Fabrication of low-cost Ti-1Al-8V-5Fe by powder metallurgy with TiH2 and FeV80 alloy

The low-cost Ti-1Al-8V-5Fe (Ti-185) alloy with a high strength is prepared by cold-compaction-and-sintering powder metallurgy process with low-cost titanium hydride (TiH₂) powders and FeV₈₀ master alloy powders. The use of simple technique process and cheap alloying elements can lead to the cost reduction for titanium alloys. The thermal decomposition of TiH₂-1Al-8V-5Fe is analyzed by thermal gravimetric analyses and differential scanning calorimetry simultaneous thermal analyzer. The shrinkage behavior of TiH₂-1Al-8V-5Fe during the sintering process is employed by the high-sensitivity dilatometer system. The microstructure of sintered Ti-185 consists of β-phase and lamellar α-phase. The results show that the sintered Ti-185 alloys have the relative density of 97.8%, homogeneous composition, and fine grains. The yield strength and the hardness are 1461?MPa and 40.1?±?1.0 HRC (unit of Rockwell hardness), which are better than that of as-cast Ti-185.     

Sintering densification behaviors of Ti-1Al-8V-5Fe alloy based on TiH2 and TiH1.5 powders

The sintering densification behaviors of Ti-1Al-8V-5Fe alloys by saturated titanium hydride (TiH₂) and unsaturated titanium hydride (TiH_1.5) powders are investigated. The results show that the TiH₂-185 specimens present better sintering densification ability compared with TiH_1.5–185 specimens, which displays that the titanium hydride with more hydrogen has a stronger densification ability. The TG-MS analysis suggests that the decompositions of TiH₂ and TiH_1.5 powders are accompanied by the H₂O releasing, and the TiH₂ releases more H₂O than that of TiH_1.5. The twice phase transformations can be observed in the TiH₂-185 specimens by DSC, which contribute to the H₂O releasing and dislocations and vacancies. Thus, TiH₂ powder is helpful to obtain higher sintering densification and better mechanical properties for Ti-1Al-8V-5Fe alloy.     

The sintering densification and microstructure evolutions of Ti-1Al-8V-5Fe alloy with Si additions

The cost-efficient Ti-1Al-8V-5Fe-xSi (denoted Ti-185-xSi hereafter, x = 0, 0.15, 0.3, 0.45, 0.6, 0.75) alloys are synthesized by cold compaction and sintering powder metallurgy (PM) technology using TiH₂ and high-pure FeV₈₀ powders. The sintering densification, microstructural evolutions and mechanical behavior of Ti-185-xSi alloys sintered at 1350°C are investigated. The results show that the Si element is favorable to enhance the sintered density of Ti-185 alloys, which should be limited to ≤0.3%. The amount and average size of precipitate Ti₅Si₃ increase in the Ti-185 alloys with increasing Si content. Meanwhile, the Rockwell hardness of Ti-185 alloy also displays an increasing tendency, suggesting the Si element can improve the hardness of Ti-185. The Ti-185–0.15Si alloy possesses a better comprehensive mechanical property of strength (937 ± 8 MPa) and elongation (3.5%). The high-performance Ti-185 alloy is successfully prepared using low-cost FeV₈₀ master alloy with slight Si impurity instead of costly V.     

Microstructure and refinement mechanism of TiB2/TiAl3 in remelted Al-5Ti-1B system

In this work, we propose a new method (by remelting Al-5Ti-1B) to investigate the grain refinement mechansim. It is found that the morphology and size of TiAl₃ phase had little effect on the grain refinement of pure Al. Therefore, further experimental studies were carried out to understand the potency of TiB₂ particles. The high-resolution transmission electron microscopy (HRTEM) observation has confirmed the existence of an atomic layer on the surface of (0001) TiB₂, which is possibly a two-dimensional (2D) (1-12) TiAl₃. Crystallographic study indicates that it is a more suitable nucleation sites for α-Al than other particles. The TiB₂ particle with TiAl₃ 2D acts as the best effective nucleation sites for α-Al.     

基于TiH2原料的粉末冶金Ti-6Al-3Nb-2Zr-1Mo合金的组织与性能研究

目的 研究烧结工艺对Ti-6Al-3Nb-2Zr-1Mo合金组织演变及力学性能的影响.方法 以TiH2粉末为原料,采用粉末冶金工艺制备低成本高性能的Ti-6Al-3Nb-2Zr-1Mo合金,分析合金在不同烧结条件下组织与性能的变化规律.结果 TiH2的脱氢温度区间集中在450～700℃;Ti-6Al-3Nb-2Zr-1...     

Control of microstructure and component shape in rapidly solidified/powder metallurgy titanium alloys

Extensive use of titanium rapidly solidified/powder metallurgy (RS/PM) components requires not only careful control of the microstructure for optimum mechanical properties but also cost-effective processing. A new direct reduction process for production of titanium alloy powder will be presented. Control of the microstructure in conventional alloys such as Ti-6Al-4V and in non-conventional dispersion strengthened terminal and intermetallic alloys will be discussed. It will be shown that RS/PM processing allows production of a fine grain size and useful dispersions of rare earth and metalloid phases; phases which normally form as gross undesirable particles. The use of hydrogen as a temporary alloying element, thermochemical processing, will be discussed and it will be demonstrated how this treatment can lead to refined microstructures with enhanced mechanical behaviour. Cost-effective processing using near-net shape techniques such as the ceramic mold process, rapid omnidirectional compaction (ROC), and the use of RS/PM preforms for subsequent isothermal forging will be presented. Microstructural control and shape-making used in unison should lead to increased use of titanium components in advanced aerospace systems. work done as a consultant to Metcut-Materials Research Group     

Ti-6Al-2Zr-1Mo-1V合金热塑性流变行为的变参数Arrhenius模型表征

在Gleeble-1500热模拟试验机上进行多组热压缩试验,获得Ti-6Al-2Zr-1Mo-1V合金在温度1073～1323K、应变速率0.01～10s-1下的真应力-应变数据,基于此分析工艺参数对流变应力演变的影响规律,识别应力-应变曲线的动态再结晶型和动态回复型软化特征及其出现时机。引入不含应变影响的传统Arrhenius型本构方程,将其进一步拓展使用,在不同应变量条件下,通过多元线性回归计算与多项式拟合,求解获得Ti-6Al-2Zr-1Mo-1V合金形变表观激活能Q、材料常数n、α及结构因子A等参量对应变的响应规律,从而建立Ti-6Al-2Zr-1Mo-1V合金含应变、温度及应变速率影响的变参数流变应力本构方程。模型预测值与实验值对比显示最大相对误差为4.55%,最大平均误差为2.19%。     

Al-V含量对TiH2粉制备钛基合金性能的影响

为了揭示Al-V含量对钛基合金性能的影响,以TiH₂粉、Ti粉为原料,制备不同含量铝、钒(质量分数:0,2.5%,5%,7.5%,10%)的钛合金试样,通过对样品的力学性能、物相、显微组织、断口形貌的分析,研究了铝钒含量对合金的微观组织和力学性能的影响。结果表明:两种原料对应烧结试样的相主要由密排六方结构α-Ti和少量的体心立方结构β-Ti构成,铝钒含量的增加对烧结样品物相的相对含量无明显影响,但XRD衍射峰稍向右偏移;纯TiH₂和纯Ti烧结试样为等轴组织,加入铝、钒合金元素后纯TiH₂粉对应的组织为片状组织,纯Ti粉对应的组织以等轴为主,随铝、钒的增加,对应组织形貌变化较小;纯TiH₂和纯Ti烧结样品的抗拉强度分别为562.88和513.44 MPa,强度较低,但延伸率高,分别为28.15%和29.09%;随铝、钒含量的增加,TiH₂和Ti对应样品的强度、硬度增加,延伸率下降,最大强度值分别为914.10和937.23 MPa,对应的延伸率分别为7.60%和10.89%。随铝钒含量的增加两类合金的脆性增加,塑性降低,加入铝钒后纯TiH₂粉对应试样断口形貌主要呈条形花样和少量韧窝,纯Ti粉对应试样断口以韧窝为主。     

(Mg2B2O5w+ND)/ZK60镁基复合材料的摩擦磨损性能研究

在湿球磨条件下以600 r/min高能球磨混粉,并将球磨后的粉末经过热压烧结-热挤压成型制备(Mg2B2O5w+ND)/ZK60镁基复合材料。研究了(Mg2B2O5w+ND)/ZK60镁基复合材料在不同载荷和转速下的干摩擦磨损性能。结果表明:干摩擦条件下,材料的摩擦系数随着滑动距离的增加会经历跑和阶段和稳定阶段;材料的质量磨损率随着转速的增大而降低,随着载荷的增大而增大,且基体镁合金的质量磨损率始终低于复合材料。随着摩擦载荷和转速的增加,材料的摩擦系数减小,然后逐渐趋于平稳。混杂增强的镁基复合材料相比基体合金具有更低的摩擦系数。     

Growth and characterization of Bi2Sr2Ca1Cu2O8+x single crystals

High-quality single crystals are well suited to the investigation of some intrinsic material properties. A modified Bridgman method using a sharp temperature gradient (300°C/cm) was used to grow Bi₂Sr₂Ca₁Cu₂O_8+x single crystals. Although the samples were contained in alumina ampoules, no aluminium contamination of the samples was detected. Blade-shaped crystals up to 7–8 mm length and 3–4 mm width could be grown by this method, although extraction from the matrix was difficult. Electron diffraction patterns of the [001] zone axis revealed a high degree of crystallinity. The narrowness of the superconducting transition temperature, as determined by ac susceptibility, also suggests the existence of well-formed crystalline domains. In order to determine the relative orientation of the crystalline domains, electron channeling patterns were recorded from several consecutive growth steps from a fracture surface. The poor contrast of these and Kikuchi patterns suggests the presence of a stacking structure. The results showed a [100] growth direction and (001) cleavage plane. Reversible oxygen loss at the peritectic decomposition temperature of 863°C was observed. Knoop indentation measurements showed that the crystals were quite soft, having a microhardness of 0.44 GPa.     

Electronic band structure calculations on thin films of the L21 full Heusler alloys X2YSi (X, Y = Mn, Fe, and Co): Toward spintronic materials

To design half-metallic materials in thin film form for spintronic devices, the electronic structures of full Heusler alloys (Mn₂FeSi, Fe₂MnSi, Fe₂FeSi, Fe₂CoSi, and Co₂FeSi) with an L2₁ structure have been investigated using density functional theory calculations with Gaussian-type functions in a periodic boundary condition. Considering the metal composition, layer thickness, and orbital symmetries, a 5-layered Co₂FeSi thin film, whose surface consists of a Si layer, was found to have stable half-metallic nature with a band gap of ca. 0.6 eV in the minority spin state. Using the group theory, the difference between electronic structures in bulk and thin film conditions was discussed.     

Doping-induced microstructural, textural and optical properties of In2Ti1−xVxO5+δ semiconductors and their role in the photocatalytic splitting of water

The physicochemical properties of V-doped indium titanates (In₂Ti_1−xV_xO_5+δ, 0.0 ≤ x ≤ 0.2) were investigated by using XPS, powder XRD, UV–vis, SEM and luminescence spectroscopy techniques. The Rietveld refinement of XRD data revealed that even though the V-containing samples were isostructural with In₂TiO₅ (orthorhombic space group Pnma), a systematic x-dependent variation was noticeable in the Ti–O bond lengths in [TiO₆] octahedral units, cell parameters and in the value of δ. XPS results confirmed the coexistence of V⁵⁺ and V⁴⁺ states, leading thereby to an enhancement in oxygen non-stoichiometry in the doped samples. A loading-dependent progressive shift from 400 to 750 nm was also observed in the onset of the absorption edge, indicating a significant narrowing of the band gap. Furthermore, the samples with higher V-content were comprised of the grain clusters having larger size and an irregular shape. The UV–vis, photoluminescence and thermoluminescence studies indicate that the doping-induced lattice defects may give rise to certain closely spaced acceptor/donor energy levels in between the band gap of host matrix. The indium titanates are found to serve as stable photocatalysts for water splitting under visible light, where oxygen was the major reaction product. The role of microstructural and morphological properties in the photocatalytic activity is discussed.