

Hastelloy C276高温合金热加工微观组织演化元胞自动机模拟

采用Gleeble热模拟试验机对Ni-Cr-Mo系高温合金Hastelloy C276进行单道次和双道次热压缩试验,获得了不同热变形条件下的流变应力曲线和微观组织,在此基础上回归了该合金热变形物理冶金模型及参数,进而构建了微观组织拓扑演化的元胞自动机模型。结果表明:Hastelloy C276高温合金在高温热压缩过程中易发生动态再结晶,当动态再结晶不完全时,在热压缩保温或道次间歇内,再结晶晶粒将进一步快速生长而发生亚动态再结晶。Hastelloy C276高温合金再结晶行为对变形温度、变形速率、应变量等工艺参数敏感;构建的元胞自动机模型,集成计算了热压缩和道次间歇过程中的位错密度、再结晶形核及晶界迁移等,可有效表征多工艺参数下Hastelloy C276高温合金热压缩过程中的微观组织拓扑结构演化和应力-应变响应。     

粗晶GH4720Li合金热变形行为与动态再结晶特点

为了模拟难变形镍基高温合金GH4720Li开坯锻造过程,采用Gleeble-3800热模拟试验机研究经均匀化处理的GH4720Li铸锭高温压缩变形时的力学流动行为,分析高温变形过程中微观组织演化规律。结果表明,GH4720Li合金在1100℃,0.1 s-1条件下应力水平达到250 MPa,且应力对热变形温度和应变速率敏感,动态再结晶是主要的软化机制。粗晶组织提高了合金动态再结晶临界变形温度和应变速率,如在变形量为60%,变形条件为1140℃,0.001 s-1和1180℃,0.001s-1才能发生完全动态再结晶。计算的粗晶GH4720Li合金热变形激活能Q=1171kJ/mol,较高的热变形激活能表明粗晶组织不利于热塑性变形和动态再结晶的发生。基于本研究,铸态GH4720Li合金开坯温度应高于1140℃,同时保证较低的应变速率,以确保动态再结晶的充分发生,实现枝晶组织破碎。     

Zn-8Cu-0.3Ti锌合金热变形的组织演变(英文)

利用Gleeble-1500热力模拟试验机在温度230~380°C,应变速率0.01~10 s-1的条件下进行均匀化态Zn-8Cu-0.3Ti锌合金的热压缩变形实验,测定真应力—真应变曲线,利用OM、SEM和TEM对变形组织进行分析。结果表明:在变形过程中该合金发生了TiZn15相的球化、析出相的粗化和基体η相的动态再结晶,形成了(η+ε+TiZn15)复相组织。变形过程中TiZn15相的球化有助于粒子协同方式实现粒子激发形核,有利于基体动态再结晶的发生。随着压缩变形温度的升高,基体动态再结晶晶粒的尺寸先减小后增大;随着应变速率和应变量的增大,动态再结晶进行得更充分;形变促进Cu原子的扩散,导致析出相的粗化,析出相的钉扎作用使组织得到细化。