室温90°模具ECAP变形工业纯钛的力学性能

采用两通道夹角Φ=90°,外圆角Ψ=20°的模具,在室温,以C方式(两次挤压道次之间试样绕纵轴旋转180°)对工业纯钛进行了4道次ECAP(Equal Channel Angular Pressing)变形,成功制得表面光滑无裂纹试样,并对其力学性能和微观组织进行了检测分析.结果表明,工业纯钛经室温4道次ECAP变形后,原始晶粒细化到170 nm左右,显微维氏硬度和抗拉强度分别由1 792 MPa、438 MPa提高到2 486 MPa、728 MPa,且保持良好的塑性,断后伸长率为21.4%.     

大角度ECAP变形模具制备纯钛的变形织构演化模拟

为了研究等径弯曲通道变形(ECAP)对纯钛变形织构的影响,本研究采用135°模具在室温条件下以C方式对纯钛实施2道次ECAP变形,然后利用X射线衍射(XRD)仪检测了原始纯钛以及ECAP变形后纯钛的织构,并与VPSC自洽理论模型计算的ECAP变形织构进行对比分析。结果表明:原始纯钛组织为等轴状,晶界清晰,其{0002}晶面极图的最大极密度为2.6,且主要为P_1织构,易发生柱面滑移,同时压缩孪生系处于易激活状态。而经1道次ECAP变形后的织构转变为P织构,同时出现C_2织构。经过2道次ECAP变形后,P织构消失,只存在C_2织构。VPSC自洽理论模型计算织构与实验织构大致相同,且2道次ECAP变形之后的纯钛试样均易发生基面滑移、拉伸孪生系更易被激活。     

超细晶纯钛疲劳裂纹的扩展行为

对纯钛进行2道次室温等径弯曲通道变形(ECAP)、等径弯曲通道变形加旋锻复合变形(ECAP+RS)并在旋锻后在300℃和400℃退火1 h,制备出4种具有不同组织的超细晶纯钛。对这4种超细晶纯钛进行疲劳裂纹扩展实验并观察分析超细晶纯钛的显微组织和疲劳断口的形貌,研究了裂纹的扩展行为。结果表明：显微组织对超细晶纯钛的疲劳裂纹扩展门槛值和近门槛区有显著的影响;超细晶纯钛的疲劳裂纹扩展门槛值随着塑性变形量的增大而增大,随着旋锻后退火温度的提高而降低;疲劳裂纹扩展速率曲线因超细晶纯钛晶粒尺寸和强度的影响出现转折,转折前ECAP+RS复合变形纯钛的抗疲劳裂纹扩展能力比ECAP变形强,且随着退火温度的提高而降低;转折后4种超细晶纯钛的疲劳裂纹扩展速率相差较小,呈现出相反的结果。疲劳裂纹扩展寿命中转折前近门槛区裂纹扩展寿命占绝大部分,因而转折前的门槛值与近门槛区的扩展速率对抗裂纹扩展能力更为重要。     

工业纯钛低温拉伸和循环变形中的孪生行为

在-196℃下对钛进行了拉伸和低周循环变形,观察分析了变形后试样的微观组织.结果表明,工业纯钛在-196℃拉伸变形后,强度比在室温下拉伸变形有了明显的提高,塑性也有明显的增加;在-196℃下循环变形时,循环应力-应变曲线位于-196℃静拉伸应力-应变曲线的上方,显示出明显的循环硬化特征.微观组织观察表明,-196℃拉伸及循环变形试样中存在着大量的孪晶,且孪晶数量随着循环应变幅及循环周次的增加而增加.在工业纯钛-196℃下的拉伸及循环变形中孪生起重要作用.     

应用于医学的ECAP处理Ti及Ti合金的研究现状

综述了目前国际上应用于医用生物材料的等通道挤压(Equal-channel angular pressure,ECAP)处理工业纯钛和钛合金的研究进展,介绍了等通道挤压技术的最新进展,ECAP处理工业纯钛的微观组织演变,ECAP处理后Ti的强度、抗疲劳性、耐腐蚀性和生物活性的改善以及ECAP处理Ti-6Al-4V的超塑性和超塑变形后的微观组织,最后展望了未来的研究方向。     

135°ECAP+旋锻变形工业纯钛的热稳定性研究

对经过135°ECAP+旋锻变形后的工业纯钛100,150,200,250,300,350,400,450℃和500℃下保温1h退火。采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、拉伸试验机及显微硬度仪等技术研究ECAP+旋锻变形工业纯钛退火后的组织与性能变化。结果表明:在400℃以下退火时,显微组织中位错密度降低,晶界逐渐清晰,变形组织未发生明显变化,材料的抗拉强度和显微硬度略有降低,伸长率增加不明显;在400℃以上退火时,随着退火温度的升高,发生再结晶,晶粒尺寸明显增大,平均晶粒尺寸约为5μm,材料的抗拉强度和显微硬度均出现明显降低,伸长率增加。拉伸断口表明,ECAP+旋锻变形退火后工业纯钛的拉伸断裂均为韧性断裂。随着退火温度的升高,韧窝尺寸变大,韧窝深度变深。     

挤压速度对工业纯钛室温ECAP变形孪晶的影响

在室温采用通道夹角为Φ=120°的模具,以不同挤压速度实现工业纯钛的单道次等径弯曲通道变形(ECAP),利用光学显微镜(OM)观察了变形前后的组织形貌特征,分析了不同挤压速度对显微组织的影响。结果表明:在单道次ECAP变形过程中,孪晶变形是主要的变形机制,且随着变形速率(即挤压速度)的增大,孪晶变细,孪晶的密度显著增大。     

工业纯钛室温ECAP变形的组织和性能

采用BC方式等径弯曲通道变形(Equal Channel Angular Pressing,简称ECAP)对工业纯钛进行了8道次室温变形,研究了变形道次对显微组织和力学性能的影响。结果表明,铁素体组织随变形道次的增加逐渐演变为等轴状大角度晶界的超细晶组织;试验材料的硬度和强度随变形道次的增加而增加,伸长率曲线以第3道次为临界点,第3道次前材料伸长率曲线随挤压道次的增加而下降,而3道次后,曲线开始上升,材料伸长率增大。     

复合形变超细晶纯钛的动态再结晶模型

采用室温等径弯曲通道变形(ECAP)+旋锻复合加工工艺制备超细晶纯钛,用GLEEBLE 3800热模拟试验机对其进行热压缩实验。研究了复合形变超细晶纯钛在温度为200、300、350、400和450℃,应变速率为0.01、0.1和1 s^-1条件下的变形行为。结果表明：实验中真应力-应变曲线的动态再结晶特征显著,出现了明显的单峰值应力。根据复合形变超细晶纯钛的峰值应力值建立的Arrhenius本构方程能预测峰值应力,平均相对误差仅为4.44%;大塑性变形试样在热压缩前进行的保温处理,增大了发生动态再结晶的临界应变值,其材料常数为0.8329;材料变形中的动态再结晶行为发生在应变大于0.1而小于0.4的阶段,应变大于0.4时发生二次硬化。     

单道次ECAP纯铝织构演变的有限元模拟

利用晶体塑性有限元(Crystal Plasticity Finite Element,简称CPFE)子程序和ABAQUS商业软件对多晶体纯铝等径弯曲通道(Equal Channel Angular Pressing,简称ECAP)变形进行了细观三维计算机模拟,获得多晶体纯铝在ECAP变形后各晶粒的取向分布数据,并据此得到晶粒取向的ODF图及极图.通过对结果的分析,初始晶粒取向随机分布的多晶体纯铝在ECAP单道次变形后,靠近模具内角的试样和靠近模具外角的试样由于形变的方式不同而形成了不同的织构形态,靠近模具内角的试样形成剪切织构,靠近模具外角的试样形成扭转织构.因此多晶纯铝在通道夹角Ф=90°、外圆角Ψ=20°模具中的ECAP变形并不是通过理想的纯剪切变形实现的.     

Microstructures and properties of ultrafine-grained pure titanium processed by equal-channel angular pressing and cold deformation

Equal-channel angular pressing (ECAP) has been used to refine the grain size of commercially pure (CP) titanium as well as other metals and alloys. CP-Ti is usually processed at about 400 degrees C because it lacks sufficient ductility at lower temperature. The warm processing temperature limits the ability of the ECAP technique to improve the strength of CP-Ti. We have employed cold deformation following warm ECAP to further improve the strength of CP-Ti. Ti billets were first processed for eight passes via ECAP route Bc, with a clockwise rotation of 90 degrees between adjacent passes. The grain size obtained by ECAP alone is about 260 nm. The billets were further processed by cold deformation (cold rolling) to increase the crystalline defects such as dislocations. The strength of pure Ti was improved from 380 to around 1000 MPa by the two-step process. This article reports the microstructures, microhardness, tensile properties, and thermal stability of these Ti billets processed by a combination of ECAP and cold deformation.     

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5%Cr alloy processed by severe plastic deformation

Microstructure, mechanical properties and electrical conductivity of industrial Cu-0.5% alloy subjected to equal channel angular pressing (ECAP) by route A and cold rolling with and without aging treatment were investigated. The lamellar grains in thickness of 100 nm were obtained after eight ECAP passes. They were not further pancake shaped, but fragmentary and obtained less sharp boundaries with more dislocations in addition to cold rolling. After aging at 450 °C for 1 h, high density of dislocations and some coarse grains were observable after ECAP and the additional cold rolling, respectively. The tensile tests show that tensile strength arrived at 460 MPa and 484 MPa after four and eight passes of ECAP, respectively, the corresponding tensile strength increased to 570 MPa and 579 MPa after the additional cold rolling. However, the electrical conductivity was not more than 35% IACS. It was proved that four passes of ECAP followed by 90% cold rolling and aging at 450 °C for 1 h offered a short process for Cu-0.5%Cr alloy to balance the paradox of high strength and electrical conductivity, under which the tensile strength 554 MPa, elongation to failure 22% and electrical conductivity 84% of IACS could be obtained. The high strength was explained by precipitation strengthening and fine grain strengthening.     

Biodegradable Zn–3Cu and Zn–3Cu–0.2Ti alloys with ultrahigh ductility and antibacterial ability for orthopedic applications

Zinc(Zn) and its alloys have been proposed as biodegradable implant materials due to their unique combination of biodegradability, biocompatibility, and biofunctionality. However, the insufficient mechanical properties of pure Zn greatly limit its clinical application. Here, we report on the microstructure, mechanical properties, friction and wear behavior, corrosion and degradation properties, hemocompatibility, and cytocompatibility of Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys under three different conditions of as-cast(AC),hot-rolling(HR), and hot-rolling plus cold-rolling(HR + CR). The HR + CR Zn–3 Cu–0.2 Ti exhibited the best set of comprehensive properties among all the alloy samples, with yield strength of 211.0 MPa, ultimate strength of 271.1 MPa, and elongation of 72.1 %. Immersion tests of the Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys in Hanks’ solution for 3 months indicated that the AC samples showed the lowest degradation rate,followed by the HR samples, and then the HR + CR samples, while the HR + CR Zn–3 Cu exhibited the highest degradation rate of 23.9 m/a. Friction and wear testing of the Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys in Hanks’ solution indicated that the AC samples showed the highest wear resistance, followed by the HR samples, and then the HR + CR samples, while the AC Zn–3 Cu–0.2 Ti showed the highest wear resistance.The diluted extracts of HR + CR Zn–3 Cu and Zn–3 Cu–0.2 Ti at a concentration of ≤25 % exhibited noncytotoxicity. Furthermore, both the HR + CR Zn–3 Cu and Zn–3 Cu–0.2 Ti exhibited effective antibacterial properties against S. aureus.     

超细晶铜力学和阻尼性能及微观结构研究

在众多阻尼材料中,金属阻尼材料既能满足高阻尼减振降噪性能,又具有较高的强度,是理想的阻尼材料.为了提高商业纯铜的力学性能,分析晶粒细化程度对纯铜力学性能和阻尼性能的影响,在室温下对商业纯铜棒进行12道次BC路径等通道转角挤压(ECAP)实验.对挤压后样品进行单轴微拉伸试验和高循环拉伸疲劳试验研究其力学性能;通过动态力学...     

Effect of ECAP consolidation temperature on the microstructure and mechanical properties of Al-Cu-Ti metallic glass reinforced aluminum matrix composite

Al_(65)Cu_(20)Ti_(15)metallic glass(AMG) reinforced Al matrix composites were consolidated by equal channel angular pressing(ECAP) process. The effects of ECAP consolidation temperature ranging from room temperature to just below the first crystallization temperature of metallic glass on the consolidation of composites were investigated in terms of the relative densities, structural evolutions and mechanical properties of composites. Some intermetallic compounds included Al_5CuTi_2, Al_3Ti and Al_4Cu_9 precipitated from metallic glass particles at consolidation temperature of 300?C. Consolidation temperature did not affect the matrix grains size of the composite. Quantitative analysis revealed that the distribution of reinforcing particles was considerably dependent on consolidation temperature. Density of the composite was increased by increasing the consolidation temperature to 250?C. The composite consolidated at250?C through ECAP process, exhibited the best combination of yield strength and ductility of 184 MPa and 48%, respectively.     

Grade-4 commercially pure titanium with ultrahigh strength achieved by twinning-induced grain refinement through cryogenic deformation

The yield strength of commercially pure(CP) Ti of ASTM grade 4, the strongest among all the CP-Ti grades, is too low for structural applications that require high-strength materials. Here, we demonstrate the strengthening of grade-4 CP Ti by cryogenic-temperature rolling(CTR), which enables deformation twinning in grade-4 CP Ti to achieve twinning-induced grain refinement. CTR activated {11.22} twinning and {10.12} twinning, which are the most common twinning systems in pure Ti, whereas room-temperature rolling(RTR) did not activate any twinning system. CTR with imposing an area reduction of just 30% significantly increased the yield strength of the CP Ti to 946 MPa, which is not achievable through typical processes performed at or above room temperature and is comparable to that of commercial Ti-6 Al-4 V. The significant increase in strength was due to microstructural strengthening caused by twinning-induced grain refinement, combined with dislocation accumulation. In contrast to RTR, CTR greatly increased the stress concentration at grain boundaries(GBs), which caused the unusual activation of twinning in the grade-4 CP Ti by facilitating twin nucleation at GBs. The stress concentration increased because CTR activated the slip to a lesser extent compared to RTR, thereby reducing the strain compatibility between neighboring grains. These results will contribute to development of ultrahigh-strength CP Ti and may thereby extend its use to structural applications that require high-strength materials.     

Effects of carbon and niobium on microstructure and properties for Ti bearing steels

The objective of the study described here is to elucidate the effect of carbon and niobium on the microstructure, precipitation behaviour, and mechanical properties of 0·09C–0·11Ti (%) steel and 0·05C–0·025Nb–0·11Ti (%) steel under ultra fast cooling condition. The strengthening mechanisms are also discussed. The ferrite grains size and the size of precipitates in Ti and Nb–Ti steels were measured respectively. The mechanical properties obtained in Ti steel were similar to Nb–Ti steel with yield stress >700 MPa, elongation >20%, and good low temperature impact toughness. The study underscores that addition of higher carbon content by 0·04% under controlled rolling and ultra fast cooling conditions, we can achieve similar strength in the absence of micro-alloying element, niobium.     

Microstructure and tensile strength of grade 2 titanium processed by equal-channel angular pressing and by rolling

Commercially pure titanium strengthened by severe plastic deformation constitutes an alternative to the use of complex Ti alloys in many medical or industrial applications. In this research, rods of grade 2 Ti were processed by up to six passes using Equal-channel angular pressing (ECAP) at 573 K followed by cold rolling at room or subzero temperatures. After four passes of ECAP, the grain size was refined down to the submicrometer scale and subsequent rolling led to further refinement. The microstructure was characterized by taking Vickers microhardness measurements and tensile testing was performed both at room temperature and in the temperature range of 573–773 K. The results show that at all temperatures the tensile strength is significantly improved by means of these processing techniques. At room temperature, the ultimate tensile strength of pure Ti after ECAP plus subzero rolling is close to that of the traditional Ti-6Al-4V alloy while maintaining adequate levels of elongation to failure.     

Cryogenic equal channel angular pressing of commercially pure titanium: microstructure and properties

Cylindrical samples of CP Titanium (Grade 2) were deformed by one, two and three passes of equal channel angular pressing (ECAP) each at temperatures 77, 300 and 575 K, respectively. The microstructure of samples processed at 77 K shows retardation of recrystallisation, high density of dislocations and deformation twins, diffuse and obscure grain boundaries compare to microstructure of samples processed at room and high temperature, where recrystallised ultrafine equiaxed grains are observed. Mechanical properties for all structural states of Ti were studied by microhardness measurements at 300 K and uniaxial compression at temperatures 300, 170, 77 and 4.2 K. Higher levels of ECAP deformation (more passes of ECAP) lead to higher values of strength and hardness at all studied temperatures. Decrease of ECAP temperature leads to increase of strength characteristics in all cases. Influence of ECAP and compression temperatures on possible changes of deformation mechanism are discussed.