Ti-6Cr-5Mo-5V-4Al合金中α相的析出行为及对力学性能的影响

对比研究了Ti-6Cr-5Mo-5V-4Al合金双时效和单时效对α相析出行为及力学性能的影响。组织观察显示,合金固溶淬火后得到等轴β晶粒。经过低温预时效后,在β晶内获得均匀弥散的α相团簇组织,但在β晶界出现无析出区(PFZ)。这种β晶内/晶界分区析出特征直接影响后续高温时效形貌。双时效后,在β晶内析出细小均匀的α相,但在β晶界,α相呈粗大片状。与之相比,单时效后,α相分布较为均匀,都为粗大层片。拉伸结果表明,与单时效试样相比,双时效试样抗拉强度高达约1630 MPa,但延伸率较差(约2%)。这种高强度归结为组织中亚微米、纳米量级α粒子强烈的析出强化效应,而急剧的延性损失主要源于β晶界处粗大α片诱发的形变局域化进而导致早期沿晶脆性断裂。     

热处理对锻态2.5vol.%(TiB TiC)/Ti复合材料组织与性能的影响

研究了热处理条件对锻态2.5vol.%(TiB TiC)/Ti复合材料显微组织和力学性能的影响。结果表明：固溶时效处理对复合材料的基体组织特征有显著影响,在两相区进行固溶时效处理后,得到等轴和双态组织,随固溶温度的升高,初生α相含量逐渐降低,而β转变组织含量逐渐升高,当固溶温度超过β转变温度时,得到全片层组织。TiB和TiC增强相在热处理过程中较为稳定,形态与分布无明显变化。固溶时效处理后,锻态复合材料的拉伸强度提高而塑性降低,随固溶温度的升高,复合材料的室温拉伸强度和塑性均有明显增加,而650 oC下拉伸强度与塑性与室温下表现出相反的规律。复合材料经1050oC/2h/AC 600oC/6h/AC处理后综合性能最好,室温拉伸强度为1215.8MPa,延伸率为3.14%,650 oC下拉伸强度为629.9MPa,延伸率为15.9%。     

Ti—Al二元合金的成分对组织和力学性能的影响

用金相、扫描电镜和X射线衍射研究了6种不同Al含量Ti-Al二元合金铸态和退火态的组织结构和相组成的特征和变化。从结晶动力学的观点,分析了合金的结晶凝固过程。采用三点弯曲方法研究了合金的抗弯性能同Al含量的关系。结果表明,Al含量为34 wt%,经1100℃/30 h退火的合金抗弯性能最好,Al含量偏离34wt%,都对合金的力学性能不利。     

Exploring corrosion protection of La-Fe-Si magnetocaloric alloys by passivation

Magnetocaloric La(Fe,Si)₁₃-based alloys are promising materials for magnetic cooling systems but their limited corrosion resistance in water-based heat transfer fluids is critical. The corrosion behavior of as-cast and annealed La-Fe-Si alloy samples was analyzed in comparison to that of La and Fe for evaluation of the impact of alloy chemistry and microstructure. Electrochemical studies were conducted in defined electrolytes starting with aerated distilled water (pH = 6) for assessing the influence of pH value changes and anion contaminations. Specifically, forced flow electrolyte conditions were applied which are closer to operation conditions of real magnetocaloric regenerator beds than stagnant ones. Corroded sample surfaces were analyzed with SEM to assess damage mechanisms. The reactive nature of the alloy constituents determines the high corrosion activity and limited passivation ability of La-Fe-Si alloys. Their exposure to distilled water is particularly detrimental under stagnant conditions as local fluid acidification enhances corrosion processes. These are based on galvanic coupling between the phases with different corrosion activities: La-rich phases > La(Fe,Si)₁₃-based matrix > alpha-Fe(Si). Laminar fluid flow is beneficial for alloy surface passivation. But anion contaminants like sulfate or hydrogen phosphate ions counteract the weak passivity in flowing distilled water. While acidic conditions lead to instable corrosive states, a pH value control of the heat transfer fluid at alkaline conditions is effective for stable passivity of the alloy surface. Also, the applicability of a phosphate conversion coating treatment in 0.15 M NaH₂PO₄ (pH = 4) was evaluated and prospects of this approach are discussed.     

Active Eutectoid Decomposition of α → γ + τ _1 and the Morphological Evolution in a Ru-Containing TiAl Alloy

The active eutectoid decomposition and its morphological evolution during slow cooling and isothermal holding were investigated in a Ru-containing Ti Al alloy. The fine τ 1/γ active eutectoid nodules precipitated at α grain boundary and interior during water quenching. The active eutectoid microstructure evolved from sheaf-like, granular to bulky net-like sluggish eutectoid morphology gradually with the decrease in quenching/holding temperatures. The active eutectoid reaction occurs from 1220 to 1290 ℃, while the beginning temperature of sluggish eutectoid locates at 1305 ± 5 ℃. The combination of the intact τ_1 phase and immature nano-sized γ laths suggests a short incubation period of τ_1 phase in the active type. Furtherly, the semiquantitative estimation shows that the growth velocity of active eutectoid is about ninety times higher than sluggish type. In addition, a representative feature of γ phase abruptly ripening along {111} crystallographic plane was also observed in the active eutectoid.     

Effects of annealing on microstructure and properties of linear friction welded dissimilar titanium joints

Linear friction welds of Ti–6Al–4V (TC4, according to Chinese classification) to Ti–6·5Al–3·5Mo–1·5Zr–0·3Si (TC11, according to Chinese classification) were subject to post-weld heat treatment (PWHT) at 650°C×4 h (PWHT1) and at 950°C×1 h+530°C×4 h (PWHT2) under air cooling. In the as welded joint, TC4 had recrystallised sufficiently compared to TC11. After PWHT1, the α grains in the TC4 weld centre zone grew to some extent and many superfine equiaxed recrystallised α grains precipitated along β boundaries on the TC11 side. The grain growth along the weld line in the weld centre zone under PWHT2 was evident. PWHT2 reduced the joint tensile strength due to the coarsening of the microstructure. The joint microhardness decreased after PWHT.     

Grain refinement of cast titanium alloys via trace boron addition

The grain size of as-cast Ti–6Al–4V is reduced by about an order of magnitude from 1700 to 200 μm with an addition of 0.1 wt.% boron. A much weaker dependence of reduction in grain size is obtained for boron additions from >0.1% to 1.0%. Similar trends were observed in boron-modified as-cast Ti–6Al–2Sn–4Zr–2Mo–0.1Si.     

Cu过渡层对激光增材制造TC4/IN718双金属结构组织性能的影响

钛合金和镍基合金各具有独特性能,二者的双金属结构在航空航天领域具有广泛的应用前景。由于2种金属的物理与化学性能差异较大,易在结合区域产生开裂。基于直接激光沉积（DLD）技术,分别制备了无过渡层和Cu过渡层的TC4/IN718双金属结构。测试分析结果表明,无过渡层双金属结构,结合区形成大量Ti-Ni脆性相,导致裂纹敏感性提高,产生开裂;Cu过渡层的双金属结构,在TC4与IN718之间形成Cu过渡区,限制TC4与IN718直接结合,降低裂纹敏感性,无裂纹等冶金缺陷产生,由于冶金反应与元素扩散的发生,在Cu过渡区中形成了少量Ti-Cu与微量Ti-Ni化合物相;化合物相在双金属结构中的产生,使Cu过渡区维氏硬度最高约为5801.6MPa,但远低于无过渡层双金属结构的维氏硬度（最高约为8281 MPa）。     

Infrared brazing of Ti–6Al–4V using two silver-based braze alloys

Infrared brazing of Ti–6Al–4V using two silver-based alloys is evaluated in the study. For the 72Ag–28Cu brazed specimen, Ag-rich matrix, eutectic Ag–Cu and Cu–Ti interfacial reaction layer(s) are observed in the experiment. In contrast, both Ag-rich matrix and interfacial titanium aluminides, TiAl or Ti₃Al, are found in the 95Ag–5Al brazed joint. In general, the shear strength of 72Ag–28Cu brazed joint is much higher than that of 95Ag–5Al brazed specimen. Additionally, the use of infrared brazing with lower brazing temperature and/or less time can significantly decrease both dissolution of the substrate into molten braze as well as excessive growth of the interfacial reaction layer(s) in the joint. Therefore, infrared brazing has the potential to be applied in industry.     

Radial Distribution Characteristics of Microstructure and Mechanical Properties of Ti–6Al–4V Butt Joint by Rotary Friction Welding

Ti–6Al–4V rods were butt-welded by rotary friction welding in this study. Additionally, the radial differences in microstructure and mechanical property of joints were investigated by hierarchy slicing method. The results displayed that the width of weld zone and heat-affected zone of joints became wider along radial direction. Meanwhile, the tensile strength of joints decreased gradually along the radial direction. According to the theoretical analysis, the temperature gradient and inhomogeneous forging pressure leaded to the radial differences. Through K-type thermocouples, the actual temperatures at different locations were measured, and the results were consistent with the theoretical analysis. Theoretically, the radial differences of rotary friction welding joint are an inherent phenomenon; thus, the size of weldment should be limited strictly below the corresponding critical size. In order to prevent radial differences from enlarging, the welding surface profile of weldment can be processed into oval shape, and a larger forging pressure can be used within the scope of the joint deformation allowed according to causes for radial differences.     

Effect of the addition of palladium on grain growth kinetics of pure titanium

In the present work, experimental research on grain growth kinetics at different temperatures and times of heat treatment for titanium and Ti---0.2Pd in the and β phases has been carried out. The grain size parameters were obtained by the image analysis technique. The aim of the present study was to quantify the progress of grain growth and the corresponding activation energy for and β titanium, and to determine the effect of Palladium. By means of EDS microanalysis, it has been observed that the effect of a higher concentration of palladium on the grain growth is to decrease the growth exponent for the Ti-0.2Pd alloy. The activation energies differ a lot between the two phases and β for Ti and Ti-0.2Pd. This difference might be due to the different crystal structures.     

Surface characterization of Ti-7.5Mo alloy modified by biomimetic method

Titanium and its alloys have been used in dentistry due to their excellent corrosion resistance and biocompatibility. It was shown that even a pure titanium metal and its alloys spontaneously form a bone-like apatite layer on their surfaces within a living body. The purpose of this work was to evaluate the growth of calcium phosphates at the surface of the experimental alloy Ti-7.5Mo. We produced ingots from pure titanium and molybdenum using an arc-melting furnace. We then submitted these ingots to heat treatment at 1100 °C for one hour, cooled the samples in water, and cold-worked the cooled material by swaging and machining. We measured the media roughness (Ra) with a roughness meter (1.3 and 2.6 μm) and cut discs (13 mm in diameter and 4 mm in thickness) from each sample group. The samples were treated by biomimetic methods for 7 or 14 days to form an apatite coating on the surface. We then characterized the surfaces with an optical profilometer, a scanning electron microscope and contact angle measurements. The results of this study indicate that apatite can form on the surface of a Ti-7.5Mo alloy, and that a more complete apatite layer formed on the Ra = 2.6 μm material. This increased apatite formation resulted in a lower contact angle.     

热处理工艺对Ti55531合金组织与性能的影响

采用正交试验研究不同热处理工艺对Ti55531合金显微组织和力学性能的影响。结果表明,显著影响合金显微组织和力学性能的因素依次是固溶温度、时效温度、时效时间。随固溶温度的升高,初生α相含量明显减少,α相的等轴性表现较好且分布更加均匀,抗拉强度逐渐增加,伸长率下降;随时效温度的升高,次生α相开始增加、长大,组织向双态组织转变,使得抗拉强度下降,伸长率增加。其合理的\"固溶+时效\"热处理工艺为\"820℃×2h固溶,空冷+580℃×10h时效,空冷\",抗拉强度为1 370MPa,伸长率为8.5%。