基于动态材料模型的Ti555211合金热加工图研究

利用Gleeble-3800热模拟实验机,在应变速率在0.001～1.000 s~(-1)以及变形温度在750～950℃范围内对Ti555211合金进行等温恒应变速率压缩实验。基于动态材料模型(DMM)和Prasad失稳准则,建立了Ti555211合金的热加工图,对合金的热加工工艺进行了优化。能量耗散率其极大值出现在(峰值区Ⅰ)应变速率0.001～0.010 s~(-1),变形温度820～850℃和(峰值区Ⅱ)应变速率0.001～0.010 s~(-1),变形温度在约920～950℃。结合微观组织分析,在(α+β)相区加工时,应该选峰值区Ⅰ的加工参数;在β相区加工时,选择峰值区Ⅱ的加工参数。在高应变速率(大于0.4 s~(-1))条件下,易发生变形失稳,主要表现为不均匀变形和加工流线,随着应变的增加,塑形失稳区向低应变速率区扩展,应该避免在此工艺条件下加工。本文通过建立动态材料模型的Ti555211合金的热加工图,从而揭示该材料在两相区和单相区的最佳的加工区和危险区,为该合金的后续产业化提供重要的技术基础。     

Cu-Ag合金热压缩流变应力行为

在应变速率为0.01~10.00 s-1、变形温度为700~850℃的条件下,通过热压缩实验研究Cu-Ag合金的高温流变行为,发现该合金高温流变应力对温度和应变速率比较敏感,且在不同条件下呈现的软化特征也有区别。通过双曲正弦本构方程和线性回归分析,得到了不同变形条件下,关于结构因子、材料参数、以及热变形激活能的6次多项式方程,从而建立了随材料参数变化的Cu-Ag合金流变应力本构模型。根据动态材料模型(DMM)建立功率耗散图和失稳图,并通过叠加得到Cu-Ag合金的热加工图,然后,利用热加工图确定了该合金的加工安全区和流变失稳区。分析可知Cu-Ag合金的最佳变形工艺参数主要处于3个区间:低温低应变速率区(变形温度为700~770℃,应变速率为0.0100~0.0316 s-1),该区域的峰值功率耗散系数η为0.46;高温中应变速率区(变形温度为780~835℃,应变速率为0.1~1.0 s-1),该区域的峰值功率耗散系数η为0.33;和高温高应变速率区(变形温度为835~850℃,应变速率为3.162~10.000 s-1),该区域的功率耗散系数η峰值为0.33。     

粉末冶金TiAl合金热变形行为及加工图的研究

采用热模拟压缩试验研究了粉末冶金TiAl合金在温度1000～1150℃、应变速率0.001～1s-1范围内的高温变形特性,发现合金的流动应力-应变曲线具有应力峰和流变软化特性。为了研究TiAl合金在有限应变下的变形行为,基于动态材料模型(DMM)建立起了TiAl合金加工图。试验结果表明,在高应变速率(0.1s-1)变形时,材料落入流动失稳区域,出现表面开裂。这对材料的变形是有害的,要避免在流动失稳区进行热加工处理。而在温度为1000～1050℃,应变速率为0.001～0.01s-1时,功率耗散率η值在35%～50%之间。这个区域对应的变形机制为动态再结晶,适合进行热加工。在高温(≥1100℃),低应变速率(0.001s-1)变形时,功率耗散率η达到最大值60%,此时材料发生超塑性变形。     

不同应变及失稳准则Ti-50.9Ni合金加工图研究

根据动态材料模型绘制并分析了不同应变及失稳准则下Ti-50.9%Ni(原子分数)形状记忆合金的加工图。结果表明,应变量对等轴组织Ti-50.9%Ni形状记忆合金加工图的影响较大,Ti-50.9%Ni形状记忆合金热加工的非稳定流动区域随着应变量的增大逐渐由低温高应变速率区域向高温及低应变速率区域扩展。在温度为700~800℃、应变速率约为0.001~0.010 s-1和温度为800~950℃、应变速率约为0.005~0.030 s-1两个区域中,真应变小于0.6时能量耗散效率值η皆大于40%,是适合Ti-50.9%Ni形状记忆合金进行热加工的区域。基于Prasad失稳准则和Murty失稳准则得到的Ti-50.9%Ni形状记忆合金的能量耗散效率等值线分布及塑性失稳区分布相似,且Prasad失稳准则得到的Ti-50.9%Ni形状记忆合金加工失稳区更大一些,而Malas失稳准则确定的Ti-50.9%Ni形状记忆合金进行热加工时的稳定变形区位于中等温度和中等应变速率区域。     

基于BP神经网络预测的TC4热加工图

在Gleeble-1500热模拟实验机上对多组TC4钛合金试样进行热压缩实验,获得了变形温度在1053~1273 K、应变速率在0.01~10.00s-1情况下的真应力-应变曲线。通过BP神经网络对实验数据进行训练,建立了流变应力与应变、应变速率和温度相对应的预测模型,并对该模型的预测性能进行评估验证,采用预测数据构造了预测加工图,最后结合微观组织对预测加工图的可行性进行验证。结果表明,预测数据和实验数据的相关系数R为0.99886,平均相对误差为-0.21%,相对误差标准偏差为2.48 MPa,此模型具有良好的预测性能。预测加工图与实验加工图能够很好的吻合,通过预测加工图对材料的可加工性能进行预测,在一定程度上可以解决实验数据不足的缺陷。真应变为0.916的预测加工图大致分为A,B,C3个区域。失稳A区η值出现极小值(-0.16),应变速率较高时,材料局部发生动态再结晶,出现局部变形失稳的现象;应变速率较低时,组织很不均匀,易失稳。稳定B区具有较大的η值,并出现极大值(0.45),其α相球化效果显著、组织均匀,在相界处出现一定数量的细小等轴组织和较大比例的片状组织,确定此区为最优加工区。稳定C区α相球化效果比较明显,可作为加工区。     

40%SiCp/Al复合材料热变形行为及热加工图

采用Glebble-1500D热模拟试验机，在350～500℃变形温度、0.01～10.00 s^-1应变速率条件下进行等温压缩变形，研究40%Si Cp/Al复合材料(体积分数)的热加工性能。通过热变形真应力-真应变曲线分析复合材料的热变形规律，建立材料本构方程，利用动态材料模型计算出应变速率敏感指数和功率耗散效率系数，绘制出功率耗散图、失稳图及二维加工图。结果表明，应变速率和变形温度显著影响流变应力，应变速率一定时，变形温度升高，流变应力减小；在相同的变形温度下，随应变速率的增加，流变应力也随之升高。根据加工图可知，在高温高应变速率条件下，材料的功率耗散效率系数大，说明该变形区域发生了组织转变；应变对失稳区域和加工区域影响不大，功率耗散效率系数随应变的增加而增大。40%Si Cp/Al复合材料建议热加工条件为变形温度436～491℃，应变速率0.04～9.97 s^-1。     

基于热加工图的中碳钢加工性能分析

以LZ50钢为研究对象,分析了其热压缩应力应变曲线。运用线性回归方法建立了峰值应力应变、临界应力应变、稳态应力应变及材料发生最大软化时应力应变的数学模型。绘制了不同应变下LZ50钢的热加工图以预测锻造过程中组织演变行为,指导生产加工。结果表明,加工硬化率随温度降低或应变速率增加而升高。构建了基于Prasad准则、Murty准则及Poletti准则3种不同失稳判据下的热加工图,通过对比分析得出依据Murty准则的热加工图最适宜预测LZ50钢成形过程中的组织演变。研究发现高温高应变速率区域并没有明显组织缺陷,为"伪失稳区"。最适合LZ50钢锻造的区域为中等温度、中等应变速率区,如1 020℃、0.5s-1,该条件下锻后组织均匀,晶粒呈等轴状。     

粉末冶金纯钛的热变形本构方程及热加工图研究

采用热模拟试验方法研究粉末冶金纯钛在温度为400~700℃、应变速率为0.001~1 s-1的变形条件下的热变形行为,推导出了粉末冶金纯钛的高温变形流变本构方程,建立基于动态材料模型(DMM)的粉末冶金纯钛的加工图。研究结果表明:粉末冶金纯钛的高温流变应力与变形条件之间的关系可用双曲正弦函数描述,其高温变形激活能为221.23 k J/mol;在高应变速率条件下(0.1 s-1)变形时,材料发生失稳变形。粉末冶金纯钛的最佳变形参数区间为450~550℃/0.001~0.01 s-1和625~700℃/0.001~0.01 s-1。     

TA17钛合金热变形行为及加工图

为探索TA17钛合金热变形行为和变形特性,采用Gleeble-3800热模拟机开展温度为700~1 100℃、应变速率为0.1~40 s~(-1)、变形程度为60%的热压缩试验。基于Arrhenius模型构建TA17钛合金的本构方程,基于动态材料模型构建TA17钛合金的热加工图(ε=0.6),并结合显微组织分析对热加工图进行验证。结果表明:热加工图预测结果与组织分析相符,当温度低于750℃或者应变速率大于10 s~(-1)的区域为TA17钛合金的加工失稳区域,失稳区以外是安全加工区域,热加工性能最佳的区域是800℃、0.1 s~(-1)。     

新型热作模具钢5CrNiMoVNb的热变形行为研究

为了研究热作模具钢5CrNiMoVNb的热变形行为，利用Gleeble3800热模拟试验机进行单道次热压缩实验，获得了应变速率为0.001～0.1 s^-1和变形温度1 030～1 230℃条件下的高温流变应力曲线。应用双曲正弦函数构建了与应变有关的材料本构模型并验证，并基于动态材料模型构建了三维功率耗散图和三维失稳图，将二者叠加得到典型应变下的热加工图。结果表明，所有变形条件下的高温流变应力曲线均呈现典型动态再结晶特征，并且由于奥氏体基体析出强化相含量、动态再结晶体积分数的影响，流变应力随变形温度的降低或应变速率的增大而增大。基于5CrNiMoVNb钢的本构模型计算的流变应力值与实验值的相关性系数为0.992 7,较高的相关性系数表明建立的高温流变应力模型能够比较准确地预测合金的流变应力。此外，根据不同条件下的三维功率耗散图和三维失稳图可知，随着应变的增大，功率耗散峰值区向中温、高应变速率区域扩散，热变形失稳仅容易出现在低应变、低变形温度和高应变速率区域。真应变为0.8时，最佳的加工工艺参数范围为：变形温度为1 080～1 200℃,应变速率为0.01～0.1 s...     

耐热合金热压缩修正后本构方程及热加工图

通过热模拟压缩实验研究了耐热合金CN617在变形温度为950~1 150℃、应变速率为0.01~10s-1条件下的热变形行为,修正了实验中由于摩擦和变形热效应引起的流变应力误差,并采用修正后的流变应力值,通过回归分析建立了CN617合金的热变形本构方程并绘制了热加工图。计算得出锻态耐热合金CN617热变形的热激活能平均为550kJ/mol。利用热加工图确定了CN617合金热变形时流变失稳区,分析得到了CN617合金流变失稳的原因是极少动态再结晶发生以及局部绝热变形带的形成。     

Effect of ageing on the drawability characteristics of Nimonic C — 263 alloy sheet by numerical simulation

The drawability characteristics, in terms of Limit Drawing Ratio and Limit Strains of Nimonic C — 263 alloy sheet in solution treated (ST) and in peak aged (ST+1073K/8h aged) conditions are investigated, compared and presented using an explicit finite element code LSDYNA 3D. The material properties and the material model are evaluated by the conduct of tensile tests. Also reported in brief are the details of microstructure, texture and tensile fracture behaviour as a function of ageing and sheet thickness. The limit drawing ratio for the alloy was found to be significantly lower in both the heat treatment conditions — 1.34 in ST and 1.23 in peak aged conditions. The study reveals that the safer forming limits in strain space are higher for ST alloy and in stress space is higher for ST + aged alloy.     

Ti600合金的流变失稳特性研究

在Gleeble-1500热模拟实验机上采用等温压缩实验的方法研究了Ti600合金两种状态下的热塑性变形行为,分析了合金在变形过程中的流变失稳特征。结果表明：在800—930℃,0．03～10s^-1区域内产生流变失稳现象,如出现局部塑性流动,形成绝热剪切带,进而发生开裂。在低温、高应变速率区域（T=800℃,ε=10s^-1）,可以看到明显的45。开裂现象;在中温、高应变速率区（T：850℃,ε=10s^-1）,压缩试样侧面出现纵向开裂。     

底商住宅楼工程造价预算费用分析

依据底商住宅楼的施工图 ,立足工程造价预算专业 ,以土建工程造价控制为主 ,配套以给排水系统、电气照明系统为辅 ,对施工图预算进行统计分析 ,便于今后类似工程的投资控制提供参考     

High-temperature deformation behavior of a gamma TiAl alloy—Microstructural evolution and mechanisms

The present investigation was carried out in the context of the internal-variable theory of inelastic deformation and the dynamic-materials model (DMM), to shed light on the high-temperature deformation mechanisms in TiAl. A series of load-relaxation tests and tensile tests were conducted on a fine-grained duplex gamma TiAl alloy at temperatures ranging from 800 °C to 1050 °C. Results of the load-relaxation tests, in which the deformation took place at an infinitesimal level (ε ≅ 0.05), showed that the deformation behavior of the alloy was well described by the sum of dislocation-glide and dislocation-climb processes. To investigate the deformation behavior of the fine-grained duplex gamma TiAl alloy at a finite strain level, processing maps were constructed on the basis of a DMM. For this purpose, compression tests were carried out at temperatures ranging from 800 °C to 1250 °C using strain rates ranging from 10 to 10⁻⁴/s. Two domains were identified and characterized in the processing maps obtained at finite strain levels (0.2 and 0.6). One domain was found in the region of 980 °C and 10⁻³/s with a peak efficiency (maximum efficiency of power dissipation) of 48 pct and was identified as a domain of dynamic recrystallization (DRx) from microstructural observations. Another domain with a peak efficiency of 64 pct was located in the region of 1250 °C and 10⁻⁴/s and was considered to be a domain of superplasticity. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

A general approach for predicting the drawing fracture load and limit drawing ratio of an axisymmetric drawing process

Based on Hill’s theory of plasticity and the Swift diffuse instability criterion, new theoretical models are proposed for predicting the drawing fracture load and limit drawing ratio (LDR) of an axisymmetric cup drawing. These models take into account the influence of triaxial stress state, anisotropy, strain hardening, bending, and tool geometry. By introducing both conventional and modified Hollomon’s equations, the influences of these variables on the constitutive relation of sheet steels are also analyzed. It is shown that the theoretical predictions of the drawing fracture load are in good agreement with experimental results for a wide range of sheet steels currently used in the automotive industry. Specific tool geometries are found to decrease the drawing fracture load and the LDR, because of increased triaxial stress states and bending effects at the critical section of the workpiece. The optimum punch-profile radius is found to be between 5.0 and 7.0 times the thickness of the sheet. Additionally, the role of both the anisotropy and strain-hardening properties of the sheet steels in determining the drawing fracture load and the LDR are, subsequently, discussed.     

Study of Kinetics of Mill Scale Reduction: For PM Applications

In the deep drawing process, material of blank is transformed into the desired complicated shape by a punch. In this paper, a technique for increasing the drawability of AA1200 aluminium alloy cylindrical cups has been developed. Effects of die and punch geometry including die and punch fillet radius, on limiting drawing ratio (LDR), drawing load with respect to punch stroke and strain of the cup wall have been investigated numerically for optimal process design. A commercial finite element simulation package, ANSYS 14.0, is used in order to determine the optimum limiting drawing ratio. An experimental setup is built accordingly with a half cone angle of 18°. In the experimental and finite element analysis, AA 1200 alloy sheets are used. The effects of the original blank thickness (t = 2 mm) on the various LDR and punch load are numerically investigated. The present process successfully produces cylindrical cups with drawing ratio of 2.64.     

Prasad与Murthy流变失稳准则下9310钢热加工图的建立与分析

 在Gleeble-3800热模拟试验机上对9310钢进行了900～1 200 ℃温度范围内的高温轴向压缩试验。基于动态材料模型理论(DMM),在Prasad和Murthy 2种流变失稳准则下建立了9310钢的热加工图,并结合变形过程中的显微组织进行了热加工参数优化的分析。结果表明,本试验条件下,9310钢热变形在Prasad和Murthy流变失稳准则下的稳定性函数[ξ(ε·)]均大于0;在变形条件为950～1 050 ℃,0.01～0.1 s-1时具有最佳的热加工性能,此区域内功率耗散率值均大于32%;能量耗散功率恒定时,变形温度对动态再结晶晶粒尺寸起主导作用,变形温度恒定时,高应变速率下的动态再结晶晶粒更加细小均匀。