FGH96合金双道次热变形及其热加工图

采用 Gleeble-1500热模拟试验机对 FGH96合金进行双道次真应变量为0.6+0.6和0.3+0.9的等温间断热压缩试验,研究了变形温度为1050~1125℃、变形速率为0.001~0.1 s -1时合金的热变形行为和组织演变.热变形过程中合金发生了再结晶,第一道次较小的真应变量减轻了合金的开裂.当第一道次真应变量小时,随着温度和变形速率的上升,合金道次间再结晶软化率增加.不同应变量以及不同道次真应变量均对合金热加工图产生明显影响.在相同变形条件下,当能量耗散率随应变量的增加而下降时,合金中组织由细晶向粗晶转变,反之则由粗晶向细晶转变;当能量耗散率不随应变量的变化而变化时,能量耗散率低于20%的合金中出现大量的不完全再结晶组织,能量耗散率高于35%的合金中出现细小完全再结晶组织.     

Hot deformation behavior of uniform fine-grained GH4720Li alloy based on its processing map

The hot deformation behavior of uniform fine-grained GH4720Li alloy was studied in the temperature range from 1040 to 1130℃ and the strain-rate range from 0.005 to 0.5 s?1 using hot compression testing. Processing maps were constructed on the basis of compression data and a dynamic materials model. Considerable flow softening associated with superplasticity was observed at strain rates of 0.01 s?1 or lower. According to the processing map and observations of the microstructure, the uniform fine-grained microstructure remains intact at 1100℃ or lower because of easily activated dynamic recrystallization (DRX), whereas obvious grain growth is observed at 1130℃. Metallurgical instabilities in the form of non-uniform microstructures under higher and lower Zener–Hollomon parameters are induced by local plastic flow and primary γ′ local faster dissolution, respectively. The optimum processing conditions at all of the investigated strains are proposed as 1090–1130℃ with 0.08–0.5 s?1 and 0.005–0.008 s?1 and 1040–1085℃ with 0.005–0.06 s?1.     

齿轮钢SAE8620 H高温变形行为及热加工图

通过高温压缩试验研究齿轮钢SAE8620H在950~1100℃、应变速率0．01~10 s-1条件下的高温变形行为.该合金钢的流动应力符合稳态流变特征,流变应力随变形温度升高以及应变速率降低而减小,其本构方程可以采用双曲正弦方程来描述.基于峰值应力、应变速率和温度相关数据推导出SAE8620H高温变形激活能Q=280359．9 J·mol-1.根据变形量40%和60%下应力构建该齿轮钢的热加工图,通过热加工图中耗散值及流变失稳区确定其热变形工艺参数范围. SAE8620H钢在在变形程度较小时宜选取低的应变速率进行成形,而在变形程度大时则要选取低温低应变速率或者高温高应变速率.     

电热合金Cr20 Ni80的热变形行为及热加工图

为了解决Cr20 Ni80电热合金锻造开裂的问题,在Gleeb-1500D热模拟试验机上对该合金进行热压缩试验,研究变形温度为900~1220℃,应变速率为0.001~10 s-1条件下的热变形行为,并根据动态材料模型建立合金的热加工图.合金的真应力-真应变曲线呈现稳态流变特征,峰值应力随变形温度的降低或应变速率的升高而增加;热变形过程中稳态流变应力可用双曲正弦本构方程来描述,其激活能为371.29 kJ·mol-1.根据热加工图确定了热变形流变失稳区及热变形过程的最佳工艺参数,其加工温度为1050~1200℃,应变速率为0.03~0.08 s-1.优化的热加工工艺在生产中得到验证.     

纯镍N6平面热压缩变形行为及加工图

利用Gleeble-3800热模拟试验机对纯镍N6在变形温度800~1100℃,应变速率5~40 s-1,应变量70%条件下进行了高温塑性变形压缩试验,分析纯镍N6高温高应变速率热变形行为,得到了材料在不同变形参数条件下的组织变化规律及流变应力变化曲线,利用动态材料模型绘制出了纯镍N6在不同应变条件下的热加工图。通过对组织及热加工图的分析研究,得出变形温度为1000~1100℃,应变速率为5~7 s-1或20~40 s-1以及变形温度为800~900℃,应变速率为5~10 s-1为纯镍N6材料高温高应变速率热变形的两个合理变形参数区间,在参数区间内N6组织均匀;而流变失稳区变形参数条件下得到的组织比较紊乱,晶粒大小不一。纯镍N6热变形后的晶粒尺寸随变形温度升高及应变速率减小而增大。     

Cr-Co-Mo-Ni齿轮钢的热变形行为及模锻工艺的有限元模拟

在Gleeble-3800热模拟试验机上进行大变形等温压缩试验,研究Cr-Co-Mo-Ni齿轮钢的高温热变形行为和显微组织,分析材料流变应力与变形温度和应变速率的关系,建立热变形过程的本构方程和热加工图.该材料的流变应力随着温度的升高而下降,随应变速率的增加而增加;用双曲正弦函数式可描述其在热变形过程中的流变应力,热变形活化能为487.21kJ·mol-1;热加工图显示的适宜加工区间为温度1000～1100℃,应变速率0.1 ～1s-1.在热模拟试验基础上进行该钢种锻造工艺的有限元模拟,并结合热加工图分析初锻温度和加工道次对于锻件温度和应变速率的影响,得出适宜的模锻工艺参数为初锻温度1000～1100℃,锻造道次15次.     

GH864合金组织特征对裂纹扩展速率的影响

利用光学显微镜、场发射扫描电镜等手段,研究了GH864合金三种轧制态组织经热处理后的演变过程,分析了热处理后不同组织对室温冲击韧性及高温650℃裂纹扩展速率的影响.结果表明,GH864合金由初始轧制态组织经标准热处理后（1020℃,4h/空冷→845℃,4h/空冷→760℃,16h/空冷）获得的晶粒组织,其晶粒组织演变具有明显的一致性,而合金的晶界碳化物分布及基体γ＇强化相没有明显差别,其分布状态及尺寸大小基本一致.热处理后的晶粒尺寸越大,抗裂纹扩展能力越好,合金的室温冲击韧性越低;热处理后形成的项链状组织,对合金冲击韧性及裂纹扩展速率有较好的影响.     

Deformation behavior and microstructural evolution during hot compression of an a+b Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

The effect of processing parameters on the flow response and microstructural evolution of the a+b titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si has been studied by conducting isothermal hot compressive tests at a strain rate of 0.01-10 s-1 at 860-1100°C. The true stress-true strain curves of the sample hot-compressed in the a+b phase region exhibit a peak stress followed by continuous flow softening, whereas in the b region, the flow stress attains a steady-state regime. At a strain rate of 10 s-1, the alloy exhibits plastic flow insta-bilities. According to the kinetic rate equation, the apparent activation energies are estimated to be about 674-705 kJ/mol in the a+b region and 308-335 kJ/mol in the b region, respectively. When deformed in the a+b region, the globularization process of the a colony structure occurs, and a dynamic recrystallized microstructures are observed to show bimodal. Dynamic recrystallization can take place in the b region irrespective of starting deformed structures.     

Hot deformation mechanism and microstructure evolution of an ultra-high nitrogen austenitic steel containing Nb and V

The flow curves of an ultra-high nitrogen austenitic steel containing niobium (Nb) and vanadium (V) were obtained by hot compression deformation at temperatures ranging from 1000℃ to 1200℃ and strain rates ranging from 0.001 s-1 to 10 s-1. The mechanical behavior during hot deformation was discussed on the basis of flow curves and hot processing maps. The microstructures were analyzed via scanning electron microscopy and electron backscatter diffraction. The relationship between deformation conditions and grain size after dynamic recrystallization was obtained. The results show that the flow stress and peak strain both increase with decreasing temperature and increasing strain rate. The hot deformation activation energy is approximately 631 kJ/mol, and a hot deformation equation is proposed. (Nb,V)N precipitates with either round, square, or irregular shapes are observed at the grain boundaries and in the matrix after deformation. According to the discussion, the hot working should be processed in the temperature range of 1050℃ to 1150℃ and in the strain rate range of 0.01 to 1 s-1.     

AZ310.5Sr1.5Y热变形行为分析

采用Gleeble-1500D型热模拟试验机,在变形温度为250~450 ℃,应变速率为0.01~1 s-1,最大应变量为0.85的条件下,对AZ31-0.5Sr-1.5Y进行单向热压缩实验。对材料的热变形行为和热加工性能进行了研究,建立了合金热变形过程中的本构方程和热加工图,并结合金相显微组织观察对加工图进行了分析。结果表明：AZ31-0.5Sr-1.5Y在热变形过程中的稳态流变应力可用双曲正弦函数关系式进行描述,其应变激活能为186.83 kJ/mol,热加工图分析表明,在本实验条件下,当真应变为0.6时,材料存在着非稳态流变区,其温度为250 ~300 ℃,应变速率为0.3~1 s -1,材料的最佳热加工工艺参数为：温度300~400 ℃,变形速率0.01 ~1 s -1。     

铅的压缩有限变形本构关系研究

有限变形理论应用于金属塑性成形过程模拟的基础之一是确定材料的本构模型.该文以铅作为试验材料,测定单向压缩有限变形和双向受约束两种情形下的载荷位移曲线,建立了基于欧拉描述的铅有限变形本构方程.由有限变形理论推导出单向压缩和平面应变有限元模型.数值算例给出了载荷位移变化规律.结果表明,欧拉描述有限变形本构方程适合于铅的有限变形压缩规律的描述.     

高温合金GH4169与GH4202在富氧气氛中的燃烧行为

采用富氧燃烧实验方法,通过光学显微镜、扫描电子显微镜和能谱仪等手段对GH4169和GH4202高温合金燃烧试样进行分析,建立合金燃烧质量、热量和氧传输模型,探究两种合金的富氧燃烧机理并提出提高新型高温合金抗燃烧性能的措施。结果表明：GH4202与GH4169合金在富氧条件下均发生燃烧,GH4202抗燃烧性能优于GH4169;两种合金以液相进行燃烧,在合金燃烧前沿存在由未完全燃烧的金属颗粒和氧化物组成“燃烧层”,燃烧层中合金元素的燃烧行为是决定合金整体燃烧的关键性因素;合金元素在燃烧前沿呈现“选择性燃烧”规律,Nb、Ti、Al、Cr等元素易于与氧发生燃烧,Ni滞后燃烧且燃烧热低,起到良好的抗燃烧作用。     

Recrystallization behavior of Ti40 burn-resistant titanium alloy during hot working process

The recrystallization behavior of deformed Ti40 alloy during a heat-treatment process was studied using electron backscatter diffraction and optical microscopy. The results show that the microstructural evolution of Ti40 alloy is controlled by the growth behavior of grain-boundary small grains during the heating process. These small grains at the grain boundaries mostly originate during the forging process because of the alloy’s inhomogeneous deformation. During forging, the deformation first occurs in the grain-boundary region. New small recrystallized grains are separated from the parent grains when the orientation between deformation zones and parent grains exceeds a certain threshold. During the heating process, the growth of these small recrystallized grains results in a uniform grain size and a decrease in the average grain size. The special recrystallization behavior of Ti40 alloy is mainly a consequence of the alloy’s high β-stabilized elemental content and high solution strength of the β-grains, which partially explains the poor hot working ability of Ti–V–Cr-type burn-resistant titanium alloys. Notably, this study on Ti40 burn-resistant titanium alloy yields important information related to the optimization of the microstructures and mechanical properties.     

弥散铜材料的高温本构方程

弥散铜是一种新型的粉末体电极材料 ,在加工制备过程中其变形行为会不同于致密体 .针对粉末体材料的变形特性 ,提出了弥散铜的高温本构方程的数学模型 ,并通过大量的热模拟压缩实验 ,确定了该材料高温本构方程的具体形式     

挤压态CuCr25合金热变形行为及其加工图

在Gleeble-3500D热模拟试验机上,对挤压态CuCr25合金在应变速率为0.01~10s~(-1),变形温度为750~900℃的条件下进行恒温压缩模拟实验.结果表明:挤压态CuCr25合金在热变形过程中流变应力随变形温度升高和应变速率降低而减小;可用双曲正弦模型来描述合金的流变行为,其平均激活能为383.4kJ/mol;基于动态材料模型获得了挤压态CuCr25合金的热加工图,并结合金相显微组织分析得到了该合金在实验参数范围内较优的热加工工艺参数范围:加工温度830~900℃,应变速率为0.01~0.1s-1.     

T122耐热钢热变形加工图及热成形性

在Gleeble 3500热模拟试验机上进行热压缩实验. 采用动态材料模型理论、双曲线本构方程及Liapunov稳定性判据,建立了T122耐热钢热变形加工图. 利用所建立的加工图,分析了不同温度和应变速率下T122钢的热成形性及其与显微组织的关系. 结果表明:T122钢在1085℃以上、应变速率小于0.37s-1压缩变形时,功率耗散效率达到峰值0.2,此时发生了完全动态再结晶;对于工业热加工,建议在变形温度为1085～1150℃和应变速率大于0.13s-1的范围内选择加工参数.     

6063铝合金高温流变本构方程

采用圆柱试样在G1eeb1e—1500热模拟机上进行高温等温压缩实验，研究了6063铝合金在高温塑性变形过程中流变应力的变化规律．结果表明：应变速率和变形温度的变化强烈地影响6063铝合金流变应力，流变应力随变形温度升高而降低，随应变速率提高而增大，在高应变速率下出现明显的动态软化．     

高锰TWIP钢热变形行为及应变补偿型本构方程的建立

对高锰TWIP钢进行不同温度(850~1100℃)和应变速率(0.01,0.1,1,5,10s^-1)的绝热压缩试验,研究试验钢高温热变形行为. 分析了变形温度和应变速率对流动特性的影响,建立了应变补偿型本构方程,并采用三种标准统计参数对应变补偿型本构方程的精确度进行了评估. 结果表明:流动应力对变形温度和应变速率的敏感程度很高,且随着变形温度的提高或应变速率的降低,流动应力呈下降趋势;应变速率对动态再结晶过程有着很复杂的影响;流动应力预测值与试验值具有较高的吻合度,表明建立的应变补偿型本构方程能够精确预测流动应力.     

一种含氮高铬冷轧辊用钢的热变形行为研究

对一种8%Cr冷轧辊用钢在950～1200℃以0.1～10s^-1的变形速率进行热压缩变形,通过流变曲线分析、动力学分析及热加工图技术等方法表征其热变形时的力学行为,并对变形后的显微组织进行观察。结果表明:Cr8N钢的加工硬化率和流变应力随着变形温度的升高和应变速率的降低而降低,功率耗散百分数随着Z参数的增大而降低;上述变形条件下Cr8N钢的热变形激活能为542kJ/mol,加工硬化指数为5.25;获得了该钢的热变形方程以及Z参数和峰值应力间的关系。     

真空热压烧结CuW30复合材料的热压缩变形特性

采用真空热压烧结法制备了CuW30复合材料,在Gleeble-1500D热模拟机上对该材料进行等温热压缩模拟试验.研究了温度为650~950 ℃、应变速率为0.01~5 s^-1、最大变形量为50%条件下的流变应力行为.结果表明：CuW30复合材料存在明显的动态再结晶特征.材料的稳态流变应力随应变速率的增大而增大,在恒应变速率条件下,合金的真应力水平随温度的升高而降低.热变形过程的流变应力可用双曲正弦本构关系来描述.在给定的变形条件下,计算的热变形激活能为231.150 kJ/mol.根据试验分析,合金的热加工宜在850~950 ℃范围内进行,应变速率为0.01~0.1 s^-1.