显微组织类型对TC4钛合金丝材性能的影响

α+β两相区轧制的TC4钛合金丝材经不同工艺热处理后,获得等轴组织、双态组织和片层组织,研究了微观组织特征及其对合金拉伸性能和疲劳性能的影响。结果表明：等轴组织α晶粒最为细小且具有较高的位错密度,表现出最高强度;双态组织α相较等轴组织显著长大,位错密度明显降低,具有最好的工艺塑性;片层组织原始β晶粒粗大,塑性最低。3种组织中片层组织疲劳性能最好,当裂纹长度<250μm时,不同显微组织对应的裂纹扩展速率差异较大,片层组织的扩展速率最低,等轴组织最高;当裂纹长度>250μm时,3种组织的裂纹扩展速率无显著差异。综合考虑TC4钛合金丝材的力学性能和工艺塑性,应选择双态组织作为产品的最终组织状态。     

粉末冶金法制备细晶TC4钛合金的微观组织与力学性能

本文采用真空热压烧结+热挤压+退火工艺制备细晶TC4钛合金,对制备过程中钛合金的微观组织与力学性能演变规律进行研究。结果表明,热压烧结态TC4钛合金主要由α和β相组成,α相以等轴状分布,而β相则以细长片层状/针状分布于α相晶粒内部或晶界处。热挤压可以使合金中的α和β相尺寸明显降低,形成板条状细晶,从而使TC4钛合金室温抗拉强度从热压烧结态的837 MPa提高至983 MPa,但此时TC4钛合金的断后伸长率最低,为9.6%。进一步的退火能够使热挤压态TC4钛合金发生回复和再结晶,β相由片层状/针状向颗粒状转变,分布于α相晶界处,从而有利于TC4钛合金塑韧性的提高。因此,经过热压烧结+热挤压+退火处理得到的细晶TC4钛合金具有较为优异的综合性能。     

不同锻造工艺对TC4钛合金棒材显微组织与力学性能的影响

研究了α+β两相区锻造、近β锻造和β锻造3种不同锻造工艺对TC4钛合金棒材显微组织和力学性能的影响。结果表明,TC4钛合金经α+β锻造、近β锻造和β锻造3种工艺锻造后,分别获得等轴组织、混合组织以及片层组织;3种组织的强度相当,等轴组织和混合组织的塑性较好,混合组织和片层组织的冲击韧性较好。采用近β锻造方式,可使TC4钛合金棒材获得最佳的综合性能。     

β热处理条件与Ti-5321合金显微组织特征的关系研究

研究了β热处理条件与新型高强韧Ti-5321合金显微组织特征的关系。结果表明,在860～920℃温度范围内热处理,Ti-5321合金显微组织为细小等轴β晶粒,同时保温时间越长,晶粒尺寸越均匀。自β相区缓慢冷却到(α+β)相区,α片层生长符合感生形核生长特征。β热处理后冷却速率和冷却时间对Ti-5321合金α片层集束尺寸和片层宽度影响较大,片层宽度随着冷却速率的增大基本呈线性减小,随冷却时间的延长呈现由缓慢增大到快速增大再到缓慢增大的规律。α片层集束尺寸在冷却速率为0. 25～1℃/min时,随冷却速率的增大快速减小,冷却速率为1～2℃/min时,集束尺寸减小较为缓慢。     

氢处理细晶钛合金的拉伸性能及其在牙科上的应用

正氢处理是能够使钛合金晶粒尺寸达1μm以下的为数较少的方法之一。利用这种方法可以使α+β型钛合金Ti-6Al-4V及富β的α+β型钛合金Ti-4.5Al-3V-2Mo-2Fe获得晶粒尺寸小于0.5μm的等轴细晶组织,使合金具有优异的超塑性能。日本学者中東潤对这两种合金进行氢处理,研究其常温性能及超     

固溶处理对Ti-6Cr-5Mo-5V-4Al合金组织与性能的影响

研究了固溶处理对一种新型Ti-6Cr-5 Mo-5V-4Al合金组织与室温拉伸性能的影响.研究发现:Ti-6Cr-5 Mo-5V-4Al合金在β/β固溶处理后的典型组织为:变形拉长的β晶粒,晶粒破碎,原始β晶界处有项链状初生α相析出,经时效后,晶内则析出纵横交错的细小次生α相.β固溶处理后的典型组织为:等轴β晶粒,经时效后晶界处沿着一定取向析出次生α相薄片层,晶内弥散分布着平行交错的细小次生α相.随着固溶温度的升高,β晶粒尺寸逐渐增大,初生α相的含量逐渐减少,相转变温度以上固溶处理后初生α相完全消失.α/β固溶+时效后显微组织中次生α相尺寸较小,大小均匀,长度在500nm左右;而β固溶+时效后显微组织中次生α相尺寸较大,且大小不均,长度在200～1500 nm左右.该合金经固溶处理后具有中等强度水平和良好的塑性,且在实验温度范围内,固溶温度越高,合金强度越低,塑性越好;经时效后,α/β固溶处理的时效强化效应明显强于β固溶处理后,强度差值达360 MPa,主要是因为α/β固溶处理后初生α相的析出,导致残余β相更加稳定,时效时次生α相的驱动力小,以及残余大量的位错等缺陷为α相提供了较多的形核位置,因此次生α相尺寸细小且分布均匀弥散.     

细晶Ti-6Al-4V合金的超塑性变形行为与组织演变

对不同温度下退火处理后的细晶TC4合金板材进行超塑性拉伸变形,研究该合金在750~850℃,应变速率为3×10-4~1×10-3 s-1条件下的超塑性拉伸变形行为,分析晶粒尺寸、变形温度和β相含量对合金性能的影响。结果表明:退火后的(α+β)型细晶Ti-6Al-4V合金表现出良好的超塑性,并且晶粒越细,最佳超塑性变形温度越低。晶粒直径为2.5μm、β相含量(体积分数)为9.6%的TC4合金在温度为800℃、应变速率为1×10-3 s-1的变形条件下,伸长率最大,达到862%。不同晶粒度合金的应变速率敏感系数m均随变形温度升高先上升后下降,最高达0.61。β晶粒处于α晶粒三叉晶界处,升温或拉伸变形时聚集并沿α晶界长大,形成细长的β晶粒并逐渐变粗大,因此在900℃以上高温下合金的超塑性变形能力降低。     

高氧TC4钛合金β相区变形行为研究

采用Gleeble-3800热模拟压缩试验机研究了高氧TC4钛合金在温度为990～1 030℃、应变速率为0. 01～1. 0 s~(-1)、变形量为60%时的变形行为及微观组织特征,并构建了该合金的本构方程。结果表明,高氧TC4钛合金在β单相区变形时随着应变速率的增加和变形温度的降低,其流动应力显著增加,该合金在β相区的变形激活能为141 kJ/mol。在990～1 030℃加热温度下,原始β晶粒尺寸在250～255μm范围内,晶粒尺寸对温度不敏感。随着应变速率的增大,原始β晶粒沿着垂直于压缩轴方向被拉长,在被拉长的原始β晶界上可观察到β再结晶晶粒。     

β热处理对SEBM Ti-6Al-4V Diamond点阵材料显微组织和力学性能的影响

采用电子束选区熔化(SEBM)技术制备Ti-6Al-4V Diamond点阵材料,研究β热处理(1100℃/2 h/FC)对其显微组织与力学性能的影响。结果表明,经β热处理后,Ti-6Al-4V Diamond点阵材料的显微组织由原始β柱状晶转变为等轴晶,针状马氏体α′相以及α+β细片层组织转变为相互平行的α+β粗片层组织,且α片层平均厚度由0.8μm增加至7.4μm。此外,Ti-6Al-4V Diamond压缩应变增加,最大可达13.1%,但强度降低;热处理对点阵材料的模量影响较小。点阵材料的结构与材料具有独立性,热处理不会改变Ti-6Al-4V Diamond点阵材料强度、模量与相对密度的指数关系。     

热变形及热处理过程中TC17钛合金组织与取向的关联性

为了进一步研究热压缩及热处理过程对组织及取向变化的关联性, 通过对TC17进行热压缩变形及后续热处理, 利用光学显微镜和背散射电子衍射等分析方法, 结合晶粒尺寸、织构分布图、极图以及反极图, 研究变形后及热处理后的TC17的组织结构、晶粒尺寸的变化和取向的演变规律以及两者之间的关联性.结果表明: 随着变形温度升高, 初生α相含量大幅减小, 尺寸减小, 大部分α相晶粒分散分布, 且位于高温β相晶粒的三叉晶界上; 热处理后, α相和β相组织特征清晰, 界限明显, 初生α相依旧存在, 且趋于等轴化, 亚稳定β相发生转变, 形成片层状β转变组织; 热变形使α相织构极密度值减小, 且随之温度增加, α相织构极密度值也变小; 热变形后的α相已不存在明显的强织构, 热变形对α相晶粒的取向影响较大, 很明显的改善了其取向的均匀性; 热变形同样使β相织构极密度值减小, 但效果不明显.β相仍存在取向集中现象, 取向均匀性相对较差.      

TA12A钛合金热处理过程中等轴和片层α相演变行为研究

对近α型TA12A钛合金进行热处理实验,利用扫描电子显微镜(SEM)和电子背散射衍射(EBSD)技术对热处理后的微观组织进行观察,研究了两相区固溶温度和冷却速率对微观组织的影响。研究表明:TA12A钛合金在980和1000℃保温后冷却时,β相向α相转变,一方面可以使得等轴α相长大,另一方面也可析出片层α相。等轴α相长大过程中,新长大的区域与初始等轴α相存在成分差异,从而使新长大的区域在背散射电子成像模式下表现出α环状组织。空冷时,因冷却速率较快,使得片层α相快速形核并长大,从而抑制了等轴α晶粒的长大。但是,固溶温度对等轴α晶粒的长大和片层α相的析出行为影响较小。同时,冷却速率显著影响片层α相的形核位置,这与等轴α相的含量密切相关。     

TC4钛合金异形锻件锻造工艺探索

研究了两类锻造工艺对航天用TCA钛合金异形锻件的显微组织及拉伸性能的影响。其中Ⅰ类锻造工艺中第1火及第2火加热温度均在β单相区,Ⅱ类锻造工艺第1火加热温度在β相单区而第2火加热温度在（α＋β）两相高温区。实验结果表明：Ⅰ类锻造工艺下最终得到具有粗大晶粒的片层组织,该类型组织强度及塑性均较低,不能满足指标要求;采用Ⅱ类锻造工艺即第2火加热温度在高温两相区且采用大锻造比可以获得条状α和细小等轴α构成的细小的混合组织,该组织具有较好的拉伸性能,满足指标要求。锻造时采用换向拔长镦粗的方式能保证异形锻件的宏观组织均匀。     

硼对TC4／B钛合金铸造组织与性能的影响

采用熔铸工艺法制备了含B量为0．2％-1．0％的TC4／B钛合金,分析并测试了合金的铸态组织和力学性能。研究结果表明：TiB相提高了TC4／B钛合金铸棒的弹性模量,B元素添加量为0．2％～1．0％范围内,合金弹性模量提高15％～30％;显微组织由片层α、晶界β及第二相（TiB）组成,第二相（TiB）聚集在卢晶界上呈链状分布,随B含量增加,显微组织细化效果越明显。由拉伸断口分析可知,随着B含量增加合金由典型的延性沿晶断裂向混合型断裂转变。     

Creep deformation in near-γ TiAl: Part 1. the influence of microstructure on creep deformation in Ti-49Al-1V

The influence of microstructure on creep deformation was examined in the near-y TiAl alloy Ti-49A1-1V. Specifically, microstructures with varying volume fractions of lamellar constituent were produced through thermomechanical processing. Creep studies were conducted on these various microstructures under constant load in air at temperatures between 760 °C and 870 °C and at stresses ranging from 50 to 200 MPa. Microstructure significantly influences the creep behavior of this alloy, with a fully lamellar microstructure yielding the highest creep resistance of the microstructures examined. Creep resistance is dependent on the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. Examination of the creep deformation structure revealed planar slip of dislocations in the equiaxed y microstructure, while subboundary formation was observed in the duplex microstructure. The decrease in creep resistance of the duplex microstructure, compared with the equiaxed y microstructure, is attributed to an increase in dislocation mobility within the equiaxedy constituent, that results from partitioning of oxygen from the γ phase to the α₂ phase. Dislocation motion in the fully lamellar microstructure was confined to the individual lamellae, with no evidence of shearing of γ/γ or γ/α₂ interfaces. This suggests that the high creep resistance of the fully lamellar microstructure is a result of the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion over that found in the duplex and equiaxed y microstructures. BRIAN D. WORTH, formerly with the Department of Materials Science and Engineering, The University of Michigan     

大规格TC4钛合金厚板研制

采用经三次真空自耗电弧熔炼、多向锻造得到的TC4钛合金板坯为原料,以热模拟试验所获得的热加工图为参考,利用西部钛业有限责任公司2 800 mm四辊热轧机成功制备出了宽度为2 300 mm,厚度达到40~70 mm的大规格TC4钛合金厚板,研究了热轧工艺对其组织和室温力学性能的影响。结果表明,轧制温度、道次变形率和应变速率是制备大规格TC4钛合金厚板的关键工艺因素。所制备的TC4钛合金厚板的显微组织为双态组织,由平均晶粒尺寸为25μm的等轴初生α相、拉长的次生α相及晶间β相组成,其室温抗拉强度为925~960 MPa,屈服强度为870~910 MPa,延伸率为12.0%~14.5%。     

Effect of phase morphology on fatigue crack growth behavior of α-β titanium alloy—A crack closure rationale

Effect of phase morphology on fatigue crack growth (FCG) resistance has been investigated in the case of an α-β titanium alloy. Fatigue crack growth tests with on-line crack closure measurements are performed in the microstructures varying in primary α (elongated/equiaxed/Widmanstätten) and matrix β (transformed/metastable) phase morphologies. The microstructures comprising metastable β matrix are observed to yield higher FCG resistance than those for transformed β matrix, irrespective of primary α phase morphology (equiaxed or elongated). But, the effect of primary α phase morphology is dictated by the type of β phase (transformed or metastable) matrix. It is observed that in the microstructures with metastable β matrix, the equiaxed primary α as second phase possesses higher FCG resistance as compared to that of elongated α morphology. The trend is reversed if the metastable β matrix is replaced by transformed β phase. The fatigue crack path profiles are observed to be highly faceted. The detailed fractographic investigations revealed that tortuosity is introduced as a result of cleavage in α or β or in both the phases, depending upon the microstructure. The crack closure concept has been invoked to rationalize the phase morphology effects on fatigue crack growth behavior. The roughness-induced and plasticity-induced crack closure appear to be the main mechanisms governing crack growth behavior in α-β titanium alloy.     

Influence of test temperature and microstructure on the tensile properties of titanium alloys

Tensile tests were performed between room temperature and 500 °C on age-hardened Ti-Al and Ti-6A1-4V alloys to study the effect of various microstructural parameters on the temperature dependence of the yield stress. It was found that the concentration of interstitial solute atoms is responsible for the strong temperature dependence of the yield stress. Small interstitial concentrations increase the yield stress significantly at low test temperatures, while this hardening effect almost disappeared at temperatures above about 300 °C. Through variations of degree of age-hardening, grain size, texture, phase morphology, and phase dimensions of (α + β) microstructures, the absolute yield stress values were changed by constant amounts over the test temperature range without changing significantly the temperature dependence. The yield stress increased by increasing the degree of age-hardening, by decreasing the grain size or phase dimensions, by texture hardening, and by choosing equiaxed instead of lamellar phase morphologies.     

不同热处理工艺下TC4-DT钛合金的显微组织及力学性能

研究了几种热处理制度对TC4-DT钛合金板材显微组织和力学性能的影响。结果表明:等轴或双态组织具有好的拉伸性能,片层组织能够有效提高材料的断裂韧性;控制单相区固溶的冷却速度以及第二重热处理的温度和冷却速度,可以获得不同尺寸的片层组织;单相区固溶后空冷,再经两相区第二重热处理,空冷的组织中含有粗的初生α片层和细小的次生α片层,炉冷的组织中α片层变厚,单相区固溶后水冷得到马氏体组织,在两相区热处理保温时,马氏体组织直接分解成粗的α片层。采用1 015℃/1 h/AC+955℃/1.5 h/AC+550℃/6 h/AC多重热处理,可以获得粗细相间的片层组织,具有更好的强度-塑性-断裂韧性的综合匹配。     

Effect of the lamellar grain size on plastic flow behavior and microstructure evolution during hot working of a gamma titanium aluminide alloy

The kinetics of dynamic spheroidization of the lamellar microstructure and the associated flow-softening behavior during isothermal, constant-strain-rate deformation of a gamma titanium aluminide alloy were investigated, with special emphasis on the role of the prior-alpha grain/colony size. For this purpose, fully lamellar microstructures with prior-alpha grain sizes between 80 and 900 μm were developed in a Ti-45.5Al-2Nb-2Cr alloy using a special forging and heat-treatment schedule. Isothermal hot compression tests were conducted at 1093 °C and strain rates of 0.001, 0.1, and 1.0 s⁻¹ on specimens with different grain sizes. The flow curves from these tests showed a very strong dependence of peak flow stress and flow-softening rate on grain size; both parameters increased with alpha grain/colony size. Microstructures of the upset test specimens revealed the presence of fine, equiaxed grains of γ + α ₂ + β phases resulting from the dynamic spheroidization process that initiated at and proceeded inward from the prior-alpha grain/colony boundaries. The grain interiors displayed evidence of microkinking of the lamellae. The frequency and severity of kinking increased with strain, but were also strongly dependent on the local orientation of lamellae with respect to the compression axis. The kinetics of dynamic spheroidization were found to increase as the strain rate decreased for a given alpha grain size and to decrease with increasing alpha grain size at a given strain rate. The breakdown of the lamellar structure during hot deformation occurred through a combination of events, including shear localization along grain/colony boundaries, microbuckling of the lamellae, and the formation of equiaxed particles of γ + β ₂ + α ₂ on grain/colony boundaries and in zones of localized high deformation within the microbuckled regions.