时效工艺强化Ti-10V-2Fe-3Al合金研究

对比研究了单重时效、低温-高温双重时效、时效加热速度等工艺对经热变形后的Ti-10V-2Fe-3Al合金显微组织和力学性能的影响.结果表明:经过高温变形后的合金,在双重时效处理过程中,先析出的ω相为α相的沉淀析出提供了均匀的形核位置,使合金获得了比单重时效处理更加均匀细小的α+β显微组织,使得强度获得了较大幅度的提高;合金在较低的升温速度(0.1℃·s-1)加热过程中,细小弥散分布的等温ω相有充足的时间析出,从而为后续α相的析出提供有利的形核位置,产生细小盘状α相,获得了与双重时效相同的强化效果.     

Ti-10V-2Fe-3Al合金热工艺的研究

利用Gleeble-1500热模拟试验机以压缩变形方式研究了Ti-10V-2Fe-3A1合金热变形行为，并研究了经不同变形参数变形后两种热处理制度下微观组织的变化。研究结果表明，合金在B相变点以上或以下的变形时，变形速率和变形温度对合金的流变应力影响不同。在相变点以下变形时，相同应变下变形温度的选择并没有明显影响合金最终的微观组织，合金在变形过程中没有发生动态再结晶。具相同应变时，较高的应变速率比较低的应变速率更容易破碎合金中的初生α相。经过变形和热处理后，同一温度变形的合金在低应变速率下变形时比较高应变速率有较大的晶粒(相变点及以上)和较长的α相(相变点以下)。     

Processing properties relationships of Ti-10V-2Fe-3Al

Beta alloys, such as Ti-10V-2Fe-3Al, can be processed and heat treated to provide a wide range in mechanical and fracture properties. A systematic study of the effect of processing and heat treatment variations on the properties combinations achievable was undertaken. The ductility and fracture toughness can be very significantly influenced by processing and heat treatment variations. The ductility increases and the toughness decreases as the morphology of the primary alpha changes from acicular to equiaxed. This morphology change was caused by alterations in forging procedures. Reducing the strength increases both fracture toughness and ductility. Microstructure has only a minor influence on fatigue performance in the high strength (about 1310 MPa UTS) condition. The micro-structure does, however, have a significant effect on fatigue behavior in a low strength, about 1034 MPa UTS, condition. More lamellar alpha results in improved notched fatigue performance, while a more equiaxed alpha improves smooth fatigue performance. These changes in properties are rationalized in terms of microstructure.     

Microstructural influences on fatigue crack propagation in Ti-10V-2Fe-3Al

Tensile properties and Fatigue Crack Propagation (FCP) rates have been measured in laboratory air for a wide variety of different Ti-10-2-3 microstructures, all having nominal yield strengths of 1240 MPa. These microstructural variations included both recrystallized and unrecrystallized conditions, as well as varying amounts of primary α, both α- and Ω-aged conditions, and also several hot forming histories. With one exception, microstructure was found to have very little or no influence on FCP. Not only was the rate of FCP unaffected, but moreover, the macroscopic fracture surface roughness was largely unaltered. The one exception was a notable one: the Ω-aged condition. Strengthening through the precipitation of Ω instead of α was found to retard FCP significantly; no significant change in macroscopic fracture surface roughness was found, however. The retardation was attributed to changes in slip character and reversibility. Formerly with Carnegie-Mellon University Formerly with BrownBoveri in Switzerland     

Formation and reversion of stress induced martensite in Ti-10V-2Fe-3Al

The formation and reversion behavior of stress induced orthorhombic martensite (α″) in Ti-10V-2Fe-3Al has been studied, and several interesting features found. Reversion appears to take place in four stages. First, there is an athermal reshearing of α″ back to the b.c.c. parent phase, which is accompanied by a significant one-way shape memory effect between 165° and 240°C. This athermal reversion competes with an isothermal stabilization of the α″ plates. Further heating results in the isothermal precipitation of α, which seems to reproduce the preferred orientations of the previous α″, and is thus also accompanied by a shape memory effect; an isothermal shape memory effect in the opposite direction as the preceeding athermal shape change. The precipitation of α occurs on two microstructural scales, extremely fine α nucleating in the β matrix on extant isothermal ω particles, and the direct transformation of the unreverted α″ plates to α. Finally, when heating is continued to the β-transus temperature, the α begins to dissolve back to the parent β. This final dissolution is accompanied by a textural loss in the α phase, and consequently gives rise to several final “shape adjustments”, the nature of which have not been fully explained.     

Stress-Induced Twinning and Phase Transformations during the Compression of a Ti-10V-3Fe-3Al Alloy

A metastable β Ti-10V-3Al-3Fe (wt pct) alloy containing different α phase fractions after thermo-mechanical processing was compressed to 0.4 strain. Detailed microstructure evaluation was carried out using high-resolution scanning transmission electron microscopy and electron back-scattering diffraction. Stress-induced β → α′′ and β → ω transformation products together with {332}〈113〉β and {112}〈111〉β twinning systems were simultaneously detected. The effects of β phase stability and strain rate on the preferential activation of these reactions were analyzed. With an increase in β phase stability, stress-induced phase transformations were restricted and {112}〈111〉β twinning was dominant. Alternatively, less stable β conditions or higher strain rates resulted in the dominance of the {332}〈113〉β twinning system and formation of secondary α′′ martensite.     

The effect of hydrogen on mechanical properties in Ti-10V-2Fe-3Al

The effect of hydrogen on the mechanical properties of the metastable β alloy Ti-10V-2Fe-3Al was examined. The material was beta annealed and water quenched (B/WQ) to yield a nominally all-β microstructure, with a small volume fraction of athermal omega present. Tensile and notched bend bar tests were performed with differing levels of hydrogen concentration (~0 to >30 at. pct) obtained by Sieverts (gaseous) charging prior to beta annealing. The β phase was transformed to orthorhombic alpha double prime martensite (β") upon deformation. The volume fraction and morphology of the alpha double prime depended on the hydrogen concentration. The deformation-induced martensitic transformation changed from being stress-induced to being strain-induced with increased hydrogen concentration. High hydrogen concentrations also resulted in changes in fracture mode. At high hydrogen concentrations, where little or no martensite formed upon deformation, “intrinsic” (i.e., independent of microstructural modification) hydrogen effects were observed in the β phase. These intrinsic hydrogen effects, deleterious in nature, were taken to be evidence of hydrogen embrittlement in the body-centered cubic β phase. Formerly at Carnegie Mellon University.     

The microstructural evolution of near beta alloy Ti-10V-2Fe-3Al during subtransus forging

The microstructural evolution of titanium alloys during subtransus isothermal forging (IF) has been effectively demonstrated using a testing methodology developed at Imperial College London. Double truncated cone specimen geometries were isothermally deformed at near β transus temperatures to obtain microstructural information for a range of strains within a single specimen. The methodology was applied to the near β alloy, Ti-10V-2Fe-3Al, to determine the effect of strain, strain rate, and IF subtransus temperature on microstructural evolution. An erratum to this article is available at .     

Phase transformations and tensile properties of Ti-10V-2Fe-3AI

The effect of heat treatment on the microstructure of the metastableα-Ti alloy Ti-10V-2Fe-3Al has been studied using light and electron metallography, analytical electron microscopy, and X-ray diffraction. A survey of the effects of microstructure on tensile properties of the alloy also has been conducted. It has been found that the alloy contains inclusions which are rich in Ti, S, Si, and P. The alloy has been shown to form ω-phase both athermally and isothermally. The isothermal ω can have either an ellipsoidal or a cuboidal morphology. The reasons for this are enumerated. The formation of α-phase has been studied, and three distinct modes of formation are described. A stress induced orthorhombic martensite also has been observed. The effect of this stress induced product on tensile behavior is discussed. The relative roles of inclusions and α-phase precipitates in the tensile fracture also have been examined. Formerly at Carnegie-Mellon University, is now at Brown, Boveri & Cie, AG, Baden, Switzerland,     

Ti-5Mo-5V-2Cr-3Al合金热压缩变形行为

对Ti-5Mo-5V-2Cr-3Al钛合金进行等温压缩实验,变形温度范围为923～1123 K,应变速率为0.001～1 s<'-1>.分析表明该材料的流变应力对温度与应变速率敏感:当变形温度为923～1023 K时,流变应力曲线呈现动态再结晶曲线特征;当变形温度为1073 K时,低应变速率(0.001s<'-1>)的流变应力曲线呈现动态再结晶曲线特征,高应变速率(0.01-1 s<'-1>)的流变应力曲线呈现动态回复曲线特征;当变形温度为1123 K时,流变应力曲线呈现动态回复曲线特征;峰值流变应力随着变形温度的升高而下降,且下降速率随着温度升高而降低;峰值流变应力随着应变速率的升高而升高,升高速率在923～1023 K范围内随着应变速率升高而下降,在1073 K时随着应变速率升高而升高,在1123 K时随着应变速率升高无变化.Ti-5Mo-5V-2Cr-3Al钛合金在等温压缩变形时的流变行为可用包含Zener-Holomon参数的Arrhenius本构方程描述,变形激活能为789 kJ·mol-1.     

Ti-5Mo-5V-2Cr-3Al合金中的冲击相变研究

利用Hopkinson压杆装置,对Ti-5Mo-5V-2Cr-3Al(TB10)合金进行高速冲击试验,采用光学显微镜和透射电镜分析其冲击相变与动态承载能力之间的关系.结果表明,显微组织状态对绝热剪切敏感性影响很大,在相同的应变率条件下,两相区固溶+时效、两相区固溶+双重时效的TB10合金试样中均可观察到明显的绝热剪切带...     

Influence of β grain size on tensile behavior and ductile fracture toughness of titanium alloy Ti-10V-2Fe-3Al

The β grain size of the alloy Ti-10V-2Fe-3Al was varied by heat treatment, and the tensile behavior and fracture toughness were evaluated as a function of β grain size at room temperature. The alloy showed stress-induced martensitic transformation, and the triggering stress for this transformation varied with grain size. The 0.2 pct yield stress exhibited a Hall-Petch relationship with grain size. The ductile fracture toughness was found to increase with decrease in grain size, and it was also shown to follow a Hall-Petch kind of relationship. The grain boundary and the stress-induced martensitic contribution to fracture toughness were separated out.     

Microstructure,tensile deformation,and fracture in aged ti 10V-2Fe-3Al

In the /3-Ti alloy Ti-10V-2Fe-3Al a variety ofα-andω-aged microstructures with different yield stresses was established by combinations of forging and heat treatment. Tensile tests have shown that plastic deformation and fracture are strongly influenced by the morphology, size, and volume fraction of the different types of a-phase (primary a, secondaryα, grain boundaryα), as well as by the-phase. A detailed microscopical study revealed several deformation and fracture modes. It appears that at several sites stress and strain concentrations and subsequent void nucleation can occur and that the quantitative combinations of the differentα-types determine which sites are active. The dominant deformation mode for the (α +gb) solution treated andα-aged conditions was a strain localization in theα-aged matrix leading to voids at the interface between aged matrix and primary a-phase. In case of theβ-solution treated andα-aged microstructures the grain boundaryα leads to a strain localization in the softα-film and to void nucleation at grain boundary triple points at low macroscopic strains. Based on the above mechanisms it is discussed in detail how varying size, volume fraction, and morphology of theα-phase affect the ductility. The embrittling effect ofω-particles can be largely reduced by a grain refinement.     

Effect of grain size on the tensile behaviour and fracture toughness of Ti-10V-4.5Fe-3Al beta titanium alloy

The tensile and fracture toughness behaviour of Ti-10V-4.5Fe-3Al alloy in the beta solution treated condition was investigated as a function of β grain size and the behaviour was compared with that of Ti-10V-2Fe-3Al alloy. It was found that this alloy, unlike the Ti-10V-2Fe-3Al alloy, did not exhibit any stress induced martensitic transformation during tensile testing. This was attributed to the higher stability of the β phase in this alloy as compared to that in Ti-10V-2Fe-3Al alloy because of the higher iron content. The yield strength, ultimate tensile strength, total elongation and fracture toughness in this alloy were found to decrease with increase in grain size. The yield strength of this alloy was found to obey the Hall-Petch relationship with grain size, similar to the observation in Ti-10V-2Fe-3Al alloy. However, the σ_i value was higher and k value lower than that observed in Ti-10V-2Fe-3Al alloy. The fracture toughness in Ti-10V-4.5Fe-3Al alloy was also found to increase linearly with inverse square root of grain size; however, the slope was significantly less than that observed in Ti-10V-2Fe-3Al alloy.     

Hot Deformation Behavior of Beta Titanium Ti-13V-11Cr-3Al Alloy

Hot compression tests were conducted on Ti-13V-11Cr-3Al beta-Ti alloy in the temperature range of 1203 K to 1353 K (930 °C to 1080 °C) and at strain rates between 0.001 and 1 s^?1 The stress–strain curves showed pronounced yield point phenomena at high strain rates and low temperatures. The yield point elongation and flow stresses at the upper and lower yield points were related to the Zener–Hollomon parameter. It was found that dynamic recovery at low strain rates and dynamic recrystallization at high strain rates were the controlling mechanisms of microstructural evolution. The results also showed that strain rate had a stronger influence on the hot deformation behavior than temperature. The microstructural observations and constitutive analysis of flow stress data supported the change in the hot deformation behavior of the studied alloy varies with strain rate. For various applied strain rates, the activation energy for hot deformation was calculated in range of 199.5 to 361.7 kJ/mol. At low strain rates (0.001 and 0.01 s^?1), the value of activation energy was very close to the activation energy for the diffusion of V, Cr, and Al in beta titanium. The higher value of activation energy for deformation at high strain rates (0.1 and 1 s^?1) was attributed to the accumulation of dislocations and the tendency to initiate dynamic recrystallization.     

Fabrication and properties of heavy section extrusions of Ti-6Al-6V-2Sn and Ti-8Mo-8V-2Fe-3AI alloys

This study is concerned with the fabrication in heavy section of the titanium alloys Ti-8Mo-8V-2Fe-3Al (Ti-8823) and Ti-6Al-6V-2Sn (Ti-662). The technique utilized to achieve 84 pct reduction during the extrusion of heavy section cylindrical hollows is given. The response to subsequent aging of both alloys is described in terms of the effect on important mechanical properties such as yield and ultimate tensile strength, ductility and fracture toughness. For the Ti-8823 alloy extruded in heavy section, it is shown that the optimum heat treatment consists of aging directly after hot working rather than the more common solution treatment and age cycle. With the former heat treatment, uniform through the thickness mechanical properties are obtained. Uniform mechanical properties are also obtained through the section of the Ti-662 extrusion with a solutionizing and overaging heat treatment.     

Effect of mean stress (stress ratio) and aging on fatigue-crack growth in a metastable beta titanium alloy, Ti-10V-2Fe-3Al

The effect of mean stress, or the stress ratio (R), on the fatigue-crack growth (FCG) behavior of α-aged and ω-aged microstructures of the beta titanium alloy Ti-10V-2Fe-3Al was investigated. While the mean stress had a negligible effect on the FCG behavior of the α-aged microstructure, a strong effect was observed in the ω-aged microstructure. In particular, the values of the threshold stress-intensity range (ΔK _th ) exhibited a strong dependence on R in the ω-aged microstructure, while this dependence was weak in the α-aged microstructure. These effects seem to arise primarily from fracture-surface roughness-induced crack closure. The crack closure levels for the α-aged microstructure were found to be very low compared to those for the ω-aged microstructure. Transmission electron microscopy and scanning electron microscopy studies of microstructures and fracture surfaces were performed to gain insight into the deformation characteristics and crack propagation mechanisms, respectively, in these microstructures. The microstructure-induced differences in FCG behavior are rationalized in terms of the effect of aging on slip and crack closure.     

热处理对Ti-5Mo-5V-2Cr-3Al合金组织和性能影响

通过扫描电镜(SEM), 光学显微镜(OM)和X射线衍射分析(XRD)等对Ti-5Mo-5V-2Cr-3Al(Ti5523)合金棒材分别经固溶和固溶时效处理后得到的微观组织, 相含量等进行分析, 结合性能数据, 分析了微观结构对性能的影响. 研究发现, 在720 ℃固溶0.5 h, 并在540 ℃时效6 h后, 获得了一种规则的垂直有序排列的亚结构, 这种网篮状亚结构起到了组织细化的作用, 从而使得断面收缩率非常高. 研究还发现, 两相区固溶后析出相不仅使得强度提高, 对材料的塑性也有贡献.