Mechanical behavior of ultrafine-grained titanium rods obtained using severe plastic deformation

We present the results of the investigation of the mechanical behavior of ultrafine-grained (UFG) titanium rods—semifinished products obtained by equal-channel angular (ECA) pressing in combination with subsequent thermomechanical treatment. This material shows ultimately high values of strength (1240 MPa) and plasticity (relative elongation 12.5%) at room temperature. At the same time, at elevated temperatures the UFG titanium exhibits signs of superplastic behavior with large relative elongations and an enhanced strain-rate sensitivity to the flow stress. The greatest elongation at fracture equal to approximately 300% was reached at 500°C and a strain rate of 10^?4 s^?1. The microstructure and microhardness of the samples after superplastic deformation have been investigated. It has been established that superplastic treatment can favor “structural improvement” of the UFG titanium and further enhancement in its strength.     

LY12合金粗晶材料的超塑性变形机制

采用单轴拉伸对LYl2粗晶材料进行超塑性研究，温度一定时，在较高和较低的应变速率下都得到了大延伸率，而处于中间应变速率的试样延伸率较低。SEM断口分析表明，晶界上产生的粘性物质对粗晶超塑性行为有决定性影响。在高应变速率下，晶界上粘性层很薄，被粘性层包围着的晶粒和亚结构在相互挤压和相对转动中容易细化，有利于超塑性变形能力的提高且不易产生孔洞，室温性能良好；低应变速率下，大多晶界上都有粘性物质包围且粘性层厚度增大，粘性物质的增多使超塑性变形能力增强，但易产生孔洞，使室温性能恶化；而中间应变速率区间，晶粒细化程度不够，晶界上末产生较多粘性物质，有少量孔洞产生且变形能力较差。     

Superplastic behaviour and microstructure evolution of a fine-grained TA15 titanium alloy

The fine-grained microstructure of TA15 titanium alloy was prepared through two-step forging technology combined with high and low temperatures, and a transnormal superplastic elongation of more than 2000% was obtained. The superplastic behaviour and microstructure evolution were systematically researched at different temperatures and strain rates through superplastic tensile test. The results indicate that the fine-grained TA15 alloy exhibits superplasticity at temperatures of 760–980°C and initial strain rates from 1.1 × 10⁻² to 5.5 × 10⁻⁵ s⁻¹. The optimal superplastic conditions are 940°C and 3.3 × 10⁻⁴ s⁻¹, in which the average elongation is 2526% and the maximum elongation is 2743%. During superplastic deformation, dynamic recovery and recrystallization occur obviously, and the corporate effect of strain hardening and recrystallization softening decides the superplastic ability directly.     

温度对TNW700高温钛合金双向超塑性锥杯成形的影响

在910,930和950℃这3种温度下,针对我国新型TNW700高温钛合金薄板开展了双向超塑性圆锥胀形试验,并对圆锥胀形过程进行了理论分析。结果显示:在稳定加载气压的作用下,随着温度的升高,TNW700高温钛合金板料的超塑性变形能力呈先提升、后下降的趋势,在930℃时获得最佳的成形高度和表面应变,且试件具有最均匀的壁厚分布和最稳定的塑性流变。950℃的试样比930℃的试样的最大表面应变下降了11.8%,但其具有最大的平均应变速率。对试件的微观组织观察可知:随着温度的升高,材料不仅发生了晶粒长大的现象,而且伴随有β相的产生;在同一温度下,随着变形量的增加,一定体积分数的β相增加有利于稳定该材料的塑性流变。     

三种工业铝合金超塑压缩性能的比较

对ＬＦ３．ＬＹ１２及ＬＤ５三种工业铝合金在未经超细化预处理的状态下，在几种变形温度，变形速度，以及试样不同高度／直径（Ｈ／Ｄ）条件下进行超塑性压缩变形试验研究，得出它们超塑性压缩的最佳工艺参数，并分析了变形温度，变形速度以及试件尺寸Ｈ／Ｄ对真应力，真应变的影响。     

一种新型锆钛合金的动态力学行为研究

通过对一种新型锆钛合金在室温下的准静态压缩和不同温度下的动态压缩实验,发现该合金在准静态和动态压缩条件下均具有良好的强度和塑性,且随着应变速率的增加和温度的降低,合金强度升高,塑性下降.基于Johnson-Cook模型,建立了该锆钛合金动态压缩下的本构关系.     

Surface hardening of die steel by superplastic deformation of thermo-sprayed powder alloy

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Mechanical Characteristics of Superplastic Deformation of AZ31Magnesium Alloy

As the lightest constructional metal on earth, magnesium (and its alloys) offers a great potential for weight reduction in the transportation industry. Many automotive components have been already produced from different magnesium alloys, but they are mainly cast components. Production of magnesium outer body components is still hindered by the material’s inferior ductility at room temperature. Magnesium alloys are usually warm-formed to overcome this problem; however, it was observed that some magnesium alloys exhibits superior ductility and superplastic behavior at higher temperatures. More comprehensive investigation of magnesium’s high temperature behavior is needed for broader utilization of the metal and its alloys. In this work, the high temperature deformation aspects of the AZ31B-H24 commercial magnesium alloy are investigated through a set of uniaxial tensile tests that cover forming temperatures ranging between 23 and 500 °C, and constant true strain rates between 2 × 10⁻⁵ and 2.5 × 10⁻² s⁻¹. The study targets mainly the superplastic behavior of the alloy, by characterizing flow stress, elongation-to-fracture, and strain rate sensitivity under various conditions. In addition, the initial anisotropy is also investigated at different forming temperatures. The results of these and other mechanical and microstructural tests will be used to develop a microstructure-based constitutive model that can capture the superplastic behavior of the material. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

双重退火对BT25钛合金组织与性能的影响

研究双重退火时不同退火温度对BT25钛合金组织与力学性能的影响。结果表明:双重退火后的室温和高温拉伸性能都强于单一退火,具有良好的综合性能。双重退火时,随着第1退火温度的提高,初生等轴α相含量减少,颗粒逐渐增大,次生α相增多增大;合金的强度降低,塑性及韧性提高。随着第2退火温度的升高α颗粒尺寸稍有增大,球化程度进一步提高;合金强度、塑性及韧性变化不大,高温性能稳定。BT25钛合金采用(940~980)℃×1 h,空冷+(530~570)℃×6 h,空冷的双重退火工艺时,可得到较理想的显微组织和良好的综合性能。     

Hard and wear-resistant titanium nitride coatings for cemented carbide cutting tools by pulsed high energy density plasma

Hard and wear-resistant titanium nitride coatings were deposited by pulsed high energy density plasma technique on cemented carbide cutting tools at ambient temperature. The coating thickness was measured by an optical profiler and surface Auger microprobe. The elemental and phase compositions and distribution of the coatings were determined by Auger microprobe, x-photon electron spectroscope, and X-ray diffractometer. The microstructures of the coatings were observed by scanning electron microscope and the roughness of the sample surface was measured by an optical profiler. The mechanical properties of the coatings were determined by nanoindentation and nanoscratch tests. The tribological properties were evaluated by the cutting performances of the coated tools applied in turning hardened CrWMn steel under industrial conditions. The structural and mechanical properties of the coatings were found to depend strongly on deposition conditions. Under optimized deposition conditions, the adhesive strength of TiN film to the substrate was satisfactory with the highest critical load up to more than 90 mN. The TiN films possess very high values of nanohardness and Young’s modulus, which are near to 27 GPa and 450 GPa, respectively. The wear resistance and edge life of the cemented carbide tools were improved dramatically because of the deposition of titanium nitride coatings.     

Deformation Mechanisms of Ti-6Al-4V During Tensile Behavior at Low Strain Rate

A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 × 10⁻⁴ s⁻¹ and at temperatures up to 1050 °C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800 °C; this is quite a bit lower than the 925 °C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

YZTC4钛合金的超塑性及其等温精锻工艺参数研究

本文通过高温拉伸试验研究ＹＺＴＣ４钛合金的高温力学性能和超塑性能，探求该合金超塑性等温精锻工艺参数。研究结果表明，经过细化处理的ＹＺＴＣ４在Ｔ＝８５０℃和ε０＝１．３×１０－３ｓ－１的变形条件下，具有最佳的超塑性能，Ｍ值为０．８０，最大延伸率可达１０８０％。     

SUPERPLASTIC BEHAVIOR OF HOT-FORGED TiAl-BASED ALLOY

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温度和应变速率对Mg61Cu20.3Ag8.7Er10非晶合金力学行为的影响

采用XRD、SEM等技术分析了Mg61Cu20.3Ag8.7Er10合金的结构和断口形貌,研究了Mg61Cu20.3Ag8.7Er10非晶合金在不同温度和不同应变速率条件下的力学行为。结果表明,室温下非晶合金的断裂强度随应变速率的增加而降低。-100℃时,非晶合金不仅具有较高的强度,同时还表现出一定的塑性行为,此时,应变速率对于非晶合金的强度和塑性几乎没有影响。     

回火温度对铬镍合金结构钢组织性能的影响

利用SEM、TEM手段研究了不同回火温度对铬镍合金结构钢组织性能影响。结果表明:随回火温度的升高,试验钢的硬度、强度呈下降趋势;塑性、韧性先下降,随后出现缓慢上升平台,最后迅速提高;低温下剪切唇主要为韧窝状,有的韧窝较大且较浅,断口心部呈现准解理断裂特征,随回火温度升高,心部的韧窝数量随之增加;淬火后,200 ℃回火组织为合金渗碳体尺寸细小、板条界面清晰的回火马氏体,400 ℃回火组织为合金渗碳体呈杆状、界面较模糊的回火托氏体,600 ℃回火组织为合金渗碳体呈球状、无板条状特征的回火索氏体。     

Corrosion during incineration of a sulphur and chlorine bearing mixture of rubbers and plastics

Exposures of materials to conditions arising from the incineration of sulphur and chlorine bearing rubbers and plastics for up to 556 days have shown a clear ranking of resistant materials. At material temperatures of 1000°C, with daily cycling to room temperature, only ceramics, notably alumina and silicon carbide, had adequate resistance. At 900°C, with daily temperature cycling to room temperature, the most resistant alloys were the nickel-based superalloys containing 16–19% Cr, and 2.9–3.4% of each of aluminium and titanium. These alloys were the most resistant under low and high air flow rates during incineration and to air/HCl mixtures. Somewhat less resistant were the cobalt ?26% Cr alloys not containing iron. Sulphur attack was not prominent for these resistant alloys but was very apparent for the less resistant nickel alloys. Particularly aggressive components of the rubbers and plastics were the chloride levels and brass and lead contamination. A wide range of coatings were shown to be ineffective.     

焊接区表面高频淬火后钢的超塑焊接

探讨了结构钢与工具钢待焊接区表面高频淬火后超塑焊接的可行性及影响因素。试验表明,焊接区局部高频淬火后的结构钢与工具钢在其超塑变形温度及应变速率范围内,经短时超塑压接即可实现接头抗拉强度达到母材强度的固相焊接。     

Post-Superplastic Forming Analysis Under Different Loading Paths. Part One: Uniaxial Loading Case

In a previous work, an optimization approach for superplastic forming based on a multiscale stability criterion, and yielding a variable strain rate loading path instead of the commonly used constant strain rate one, was presented. The approach was experimentally validated using the AZ31 magnesium alloy, where it was proven effective in reducing forming time without sacrificing the uniformity of deformation. In this work, the validation process is taken to a different level, where the post-superplastic forming mechanical properties, often ignored in superplasticity, become the criteria. The material is first superplastically deformed under uniaxial loading at an elevated temperature, following both loading paths; constant strain rate versus optimized variable strain rate. Thereafter, specimens extracted from the deformed material are tested at room temperature to evaluate the changes in mechanical properties, in reference to those of the as-received material. The results emphasize on the necessity of a combined forming and post-forming analysis in optimizing the superplastic forming process. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Baltimore, MD, June 25-28, 2007.     

Constitutive Equation with Varying Parameters for Superplastic Flow Behavior

In this study, constitutive equations for superplastic materials with an extra large elongation were investigated through mechanical analysis. From the view of phenomenology, firstly, some traditional empirical constitutive relations were standardized by restricting some strain paths and parameter conditions, and the coefficients in these relations were strictly given new mechanical definitions. Subsequently, a new, general constitutive equation with varying parameters was theoretically deduced based on the general mechanical equation of state. The superplastic tension test data of Zn-5%Al alloy at 340 °C under strain rates, velocities, and loads were employed for building a new constitutive equation and examining its validity. Analysis results indicated that the constitutive equation with varying parameters could characterize superplastic flow behavior in practical superplastic forming with high prediction accuracy and without any restriction of strain path or deformation condition, showing good industrial or scientific interest. On the contrary, those empirical equations have low prediction capabilities due to constant parameters and poor applicability because of the limit of special strain path or parameter conditions based on strict phenomenology.     

The effect of mechanical strains on the ferroelectric and dielectric properties of a model single crystal – Phase field simulation

The effect of applied mechanical strains on the ferroelectric and dielectric properties of a model single crystal is investigated using a phase field model based on the time-dependent Ginzburg–Landau equation, which takes both multiple-dipole–dipole-electric and -elastic interactions into account. The evolution of the ferroelectric domain structure is simulated at different temperatures and applied strains. The results show that the paraelectric/ferroelectric phase transition temperature linearly increases with the applied mechanical strain under mechanical clamping conditions. Analogous to the classical Ehrenfest equation, a thermodynamics equation is derived to describe the relationship between the transition temperature and the applied strain. The change in the domain structure with temperature under applied inequiaxial strains is different from that under applied equiaxial strains. The simulations also illustrate the changes in the coercive field, the remanent polarization and the nonlinear dielectric constant with the applied strain.