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1.
The hot deformation behavior of a nickel-based superalloy was investigated by means of isothermal compression tests in the strain rate range of 0.001–10 s−1 at 1110 °C. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique were used to study the effect of strain rate on the microstructure evolution of the alloy during hot deformation. The results revealed that the dynamic recrystallization (DRX) process was stimulated at high strain rates (ε̇5s-1) due to the high dislocation density and adiabatic temperature rise. Meanwhile, high nucleation of DRX and low grain growth led to the fine DRX grains. In the strain rate rage of 0.001–1 s−1, the volume fraction of DRX grains increased with the decreasing strain rate, and the grain growth gradually governed the DRX process. Moreover, the strain rate has an important effect on DDRX and CDRX during hot deformation. On the other hand, particular attention was also paid to the evolution of twin boundaries during hot deformation. It was found that there was a lower fraction of Σ3 boundaries at the intermediate strain rate of 1 s−1, while the fractions of Σ3 boundaries were much higher at both the lower strain rates (ε̇0.1s-1) and higher strain rates (ε̇5s-1).  相似文献   
2.
The true stress-strain curves of TC21 titanium alloy charged with up to 0.7 wt.% hydrogen were obtained by the isothermal hot compression tests which were carried out on an Instron 5500 machine at 1023 to 1223 K and 0.001 to 0.1 s−1. The dependence of the steady state flow stress on hydrogen content was determined. The results showed that with the increase of hydrogen content flow stress decreased at lower hydrogen content and then increased at higher hydrogen content. Suitable hydrogen addition can significantly decrease the flow stress and improve the hot workability of TC21 titanium alloy. The flow stress behaviors and the dependence of hydrogen content on flow stress were clarified by microstructural observation. The optimum hydrogen content at different deformation temperature was determined.  相似文献   
3.
利用热加工图分析了FGH4096粉末高温合金的热变形行为,评定了益加工区,预测了变形失稳区;结合热加工图与组织分析建立了此合金在真应变0.65下的微观变形机制示意图。不同应变量下获得的热加工图表现出一致的特征:从低温/低速区到高温/高速区存在明显的益加工带;而低温/高速区和高温/低速区则是被预测的变形失稳区。HIPedFGH4096合金的热加工性能直接受动态再结晶的影响:在低温/低速和高温/高速下发生的完全再结晶及其粗化过程均对应着高的能量耗散率,有利于合金的热加工;而在低温/高速下动态再结晶受到抑制,潜在着原始颗粒边界萌生裂纹而导致变形失稳的可能性。  相似文献   
4.
CVD aluminide coatings deposited on a Directionally Solidified (DS) substrate were oxidized at 1,100 °C up to 240 h under isothermal and cyclic oxidation conditions to study the growth mechanisms of the oxide scales and the possible degradation of the coatings. The specimens were investigated using light and scanning electron (SEM) microscopy, energy-dispersive spectrometry (EDS) and X-Ray Diffraction (XRD). The results indicate that the coatings provide a much greater beneficial effect under isothermal conditions than upon cycling. The cycled specimens undergo oxide-scale spallation and increased roughening, which can derive from growth and thermal stresses as well as from the NiAl → Ni3Al phase transformation associated with Al depletion. Under isothermal conditions, typical oxide scales formed with the appearance of some rumples. However, the origin of rumpling is uncertain from these experimental results.  相似文献   
5.
基于CA算法的轧制工艺动态再结晶过程模拟   总被引:1,自引:1,他引:0  
为研究低碳钢轧制变形过程的组织演化,建立了一套奥氏体动态再结晶模型。利用CA算法,基于Deform研究了热轧过程中的再结晶比率和晶粒尺寸的变化。结合变形条件对模型系数的影响,将模型计算所得的组织演变、再结晶体积分数、晶粒尺寸与实验进行了比较,证明了模型的有效性。  相似文献   
6.
Short fibers and fine particles of β-SiC were obtained by pyrolysis of Colombian rice husk (RH). The synthesis of SiC was carried out in a gas furnace: a mathematical model was developed in order to design and build this equipment and the process was optimized using an experimental design that included variables such as temperature, pyrolysis time, type of catalyst, and process atmosphere. The obtained material was characterized by using FTIR, DRX and SEM for microstructural characterization and EDS technique for chemical analysis.  相似文献   
7.
15Cr-25Ni-Fe基合金高温塑性变形行为的加工图   总被引:13,自引:1,他引:12  
鞠泉  李殿国  刘国权 《金属学报》2006,42(2):218-224
在Gleeble-1500热模拟机上对15Cr-25Ni-Fe基合金GH2674进行了热压缩实验,采用动态材料模型的加工图研究了其在950-1200℃和0.001-10S^-1条件下的热变形行为.结果表明:GH2674合金在热变形时呈现两个微观机制不同的动态再结晶峰区.再结晶Ⅰ区:功率耗散效率峰值为38%,峰值对应的温度和应变速率分别为1040℃与10s^-1;再结晶Ⅱ区:功率耗散效率峰值为40%,峰值对应的温度和应变速率分别为1075℃与0.04s^-1.在1075-1100℃温度区间内,可能是晶界相M382的溶解造成该合金的晶粒粗化,这在一定程度上会影响合金的热加工性能.在应变速率小于0.01s^-1、形变温度高于1050℃条件下,合金呈现晶粒急剧粗化现象,进而导致在热变形过程中楔形裂纹的产生;在应变速率高于0.1s^-1、形变温度低于1000℃条件下,合金有出现剪切变形带的趋势.根据上述加工图对GH2674合金的热变形工艺进行了初步设计.  相似文献   
8.
目的 建立Inconel 718镍基合金动态再结晶组织演变三维介观尺度计算模型.方法 采用Gleeble-1500型热力模拟试验机进行恒温恒应变速率压缩实验,获得Inconel 718高温合金热变形的真应力-应变曲线,并结合光学显微镜分析热变形后的材料的塑性流动规律与组织演化特征,获得材料参数.结果 基于流变和组织行为的分析,建立了考虑动态再结晶特征的组织演变三维元胞自动机模型.结论 该模型可以较准确地描述材料的热变形行为,追踪热变形过程再结晶晶粒的演变,为实际零件的锻造工艺制定提供宏微观计算依据.  相似文献   
9.
使用圆柱形TB6钛合金试样在Thermecmaster-Z型热模拟试验机上进行热模拟压缩实验(变形温度为825~1100℃,应变速率为0.001~1 s-1)。对采集的流变数据进行加工硬化率处理,确定动态再结晶体积分数,研究了TB6钛合金β区变形的动态再结晶动力学。结果表明,流变应力随着变形温度的降低或应变速率的提高而增大,流变曲线呈现出动态再结晶类型的特征。随着应变速率的降低和变形温度的提高,动态再结晶的体积分数和晶粒尺寸增大。在变形温度高于950℃、应变速率低于0.001 s-1条件下,动态再结晶的晶粒严重粗化。动态再结晶动力学曲线经历缓慢增加—快速增加—缓慢增加三个阶段,呈现出典型的“S”型特征。确定了动态再结晶的体积分数达到50%时的应变,建立了TB6钛合金的动态再结晶动力学模型。  相似文献   
10.
在温度950~1200℃、应变速率0.13~6.5 s~(-1)及工程应变50%的条件下,利用Gleeble-3500~(TM)热模拟试验机对喷射成形GH738合金进行热压缩试验,研究了合金的热流变行为并建立了流变本构关系,结合显微组织分析及统计技术研究了合金的组织演变情况。结果表明,流变应力随温度的升高和应变速率的减小而降低。合金热变形激活能为580.81kJ·mol~(-1)。随着形变温度的升高,高位错密度处晶界弓出形核使晶界"锯齿"化并形成项链组织,在1100℃获得完全动态再结晶组织,随温度继续升高及应变速率的降低组织明显长大。  相似文献   
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