Prediction of hot deformation behavior in Ni-based alloy considering the effect of initial microstructure

High temperature heat treatments were conducted for as-cast N08028 alloy to obtain various microstructures with different amounts of σ-phase,and then hot compression tests were carried out using Gleeble-3500 thermo-mechanical simulator in deformation temperature range from 1100 to1200 ℃ and strain rate range from 0.01 to 1 s-1. For the same initial microstructure, the flow stress was observed to increase with increasing the strain rate and decreasing the deformation temperature, while for the same deformation condition, the flow stress was found to increase with increasing the amount of σ-phase in the initial microstructure. Moreover, dynamic recrystallization was found to be the main dynamic soften mechanism. On this basis, Arrhenius-type constitutive equations and artificial neural network(ANN) model with back-propagation learning algorithm were established to predict hot deformation behavior of the alloy. Furthermore, the parameters of constitutive equations were found to be dependent on the initial microstructure, which was also as one of the inputs for the ANN model. Suitability of the two models was evaluated by comparing the accuracy, correlation coefficient and average absolute relative error, of the prediction. It is concluded that the ANN model is more accurately than the constitutive equations.     

Hot deformation behavior and the processing map of Zr–1.0Be alloy in single α phase

The hot deformation behavior,hot workability and dynamic recrystallization evolution of Zr-1.0(wt%) Be alloy in single a phase were investigated by conducting hot compression tests.The strain rates ranging from 10~(-3) s~(-1) to 10° s~(-1) and testing temperatures varying from 650 ℃to 850℃ were used.Flow stress was found to increase with increasing strain rate and decrease with the increment of the deformation temperature.A constitutive equation of flow behavior was established to describe the dependence of flow stress on strain rate and deformation temperature.The activation energy for deformation of Zr-1.0Be alloy was determined to be Q= 301 kJ/mol.The processing map of Zr-1.0Be alloy was constructed at strain rates ranging from 10~(-3) s~(-1) to 10° s~(-1) and deformation temperatures varying from 650 ℃ to 850 ℃ at the true strain of 0.7.A processing map was used to identify the best domains of thermal processing,including a domain at a temperature of 650 ℃ and strain rate of 10~(-3) s~(-1) as well as another domain at deformation temperatures ranging from 800 ℃ to 850 ℃ and strain rates varying from 10~(-3) s~-~(-1) to 10~(-1) s~(-1).Microscopic analysis of Zr-l.OBe alloy showed that the flow instability and kink were very obvious at low temperatures and high strain rates.At high temperatures and low strain rates,the dynamic recrystallization became the main softening mechanism during hot working.     

基于ANSYS有限元的Ag-Cu-Ti合金钎焊金刚石磨粒残余应力分析与优化研究

研究金刚石包埋深度分别为20%、40%、50%、60%、80%的钎料对单层钎焊金刚石工具性能的影响。利用有限元软件ANSYS对Ag-Cu-Ti合金钎焊金刚石过程中形成的残余应力进行数值模拟,采用线性和静态的分析方法。研究结果表明,最大应力值位于金刚石和钎料界面结合处的最底部,应力从金刚石底部到顶部逐渐减小,金刚石受拉应力,钎料和工具基体受压应力。当金刚石的包埋深度介于20%与40%之间时,钎焊残余应力最小。     

一体式电液复合制动系统轮缸压力的精细调节

针对基于一体式主缸的电液复合制动系统,进行了轮缸压力的精细调节研究,分析了一体式复合制动系统轮缸压力调节过程及其结构特点.探讨了制动间隙对盘式制动器轮缸压力调节的影响,确定了轮缸压力控制的非线性区及线性区,采用阶梯估算和基本插值数表的方法对轮缸压力进行估计,并考虑了线性区轮缸活塞运动迟滞特性对插值数表的影响,综合上述因素制定了分段阶梯查表的轮缸压力精细调节策略.采用xPC target搭建了硬件在环仿真台架,进行了正弦曲线跟随和与单一增/减压数表法的对比试验.试验结果表明:轮缸压力能够实时跟随目标曲线变化,所提出的结构及控制方法能够满足轮缸压力精细调节的控制需求.     

再结晶退火对ECAP变形5083铝合金力学性能的影响

为改善5083铝合金的力学性能,先后对其进行一道次等通道转角挤压处理及再结晶退火处理,再进行拉伸实验,分析变形温度、变形速率对合金伸长率和抗拉强度的影响,并观察合金的断口形貌.结果表明,在拉伸温度为100℃,应变速率为6.67×10-4 s-1时,合金的抗拉强度最高,达到319.7 MPa;当拉伸温度为300℃,应变速率为1.67×10-4 s-1时,合金的伸长率最大,达到75.8％.在拉伸变形过程中,合金出现应变硬化和应变软化现象,并且伴随有锯齿形流变现象.拉伸试样的断裂形式宏观表现为韧性断裂,微观形式为穿晶断裂,断口形貌由韧窝组成.随着变形温度的升高,韧窝的数量增多,尺寸变大,分布变均匀.     

镁合金薄带双辊铸轧过程的数值模拟

基于立式薄带双辊铸轧工艺的特点,采用有限元法求解镁合金薄带双辊铸轧过程的三维宏观传输方程,并应用ANSYS软件的智能网格划分技术,实现了对铸轧过程中熔池内部温度场、速度场及凝固过程的耦合模拟.分析了铸轧速度及浇注温度等主要工艺参数对熔池内流场、温度场和凝固终了点的影响规律.研究结果表明,随着浇注温度和铸轧速度的增加,熔池出口处的温度升高,凝固终了点向熔池出口处移动.通过对模拟结果的讨论,给出了适合镁合金薄带铸轧过程的工艺参数:浇注温度为640~660℃,铸轧速度为20~30 m/min.     

等径角挤压工艺对Ti5553合金冲蚀磨损性能的影响

摘要： 考察了经等径角挤压（ECAE）处理前后的Ti5553合金在含泥沙海水环境中的冲蚀磨损特性,采用扫描电子显微镜观察冲蚀磨损后的试样表面形貌并结合MATLAB软件进行定量分析,探讨了Ti5553合金显微组织、力学性能及冲蚀机理的演变对其冲蚀磨损性能的影响.结果表明：经ECAE处理后,Ti5553合金的抗冲蚀磨损性能明显提高,这是由于ECAE工艺能够通过细晶强化而提高Ti5553合金的强度与韧塑性、改善其微观组织所致;未经ECAE处理的Ti5553合金的冲蚀磨损机理为冲击变形及犁沟剥落,并伴随大面积划痕和冲击坑裂纹的产生,而经ECAE处理的Ti5553合金的冲蚀机理为轻微冲击变形及犁沟剥落,划痕和冲击坑裂纹的扩展趋势不明显.     

放电等离子烧结参数对 Al70Si30合金组织及性能的影响

探讨了放电等离子烧结（Spark Plasma Sintering ,SPS）技术对Al70 Si30合金中初晶硅分布、生长以及对其力学性能的影响。通过X射线衍射仪（XRD ）,扫描电子显微镜（SEM ）图谱分析发现,在500 M Pa ,590 K的烧结条件下,合金中的初晶硅尺寸保持在10μm左右。烧结后块体合金的维氏硬度达到190,致密度达到98．2％。     

美国体育类专业硕士发展历程及特点

随着现代体育专业硕士培养方式的不断更新与发展,越来越多的体育管理人才为不同的专业领域提供专业服务.作为现代体育类专业人才培养典范的美国,其体育类专业硕士培养特点(培养目标明确,入学机制严格,课程目标协调,实践教学内容丰富,校企合作联合培养),对于中国体育类专业硕士的培养有积极的启示作用.     

热处理对CuNi2Si合金组织和性能的影响

研究了不同预冷变形条件下时效温度及时间对CuNi2Si合金组织和性能的影响.结果表明:合金在880 ℃×2.5 h固溶,经不同预冷变形后时效,具有较强的时效强化特性;同时预冷变形能够促进时效过程中第二相的析出,并具有晶界析出倾向;当预冷变形达40%,500 ℃×1 h时效,合金布氏硬度(HB)达193,抗拉强度(R_m)达765 MPa,伸长率达11%,与未进行预冷变形的合金相比,可获得较高的硬度、强度及较好的综合性能.合金热处理后的拉伸断口为韧性断裂,形貌特征为沿晶型韧窝,这与析出相具有晶界析出倾向的特性一致.