GH3230高温合金热变形行为及本构模型研究

采用高温拉伸试验研究了GH3230合金在温度1144~1273 K、应变速率1×10-3~1×10-1s-1条件下的热变形行为。计算了变形激活能,并采用Zener-Hollomon参数法构建合金的高温变形的本构关系。结果表明:温度和应变速率对GH3230合金的高温力学性能有显著影响,流变应力随变形温度的升高而降低,随着应变速率的增加而升高。GH3230合金的高温流变行为可用Zener-Hollomon参数的双曲正弦函数来描述,热变形材料常数为:A=5.179×1016s-1,a=0.0088,n=3.9893,并计算出合金的平均变形激活能Q=455.203 k J·mol-1,且变形激活能更容易受到应变速率的影响。扫描电镜(SEM)断口分析表明GH3230合金在高温下(1144~1273 K)应变率范围为1×10-3~1×10-1s-1时的拉伸断裂都是由损伤引起的韧性断裂,且温度对断口形貌影响不大,但应变速率增大会使韧窝尺寸和深浅变小。     

07MnNiMoDR板轧制热变形本构方程

利用Gleeble-3500热模拟实验机完成了07MnNiMoDR钢热等温平面应变压缩实验,获得了温度900～1 100℃、应变速率0.01～1 s^-1、变形率45%等条件的高温流变行为,其中温度和应变速率对流变应力的影响明显。基于对Arrhenius方程和Zener-Hollomon参数的解析,获得了热变形激活能Q,确定了峰值应力本构模型;通过分析应力应变与位错的关系,获得了硬化率及Z参数等与应力之间的内在关联性,建立了加工硬化-动态回复过程的流变应力模型;基于动态再结晶理论,采用Avrami模型计算了动态再结晶体积分数,获得Z参数计算方法,建立了动态再结晶过程的流变应力模型。利用所建立的本构模型完成了预测及对比分析,相关系数r为0.99,所建立的本构关系模型精度很高。     

7050高强铝合金高温塑性变形的流变应力研究

通过在Gleeble1500D热模拟试验机上进行等温热压缩试验,研究了7050高强铝合金在变形温度为300～450℃和应变速率为0.01～10s-1条件下的流变应力变化规律,计算推导出包含Arrhenius项的zener-Hollomon参数描述7050合金高温压缩流变行为的表达式.结果表明:应变速率和变形温度对7050合金的流变应力影响显著,流变应力随温度升高而降低,随应变速率的提高而增大;7050合金属于正应变速率敏感材料,合金的形变激活能为163.7425 KJ·mol-1.     

变形态2219铝合金高温塑性变形的本构模型

采用Gleeble-3500型热压缩试验机研究了变形态2219铝合金在应变速率为0.25～0.8 s-1、变形温度为420～500℃时的流变应力行为,建立了变形态2219铝合金高温塑性变形时的基于应变补偿的双曲正弦本构方程.结果表明:变形态2219铝合金的流变应力随变形温度的升高而降低,随应变速率的提高而增大.基于应变...     

耐热钢310S柱状晶组织高温变形本构方程的建立

通过Gleeble-1500热模拟实验获得了耐热钢310S柱状晶组织在变形温度为1 000~1 200℃,应变速率为0.01~30 s~(-1)条件下的应力-应变曲线。实验利用高温变形机理分析了热变形参数对流动应力的影响规律,建立了可用于轧制过程数值模拟的310S钢柱状晶组织高温变形的本构方程。     

一种新型第四代粉末高温合金热变形行为及其本构方程北大核心

采用Gleeble-3800热模拟试验机研究了热等静压态新型第四代粉末高温合金的热变形行为,变形温度1060~1140℃,应变速率0.001~1 s-1,真应变量0.69。结果表明,热等静压态合金热模拟压缩实验的高温流变曲线呈动态再结晶特征。基于双曲正弦函数型Arrhenius方程和实验数据,采用峰值应力以及应变修正两种方式构建了合金的高温流变本构方程。后者由于包含了应变量的影响,预测的合金热变形流变应力值与实际测试结果比较吻合,平均相对误差绝对值为7.87538%,能更好的反映合金在热变形过程中的流变行为,为合金热加工工艺的设计优化提供参考依据。     

耦合位错密度的6111铝合金热变形本构模型

利用Gleeble-1500热模拟试验机对6111铝合金进行高温拉伸试验,研究了其在变形温度为350、450和550℃以及应变速率为0.1、1和10 s^-1时的热变形行为.6111铝合金的流变应力随温度升高而减小,随应变速率增大而增大,其热变形从应变硬化阶段过渡到稳态变形阶段.建立了综合考虑应变、温度和应变速率对流变应力的影响以及耦合位错密度的统一黏塑性本构模型,并通过遗传优化算法求解出本构模型中的材料常数.模型计算得到的真应力-真应变曲线与试验数据吻合较好.     

Fe5Mn3Al中锰汽车用钢热变形本构方程的研究

本文研究了Fe5Mn3Al中锰汽车用钢的热变形行为,在温度为950～1 150℃时,应变速率为0.1～20 s~(-1).用Gleeble3800热模拟试验机进行单道次热压缩试验,通过对试验获得的流变应力数据的回归分析,构建双曲正弦Arrhenius方程以描述中锰汽车钢Fe5Mn3Al的高温变形行为,其热变形激活能为503.931 kJ/mol.本构方程对Fe5Mn3Al试验钢流变应力进行预测,模型预测值与试验值有很好的一致性,精度较高,平均相对误差为3.25%.     

TA9钛合金高温拉伸变形行为的研究

采用高温拉伸试验,得到TA9钛合金在800～920℃温度范围内和应变速率为0.001～0.125 s^-1条件下的应力应变曲线,分析在拉应力条件下,变形温度、应变速率和流变应力三者之间的关系,构造了Arrhenius双曲正弦函数本构方程,并进行了应变修正,绘制出变形量为20%和50%时的热加工图,总结出不同变形条件下合金显微组织演变规律。结果表明：流变应力随变形温度的提高和应变速率的降低而降低,由本构方程计算出两相区变形激活能为569.453 kJ/mol,热加工图中的失稳区主要有四个区域,分别是在800～845℃和870～920℃时,应变速率在大于0.07 s^-1和0.002～0.03 s^-1处。此外,断裂位置显微组织中α相沿着合金变形的方向被拉长,α晶界变成锯齿状,这与动态回复过程中α向沿亚晶界破碎、分割和晶界突出有关。当变形温度一定时,等轴α晶粒尺寸随应变速率的提高而减小,当应变速率一定时,等轴α晶粒尺寸随温度的升高而变大。     

38MnB5热成形钢高温变形行为及本构方程

利用Gleeble-3500热模拟试验机对38MnB5热成形钢的高温变形行为进行研究, 分别在650~950℃温度区间内, 以0.01、0.1、1和10 s-1的应变速率对其进行等温单向拉伸测试, 并得到相应条件下的真应力-应变曲线.结果表明: 38MnB5热成形钢流变应力随着变形温度的升高而减小, 随着应变速率的增大而增大.当应变速率逐渐增加时, 热变形时发生的动态回复和动态再结晶效果并不显著, 而当温度逐渐升高时, 二者作用逐渐加强.考虑了温度、应变速率和应变的综合复杂影响, 建立38MnB5热成形钢高温下的本构方程.此本构方程通过对流变应力、应变、应变速率等实验数据的回归分析, 得到与变形温度、应变速率和应变相关的材料参数多项式.计算结果与实验结果对比发现, 通过本构方程所获得的计算值与试验值吻合良好.      

2A14铝合金板材生产工艺

研究了2A14铝合金板材淬火温度、淬火时间、时效温度和时效时间等因素对组织、性能的影响。确定了2A14薄板的热处理工艺参数,淬火制度：淬火温度为500℃,淬火保温时间为10min;时效制度：时效温度160℃,时效保温时间为12h。     

铝合金踏板加工设备的设计探讨

从铝合金踏板的种类、连接方式入手,对加工建筑铝合金踏板所用的滚压机的设计进行了探讨,并重点分析了滚压机机械部分的动作顺序、液压部分油缸的选择、压辊的尺寸确定等问题。实测证明滚压后的踏板可以安全使用。     

Characterization of Fatigue Substructure of Incoloy Alloy 800 at Elevated Temperature

Transmission electron microscopy has been employed to study the fatigue substructure of Incoloy 800 at elevated temperatures. Substructure parameters such as cell or subgrain intercept size, dislocation density, and misorientation angle between adjacent cells or subgrains were evaluated and correlated with the observed fatigue properties. Observations, results and analysis of substructure data are presented and also discussed in terms of existing theories. Incoloy 800 push-pull fatigue specimens were examined after being tested at various test conditions at 538, 649, 704 and 760 °C. Subboundary intercept size and dislocation density were found to be related to both the saturation stress and the plastic strain amplitude, in accord with the “modified” theoretical predictions and the experimental findings. A critical dislocation density for cell formation was experimentally shown to exist and was found to be strongly temperature dependent. Subboundaries were also found to lie on the low index planes such as {100}, {110}, and {111}.     

Cu-Cr-Zr-Ce合金高温流变应力的研究

利用Gleeble-1500D热模拟试验机对Cu-Cr-Zr-Ce合金在变形温度为600～800℃、应变速率为0.01～5 S-1条件下进行了热压缩试验,测定了其应力-应变曲线,并通过光学显微镜观察了其热压缩过程中的微观组织.结合两者分析了动态回复和再结晶机制.结果表明,动态再结晶是该合金软化的主要机制.     

Constitutive Modeling for Elevated TemperatureFlow Behavior of 30Cr2Ni4MoV Ultra-super-crit- ical Rotor Steel

In order to perform numerical simulation of forging and determine the hot deformation processing parameters for 30Cr2Ni4MoV steel, the compressive deformation behaviors of 30Cr2Ni4MoV steel were investigated at the temperatures from 970 to 1270 ℃ and strain rates from 0. 001 to 0.1 s-1 on a Gleeble-3500 thermo-mechanical simulator. The flow stress constitutive equations of the work hardening-dynamical recovery period and dynamical recrystallization period were established for 30Cr2Ni4MoV steel. The stress-strain curves of 30Cr2Ni4MoV steel predicted by the proposed model well agreed with experimental results, which confirmed that the proposed equations can be used to determine the hot deformation processing parameters for 30Cr2Ni4MoV steel.     

Gas‐pressure Forming of an AlMg‐Alloy Sheet at Elevated Temperatures

Forming of automotive leightweight parts using aluminium offers numerous advantages. Compared to other wrought aluminium alloys, in particular AlMg‐alloys generally show a good formability which is favourable for the production of complex parts. However, forming of Mg‐containing alloys at room temperature leads to yielding patterns preventing their implementation for class‐A‐surface applications. Furthermore, the formability of steel still exceeds that of AlMg‐alloys at room temperature. Thus, in the present study, sheet metal forming is applied at a temperature range that is typical for warm forming. It is supposed to profit from the advantages of warm forming like high achievable strains and improved surface quality of the formed part, while not having the disadvantages of long production times and high energy consumption, which is correlated with superplastic forming. Applying fluid‐based sheet metal forming in this paper, nitrogen is used as fluid working medium to satisfy the demand on high temperature resistance. Concerning the blank material used, formability of Mg‐containing aluminium alloys shows strong strain rate sensitivity at elevated temperatures. To figure out the optimal strain rates for this particular process, a control system for forming processes is developed within the scope of this paper. Additionally, FE‐simulations are carried out and adapted to the experiment, based on the generated process data. FE‐investigations include forming of domes (bulging) as well as shape‐defined forming, having the objective to increase formability in critical form elements by applying optimal strain rates. Here, a closed‐loop process control for gas‐pressure forming at elevated temperatures is to be developed in the next stages of the project.     

Fracture of Precipitation-Hardened Copper Alloy Produced by Semi-Continuous Casting at Elevated Temperature

Abstract

In semi-continuously cast slabs of precipitation-hardened copper alloy, internal cracks are often observed after homogenization, although those defects can not be found out after casting. It is considered that, before stress relief takes place during homogenization, thermal stresses generated in the slab during casting will exceed the fracture stress. It is of interest to understand how internal stresses of slabs will affect the fracture during homogenization. Fracture temperatures of the material under static tensile stresses are investigated in an attempt to demonstrate the fracture evolved during homogenization. © 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

Dans les brames d'alliage de cuivre durci par précipitation et coulées en semi-continu, on observe souvent des fissures internes après homogénéisation, bien qu'on ne trouve pas ces défauts après la coulée. On considère que les ontraintes thermiques générées dans la brame lors de la coulée vont excéder la contrainte de rupture lors de l'homogénéisation, avant que l'effet de relaxation puisse se produire. Il est intéressant de comprendre de quelle manière les contraintes internes des brames affecteront la rupture lors de l'homogeneisation. On a etudie les températures de rupture du matériel sous contraintes statiques en traction dans une tentative de démontrer que la rupture a évolué lors de l'homogénéisation. © 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

TA32钛合金高温连续氧化行为研究

采用氧化增重法研究了表面有/无喷涂氮化硼高温润滑剂的TA32钛合金在热成形温度为750～850℃范围内的氧化行为,通过SEM和EDS等微观分析方法对氧化层的表面形貌和成分、截面厚度和成分进行分析,并对氧化机理进行探讨。结果表明,氧化温度、时间和氮化硼润滑剂是影响TA32钛合金氧化行为的重要因素。在750～850℃其氧化速率均符合直线-抛物线规律,800℃以上氧化剧烈且发生氧化膜脱落现象;在高温下其氧化膜随着时间逐渐增厚,氧化物由颗粒状变为短棒状和针状,氧化皮逐渐变得疏松多孔。氮化硼润滑剂对TA32钛合金有很好的氧化保护作用,其表面氧化层成分为Ti O2、Al2O3和Ti3Al。     

The Effect of Solute Atoms on Aluminum Grain Boundary Sliding at Elevated Temperature

Grain boundary sliding (GBS) is an important deformation mechanism for elevated temperature forming processes. Molecular dynamics simulations are used to investigate the effect of solute atoms in near grain boundaries (GBs) on the sliding of Al bicrystals at 750 K (477 °C). The threshold stress for GBS is computed for a variety of GBs with different structures and energies. Without solute atoms, low-energy GBs tend to exhibit significantly less sliding than high-energy GBs. Simulation results show that elements which tend to phase segregate from Al, such as Si, can enhance GBS in high-energy GBs by weakening Al bonds and by increasing atomic mobility. In comparison, intermetallic forming elements, such as Mg, will form immobile Mg-Al clusters, decrease diffusivity, and inhibit GBS.     

5052铝合金板材生产工艺研究

重点介绍了5052铝合金板材的应用及其生产工艺控制,并对5052合金板材的组织结构、力学性能进行了分析.通过一定厚度板材的等时退火,确定了5052合金再结晶退火温度.