Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe合金热加工性能研究

通过对真空非自耗电弧炉制备的Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe(x=0, 1,2, 3, 5, at%) 5种铌硅合金的热变形行为进行探索和研究,分别绘制了5种铌硅合金的热加工图,并分析了不同变形参数下合金显微组织的变化,确定了各合金的最佳变形工艺范围,为后续铌硅合金的设计及热加工研究提供了理论依据。合金耗散效率因子η的最大值出现在低应变速率及高温区域;最小值则出现在低温和高应变速率区域。不同Fe含量合金的热加工图中均存在失稳变形区,主要分布区域与低耗散效率因子区重合,同时,失稳区晶粒明显拉长,晶界出现弯曲扭折现象,晶粒大小分布不均匀,发生了局部塑性流动。稳定变形区存在链状的动态再结晶组织,细小的再结晶晶粒沿晶界分布,随着变形温度的升高和应变速率的降低,动态再结晶晶粒的尺寸增大。     

基于动态材料模型的Cr8钢的热加工图

采用Gleeble-1500D热模拟试验机对Cr8钢进行了高温压缩试验,研究了Cr8钢在变形温度为900～1200℃、应变速率为0. 005～5 s~(-1)条件下的热变形行为。基于试验得到Cr8钢的真应力-真应变曲线,采用动态材料模型和Ziegler失稳判据建立了Cr8钢的热加工图。结果表明:当应变速率小于1 s~(-1)时,该合金的热变形流变曲线呈现出典型的动态回复型特征;材料的失稳区主要发生在高应变速率的区域,并且随着应变的增加,功率耗散因子增加。根据已建立的热加工图,得到了Cr8钢的最佳加工工艺参数为变形温度1125～1190℃、应变速率0. 005～0. 01 s~(-1)。分析加工图中非失稳区的金相照片,该材料的显微组织发生了动态再结晶,获得的组织晶粒细小且分布均匀;分析加工图中失稳区的金相照片,该材料的显微组织中出现了很多剪切带,验证了该热加工图的正确性。     

基于DMM加工图的7050铝合金热塑性变形参数优化识别

采用Gleeble-1500热物理模拟试验机对7050铝合金在变形温度573～723 K、应变速率0.01 ～10 s-1、最大压缩量80％的条件下进行了等温压缩实验,得到该合金多组真实应力-应变数据,以此作为计算应变速率敏感指数(m值)、功率耗散系数(η值)、失稳判据(ζ值)三重判据的底层材料数据.通过m值、η值和ζ值的正负分布而三重递进识别出不同应变下稳定变形参数区和失稳区,最后将不同应变下的功率耗散图和失稳图叠加以构建含应变影响的系列加工图,基于此识别出高η值和高ζ值的最优化稳定变形参数区,以及负m值、负η值和负ζ值的最大化失稳变形参数区,可以为确定最佳的热变形工艺参数提供理论指导.     

一种新型的电火花加工工艺模型优化方法

电火花加工过程中,由于工艺参数与加工效果间的高度非线性,导致难以建立精确的数学模型.针对这种情况,文章分析了电火花加工工艺的特点及其复杂性,提出了基于微粒群优化算法的电火花加工工艺选择模型,该模型能模拟熟练操作者的决策过程.测试结果表明,该模型能真实反映机床本身的工艺特点,模型预测值和实际测量值相差较小,能实现在给定加工要求下电加工参数的自动选择.     

基于热加工图的双相不锈钢热成形机制及工艺优化

采用Gleelbe-3500热力模拟试验机对2507双相不锈钢在900～1 150℃,以0.01～10 s^-1的应变速率进行了单向热压缩试验,以研究热变形参数对其热加工行为的影响。根据热压缩变形时的真应力-真应变曲线获得双相不锈钢基于动态材料模型理论的热加工图,并通过金相检验对热加工图进行验证。结果表明：2507双相不锈钢的真应力-真应变曲线有两个特征,即高温或应变速率较大时的动态回复和低温或应变速率较小时的动态再结晶。根据热变形方程计算得到该双相不锈钢的热变形激活能Q为473.01 kJ/mol,并构建了峰值应力本构方程。结合不同变形条件下的应力-应变曲线和显微组织,建立了2507双相不锈钢的热加工图,并确定了其最佳的热加工工艺区间为变形温度950～1 100℃,应变速率0.01～0.85 s^-1,该区域的功率耗散系数均大于0.3,发生了明显的奥氏体动态再结晶。     

20CrMnTiH热变形行为及加工图

采用热模拟压缩实验获得20CrMnTiH材料温度范围为973~1173K和应变速率为0.01s-1~10s-1情况下的真应力-应变曲线,并绘制出材料热加工图。通过不同应变下20CrMnTiH材料加工图叠加,得到材料最佳变形工艺参数区间和材料失稳工艺参数区间。     

TC11钛合金热变形机制及其热加工图

研究了TC11钛合金在温度800～1050℃,应变速率0.005～5s-1条件下的高温压缩变形行为,基于动态材料模型建立了热加工图,并结合变形微观组织观察确定了该合金在实验条件下的高温变形机制.结果表明:TC11钛合金在两相区低应变速率下(0.005～0.05 s-1)变形时主要发生片状组织的球化,并且球化的效果随变形温度的降低和应变速率的增加而增加.在两相区高应变速率下(0.05～5 s-1)变形时发生热加工的非稳定流动,产生剪切裂纹和剪切带等缺陷.在β相区低应变速率下(0.005～0.05 s-1)变形时发生动态再结晶,高应变速率下(0.05～5 s-1)发生动态回复,并且应变速率大于0.1 s-1时有可能发生不稳定流动现象.在变形温度为900℃左右、应变速率为0.005 s-1时,功率耗散率达到峰值,约为57%.     

基于热加工图的铝合金6061变形行为研究

在Zwick/Roell Z020万能材料试验机上实施高温压缩试验,研究铝合金6061在变形温度范围为360～480℃,应变速率在0.001～1s-1时的热变形行为。基于动态材料模型理论,利用matlab进行三次样条插值,获取足够的数据利用origin软件绘制铝合金6061的功率耗散图。利用功率耗散图分析确定了试验参数范围内热变形过程的最佳工艺参数。在加工温度为360～440℃,应变速率为0.001～0.01s-1之间,功率耗散率的最大值为0.39,是该合金的最佳成形区域。     

Application of dynamic recrystallization model for the prediction of microstructure during hot working

During hot working operation, the work-piece deforms to the shape of the die geometry at the imposed deformation rates and temperatures. Deformation processing maps, obtained based on the concepts of Dynamic Materials Modeling, can be used to identify optimum deformation conditions. Dynamic Recrystallization (DRX) is shown to be the operating softening mechanism at these optimum deformation conditions, and results in predictable microstructures. The model proposed for explaining the microstructural evolution during DRX is extended to predict the resulting microstructure based on the information about the deformation loads and work-piece temperatures. The model predictions are validated on Al and Cu. This model can be applied for on-line process control, provided the metal forming equipment is appropriately instrumented.     

Processing map for hot working of as extruded AZ31B magnesium alloy

The deformation behavior of AZ31B magnesium alloy as extruded under hot compression conditions was characterized in the temperature range of 200 - 400 ℃ and strain rate range of 0. 001 - 1 s^-1. The processing maps were obtained at different strains. The results show that the map exhibits flow instabilities as two domains. The domain at beyond 300 ℃ and strain rate of 1 s^-1 appears with a peak efficiency of power dissipation about 56% occurring. This domain is expected to happen in a hot process, such as hot rolling, hot extrusion and hot forging. There is high efficiency of power dissipation at temperature beyond 350 ℃ and strain rate 0. 001 s^-1. Such domains suggest the occurrence of superplastic deformation.     

Hot working characteristics of HEXed PM nickel-based superalloy during hot compression

To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy, hot compression tests were conducted in the temperature range of 1020–1110 °C with the strain rates of 0.001–1 s⁻¹. It is found that the flow stress of the superalloy decreases with increasing temperature and decreasing strain rate. An accurate constitutive equation is established using a hyperbolic-sine type expression. Moreover, processing map of the alloy is constructed to optimize its hot forging parameters. Three domains of dynamic recrystallization stability and instability regions are identified from the processing map at a strain of 0.7, respectively. The adiabatic shear band, intergranular crack and a combination of intergranular crack and wedge crack are demonstrated to be responsible for the instabilities. Comprehensively analyzing the processing map and microstructure, the optimal isothermal forging conditions for the superalloy is determined to be t=1075–1105 °C and =10⁻³–10^−2.8 s⁻¹.     

Processing map for hot working of SiC_p/7075 Al composites

The hot deformation behaviour of 7075 aluminium alloy reinforced with 10%of SiC particles was studied by employing both"processing maps"and microstructural observations.The composite was characterized by employing optical microscope to evaluate the microstructural transformations and instability phenomena.The material investigated was deformed by compression in the temperature and strain rate ranges of 300-500℃and 0.001-1.0 s-1,respectively.The deformation efficiency was calculated by strain rate sensitivity(m)values obtained by hot compression tests.The power dissipation efficiency and instability parameters were evaluated and processing maps were constructed for strain of 0.5.The optimum domains and instability zone were obtained for the composites.The optimum processing conditions are obtained in the strain rate range of 0.1-0.9 s-1and temperature range of 390-440 ℃with the efficiency of 30%.     

DH780钢的热变形行为及热加工图

采用Thermecmastor-Z热模拟试验机研究了试验钢在800~1150 ℃、应变速率0.01~10 s^-1的热压缩变形行为,并观察变形后显微组织。基于试验数据分析,确定了试验钢在奥氏体区的热变形方程,建立试验钢在0.8真应变下的热加工图。结果表明:试验钢的流变应力和峰值应变随变形温度的升高而减小;试验钢在奥氏体区的热变形激活能为385.91 kJ/mol。根据试验钢功率耗散及流变失稳判据确定最佳热加工工艺参数为热变形温度范围1050~1150 ℃和应变速率0.01~0.1 s^-1。在该范围内,试验钢发生完全动态再结晶,功率耗散系数为17%~32%。     

基于热拉伸试验的DP590高强钢变形本构关系及热加工图

在变形温度为1123~1423 K和应变速率为0.01~10 s-1条件下,对DP590高强钢进行高温热拉伸试验,得到其真应力-真应变曲线,分析了温度和应变速率对DP590高强钢热变形时流动应力的影响。结果表明,当应变量一定时,流动应力随应变速率的升高和温度的降低而增大。基于热拉伸试验数据,通过线性回归分别确定了在峰值应力下DP590高强钢的高温材料常数:应变硬化指数n=3.194,热变形激活能Q=508.29 k J·mol-1,α=0.0153和A=2.126×1017s-1。构建了DP590高强钢的Arrhenius双曲正弦本构关系,与试验值相比,模型的最大误差为7.8%,最小误差为0.18%。根据DMM动态材料模型建立了DP590高强钢在应变为0.3条件下的热加工图,确定了DP590高强钢的适宜热成形区为:应变速率为0.01~0.1 s-1,变形温度为1250~1375 K。     

两种冶炼工艺下A286高温合金的热变形行为

为了探究真空感应+真空自耗(VIM+VAR)和电炉+精炼+真空自耗(EAF+LF+VAR)两种工艺冶炼A286高温合金的热变形行为,利用Gleeble-3800热模拟试验机在温度950~1150 ℃和应变速率0.01~10 s^-1范围内进行热压缩试验。基于摩擦和绝热加热修正后的真应力-真应变曲线和应变硬化率曲线建立了A286合金的Arrhenius本构方程,确定了VIM+VAR合金和EAF+LF+VAR合金的热激活能分别为358.15和372.54 kJ·mol^-1。利用临界应变和动态再结晶体积分数50%应变引入动态再结晶速度参数k_v,建立新的动态再结晶模型。采用Prasad 准则绘制两种钢在应变0.2、0.5和0.9下的热加工图,并结合组织分析,确定VIM+VAR合金的最佳热加工工艺条件为1050~1100 ℃,0.01~1 s^-1和1100~1150 ℃,0.1~10 s^-1;EAF+LF+VAR合金的最佳热加工工艺条件为1050~1100 ℃,0.01~1 s^-1和1100~1150 ℃,0.1~3 s^-1,得出VIM+VAR合金的热加工区间较宽,其热加工性能优于EAF+LF+VAR合金。     

基于热加工图的20CrMnTiH钢热成形性能及斜齿轮热成形模拟

针对齿轮材料20Cr Mn Ti H钢的热加工工艺优化的需求,建立了其基于动态材料模型(DMM)的不同应变下的热加工图,揭示了应变对其加工性能的影响规律,得到了成形过程中的安全区和失稳区,并获得了该材料最佳热加工工艺窗口。结合有限元组织模拟和微观组织观察分析,验证了热加工图的可靠性和其热变形组织模拟的准确性。基于DEFORM-3D建立了斜齿轮变形-传热-微观组织演化耦合的有限元模型,结合热加工图所获得的优化变形温度和变形速率区间,模拟分析了斜齿轮热精密成形微观变形规律。