Cu-Ni-Si-Ag合金动态再结晶及组织演变

在Gleeble-1500D热模拟试验机上,采用高温等温压缩试验,对Cu-2.0Ni-0.5Si-0.15Ag合金在应变速率为0.01～5s-1、变形温度为600～800℃、最大变形程度为60%条件下的流变应力行为进行了研究.分析了实验合金在高温变形时的流变应力和应变速率及变形温度之间的关系.并研究了在热压缩过程中组织的变化.结果表明:热模拟实验中,应变速率和变形温度的变化强烈地影响合金流变应力的大小,流变应力随变形温度升高而降低,随应变速率提高而增大.从流变应力、应变速率和温度的相关性,得出了该合金高温热压缩变形时的应力指数n,应力参数α,结构因子A,热变形激活能Q和流变应力方程.合金动态再结晶的显微组织强烈受到变形温度的影响.     

2219铝合金热加工及组织演化

利用Gleeble-1500试验机进行变形温度为400~480℃、变形速率为0.001~10 s^-1的单轴热压缩试验,得到了不同变形条件下的真应力-真应变曲线,建立了不同应变量下的热加工图,研究了挤压态2219铝合金在不同变形条件下的微观组织演变规律。研究表明:在所选择的变形区间内,变形抗力随着变形温度的增加以及变形速率的降低而降低。分析了不同应变量条件下的2219铝合金热加工图,并结合微观组织进行验证,结果吻合良好。最终,确定了2219铝合金最佳热变形区间为:应变速率为0.001~0.368 s^-1、变形温度为430~480℃,在所确定的可加工区域动态软化机制为动态再结晶,热加工之后晶粒为均匀等轴状。     

Hot deformation behavior and microstructure evolution of titanium alloy Ti-Al-Zr-Sn-Mo-Si-Y

Samples of Ti-Al-Zr-Sn-Mo-Si-Y alloy were compressed on the Gleeble-1500 heat stimulation machine. The compression test was carried out in the temperature range from 800 ℃ to 1 100℃ and strain rate range from 0.001 s^-1 to 10 s^-1. Stress-strain behavior and variation of microstructure of the alloy during hot compression were investigated. The experimental results show that the alloy is sensitive to temperature and strain rate, and the flow softening behavior is more obvious with the decrease of deformation temperature. At higher strain rate, discontinuous yielding is observed in β phase region. When deformed in α＋β phase region, with the increment of deformation temperature, the lamellar a structures globularization is more quick and more uniform. When deformed in β phase region, coarse β grains can be got because of high deformation temperature.     

Coupled deformation and compositional evolution in a thin layer alloy material

In a discussion of spinodal decomposition in solid solutions, Cahn [Acta Met. 9 (1961) 795] showed that stress due to elastic misfit could have a strong stabilizing influence on a uniform composition. The purpose here is to illustrate that the stabilizing influence is diminished significantly in small material structures, for example, thin layers or particles, as a consequence of proximity of material to free surfaces.     

GH3128合金的高温流变行为与组织演变规律

通过对GH3128合金进行热模拟压缩试验,研究了该合金在变形温度950~1150 ℃、应变速率0.01~10 s^-1及应变量30%~70%条件下的流变特征。通过绘制合金流变应力曲线,并基于Arrhenius模型建立了GH3128合金的本构方程。在此基础上,获取了变形量30%~65%的材料加工图,并结合GH3128合金完全再结晶条件图,明确了合金在高温变形过程中组织演变同塑性变形参数之间关系。此外,通过对碳化物的金相分析,探明了合金在热变形过程中碳化物的演变规律。结果表明:GH3128合金热加工激活能约为305 kJ/mol,合理的加工区域为:变形温度1050~1100 ℃,应变速率0.1 s^-1左右。此时合金内碳化物基本回溶,组织再结晶充分,晶粒尺寸可控制在10 μm以下。     

钛合金激光沉积热行为及组织演变

为了考察激光沉积过程热行为对其微观组织的影响,采用了有限元方法对激光沉积过程进行建模,分析了多层多道激光沉积TA15钛合金试样的温度分布及内部节点的热循环特性变化,并对试样的组织进行了考察。模拟结果显示基材和沉积层上任一节点均要经历循环加热和冷却的过程,由于热量累积效应使冷却速度下降,且温度的谷值有上升的趋势。沉积试样的组织由基材的双态组织,经由热影响区,过渡到宏观组织为粗大的初生β晶粒的激光沉积区。因各沉积层经历的热循环和热历史的不同,晶内α相分别呈现针状、片层状和板条状。因冷却速度较快,α相同时在晶界处和β晶内析出,呈现网篮状魏氏体和网篮状混合集束状魏氏体形貌。主要合金元素Al、Zr、Mo、V由基体到激光沉积区均匀分布,无宏观偏析,表明沉积层组织形貌的变化跟成分偏析无关。     

一种新型Ni-Cr-Co基合金的热变形行为及其组织演变研究

采用Gleeble-3800热压缩实验机研究了新型Ni-Cr-Co基合金在1050~1250 ℃、0.001~1 s_^-1条件下的热变形行为,并利用EBSD探讨了变形温度和应变速率对合金组织演变和动态再结晶形核机制的影响。结果表明,流变应力随变形温度的升高而降低,而随应变速率的增大而增加。基于流变应力曲线,建立合金的Arrhenius本构方程和热加工图,得到热变形激活能为520.03 kJ/mol,最佳热加工区间为1175~1250 ℃、0.006~1 s_^-1,该区域最大功率耗散效率为45％。动态再结晶分数随变形温度的升高和应变速率的降低而增加,且动态再结晶过程形成均匀细小的等轴晶粒以及∑3孪晶界。动态再结晶形核主要以晶界“弓出”为特征的不连续动态再结晶机制主导。低温高应变速率下,持续亚晶转动诱导的连续动态再结晶作为辅助形核机制发挥作用。     

Hot deformation behavior and microstructure evolution of TC4 titanium alloy

The hot deformation behavior of Ti-6Al-4V(TC4) titanium alloy was investigated in the temperature range from 650 °C to 950 °C with the strain rate ranging from 7.7×10-4 s-1 to 7.7×10-2 s-1.The hot tension test results indicate that the flow stress decreases with increasing the deformation temperature and increases with increasing the strain rate.XRD analysis result reveals that only deformation temperature affects the phase constitution.The microstructure evolution under different deformation conditions was characterized by TEM observation.For the deformation of TC4 alloy,the work-hardening is dominant at low temperature,while the dynamic recovery and dynamic re-crystallization assisted softening is dominant at high temperature.     

Ti-55钛合金连续冷却转变曲线的测绘及显微组织的演变

通过Gleeble热模拟实验,测绘Ti-55钛合金的连续冷却转变曲线(CCT图)。结果表明:当冷速由0.1℃/S加快到150℃/s时,Ti-55钛合金中主要发生β→α与β→α′的相转变过程,其中β→α′转变开始的临界冷速为5℃/s左右,Ti-55钛合金中马氏体转变开始温度为855℃,转变结束温度为818℃。     

半固态Al-4Cu-Mg合金的变形行为及组织演化

以热模拟压缩实验为基础,研究了变形工艺参数(包括变形温度、应变速率和变形程度)对半固态Al-4Cu-Mg合金变形力学行为和微观组织的影响.研究结果表明:半固态Al-4Cu-Mg合金的流变应力峰值对变形温度和应变速率的变化比较敏感;变形温度和应变速率对稳态流动应力影响较小.应变速率对流变应力峰值的影响与变形温度有关.变形工艺参数对微观组织的影响为:随着变形温度的升高和应变速率的减小,α相晶粒平均尺寸增大,半固态Al-4Cu-Mg合金变形后的组织仍保持近球状组织,这与变形过程中固态α相的流动方式有关.     

Solid solubility extension and microstructure evolution of cast zirconium yttrium alloy

Yttrium addition can improve the oxidation resistance,mitigate hydrogen embrittlement and thus enhance the mechanical properties of the zirconium alloy.To study solid solubility extension of yttrium in zirconium alloy,the lattice parameters of a-Zr phase in Zr–Y alloy were accurately determined by X-ray diffraction(XRD).Yttrium exhibits solid solubility extension in the cast zirconium alloy which forms a metastable supersaturated solid solution with solubility limit of around 3 wt%.The effect of yttrium and thermal treatment on the microstructure of the alloys was investigated by optical microscopy(OM)and scanning electron microscope(SEM).The cast Zr–Y alloy shows a normal polycrystalline structure with dispersed a-Y particles when Y content is lower than 4 wt%,while the alloy shows a eutectic structure with dendrites formation when the Y content is higher.Yttrium exhibits a strong grain refining effect on zirconium alloy and precipitates from the metastable supersaturated Zr matrix after annealing at 700 and 900 °C.     

Fabrication and microstructure evolution of semi-solid LY11 alloy by SIMA

For semi-solid metal forming, it is essential to fabricate the semi-solid materials with spheroidal microstructure. Among several fabrication techniques of the semi-solid materials, (strain-induced melt activation (SIMA) is an ideal candidate with the advantages of simplicity and low equipment costs. In this paper, the microstructure evolution of LY11 alloy (approximately corresponding to ASTM 2017) was investigated in the SIMA process, which had two essential stages: deformation and isothermal heat treatment. The deformation stage was conducted using a CSS-1100C material testing machine and the isothermal heat treatment stage was performed in a resistance furnace. Different levels of deformation temperatures, ram velocities, isothermal temperatures, and holding times were used in this investigation. The microstructure of LY11 alloy was observed by a NEOPHOT-1 optical microscope. The results indicated that the processing parameters must be selected properly to obtain the fine, uniform and spheroidal microstructure by SIMA. The deformation-recrystallization mechanism for microstructure evolution in SIMA process was supported by experimental evidence.     

TC4合金高温拉伸变形力学行为与微观组织演变关联研究

基于TC4合金高温恒应变速率拉伸试验和微观组织观察,研究了工艺参数对TC4合金流动应力、应变速率敏感性指数、应变硬化指数和微观组织演变的影响规律,获得了TC4合金高温拉伸变形时宏观力学行为与微观组织演变的关联机制。结果表明:当变形温度为1123~1213 K、应变速率为0.1 s-1时,TC4合金的拉伸应变不超过0.7就会出现局部颈缩并导致开裂;当应变速率为0.01 s-1、变形温度为1183 K时,TC4合金的应变速率敏感性指数m值最大,归因于该变形条件下初生α相呈等轴状且较细小;当应变速率为0.01 s-1时,随着应变增加,应变硬化指数n值呈逐渐减小的趋势,归因于加工硬化和动态软化的共同作用;随着变形温度升高,初生α相由长条状转变为等轴状,随着应变速率增加,初生α相呈现出明显的取向性,不利于晶界滑动或旋转;应变对初始α相形貌和含量影响较小,但对次生α相影响显著。     

Zr-Sn-Nb-Fe锆合金板材轧制及热处理过程中的晶粒组织演变

采用光学显微镜(OM)和扫描电镜(SEM)分析研究了Zr-Sn-Nb-Fe锆合金板材在热轧及退火→中间冷轧及退火→成品轧制及退火的全工艺流程中晶粒组织的演变规律。结果表明,热轧后合金组织沿轧制方向呈带状分布,晶粒粗大并破碎变形;中间冷轧和成品轧制后合金为沿轧制方向带状分布的细小形变组织,合金组织明显细化;中间退火和成品退火后合金中晶粒再结晶程度较热轧退火时明显提高,晶粒取向差逐渐向正态分布变化,晶粒组织也逐渐均匀化和细化,最终获得细小、均匀分布的完全再结晶晶粒组织,晶粒度12级。     

Texture and microstructure evolution during tempering of gamma-massive phase in a TiAl-based alloy

This work focuses on the mechanisms of microstructure and crystallographic texture evolution during gamma-massive transformation and subsequent tempering treatments, in the case of the Ti–48Al–2Nb–2Cr (at%) TiAl-based alloy. A complete massive structure is obtained by ice-water quenching. The temperature range for the destabilization of this massive structure is estimated from DSC measurement. Then, tempering is performed in both α₂–γ and α–γ phase fields. Microstructure evolution is studied by transmission and scanning electron microscopy observation of samples from different stages of the heat treatments. Isotropic samples resulting from a powder-metallurgy route are used for this purpose. Then, working on the samples from investment casting, the reduction of solidification texture through massive then tempering treatments is analyzed at the light of the mechanisms of microstructure evolution identified previously.     

Al-Li合金弯曲过程中微观组织结构演变与应变集中的DIC/EBSD耦合分析

本文通过SEM、EBSD和DIC相结合的方法对2060-T8铝合金在弯曲变形过程中微观组织结构进行表征并对其损伤机制进行了研究。文章基于DIC和EBSD准原位技术,发展了一种以弥散分布的铜粉末为标记点的同一区域应变测量和微观结构表征技术。实验结果显示合金在弯曲过程中形成了宏观剪切带且裂纹的扩展也是沿着宏观剪切带进行,造成这种现象的原因是由于在形变过程中在宏观剪切带上由于产生了大量的小角晶界,而裂纹沿此方向进行扩展所需的能量是最小的。     

镍基合金焊缝凝固组织演变过程模拟和仿真

建立了一个元胞自动机与有限差分的耦合模型,并将其应用于镍基合金TIG焊熔池凝固过程的模拟.首先对焊接熔池内的各种凝固组织的生长进行了模拟,成功地模拟了平面晶、胞状晶、树枝晶、等轴晶的形态,并与试验结果进行了比照.进一步模拟熔池凝固时的凝固组织不同形态的演变过程,再现了胞状晶到树枝晶、树枝晶到等轴晶的转变过程.同时,采用溶质扩散模型模拟了扩散对溶质场分布的影响.结果表明,模拟结果与试验结果吻合良好.     

Interpretation and optimization of material flow via system behavior reconstruction

In this article, a method for a scalable autonomous data acquisition for an analysis and optimization of production systems based on interpretation of the material flow within small and medium-sized manufacturing enterprises is presented. The data is acquired locally and combined centrally to interpret the material flow as a basis for the optimization of the material flow as well as individual processes. When it is not completely observable for efficiency reasons or due to technical restrictions, one can also reconstruct relevant but unobservable system behavior based on system knowledge and actual measurements. A validation of the method is carried out in a company maintaining engines. The application of the model shows that with the presented method it is possible to reduce buffers in the production, optimize transportation routes and reduce waiting and therefore cycle times in job shop productions for an increasing productivity.     

GH625镍基合金的高温压缩变形行为及组织演变

在Gleeble-1500D热模拟机上采用等温压缩实验研究GH625合金的高温压缩变形行为,获得合金在温度为1000～1200℃、应变速率为10-2～10s-1的条件下的真应力—应变曲线,并在考虑摩擦和变形热效应的基础上对真应力—应变曲线进行修正。对修正后的峰值应力进行线性回归,得到合金的高温材料常数:Q=635.38kJ/mol,α=0.008404MPa-1,n=3.52。通过非线性回归建立GH625合金包含应变量的高温变形本构模型。在应变速率为0.1s-1时,随着热变形温度的升高,合金发生动态再结晶的体积分数随之增加,在1000～1100℃发生部分动态再结晶,当温度达到1200℃时,发生完全动态再结晶,此时平均晶粒尺寸约为22.21μm。     

FeCrNiAl系高熵合金高温氧化行为及组织演变研究

研究了FeCrNiAl系高熵合金的高温氧化行为,建立了合金的氧化动力学模型,同时借助XRD、SEM和能谱分析,对合金氧化物相结构及形貌和成分进行表征,分析了合金的氧化机理。结果表明合金在800~1000℃都是完全抗氧化的,随着氧化温度的提高,合金氧化速率先增加后减小,1000℃的平均氧化速率小于800℃的平均氧化速率;各个温度下试样单位面积的氧化增重与氧化时间的关系满足抛物线规律,计算得到合金的氧化激活能为167.507 kJ/mol;800℃下枝晶内的氧化产物全部是棒状的金红石结构TiO_2,而枝晶间氧化产物则主要是片层状、紧密相连的Cr_2O_3和TiO_2;900和950℃下形成的氧化膜中主要氧化物均为TiO_2,900℃还含有Cr_2O_3和Fe2O3,950℃氧化膜中还含有α-Al_2O_3。在1000℃合金表面仅形成致密的α-Al_2O_3薄膜,使合金表现出更为优异的抗氧化性能。