不同应变速率条件下Al67Ti25Mn8金属间化合物的高温拉伸力学行为

研究了Al67Ti25Mn8金属间化合物在高温不同应变速率条件下的拉伸力学行为.结果表明在3．34×10－5-6.68×10－4s－1范围,随着应变速率的降低,材料的屈服强度显著下降,而拉伸塑性明显升高,塑性最高可达到21％;在低应变速率区高拉伸塑性的获得是由于材料在高温变形过程中发生的动态回复和动态再结晶所致;在高温拉伸时Al67Ti25Mn8金属间化合物是以沿晶方式发生断裂在较高应变速率下材料的低塑性沿晶断裂表明Al67Ti25Mn8的晶界结合强度仍较弱     

等通道转角挤压超细晶纯铝高温压缩变形特点的应变速率依赖性（英文）

为了探索应变速率对超细晶材料高温变形特点的影响,通过压缩实验以及显微观察,系统研究在不同温度和应变速率下等通道转角挤压Al的变形和损伤特点以及显微微组织。结果表明:应变速率的提高消除了等通道转角挤压Al在变形温度T≤473 K时表现出的应变软化现象,并且大大提高了变形温度在473~573 K范围的屈服强度和流变应力。等通道转角挤压Al的塑性变形主要由剪切变形控制。当应变速率为1×10~(-3)s~(-1)时,变形温度T≥473 K时可观察到沿剪切带形成了大量裂纹,并且二次剪切带基本消失。而当应变速率为1×10~(-2)s~(-1)时,只有在变形温度低于473 K时才能观察到沿剪切带形成的裂纹,并且当压缩温度T≥473 K时,二次剪切带变得更加清晰。等通道转角挤压Al的显微组织主要由亚晶组成,应变速率的提高抑制了亚晶的长大,从而导致高温屈服强度和流变应力的提高。     

Ti2AlNb合金高温拉伸性能研究及本构方程的建立

通过高温拉伸试验研究了Ti2AlNb合金在温度为900~1000℃、应变速率为0.0001~0.01 s~(-1)下变形温度及应变速率对材料伸长率和抗拉强度的影响,并基于试验结果研究了材料应变速率敏感性指数随温度及应变速率的变化趋势。结果表明:Ti2AlNb合金应变速率敏感性指数随温度及应变速率的变化呈先升高后下降的趋势,在温度为975℃、应变速率为0.0005 s~(-1)条件下达到峰值,随后快速下降。通过扩展Rossard提出的粘塑性关系式,修正了基于Backoften方程所建立的应力-应变本构关系式,建立了材料在不同温度下的热变形本构方程。试验结果与模型计算结果基本吻合,可用于表征Ti2AlNb合金在高温下的热变形行为。     

Ti6Al4V钛合金高温损伤模型及损伤机理

在800～1000℃及应变速率为0.01～5 s^-1条件下对Ti6Al4V钛合金进行了高温拉伸试验,研究了其高温损伤行为。基于Normalized Cockcroft-Latham(NCL)损伤模型,提出了考虑温度及应变速率的高温损伤模型,采用Gleeble Fracture Limit (GFL)方法测定了Ti6Al4V合金的临界损伤值。对Ti6Al4V合金拉伸过程进行了仿真模拟,并与拉伸试验的断裂长度进行对比。观察了合金的拉伸断口,分析变形条件对其断口形貌的影响。结果表明：模拟结果与试验结果的吻合度较高,相关系数R为0.993,表明该损伤模型对Ti6Al4V合金的损伤具有较高的预测精度;断口分析表明Ti6Al4V合金高温下为韧性断裂,且在较高的温度和较低的应变速率下表现出较好的塑韧性。     

Ti3Al5Mo5V合金在热压缩变形状态下的组织和应力分析

采用Gleeble-1500热模拟机对Ti3Al5Mo5V合金进行热压缩变形，对α β相、β相钛合金变形后的显微组织进行了分析，比较了合金在不同变形条件下所产生的应力变化趋势和影响因素。结果表明，在Ti3Al5Mo5V合金热变形中，α β相无论在高应变速率还是在低应变速率下，都发生了再结晶，且随温度升高所产生的应力急剧下降，流变软化明显，应力对温度变化敏感。β相在高应变速率下产生动态回复，低应变速率下只发生晶界滑移，应力对温度变化不敏感。     

Ti3Al基合金的热变形行为及加工图

采用THERMECMASTER-Z热模拟试验机对Ti3Al基合金进行等温恒应变速率压缩试验,基于动态材料模型的加工图技术研究该合金在950~1350 ℃和0.001~10 s-1范围内的高温变形特性,并优化出其适宜的高温变形参数范围。结果表明,在应变速率较高(≥0.05 s-1)时,变形多处于失稳区域。在变形温度为950~1100 ℃,应变速率为0.05~10 s-1区域,发生了绝热剪切和局部流动现象;在变形温度为1100~1350 ℃,应变速率为0.1~10 s-1区域发生了β组织的不均匀变形。在变形温度为1250~1350 ℃,应变速率低于0.01 s-1时,变形组织粗大,其变形机制为动态回复。在变形温度为1100~1180 ℃,应变速率为0.001~0.015 s-1时,功率耗散效率多大于0.55,变形组织中出现了亚晶;在温度为970~1010 ℃,应变速率为0.001~0.01 s-1时,功率耗散系数大于0.5,其变形机制可能为超塑性成形,这2个区域为Ti3Al基合金适宜的热变形工艺参数范围     

挤压态6082-T6铝合金的高温拉伸力学性能及微观组织

通过Gleeble3500热模拟试验机研究了变形温度和应变速率对挤压态6082-T6铝合金高温拉伸力学性能的影响,采用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)分析了合金在高温拉伸过程中的微观组织演变。结果表明：在恒定的应变速率下,挤压态6082-T6铝合金的拉伸强度随着拉伸温度的升高而下降;在恒定的拉伸温度下,其拉伸强度随着应变速率的升高而上升。挤压态6082-T6铝合金在高温(300～450℃)拉伸条件下表现为韧性断裂,在较高的变形温度和较低应变速率条件下,合金的韧窝增大且更深,表现出较好的塑性。在高温变形过程中,随着拉伸温度的升高,合金内部的位错密度下降,并出现了析出相粗化现象,导致合金的变形抗力下降。     

金属间化合物Ti2AlNb的高温变形行为和变形机理（英文）

对金属间化合物Ti2AlNb基合金在加热状态下的变形行为和变形机理进行研究。首先,利用单向拉伸试验得到不同温度和应变速率下合金的真应力-应变关系;然后,通过拉深和弯曲试样得到合金的极限拉深比(LDR)及弯曲性能参数;最后,通过金相实验和断口形貌分析研究Ti2AlNb基合金在不同加热条件下的高温变形机制。结果表明:在750~950℃、应变速率0.001 s~(-1)的条件下,随着温度的升高,合金的伸长率从13.58%增大至97.82%,屈服强度从788 MPa降低至80 MPa;当温度达到950℃时,应变速率对合金的变形性能有明显影响。同时,在该温度范围内,材料发生由O相向B2和α2相的组织转变,从微观组织演变揭示了Ti2AlNb基合金塑性提高的变形机理。     

新型无磁合金高温变形行为与组织演变研究

利用Gleeble-3800热模拟试验机,在变形温度为1050～1200℃,应变速率为0. 1～10 s-1,变形量为20%、40%和60%的条件下,对00Cr40Ni55Al3Ti无磁合金进行热压缩变形实验,研究了变形量、应变速率和变形温度等变形工艺参数对00Cr40Ni55Al3Ti无磁合金组织演变及流变应力的影响规律,建立了00Cr40Ni55Al3Ti无磁合金热变形的本构方程和热加工图。结果表明:00Cr40Ni55Al3Ti无磁合金的临界变形量为10. 8%,变形量大于此临界值时,合金中的奥氏体发生动态再结晶和球状α-Cr相形核长大;应变速率为0. 1 s~(-1)时,合金发生不连续动态再结晶,应变速率为5 s-1时,晶界处球状α-Cr相形核长大引起变形不协调,在峰值应力后出现软化波动现象;合金变形量为60%时的热变形激活能为397. 077 k J·mol~(-1)。根据热加工图确定适宜的热加工区域为:变形温度为1080～1100℃、应变速率为0. 1～0. 35 s~(-1)和变形温度为1120～1190℃、应变速率为4. 5～10 s~(-1),合金在该区域进行锻造可获得质量良好的锻件。     

TC4钛合金的力学性能及热处理模拟

采用分子动力学方法建立了TC4模型，基于混合嵌入式原子法势函数计算了Ti、Al和V不同原子之间的相互作用力，通过拉伸与剪切模拟计算得到了拉伸、剪切应力-应变曲线。通过温度的设置，完成了热处理工艺中加热、保温、冷却各个阶段的模拟。在单独退火的模拟基础上进行了同时固溶与时效的模拟，比较了不同固溶温度(800、954和1020℃)和时效温度(400、538和620℃)对TC4拉伸和剪切力学性能的影响。结果表明，退火和固溶时效处理提高了TC4模型的拉伸与剪切强度，最大拉伸强度一般随着固溶温度的升高而升高；在538℃时效时，剪切强度同样随固溶温度的升高而升高，但在954℃固溶温度时，剪切强度随时效温度的升高而下降。HCP模型沿[0001]晶向的拉伸强度大于■晶向，并且拉伸强度随着拉伸速率的升高而升高。     

Zr50Ti5Cu18Ni17Al10块体金属玻璃的热稳定性和力学性能

采用差示扫描量热仪以连续加热的方式研究了Zr50Ti5Cu18Ni17Al10块体金属玻璃的热稳定性。其玻璃转变激活能(Eg)以及晶化激活能(Ep1和Ep2)分别为438±11,284±8和323±11kJ/mol。采用压缩试验研究了金属玻璃的室温力学性能,初始应变速率为1×10-4s-1。直径为3mm的金属玻璃棒呈现良好的力学性能,最大塑性应变达3%,杨氏模量和断裂强度的最大值分别为90GPa和1968MPa。多条剪切带的交织、分叉和滑移以及宽度为60?m的较大临界剪切台阶是Zr50Ti5Cu18Ni17Al10块体金属玻璃具有较高压缩塑性的主要原因。     

Al0.1CoCrFeNi高熵合金力学性能的分子动力学研究

通过分子动力学方法研究了Al_0.1CoCrFeNi单晶高熵合金在室温（300 K）下沿轴向拉伸后的组织和力学性能变化。通过改变模拟应变速率和温度,分析了单晶高熵合金的拉伸性能;通过模拟室温拉伸实验,研究了含表面小裂纹单晶的显微组织和抗拉伸性能。结果表明,当应变速率在一定范围内时,抗拉伸强度随应变速率增大而增大;当应变速率为10¹⁰ s^-1时,杨氏模量和抗拉伸强度随温度降低而增大。表面有贯穿小裂纹的单晶高熵合金在拉伸一段时间后出现颈缩现象,随着大量滑移位错的快速发展,裂纹尖端出现应力集中,导致快速断裂。     

全层状TiAl合金室温拉伸性能的影响因素

研究了显微组织和应变速率对全层状Ti-47Al-2Cr(at%)合金室温拉伸性能的影响，结果表明，全层状TiAl基合金的室温拉伸强度和室温延伸率随晶团尺寸和层片间距的减小而提高；其室温拉伸强度随应变速率的加快而提高；而应变速率对其室温延伸率的影响与显微组织相关，低延性全层状TiAl基合金的室温延伸率对应变速率不敏感，而高延性全层状TiAl基合金的室温延伸率对应变速率敏感，并随应变速率的加快而提高。     

钛的电阻钎焊技术研究

研究了Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ和Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ金属间化合物合金的热轧组织与性能,结果发现：随着变形量的增加,两种合金第二相Ｔｉ５Ｓｉ３变得细小且趋向于均匀分布。变形量越大,合金的室温四点弯曲程度越大,含Ｔｉ５Ｓｉ３较多的Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ合金的弯曲强度较高。两种合金的室温弯曲断口形貌均为准解理形式,两相界面结合较强。高温拉伸试验表明：随变形量的增大,Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ合金的拉伸强度和塑性都增加。Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ合金由于变形量较大和较高的强化相体积含量,拉伸强度明显较Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ合金的为高,但塑性却大为降低     

Deformation and fracture of the PWA 1472 superalloy single crystal

The deformation and fracture of a PWA 1472 single crystal oriented in a soft orientation were studied by analyzing the evolution of slip bands and detailed fractography of tensile specimens tested at low (10⁻⁴/s) and high (1.0/s) strain rates at room temperature. The results of this study indicated that the slip did not start on the system with the highest Schmid factor. This yielding anisotropy has been attributed to the deformation of the γ′-Ni₃Al precipitates. The plastic deformation was heterogeneous and occurred by the propagation of a Lüders band. Cleavage fracture occurred along the kink bands within a coarse shear band that developed after the activation of the secondary slip system. An increase in the strain rate did not affect the yield strength significantly, but it enhanced the deformation localization, and hence, decreased the ductility and increased the percentage of the cleavage facets. The effect of strain rate is discussed in terms of cross-slip processes.     

Hot Deformation Behavior of 6061 and 7108 Al-SiCp Composites

Hot deformation behavior of Al 6061- and Al 7108-SiC particulated composites (Al-PMMCs), prepared by stir casting with SiC particulates (SiCp) size of 8 and 15 μm and volume fraction from 0 to 20% is studied by uniaxial compression test carried out at temperature range from room temperature to 500 °C. The flow stress, work hardening behavior, and Young’s modulus are determined. Dynamic recrystallization is also studied. Work hardening and Young’s modulus are directly correlated with composite constituents, whereas the flow stress is greatly influenced by the porosity and SiCp agglomeration. The role of the SiCp in increasing the flow stress decreases by increasing the deformation temperature. The dynamic recrystallization process is stimulated by refining the SiCp and increasing their fraction in soft Al matrix. On the other hand, the PMMCs with Al6061 matrix has more potential for strain hardening than that with Al 7108 matrix. The strain hardening rate is influenced by the matrix type more than the SiCp volume fraction and size.     

微量硼和应变速率对变形TiAl合金室温力学性能的影响

以形变Ｔｉ４７Ａｌ２Ｍｎ２Ｎｂ合金为对象,研究了微量硼合金化和应变速率对ＴｉＡｌ合金室温力学性能的影响。发现添加微量（１．０％,摩尔分数）硼就能有效地细化形变Ｔｉ４７Ａｌ２Ｍｎ２Ｎｂ合金的近全片层组织,显著提高其室温强度,并在一定程度上改善室温塑性;变形ＴｉＡｌ合金不论添硼与否,其室温强度均随应变速率的升高而升高,而延伸率对应变速率不太敏感;微量硼合金化和应变速率对变形ＴｉＡｌ合金室温断裂方式无明显影响。     

Microstructure and properties that change during hard cyclic visco-plastic deformation of bulk high purity niobium

The effect of strain amplitude and strain rate on the microstructure and the properties that change during hard cyclic visco-plastic deformation of bulk niobium of high purity at room temperature are systematically measured. These changes in the refractory metal niobium were studied at different tension-compression strain amplitudes (up to Ɛ = ±2%) and strain rates (up to έ (t) = 0.4 s⁻¹) during hard cyclic visco-plastic deformation in dependence on von Mises strain (up to Ɛ_vM = 13.8) during the equal channel angular pressing, respectively. The pure Nb was specified with respect to microstructure, micromechanical properties, density, gas content, tensile strength, Young's modulus, viability and fracture mechanics at fatigue failure for use in industry. The micro hardness and the indentation modulus of the nanostructured shear bands were significantly higher, but the plasticity was lower than that of the body metal between the shear bands. The decreasing Young's modulus (when increasing the strain rate) is related to the fatigue failure of the niobium during the tension-compression cycling and shows nucleation and thickening of the shear bands, as well as the changes in grain boundaries in the pre-fracture state.     

铀表面Al/Ti复合镀层热应力的有限元分析

对铀表面Al/Ti复合镀层的热应力进行了热弹塑性有限元分析,表明Ti镀层内为压应力,Al镀层内为拉应力,并达到铝的屈服强度,靠近试样侧边,存在边缘效应引起的应力分布不均匀性,离试样侧边2倍镀层厚度处,不均匀性逐渐消失,试样侧边U-Al界面剪切应力大于中部区域.对沉积温度、镀层厚度及镀层力学性能对镀层热应力和塑性应变的研究表明,随着沉积温度升高,镀层内热应力和塑性应变明显增大,减薄Al镀层和增厚Ti镀层可降低镀层内热应力和塑性应变,Al镀层屈服强度及Ti镀层弹性模量对镀层热应力和塑性应变有重要影响.     

Low Young’s modulus of Ti–Nb–Ta–Zr alloys caused by softening in shear moduli c′ and c44 near lower limit of body-centered cubic phase stability

The composition and temperature dependence of the elastic properties and phase stability of quaternary Ti–Nb–Ta–Zr β-phase alloys with a body-centered cubic structure, developed for biomedical applications, were investigated using their single crystals, in order to clarify the origin of the low Young’s modulus in polycrystals. Transmission electron microscopy observations clarified that α″ martensitic transformation occurred in a temperature range that depended on the β-phase stability below room temperature. Electromagnetic acoustic resonance measurements clarified that the shear moduli c′ and c₄₄ of single crystals softened upon cooling from room temperature and became rather low near the martensitic transformation start temperature, i.e. the lower limit of β-phase stability. An analysis by the Hill approximation indicates that low c′ and c₄₄ caused the low Young’s modulus, and thus it is probable that the softening in c′ and c₄₄ is the origin of the low Young’s modulus.