热处理对Ti-8V-8Cr-2Zr-3A1合金丝材组织和性能的影响

分别选用不同的固溶温度、固溶冷却方式和时效保温时间对Ti-8V-8Cr-2Zr-3A1合金丝材进行热处理,研究了热处理制度对丝材室温拉伸性能及金相显微组织的影响。结果表明：固溶处理温度在740～820℃范围内,力学性能及显微组织对温度不敏感,固溶温度继续提高时,材料晶粒明显变大,强度降低,塑性下降;固溶温度为740℃,分别以水淬、空冷方式冷却,材料的组织、性能无明显变化,以炉冷方式冷却,强度提高,塑性下降。眼镜架用Ti-8V-8Cr-2Zr-3A1合金丝材较为理想的热处理工艺为740℃×10min／AC＋550℃×（4～6）h／AC,经该工艺处理后,材料的抗拉强度约1120MPa,延伸率大于12％,能够满足用户要求。     

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.     

Phase transformations in Ti- 3AI- 8V- 6Cr- 4Zr- 4Mo

The time-temperature-transformation behavior of a metastable β-titanium alloy, Ti-3A1-8V-6Cr-4Zr-4Mo (RMI 38644), has been examined using hardness, X-ray measurements, and optical and transmission electron microscopy. This examination has shown that a variety of metastable and stable phases may form in this alloy system. These include metastable zones, ω, both Burgers (Type 1) α and non-Burgers (Type 2) α, TiCr₂, and a Ti-Zr-silicide. A composite TTT diagram is presented which describes the influence of aging time and temperature on the stability of these phases. Finally, the appearance of these transformation products is correlated with the observed hardness changes when RMI 38644 is aged at elevated temperatures.     

添加Nd元素对Ti-6Al-4V-2Cr合金组织细化的影响

采用冷等静压–真空烧结法制备Ti-6Al-4V-2Cr-1Nd合金,然后进行固溶及时效热处理,通过实验与最小错配度理论计算,研究Nd元素对该合金组织细化的影响,并分析细化机理。结果表明,添加1%(质量分数)的稀土元素Nd后,析出相Nd2O3能有效促进晶粒细化。二维错配度的计算结果证明析出相Nd2O3是有效的形核剂,可促进非均匀形核,增加形核率,从而使晶粒细化。通过对合金试样薄区进行高分辨率观察,发现另一种絮状的、非常细小的、弥散分布的Nd2Ti4O11相,由于其界面错配度较低,也可作为非均匀形核的核心,促进形核,起到细化晶粒的作用。     

Ti-6Al-4V-2Ni as a matrix material for a SiC-reinforced composite

Ti-6Al-4V-2Ni is being considered as a composite matrix material because of its potential for a lower consolidation temperature and reduced reaction product formation compared with conventional Ti-6A1-4V. Stress/strain-rate measurements of Ti-6Al-4V-2Ni in sheet form provided data for calculation of diffusion bonding parameters required for efficient consolidation. These data were used as consolidation parameters for fabrication of SiC (SCS-6) reinforced Ti-6Al-4V-2Ni. The composite with 10.5 vol pct SiC exhibits room temperature tensile strength approximately 80 pct of that observed for conventional Ti-6Al-4V/SiC having 35 to 40 vol pct SiC. Scanning and transmission electron microscopy revealed that the fiber-matrix reaction zone is roughly one-half the thickness of that found in SiC-reinforced Ti -6A1-4V, and that it consists of TiC and Ti₅Si₃. Nickel does not enter into the reaction zone products, but rather promotes the formation of Ti₂Ni in the matrix.     

双相区固溶温度对Ti-55531合金组织和力学性能的影响

通过对Ti-55531合金在双相区不同温度(730~830℃)固溶2 h空冷后,经相同的时效工艺(600℃/6 h/空冷(AC))处理;再结合扫描电子显微镜(SEM)和拉伸试验等分析方法,系统研究了双相区不同固溶温度对该合金组织和力学性能的影响规律。结果表明,随固溶温度的升高,等轴αp含量降低,尺寸减小;后续时效析出的αs含量增多,形态也有显著变化,由全短棒状向短棒状+针状、针状+长片状、全长片状的顺序转变。固溶温度从730℃升高到780℃,塑性较好的αp含量减少导致合金塑性降低,αs含量增加导致合金强度提高;固溶温度从780℃升高到800℃,αs含量继续增多导致合金强度上升,适量的长片状αs促进了合金塑性提高;固溶温度从800℃升高到相变点830℃,过多的长片状αs导致合金强度和塑性都显著下降。合金的强塑性匹配较好时对应的固溶温度为780~800℃。合金的断裂方式都是以微孔聚集型为主、含解理撕裂和沿晶开裂的混合断裂机制,且随固溶温度的增加,合金塑性断裂机制减小,脆性断裂机制增加。     

Silicide Formation in Ti-3Al-8V-6Cr-4Zr-4Mo

TEM, including convergent beam electron diffraction (CBED), SEM, and EDX techniques, were used to] characterize the silicide (Ti, Zr)₅ Si₃ which forms in Beta-C (Ti-3Al-8V-6Cr-4Zr-4Mo) and other similar titanium alloys. Space group of this silicide is determined as P6/mmm. In addition, solvus of this silicide was determined and a complete phase field diagram was constructed for Beta-C alloy. It was found that morphology and distribution of the silicide strongly depends on thermal and thermomechanical treatments. Continuous grain boundary silicide was found to be detrimental for tensil ductility which results in intergranular fracture. Thermal and thermomechanical treatments were identified which can reduce or eliminate continuous grain boundary silicide precipitation.     

The influence of microstructure on mechanical properties in Ti-3AI-8V-6Cr-4Mo-4Zr (Beta-C)

The effect of microstructure on mechanical properties of a metastable beta titanium alloy has been investigated, with emphasis on the influence of α-phase precipitation on tensile strength and ductility. A commercial alloy, Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C) has been aged to produce both Type la (obeying the Burgers orientation relation) and Type 2α (not obeying the Burgers relation) as hardening precipitates in the beta matrix. Although a direct comparison of Types 1 and 2α could not be made, there did not seem to be any direct correlation between precipitate type and mechanical properties. Rather, it has been found that overaging to produce a coarse distribution of relatively large (>1000Å) noncoherent α precipitates provides the best combination of strength and duc-tility. The same strength can be achieved with a much finer distribution of small (～100-200A) coherent α precipitates, but with much reduced ductility.     

Elevated-Temperature Mechanical Behavior of As-Cast and Wrought Ti-6Al-4V-1B

This work studied the effect of processing on the elevated-temperature [728 K (455 °C)] fatigue deformation behavior of Ti-6Al-4V-1B for maximum applied stresses between 300 to 700 MPa (R = 0.1, 5 Hz). The alloy was evaluated in the as-cast form as well as in three wrought forms: cast-and-extruded, powder metallurgy (PM) rolled, and PM extruded. Processing caused significant differences in the microstructure, which in turn impacted the fatigue properties. The PM-extruded material exhibited a fine equiaxed α + β microstructure and the greatest fatigue resistance among all the studied materials. The β-phase field extrusion followed by cooling resulted in a strong α-phase texture in which the basal plane was predominately oriented perpendicular to the extrusion axis. The TiB whiskers were also aligned in the extrusion direction. The α-phase texture in the extrusions resulted in tensile-strength anisotropy. The tensile strength in the transverse orientation was lower than that in the longitudinal orientation, but the strength in the transverse orientation remained greater than that for the as-cast Ti-6Al-4V. The ratcheting behavior during fatigue is also discussed.     

变形方式和热处理工艺对Ti-662合金棒材组织和性能的影响

将Ti-662合金铸锭在快锻机和径锻机上经过7火次锻造制备出4,90mm的棒材。研究了2种不同锻造变形方式（轴向反复镦拔和换向反复镦拔）和不同热处理工艺对Ti-662合金棒材组织和性能的影响。结果表明：采用换向反复镦拔锻造获得的Ti-662合金棒材组织均匀无方向性,横向性能较轴向镦拔获得的棒材明显改善,纵、横向性能差别不大;不同的热处理实验对比得出,采用880℃×1h／WC＋600℃×4h／AC固溶加时效处理可使棒材的强度和塑性达到良好匹配,纵、横向力学性能均可满足MIL—T-904标准要求,而且经超声波探伤检测达到AMS2631B中的A1级质量要求。     

Subcritical crack-growth under sustained load in Ti-6AI-6V-2Sn

The subcritical sustained-load cracking (SLC) behavior of beta annealed, recrystallization annealed, and solution-treat-and-aged Ti-6Al-6V-2Sn was studied in dry argon and moist air. The effects of microstructure, internal hydrogen concentration, specimen orientation, and specimen thickness on threshold stress-intensity and crack-growth rate were determined under increasing stress-intensity conditions using wedge-opening load (WOL) specimens, and the fracture morphologies were studied by scanning electron microscopy. The SLC threshold stress intensities are lower and crack growth rates are higher in solution-treatand-aged condition than in beta-annealed and recrystallization conditions. The plane strain conditions increase the susceptibility to SLC. The texture effects on SLC are intensified when the cracking plane is close to the basal plane. For low interstitial-hydrogen concentrations ≈10 ppm, sustained-load crack growth is controlled by creep at the crack tip. Increased hydrogen concentration results in enhanced cleavage, lower threshold stress-intensity, and accelerated crack-growth. Of the possible mechanisms for hydrogen-assisted SLC in Ti-6Al-6V-2Sn, the most likely is that involving preferential segregation of hydrogen to beta phase, leading to fracture by α-β interface separation. Formerly with McDonnell Douglas Research Laboratories.     

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.     

Processing-microstructure relationships for Ti-6Al-2Sn-4Zr-2Mo-0.1Si

The detailed relationships between thermal-mechanical processing parameters and resulting microstructures for Ti-6Al-2Sn-4Zr-2Mo-0.1 Si (Ti-6242) have been established through compression testing and heat treatment. Beginning with either an equiaxed alpha or Widmanstätten alpha preform microstructure, isothermal compression tests were run at strain rates typical of isothermal forging (10^?3 to 10^?1 s^?1) and conventional forging (1 to 100 s^?1). Metallographic investigation of these test specimens in as-deformed and heat treated conditions was used to characterize deformation-induced microstructures and transformations. For the equiaxed alpha microstructure, it was shown that deformation, as well as post-deformation heat treatment, were more effective in promoting microstructures close to the expected equilibrium ones than heat treatment alone, a finding similar to that for other alloy systems. For the metastable Widmanstätten alpha microstructure, the deformation and heat treatment parameters that promote the development of an equilibrium, equiaxed alpha microstructure have been determined. For this microstructure, two separate temperature-strain rate regimes have been identified, and the resulting microstructures correlated with the measured flow stress behavior. For the low temperature regime, deformation is highly nonuniform, and the microstructural features are shown to be similar to those in pearlitic steels and other lamellar alloys. In the higher temperature regime, on the other hand, deformation is much more uniform. The results presented can be applied to select hot forging parameters for the control of final microstructure and properties in Ti-6242 and similarα/β titanium alloys.     

热挤压工艺对Ti-6Al-4V钛合金组织与性能的影响

研究了挤压温度和挤压比对Ti-6Al-4V钛合金挤压型材显微组织、织构及力学性能的影响.挤压温度在相变点T_β以上150~350℃、挤压比λ为25~85范围内时,型材动态再结晶均已完成,形成均匀的魏氏组织.型材的晶粒随挤压温度的降低和挤压比的提高而细化.型材织构在挤压比较低(λ=25)时强度较弱且为随机分布;当挤压比增加时,织构增强并有形成(1219)面纤维织构的趋势;当挤压比提高至85时,形成完整的(1219)面纤维织构.由于织构与晶粒细化的共同作用,使不同挤压条件下得到的Ti-6Al-4V钛合金型材综合力学性能比较稳定,即强度差异均不大于35 MPa,且延伸率和断面收缩率差值均不超过3%.      

内燃机用粉末烧结Ti-21.5Nb合金组织与力学性能研究

采用放电等离子烧结技术制备内燃机用Ti-21.5Nb-2Zr-1.2Mo-0.1Y钛合金材料(Ti-21.5Nb), 并对其进行固溶和时效处理, 通过扫描电子显微镜、金相显微镜、X射线衍射仪、万能拉伸测试仪等设备分析试样的微观形貌、组织结构、物相组成以及力学性能。结果表明: 采用等离子旋转电极法制备的预合金球形粉末相对密度较高, 并且未形成孔洞; 烧结试样和固溶试样都是由β相与α相组成, 放电等离子烧结Ti-21.5Nb合金和常规铸锭合金具有相同的相结构变化规律; 合金烧结组织由β等轴晶和一些小尺寸α相构成, 其中β等轴晶的粒径介于30~80μm; 在800 ℃下对烧结试样进行固溶时效处理, 得到的固溶组织主要是由β相构成, 同时在β相中还生成了椭球形α弥散组织; 在500 ℃下对Ti-21.5Nb固溶试样进行时效处理, 在合金基体中析出ω相, 而原先的α相全部消失; 在380 ℃时效处理时, 组织中只存在α相, ω相完全消失; 在800 ℃对Ti-21.5Nb合金进行固溶时效处理可以获得力学性能更优的钛合金材料。     

Correlation of tensile properties, deformation modes, and

The effect of plastic deformation mode on tensile properties of quenched commercial β-phase titanium alloys has been investigated at approximately constant grain size and oxygen content. In addition, stability of β-phase has been estimated from ω-reflections or diffuse streaking in electron diffraction patterns in a manner similar to the previous works on binary β-phase titanium alloys. Dominant mode of plastic deformation is 332 〈113〉 twinning in the alloys with large instability of β-phase, such as Ti-ll.5Mo-6Zr-4.5Sn and Ti-15Mo-5Zr, and is crystallographic slip in the alloys with small instability of β-phase, such as Ti-15Mo-5Zr-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15V-3Cr-3Al-3Sn, Ti-8Mo-8V-2Fe-3Al, and Ti-13V-11Cr-3Al. Twinning leads to low yield strength and large elongation, while slip results in high yield strength and small elongation in agreement with binary and ternary β -phase titanium alloys.     

Correlation of tensile properties,deformation modes,and phase stability in commercial β-phase titanium alloys

The effect of plastic deformation mode on tensile properties of quenched commercial β-phase titanium alloys has been investigated at approximately constant grain size and oxygen content. In addition, stability of β-phase has been estimated from ω-reflections or diffuse streaking in electron diffraction patterns in a manner similar to the previous works on binary β-phase titanium alloys. Dominant mode of plastic deformation is {332}<113> twinning in the alloys with large instability of β-phase, such as Ti-11.5Mo-6Zr-4. 5Sn and Ti-15Mo-5Zr, and is crystallographic slip in the alloys with small instability of β-phase, such as Ti-15Mo-5Zr-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15V-3Cr-3Al-3Sn, Ti-8Mo-8V-2Fe-3Al, and Ti-13V-11C-3Al. Twinning leads to low yield strength and large elongation, while slip results in high yield strength and small elongation in agreement with binary and termary β-phase titanium alloys.     

Hydrogen-induced slow crack growth in Ti-6Al-6V-2Sn

The effect of hydrogen and temperature on threshold stress intensity and crack growth kinetics was studied in Ti-6Al-6V-2Sn containing 38 ppm hydrogen. A slight decrease in threshold values occurred as temperature decreased from 300 K while they increased significantly above 300 K. For a given test temperature, crack growth rates exhibited an exponential dependence on stress intensity over a major portion of growth. At 300 K the rates reached a maximum. Slow crack growth occurred predominately by cleavage ofα grains which has been associated with hydride formation. The stress intensity required for hydride formation at a crack tip can be determined from hydrogen concentration and solubility considerations under stress. As these values differed from observed thresholds, a strong influence of microstructure was suggested and subsequently revealed by crack front examination. Quantification of this effect with a modified Dugdale-Barenblatt model relates the effective stress intensity at the crack tip to the applied stress intensity. Microstructure was also found to exert a strong influence on slow crack growth behavior when examined in terms of the effective stress intensity,K _eff. From Arrhenius plots of crack growth rates for variousK _eff, activation energies of 27.0 to 32.8 kJ/mol were obtained and related to the diffusion of hydrogen through theβ phase. The increase in crack growth rates with increasing temperatures up to 300 K is attributed to the temperature dependence of hydrogen diffusion. The decrease in crack growth rates above 300 K is related to a hydride nucleation problem.     

Microstructure and Mechanical Properties of Gas-Tungsten-Arc–Welded Ti-15-3 Beta Titanium Alloy

Microstructure and mechanical properties of gas-tungsten-arc (GTA)–welded Ti-15V-3Cr-3Sn-3Al alloy in direct current electrode negative mode are characterized. The thermal profile was measured during welding with continuous current (CC) and pulsed current (PC) at different frequencies. A single-step postweld aging of the welded samples at subtransus temperature was attempted to study precipitation of alpha phase. Two different morphologies of alpha phase are observed along with a partitioning of alloying elements into the two phases. Processing conditions for higher strength are identified and correlated with the thermal profile. Microstructure changes due to postweld heat treatment were characterized.