α″phase-assisted nucleation to obtain ultrafineαprecipitates for designing high-strength near-βtitanium alloys

The diffusion-multiple method was used to determine the composition of Ti−6Al−4V−xMo−yZr alloy(0.45<x<12,0.5<y<14,wt.%),which can obtain an ultrafine α phase.Results show that Ti−6Al−4V−5Mo−7Zr alloy can obtain an ultrafineαphase by using the α″phase assisted nucleation.The bimodal microstructure obtained with the heat-treatment process can confer the alloy with a good balance between the strength and plasticity.The deformation mechanism is the dislocation slip and the{1101}twinning in the primary α phase.The strengthening mechanism is α/β interface strengthening.The interface of(0001)α/(110)β has a platform−step structure,whereas(1120)α/(111)βinterface is flat with no steps.

Microstructure Distribution Characteristics of High-Strength Aluminum Alloy Thin-Walled Tubes during Multi-Passes Hot Power Backward Spinning Process

The microstructure of the thin-walled tubes with high-strength aluminum alloy determines their final forming quality and performance. This type of tube can be manufactured by multi-pass hot power backward spinning process as it can eliminate casting defects, refine microstructure and improve the plasticity of the tube. To analyze the microstructure distribution characteristics of the tube during the spinning process, a 3D coupled thermo-mechanical FE model coupled with the microstructure evolution model of the process was established under the ABAQUS environment. The microstructure evolution characteristics and laws of the tube for the whole spinning process were analyzed. The results show that the dynamic recrystallization is mainly produced in the spinning deformation zone and root area of the tube. In the first pass, the dynamic recrystallization phenomenon is not obvious in the tube. With the pass increasing, the trend of dynamic recrystallization volume percentage gradually increases and extends from the outer surface of the tube to the inner surface. The fine-grained area shows the states of concentration, dispersion, and re-concentration as the pass number increases. .

New high-strength Ti–Al–V–Mo alloy: from high-throughput composition design to mechanical properties

The high-throughput diffusion-multiple technique and thermodynamics databases were used to design new high-strength Ti alloys. The composition–microstructure–property relationships of the Ti64–xMo alloys were obtained. The phase fraction and composition of the α and β phases of the Ti64–xMo alloys were calculated using the Thermo-Calc software. After aging at 600℃, the Ti64–6 Mo alloy precipitated ultrafine α phases. This phenomenon was explained on the basis of the pseudo-spinodal mechanism by calculating the Gibbs energy curves of the α and β phases of the Ti64–xMo alloys at 600℃. Bulk forged Ti64–6 Mo alloy exhibited high strength and moderate plasticity after α/β-phase-field solution treatment plus aging. The tensile properties of the alloy were determined by the size and morphology of the primary and secondary α phases and by the β grain size.

Subsurface deformation mechanism and the interplay relationship between strength–ductility and fretting wear resistance during fretting of a high-strength titanium alloy

Fretting wear damage of high-strength titanium fasteners has caused a large number of disastrous accidents.Traditionally,it is believed that both high strength and excellent ductility can reduce fretting wear damage.However,whether strength and ductility are contradictory or not and their appropriate matching strategy under the external applied normal stress(Fw)are still confusing problems.Here,by analyzing the subsurface-microstructure deformation mechanism of several samples containing variousαprecipitate features,for the first time,we design strategies to improve fretting damage resistance under different matching relation between Fw and the tensile strength of materials(Rm).It is found that when Fw is greater than Rm or Fw is nearly equivalent to Rm,the deformation mechanism mainly manifests as serious grain fragmentation ofβandαGB constituents.Homogeneous deformation in large areas only reduces damage to a limited extent.It is crucial to improve the strength to resist cracking and wear,but it is of little significance to improve the ductility.However,when Fw is far less than Rm,coordinated deformation ability reflected by ductility plays a more important role.The deformation mechanism mainly manifests as localized deformation ofβandαGB constituents(kinking induced by twinning and spheroidizing).A unique composite structure of nano-grained/lamellar layer and localized deformation transition layer reduces fretting damage by five times compared with a single nanograined layer.Only when the strength is great enough,improving the plasticity can reduce wear.This study can provide a principle for designing fretting damage resistant alloys.

TA15/YG8复合管扩散复合工艺设计及其施压阶段的有限元模拟

目的以制备钛合金/硬质合金叠层复合管为目标,基于钛合金和硬质合金的性能特点,解决使异种管材相互靠近的载荷难以直接施加的问题,设计开发钛合金/硬质合金复合管的扩散复合工艺。方法借鉴颗粒介质成形的基本原理,提出一种钛合金管-硬质合金管扩散复合方法,并以TA15钛合金和YG8硬质合金为原材料,通过有限元模拟研究了管间间隙、固体颗粒的填充度、固体颗粒的尺寸和管坯长径比等工艺参数对扩散复合施压过程中TA15钛合金管/YG8硬质合金管界面上径向应力分布的影响。结果有限元模拟结果表明,本文设计提出的钛/硬质合金异质管制备工艺确实能将轴向压力转变为径向贴合力,并且可以通过调控下压量满足扩散复合的压力需求(最小径向应力大于10 MPa)。沿轴线方向,钛合金管与硬质合金管之间的径向应力呈不均匀分布,并且受到管间间隙、颗粒填充度、颗粒的尺寸、管坯长径比等参数的影响。管间装配精度越高、固体颗粒尺寸越小、固体颗粒的填充度越多,越有益于管坯之间的扩散复合。试验结果表明,TA15钛合金/YG8硬质合金复合管在不同部位皆实现了良好的冶金结合。结论设计开发了一种钛合金/硬质合金复合管扩散复合方法,制备出具有良好冶金结合界面的TA15钛合金/YG8硬质合金复合管。

Springback prediction of thick-walled high-strength titanium tube bending

Significant springback occurs after tube rotary-draw-bending （RDB）, especially for a high-strength Ti-3A1-2.5V tube （HSTT） due to its high ratio of yield strength to Young＇s modulus. The combination scheme of explicit and implicit is preferred to predict the springback. This simulation strategy includes several numerical parameters, such as element type, number of elements through thickness （NEL）, element size, etc. However, the influences of these parameters on spring- back prediction accuracy are not fully understood. Thus, taking the geometrical specification 9.525 mm × 0.508 mm ofa HSTT as the objective, the effects of numerical parameters on prediction accuracy and computation efficiency of springback simulation of HSTT RDB are investigated. The simulated springback results are compared with experimental ones. The main results are： （1） solid and continuum-shell elements predict the experimental results well; （2） for C3DSR elements, NEL of at least 3 is required to obtain reliable results and a relative error of 29% can occur as NEL is varied in the range of 1-3; （3） specifying damping factor typically works well in Abaqus/Emplicit simulation of springback and the springback results are sensitive to the magnitude of damping factor. In addition, the explanations of the effect rules are given and a guideline is added.

高强TA18钛管微观织构对拉伸力学性能与弯曲成形性能影响研究

目的揭示高强钛管微观织构强度与宏观各向异性指标CSR值的定量关系,阐明微观织构对钛管拉伸力学性能与弯曲成形性能的影响,为高强钛管冷轧微观织构及性能精确调控奠定重要基础。方法选取不同轧制工艺条件下获得的高强钛管进行单向拉伸测试及EBSD表征,分析微观织构对管材拉伸力学性能的影响;选取具有典型微观织构分布状态和CSR值的高强钛管进行数控绕弯试验及成形质量测试。结果单向拉伸力学性能测试结果表明,当CSR值为0.65~2.43时,随着CSR值的增大,颈缩阶段管材的应变与整体伸长率不断增大;数控绕弯试验结果表明,当高强钛管CSR值从1.27提高到1.48时,其断裂前最大弯曲角度从20°提高到110°,当CSR值增大到1.71时,可以成功实现120°的弯曲,并且随着CSR值进一步增大到2.14,弯管件的截面畸变率和壁厚减薄率不断减小。结论建立了可以准确描述宏观CSR与微观织构强度指标之间定量关系的双曲函数表达式,高强钛管径向织构强度的增强会提升高强钛管变形过程中抗壁厚减薄的能力,并有利于管材弯曲成形质量的提升。

Numerically controlled bending performance of medium strength TA18 titanium alloy tubes under different die sets

The rapid development of aviation and aerospace technologies has led to increased interest in the application of numerically controlled(NC) technology for bending light-weight titanium alloy tubes.In order to study and develop advanced NC bending technology,it is necessary to understand the bending performance of medium strength TA18(Ti-3Al-2.5V,ASTM Gr.9) titanium alloy tubes during NC bending under different die sets.This paper focuses on the bending performance of medium strength TA18 tubes under different NC bending die sets,including the variations in the stress,strain,wall thickness,cross sectional deformation,and defects.The results show that adding a wiper die to the base die set decreases the radial,hoop,and tangential compressive stress and the tangential compressive strain,and adding a mandrel to the base die set also decreases these stresses,but increases the radial and hoop tensile stress and decreases the hoop compressive strain obviously,and brings about a three-dimensional tensile stress concentration where the mandrel provides support.For the NC bending of medium strength TA18 tubes,the flattening of cross section is more sensitive index than the thinning of wall thickness.Introducing a mandrel can improve the flattening of cross section obviously but it has a little worse effect on the thinning of wall thickness,and adding a wiper die to the base die set can inhibit the occurrence of the inside bulge but worsen the flattening of the cross section remarkably.Considering the above effects of the mandrel and wiper die on bending performance,it is reasonable to apply the die set comprising a bending die,clamp die,and pressure die for tubes with a small diameter and the die set including an appropriate mandrel additionally for tubes with a larger diameter,in order to bend the medium strength TA18 tubes with high quality and at low cost.

Research progress on hot deformation behavior of high-strength β titanium alloy: flow behavior and constitutive model

High-strength β titanium alloys represented by near β titanium alloy and metastable β titanium alloy are preferred materials for large-scale load-carrying structures.In order to achieve the precise regulation of microstructure in the deformation process, massive efforts have been made to study the flow behavior and microstructure evolution of βtitanium alloy in the hot deformation process. This paper reviews the flow behavior of high-strength titanium alloy,including the effects of initial microstructure, deformation process parameters, work hardening, and dynamic softening on flow stress. Furthermore, the effects of deformation process parameters on the apparent activation energy for deformation and strain rate sensitivity coefficient are analyzed. The discontinuous yield phenomenon is discussed,and the constitutive models of flow stress are summarized.Furthermore, some microstructural evolution models are reviewed. Finally, the development direction and difficulties of the flow behavior and constitutive model are pointed out.

Analysis of anisotropy mechanism in the mechanical property of titanium alloy tube formed through hot flow forming

Anisotropy of mechanical property is an important feature influencing the service performance of titanium(Ti)alloy tube component.In this work,it is found that the hot flow formed Ti alloy tube exhibits higher yield strength along circumferential direction(CD),and larger elongation along rolling direction(RD),presenting significant anisotropy.Subsequently,the quantitative characteristics and underlying mechanism of the property anisotropy were revealed by analyzing the slip,damage and fracture behavior under the combined effects of the spun{0002}basal texture and fibrous microstructure for different loading directions.The results showed that the prismatic slip in primaryαgrain is the dominant deformation mechanism for both loading directions at the yielding stage.The prismatic slip is harder under CD loading,which makes CD loading present higher yield strength than RD loading.Additionally,the yield anisotropy can be quantified through the inverse ratio of the averaged Schmid Factor of the activated prismatic slip under different loading directions.As for the plasticity anisotropy,the harder and slower slip development under CD loading causes that the CD loading presents larger external force and normal stress on slip plane,thus leading to more significant cleavage fracture than RD loading.Moreover,the micro-crack path under RD loading is more tortuous than CD loading because the fibrous microstructure is elongated along RD,which may suppress the macro fracture under RD loading.These results suggest that weakening the texture and fibrous morphology of microstructure is critical to reduce the differences in slip,damage and fracture behavior along different directions,alleviate the property anisotropy and optimize the service performance of Ti alloy tube formed by hot flow forming.

Formability enhancement in hot spinning of titanium alloy thin-walled tube via prediction and control of ductile fracture

The damage and fracture in hot spinning of titanium alloy is a very complex process under the combined effects of microstructure evolution and stress state.In this study,their dependences on processing parameters were investigated by an integrated FE model considering microstructure and damage evolution,and revealing the effects of microstructure and stress states on damage evolution.The results show that the inner surface of workpiece with the largest voids volume fraction is the place with the greatest potential of fracture.This is mainly attributed to the superposition effects of positive stress triaxiality and the smallest dynamic recrystallization(DRX)fraction andβphase fraction at the inner surface.The damage degree is decreased gradually with the increase of initial spinning temperature and roller fillet radius.Meanwhile,it is first decreased and then increased with the increases of spinning pass and roller feed rate,which can be explained based on the variations ofβphase fraction,DRX fraction,stress state and tensile plastic strain with processing parameters.In addition,the dominant influencing mechanisms were identified and discussed.Finally,the thickness reduction without defect in the hot spinning of TA15 alloy tube is greatly increased by proposing an optimal processing scheme.

Uncertainty analysis and robust design optimization for the heat-assisted bending of high-strength titanium tube

Heat-assisted rotary draw bending(HRDB)is a promising technique for manufacturing difficult-to-form tubular components comprising high-strength titanium tubes(HSTTs)with small bending radii.However,as a multidie constrained and thermomechanical coupled process with many uncertainty factors,a high risk of several defects,such as cross-section distortion,over wall thinning,or even cracking,is present.Achieving the robust design optimization(RDO)of complex forming processes remains a nontrivial and challenging scientific issue.Herein,considering a high-strength Ti-3Al-2.5V titanium alloy tube as a case material,the five significant uncertainty factors in HRDB,i.e.,temperature distribution,tube geometrical characteristics,tube material parameters,tube/tool friction,and boost velocity had been analyzed.Subsequently,considering the preheating and HRDB of HSTT,a whole-process thermomechanical three-dimensional finite element model was established and validated for virtual experiments.Further,considering the maximum section distortion Q and maximum wall-thickness thinning t as the optimization objectives and the mean and variance of material and forming parameters,an RDO model was established.Finally,the Pareto optimal solutions were obtained using the nondominated sorting genetic algorithm II,and a minimum distance selection method was employed to obtain the satisfactory solution.Results show that the optimized solutions considering the uncertainty factors reduce the maximum section distortion rate of HSTT after bending by 38.1%and the maximum wallthickness thinning rate by 27.8%.

Pseudo-spinodal mechanism approach to designing a near-βhigh-strength titanium alloy through high-throughput technique

The main reason for the high strength in near-βtitanium alloys is the ultrafine precipitation of the acicular secondary a phase in theβmatrix.The purpose of this study is to use the pseudo-spinodal mechanism to obtain the ultrafine a phase for the design of a new high-strength near-γtitanium alloy.Thermodynamic calculations and TC21-(TC21+15 Mo)diffusion couple composition gradient experiments were used to demonstrate that TC21+3 Mo alloy can undergo a pseudo-spinodal decomposition to obtain the ultrafine a phase,resulting in a high-strength alloy.By adjusting the heat treatment process to obtain a bimodal microstructure,the alloy exhibits a good balance between ultimate tensile strength(1351 MPa)and plasticity(8.5%strain).Thus,it was demonstrated that the pseudospinodal mechanism combined with a high-throughput diffusion couple technique is an effective method for designing high-strength titanium alloys.

径向锻造加工率对TC4钛合金管材组织与性能的影响

对TC4钛合金斜轧管坯分别进行23.4%、43.8%和52.8%三种加工率的无芯轴径向锻造,研究不同加工率对管材内壁质量、尺寸、显微组织和力学性能的影响。结果表明:随着径向锻造加工率的增加,内壁起皱量和壁厚增量随之增大,同时壁厚均匀性变差;部分片状α发生球化,片状α和少量等轴α并存;抗拉强度和屈服强度随着加工率的增大而增加,塑性无明显变化。

钛合金油管螺纹接头设计与评价

由于钛合金材料的特殊性,常规碳钢油管螺纹连接结构不能直接应用于钛合金材料。介绍了一种适用于钛合金油管的螺纹结构的开发与评价过程。设计了一种特殊螺纹结构,并进行了API 5C5—2017版四级评价试验。试验结果表明,该螺纹结构完全适用于钛合金材质油管,并具有一定的推广应用价值。

大尺寸TC4钛合金环壳充气热气胀压弯成形工艺研究

钛合金环形燃料贮箱是运载火箭上面级的薄壳件的关键结构。新一代燃料贮箱对空间利用率的要求更高,因此采用环壳代替多个球形贮箱组合。环形贮箱具有大尺寸、超薄、材料难变形的成形难点,且传统分块拼焊结构可靠性差。基于此,本文提出了环壳热压弯成形工艺,开发了内置VUMAT子程序嵌入材料本构模型的钛合金环壳热气胀压弯仿真模型,研究了不同工艺参数下钛合金环壳热压弯的壁厚、贴模度变化规律。以环壳壁厚减薄率与截面最大变形率为判据,建立了支撑内压与管坯温度的热压弯工艺窗口图,确定最优工艺参数。搭建了TC4钛合金环壳热压弯成形装置,制造了全尺寸钛合金环壳,环壳中径2692 mm,截面直径500 mm,壁厚2 mm,径厚比高达250,实际工件中径尺寸与目标尺寸相差11 mm,环壳弯曲内侧最大增厚率为11.5%,环壳弯曲外侧最大减薄率为8.3%,抗拉强度与平均晶粒尺寸均优于设计指标。

钛合金管材研制及其在航空领域应用的现状与前景

分析总结了近年来国内外学者和工程技术人员在钛合金管材的研制技术、钛合金管弯曲成形技术、钛合金管端头加工与连接技术及应用方面所开展的研究工作和取得的进展及其发展趋势,并对钛合金管材在我国飞机管路系统的应用前景进行了预测。

Ti-2Al-2.5Zr合金管、板材织构研究

利用 X射线衍射极图测量技术 ,研究了 Ti- 2 Al- 2 .5 Zr合金轧制、拉拔管材的退火织构 ,并与轧制板材的织构进行了对比分析。结果表明 :轧制管材环向主织构由棱锥织构 { 10 1- 5 }和基面织构 (0 0 0 1)等组成 ;而轴向主织构则包括棱柱织构 { 10 1- 0 }和 { 112-0 }等棱锥织构 ;拉拔管材退火织构类型与轧制管材相似 ,但其主织构成分及强度与轧制管材相比则发生较大变化 ;

Ti-3Al-2.5V钛合金管材研究进展

简要介绍了航空用Ti-3Al-2.5V钛合金管材从研制到应用的全过程,确立了管材制备过程中挤压、轧制、热处理等关键工艺过程及其参数,建立了管材的组织与性能各向异性评价新参数CSR,为管材的科学评价提供了保证,提出了钛合金管路连接技术的现状及发展趋势。这些工作为我国研制和应用Ti-3Al-2.5V管材提供了重要的方法与思路。

大尺寸薄壁钛合金筒体旋压成形质量影响因素

针对大尺寸薄壁TC4钛合金筒体旋压成形,分析了工件质量影响因素,并研究了旋压成形典型缺陷成形机理和控制方法。结果表明旋压道次和变形量对工件质量影响显著,旋压道次增多,变形量过大,工件精度降低;采用微扩径反旋、坯料分区温度控制等措施,可以有效解决旋压过程中易出现的壁厚和直径超差、反挤、鼓包等缺陷。