P91耐热钢热变形行为及其流变应力本构方程

基于位错反应理论和Avrami方程,建立了包含动态应变时效影响的动态回复与动态再结晶的两阶段本构方程。采用Gleeble3500热模拟试验机对P91耐热钢进行热压缩试验,获得了950～1200℃、0.01～10s-1条件下的P91耐热钢真应力-真应变曲线。利用试验获得的流变应力数据,采用非线性拟合确定了P91钢本构方程中的材料常数。模型的计算结果表明,计算曲线与试验曲线吻合得较好,所建立的本构方程可应用于预测P91钢在950～1200℃、0.01～10s-1条件下热加工变形的流变应力。     

TB8钛合金超塑性拉伸变形流变行为与本构方程

在电子万能拉伸试验机上对TB8钛合金进行了恒应变速率超塑性拉伸试验(变形温度为720~880℃,应变速率为0.000 1~0.01s~(-1)),研究了拉伸流变行为,计算了超塑性拉伸变形激活能和相应的应力指数,建立了TB8钛合金应力-应变本构模型。结果表明,在同一应变速率下,流变应力随变形温度的增加而减少,同一变形温度下,流变应力随应变速率的增加而增加。在变形温度为840℃,应变速率为10~(-4) s~(-1),合金的伸长率最大,为356%;超塑性拉伸变形激活能和应力指数分别为251.25kJ/mol、2.389 5。     

Ti-22Al-25Nb合金板材高温拉伸变形行为的本构模型

在1203～1283 K的温度范围内,以20 K的温度间隔对O相Ti-22Al-25Nb合金进行了等温单向拉伸试验,应变速率为2.5×10^-4、5.0×10^-4、1×10^-3、2×10^-3、4×10^-3、1×10^-2和5×10^-2 s^-1,并对不同变形温度下的试样组织进行了表征。通过实验结果,确定了本构模型的材料常数;α₂+B2/β+O三相区(1203～1243 K)和α₂+B2两相区(1243～1283 K)的拉伸变形激活能分别为845 165和412 779 J/mol。构建了Arrhenius本构模型来描述Ti-22Al-25Nb合金在不同温度下的拉伸变形行为。     

TA15钛合金流变行为的一种本构模型

在Gleeble- 1500热物理模拟机上对多组TA15钛合金试样进行压缩试验,获得了不同变形温度、应变速率和应变下的应力-应变曲线.结果表明,应力迅速达到峰值后呈下降趋势,峰值应力随变形温度的升高而减小,随应变速率的增加而增大;引入包含软化因子的本构模型,并采用多元线性回归法可求解相应的系数.     

TA15合金高低温恒应变速率拉伸变形行为对比研究

为进一步研究钛合金超塑性变形行为,对TA15合金在变形温度700~900 ℃、应变速率1×10?2~1×10?4 s?1条件下进行恒应变速率拉伸实验,对比不同温度、不同应变速率下合金的变形行为。结果表明:TA15合金在初生等轴α相平均尺寸15 μm的条件下,拉伸试样的伸长率为73.3%~250.0%;在850 ℃、1×10?4 s?1变形条件下,试样伸长率最高;在700~750 ℃下,合金表现出的峰值应力较大;在750 ℃、1×10?4 s?1变形条件下,试样伸长率为183.3%。合金试样仅在高温及低应变速率条件下出现稳态流变阶段,该阶段持续时间越长,合金的伸长率越高。变形后的TA15合金组织均发生不同程度的长大,经高温、低应变速率的变形,试样组织粗化现象最为明显。     

Deformation Behavior of Finely-Lamellar Pearlite During Multiple Cold Plastic Deformation of Eutectoid Steel

Metal Science and Heat Treatment - Deformation behavior of finely-lamellar pearlite in steel with 0.78% C during multiple cold plastic deformation by drawing is considered. It is revealed that...     

Deformation Mechanisms of Ti-6Al-4V During Tensile Behavior at Low Strain Rate

A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 × 10⁻⁴ s⁻¹ and at temperatures up to 1050 °C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800 °C; this is quite a bit lower than the 925 °C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

TL1438高温流动应力应变本构方程的建立

利用Gleeble-3500热模拟机对TL1438非调质钢钢进行高温压缩试验.研究了变形速率和变形温度对TL1438钢热变形行为的影响,得出热变形时该钢的相关参数值.根据含有Zener-Hollomon参数的双曲正弦函数建立了TL1438钢高温条件下流动应力应变的本构方程,以期为模拟TL1438钢热锻过程提供依据.     

LY12合金低温拉伸变形行为研究

对人工时效后的LY12合金进行了不同温度系列拉伸试验,采用SEM和光镜对断口及其附近的显微组织进行观察,研究了温度对LY12合金拉伸变形行为的影响。结果表明,LY12合金正常时效时析出相的主要成分为Al2CuMg,随温度的逐步降低,析出相发生脆性断裂的可能性更大。同时析出相与基体分离需要吸收更多外界能量,从而使LY12合金的抗拉强度与屈服强度随温度的逐步降低单调增加;随温度的逐步降低,析出相的脆性断裂降低了对位错的阻碍作用,使位错滑移距离增长,因此材料的伸长率呈增长趋势。     

Microstructure Evolution and Strain-Dependent Constitutive Modeling to Predict the Flow Behavior of 20Cr–24Ni–6Mo Super-Austenitic Stainless Steel During Hot Deformation

Hot compression tests were carried out with specimens of 20 Cr–24 Ni–6 Mo super-austenitic stainless steel at strain rate from 0.01 to 10 s~(-1) in the temperature range from 950 to 1150 °C, and flow behavior was analyzed. Microstructure analysis indicated that dynamic recrystallization(DRX) behavior was more sensitive to the temperature than strain rate, and full DRX was obtained when the specimen deformed at 1150 °C. When the temperature reduced to 1050 °C, full DRX was completed at the highest strain rate 10 s~(-1) rather than at the lowest strain rate 0.01 s~(-1) because the adiabatic heating was pronounced at higher strain rate. In addition, flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation, especially at higher strain rates and lower temperatures. Therefore, flow curves were revised in consideration of the effects of adiabatic heating and friction during hot deformation. The results showed that adiabatic heating became greater with the increase of strain level, strain rate and the decrease of temperature, while the frictional effect cannot be neglected at high strain level. Moreover, based on the revised flow curves, strain-dependent constitutive modeling was developed and verified by comparing the predicted data with the experimental data and the modified data. The result suggested that the developed constitutive modeling can more adequately predict the flow behavior reflected by corrected flow curves than that reflected by experimental flow curves, even though some difference existed at 950 °C and0.01 s~(-1). The main reason was that plenty of precipitates generated at this deformation condition and affected the DRX behavior and deformation behavior, eventually resulted in dramatic increase of deformation resistance.     

低碳钢在恒速率变形条件下的应变硬化行为研究

研究了低碳钢在恒变形速率条件下的拉伸应变硬化行为。结果表明:在恒变形速率条件下,屈服后的应变硬化阶段并不满足Hollomon所建立的应力-应变关系(σ=Kεn),而满足关系式:σ=exp[Alnε+B2(lnε)2+C]。并依据此关系式推导出临界颈缩条件下真应变所满足的关系式。     

基于人工神经网络的DP780钢拉伸变形行为研究

采用增加动量项和学习率自适应调整的BP算法建立了DP780钢拉伸变形行为的人工神经网络预测模型。预测结果表明:采用改进BP算法建立的人工神经网络模型能够较为准确的预测出DP780钢拉伸变形规律。     

Mg-Zn-Zr-Y合金高温塑性变形本构模型及流变行为预测

采用Gleeble热力模拟试验机对Mg-Zn-Zr-Y合金进行了高温压缩变形实验,分析了合金在变形温度为573~723K、应变速率为0.001~1 s-1范围内的流变行为。结果表明,热变形条件对流变特征和流变应力影响显著,流变曲线呈现"饱和非线性"和"正偏态分布"2种特征,应力水平随着变形温度的降低和应变速率的增大而提高。基于Arrhenius和Zener-Holloman方程,线性拟合确定了合金的表观变形激活能(Q=152.307 k J·mol~(-1))和应力指数(n=5.521)等参数,建立了描述塑性流变行为的本构方程。结果显示,该本构模型数值计算出的流变应力理论值与实验结果的吻合程度依赖于热变形条件的取值范围,与"饱和非线性"稳态流变特征的塑性变形行为基本吻合;而与加工硬化突出的"正偏态分布"流变行为存在一定偏差,引起理论峰值应变前移,但峰值应力水平仍基本符合。表明该本构模型在Mg-Zn-Zr-Y合金中表现出较好的实用性,尤其适用描述高变形温度(623 K)和低应变速率(0.01 s~(–1))下稳态塑性变形行为。     

冷轧钢板中弱界面对拉伸行为的影响

Q235钢经冷轧－时效－再结晶处理后，钢中存在大量弱界面。应用TEM和SEM观察钢的微观组织结构及拉伸断口。结果表明，弱界面有阻碍位错运动、偏转主裂纹扩展方向的作用，可形成分层断口。这种断裂方式使断口表面积增加，显著提高了材料的力学性能。     

喷射沉积7075/15SiCp铝基复合材料高温拉伸变形与断裂行为

在300～450℃和0．001～0．1s6-1的条件下,对喷射沉积7075／15SiCp铝基复合材料板材的高温拉伸变形与断裂行为进行了研究，用扫描电镜（SEM）观察拉伸断口。结果表明，流变应力随温度的升高而下降，表现出相当的应变软化直至断裂。伸长率随着温度的升高和应变速率的降低而增加，但其应变速率敏感系数最大值仅为0．24,表明不存在超塑性，变形激活能为379kJ／mol，比基体7075铝合金变形激活能高。拉伸断裂行为主要由延性断裂机制控制，其基体金属可见大量局部塑性变形特征，无界面滑移是导致喷射沉积7075／SiCp复合材料过早断裂而不出现超塑性的主要原因。     

FGH96粉末高温合金双道次热变形行为及其本构方程

采用Gleeble-1500热模拟试验机对FGH96合金进行双道次变形量为45%+25%的等温热压缩实验,研究了变形温度为1050~1125℃,变形速率为0.001~0.1 s-1的热变形行为和组织变化,建立了包含应变量、变形温度、变形速率的双道次热变形本构方程,结果表明:FGH96合金的第1道次和第2道次的压缩应力应变曲线有相同的变化规律,两道次流变应力均受到γ′溶解以及由此造成晶粒长大的影响;由本构方程计算的模拟值与实验实测值具有良好的拟合性,模拟值能真实地反映应力在不同变形条件下的变化规律;选择变形温度:1075~1100℃、变形速率:0.01~0.1 s-1时能获得理想的热变形组织。     

Effect of Preliminary Cold Working on High-Temperature Tensile Behavior of Nickel-Free High-Nitrogen Austenitic Steel

Metal Science and Heat Treatment - The effect of solution treatment and preliminary cold working on the high-temperature tensile behavior of a high-nitrogen nickel-free corrosion-resistant...