Electrolytic production of Ti-Ge intermetallics from oxides in molten CaCl2-NaCl

Titanium germanium intermetallics (Ti_xGe_y) were directly prepared from titanium oxide (TiO₂) and germanium oxide (GeO₂) powders mixture by using an electrodeoxidation process. The electrochemical experiment was carried out in a molten flux CaCl₂-NaCl at 800 °C with a potential of 3.0 V. The results show that monolithic germanide Ti₅Ge₃ intermetallic can be directly produced from TiO₂-GeO₂ or CaTiO₃-GeO₂ precursors (both molar ratios are 5:3), and the obtained Ti₅Ge₃ powders exhibit homogenous particle structure. In addition, the phase composition of the final product can be dramatically affected by the initial molar ratio of TiO₂ to GeO₂. The reaction mechanism of the electrodeoxidation process was discussed based on the experimental results. It is suggested that the electrodeoxidation process is an environmentally friendly method for the preparation of Ti-Ge intermetallics.     

Preparation of low-oxygen-containing Ti–48Al–2Cr–2Nb alloy powder by direct reduction of oxides

A high-purity Ti–48Al–2Nb–2Cr alloy powder with an oxygen content as low as 0.0572 wt.% and a particle size of <150 μm was produced from a mixture of TiO₂, Al₂O₃, Nb₂O₅, and Cr₂O₃ powders through reduction with magnesium and deoxidation with calcium. The phase and composition of the products were analyzed. The final product mainly included γ-TiAl and minor α₂-Ti₃Al phases, and Ti, Al, Cr, and Nb were homogenously distributed in the powder with a mole ratio of 49.73:43.51:2.05:1.98. The reduction and deoxidation mechanisms were investigated by thermodynamic modeling using the HSC Chemistry software and Pandat software based on the Ti alloy database.     

α″相辅助形核获取超细α相高强度近β态钛合金（英文）

采用多元扩散偶实验方法,设计具有超细α相的Ti-6Al-4V-x Mo-y Zr(0.5α/(110)_β界面具有平台-台阶结构,(■20)_a/(■11)_b界面为平直界面,没有台阶。     

含氧环境中航空发动机用Ti40阻燃钛合金的摩擦点燃

采用摩擦点燃的方法,研究摩擦压力p和氧浓度xO对Ti40阻燃钛合金的抗点燃性能的影响,建立了定量描述Ti40钛合金抗点燃性能的p-xO关系曲线,并结合SEM、XRD和EDS等测试手段分析Ti40钛合金的抗点燃机理。结果表明：Ti40钛合金的p-xO关系曲线符合抛物线规律,p在0.1~0.25 MPa变化时,xO的变化范围约为25%。当 xO≥70%时,Ti40钛合金在室温条件下即会被点燃,并迅速发展为持续的稳定燃烧,且时间长于10 s。Ti40钛合金的抗点燃性能优于TC4钛合金的,Ti40合金被点燃时所对应的xO至少比TC4高40%。当xO较低时,Ti40钛合金的抗点燃性能对p较为敏感,而随着xO的增大,抗点燃性能对xO更加敏感。摩擦表面形成的具有强相互作用的V2O5、TiO2和Cr2O3氧化物融合物是Ti40钛合金的抗点燃性能提高的根本原因。     

Oxidation of Ti3SiC2 between 900 and 1200 °C in Air

Ti₃SiC₂ materials were synthesized by hot pressing using a new starting-material system consisting of a TiC_x(x=0.6)/Si powder mixture. The oxidation of Ti₃SiC₂ at temperatures between 900 and 1200 °C in air for up to 100 h resulted in the formation of an outer TiO₂ layer, an intermediate SiO₂-rich layer and an inner (TiO₂ + SiO₂) mixed layer. During oxidation, Ti diffused outwards to form the outer TiO₂ layer, and oxygen transported inwards to form the inner (TiO₂ + SiO₂) mixed layer. At the same time, the carbon in Ti₃SiC₂ escaped into the air. Below the scale, there was a narrow oxygen-affected zone, The oxidation at the scale-matrix interface proceeded by the disintegration of the lamellar Ti₃SiC₂ grains to form crystallites with a size of a few tens of nanometers containing oxygen. The detailed scale characteristics and oxidation mechanism are described.     

Formation of M_(n+1)AX_n phases in Ti–Cr–Al–C systems by self-propagating high-temperature synthesis

In this paper, phase composition of the Mn+1-AXnphases by self-propagating high-temperature synthesis(SHS) was determined using Ti, Cr, Al, and carbon black as raw materials. And, phase composition and microstructures of the Mn+1AXnphases-contained bulk by SHS with the pseudo-hot isostatic pressing(SHS/PHIP) were investigated in Ti–Cr–Al–C systems raw materials. Rietveld XRD refinement was introduced to study the lattice parameters and phase composition of the resultant phases from the SHSed and SHS/PHIPed samples. Ti2 AlCx,Ti3AlC2x, and Cr2 AlCxby SHS were detected in the Ti–Cr–Al–C systems, as well as the binary carbide of TiC and intermetallics. The mechanical properties of the synthesized bulk samples were determined, exhibiting a high strength and toughness compared with the typical monolithic Mn+1AXnphase ceramics. It is indicated that the samples prepared by SHS/PHIP are identified to be a strategy for improving the mechanical properties of monolithic Mn+1AXnphase.     

Affordable electrolytic ferrotitanium alloys with marine engineering potentials

Fe₂O₃ and TiO₂ powders were compounded in different proportions at elevated temperatures. Porous thin pellets were made from the compounded oxides and then electro-reduced to the respective ferrotitanium alloys and/or intermetallic compounds in solid state in molten CaCl₂. Typical electrolysis conditions were 800–1000 °C, 2.8–3.2 V and 4–15 h. X-ray diffraction, scanning electron and optical microscopy, and potentiodynamic polarisation were used to characterise the oxide precursors and/or the products. The results showed that the obtained Fe–Ti alloys achieved the designated elemental compositions. When the Fe content in the oxide precursor was less than 50 wt.%, the products were mainly mixed Ti and Fe–Ti alloys. At higher Fe contents, the products changed to a mixture of Fe₂Ti and Fe. Between 8 and 15 wt.% Fe, the products sintered most severely. The Fe-rich Fe–Ti alloys had better corrosion resistance than a common ship hull steel (E36) in simulated sea water, i.e. the aqueous solution of 3 wt.% NaCl. The Ti-rich Fe–Ti alloys (8 wt.% Fe) had good corrosion resistance to the 1.0 mol/L HCl solution. The addition of Nb in the alloys improved the corrosion resistance, but the addition of Al caused the opposite effect.     

制钛过程中阴极钙钛矿的形成与阳极溢出气体间的关系

采用FFC剑桥工艺在熔融CaCl₂中电解二氧化钛时,钙钛矿是阴极上不可避免形成的相。本文研究了在制备钛的过程中,阴极钙钛矿的形成与阳极释放气体的关系。结果表明,阴极上相的形成主要有三个阶段,包括钙钛矿的形成、钙钛矿的脱氧及钛的低价氧化物脱氧为TiO、和TiO到Ti的脱氧。尽管分解电压低于CaCl₂,但阴极形成的钙钛矿与从阳极释放的气体密切相关。由于短时间内钙钛矿的形成造成过电压,因而阳极释放出氯气,氯气的量取决于TiO₂和电解过程中产生的不同低价钛的量。当钛的低价氧化物介于Ti₃O₅和TiO₂之间时,在第一脱氧阶段TiO₂和氯的质量比为9：2到46：2。在氯气释放的过程中阳极没有明显的消耗。钙钛矿的形成和Ti₂O的脱氧是在熔融CaCl₂中电解制备钛的主要限制性环节。从TiO₂到Ti的总电流效率是24.07％。目前第一阶段的电流效率在22.37％~44.74％之间,第二阶段在30.18％~37.72％之间。     

Carbide stoichiometry in TiCx and Cu–TiCx produced by self-propagating high-temperature synthesis

TiC_x and Cu–TiC_x have been formed by self-propagating high-temperature synthesis (SHS) from elemental powder mixtures with a range of C/Ti ratios. When no copper was present, the carbide stoichiometry closely followed that of the starting powders. In the presence of copper, formation of copper–titanium intermetallics and solid solutions resulted in a different carbide stoichiometry.     

Influence of Feedstock Powder Modification by Heat Treatments on the Properties of APS-Sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-40% TiO<Subscript>2</Subscript> Coatings

The formation and decomposition of aluminum titanate (Al₂TiO₅, tialite) in feedstock powders and coatings of the binary Al₂O₃-TiO₂ system are so far poorly understood. A commercial fused and crushed Al₂O₃-40%TiO₂ powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al₂TiO₅. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al₂TiO₅ was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H₂ and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al₂TiO₅-Ti₃O₅ (tialite–anosovite) solid solution Al_2?xTi_1+xO₅ instead of Al₂TiO₅ existed in the initial powder and the coatings.     

添加Si/Ti对粉末冶金FiNiCrCo高熵合金物理力学和化学性能的影响（英文）

用粉末冶金法制备FiNiCrCoSi_x和FiNiCrCoTi_x高熵合金(HEAs)。其中x为0、0.3%、0.6%和0.9%(质量分数)。所有合金中均形成均匀分布的固溶体。与FiNiCrCo高熵合金相比,加入Si和Ti后,合金的密度和硬度提高,研究合金在不同载荷下的磨损率。结果表明,含0.3%Si和0.9%Ti的高熵合金磨损率最低。用XRD、SEM和EDX研究HEAs的相组或、晶粒尺寸和显微组织。通过H₂SO₄、HNO₃和HCl溶液浸泡实验,研究Si和Ti含量对烧结态FiNiCrCoSi_x和FiNiCrCoTi_x HEAs腐蚀行为和表面形貌的影响。在样品表面观察到不同尺寸的均匀腐蚀和局部点烛,且FiNiCrCoSi_0.3合金具有更小,更少的蚀坑,和优异的显微组织     

高氧强化的高强高塑Ti-Zr合金（英文）

通过粉末冶金和热加工方法制备氧含量为0.42%～0.54%(质量分数)的Ti-Zr合金。结果表明:Ti-Zr合金由具有相同α相结构的富Zr区和贫Zr区组成,富Zr区域的氧含量较高,且晶粒尺寸较小。Ti-Zr合金同时具有高强度(σ_s=700～900 MPa)和高的总伸长率(>20%),而氧的固溶强化是主要的强化机制。Zr由于与Ti具有高度结构相似性,对氧诱发Ti合金脆化的影响不大。因此,0.54%(质量分数)的高含量值仍处于韧性到脆性转变的临界氧含量范围内,不明显降低材料的延展性。     

Corrosion of Ni-Ti alloys in the molten (Li,K)2CO3 eutectic mixture

The corrosion of pure Ni and of binary Ni-Ti alloys containing 5, 10, and 15 wt.% Ti respectively in molten (0.62Li,0.38K)₂CO₃ at 650°C under air has been studied. The corrosion of the single-phase Ni-5Ti alloy was slower than that of pure Ni, forming an external scale composed of NiO and TiO₂. The two-phase Ni-10Ti and Ni-15Ti alloys underwent much faster corrosion than pure Ni, producing an external scale containing NiO and TiO₂, and a thick internal oxidation zone of titanium mainly involving the intermetallic compound TiNi₃ in the original alloys. The rates of growth of the external scales for the Ni-Ti alloys were reduced with the increase of their titanium content, while the internal oxidation was significantly enhanced. The corrosion mechanism of the alloys is also discussed.     

Structure and dielectric characterization of xNd(Mg1/2Ti1/2)O3-(1 − x)Ca0.6La0.8/3TiO3 in the microwave frequency range

The crystal structures, phase compositions and the microwave dielectric properties of the xLa(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.8Sr_0.2TiO₃ composites prepared by the conventional solid state route have been investigated. The formation of solid solution is confirmed by the XRD patterns. Doping with B₂O₃ (0.5 wt.%) can effectively promote the densification and the dielectric properties of xNd(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. It is found that xNd(Mg_1/2Ti_1/2)O₃-(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics can be sintered at 1375 °C, due to the liquid phase effect of B₂O₃ addition observed by Scanning Electronic Microscopy. At 1375 °C, 0.4Nd(Mg_1/2Ti_1/2)O₃-0.6Ca_0.6La_0.8/3TiO₃ ceramics with 1 wt.% B₂O₃ addition possesses a dielectric constant (?_r) of 49, a Q × f value of 13,000 (at 8 GHz) and a temperature coefficients of resonant frequency (τ_f) of 1 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 20,000 GHz for x = 0.9 is achieved at the sintering temperature 1400 °C.     

电解TiO2中间相的形成与溢出气体间的关系

熔盐电解TiO₂制备金属钛的过程中,钙钛矿是不可避免的中间相,这已得到国内外研究者的公认。本研究借助间断性实验,主要研究了熔盐电解TiO₂制备金属钛过程中,钙钛矿的形成与TiO₂脱氧及阳极产生气体间的关系。研究结果表明,CaCl₂熔盐中电解TiO₂制备金属钛的过程,按其脱氧进程可分为三个主要阶段。第一阶段为 TiO₂脱氧生成钛的低价氧化物,同时O_2-、熔盐Ca₂₊和未脱氧的TiO₂形成CaTiO₃。第二阶段为CaTiO₃脱氧、脱钙及钛低价氧化物继续脱氧为Ti₂O。第三阶段为Ti₂O进一步脱氧为Ti(2% O)。TiO₂脱氧量、熔盐消耗量及形成CaTiO₃量之间的摩尔比为1:1:1, 且钙钛矿形成阶段阳极只有Cl₂放出,钙钛矿形成结束后阳极放出CO₂、CO气体,无Cl₂放出。若以电解TiO₂到含2%氧的Ti[O]所消耗的时间记为100%的话,那么钙钛矿脱氧、脱钙过程约占总时间的38.9%,而钙钛矿形成的时间只占5.6%,其余时间为钛低价氧化物的脱氧过程。因此钙钛矿的形成是该工艺电流效率低的主要原因之一,钛低价氧化物深脱氧速率低是该工艺的主要限制性环节。     

Microstructures and mechanical properties of Ti–Al–V–Nb alloys with cluster formula manufactured by laser additive manufacturing

Ti–Al–V–Nb alloys with the cluster formula, 12[Al–Ti₁₂](AlTi₂)+5[Al–Ti₁₄](V,Nb)₂Ti, were designed by replacing V with Nb based on the Ti–6Al–4V alloy. Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.% were prepared by laser additive manufacturing to examine their formability, microstructure, and mechanical properties. For single-track cladding layers, the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability. The alloy, Ti–5.96Al–1.94V– 3.54Nb (wt.%), exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder. The microstructures of the bulk samples contained similar columnar β-phase grains, regardless of Nb content. These grains grew epitaxially from the Ti substrate along the deposition direction, with basket-weave α-phase laths within the columnar grains. The α-phase size increased with increasing Nb contents, but its uniformity decreased. Along the deposition direction, the Vickers hardness increased from the substrate to the surface. The Ti–5.96Al–1.94V–3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between the α-phase size and its content among the designed alloys.     

High-velocity oxyfuel reactive spraying of mechanically alloyed Ni-Ti-C powders

Recently, there has been considerable interest in producing cermet coatings with nanoscale carbide grains in the size range 50 to 500 nm. In this article, the production of nanoscale TiC grains in a Ni-based alloy matrix by reactive high-velocity oxyfuel (HVOF) spraying of metastable Ni-Ti-C powder is reported. Mechanical alloying of a Ni(Cr) prealloyed powder and Ti and C elemental powders was performed in a planar-type ball mill, and materials were characterized in detail using x-ray diffraction (XRD) and scanning electron micros-copy (SEM). Phase changes were correlated with milling time and other processing conditions. Results show that, by the selection of appropriate conditions, a metastable Ni-Ti-C powder could be obtained with the nominal composition 50wt.%Ni-40wt.%Ti-10wt.%C. Following sieving and classification, powder was produced with a particle size range of −38 to 8 μm, which is suitable for HVOF spraying. Coatings, approximately 250 μm thick, were deposited by HVOF spraying onto mild steel substrates, and the microstructures formed were investigated. XRD showed that a self-propagating high-temperature synthesis (SHS) reaction had occurred in the powder particles during spraying and that the principal phases present in the coating were TiC and a Ni-rich solid solution; small quantities of NiTi, TiO₂, and NiTiO₃ were also present. SEM revealed that the coatings had a characteristic, splatlike morphology and that TiC formed as a nanoscale dispersion, with a size range of ∼50 to 200 nm, within solidified splats. The microstructures of these reactively sprayed Ni-TiC coatings are briefly compared with those observed in HVOF-sprayed coatings deposited using prereacted SHS powder. The original version of this paper was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

Thermodynamics of titanium,nitrogen, and oxygen in liquid alloy steels

The thermodynamics of Ti, N, and O in liquid iron was studied in order to establish a database to predict the TiN and TiO_x formation in liquid steels as a function of temperature. The interaction parameters between Ti, N, and O in liquid iron and the equilibrium constants for the formation of TiN, Ti₂O₃, and Ti₃O₅ in liquid iron were determined as a function of temperature. Formerly Graduate Student, Department of Metallurgical and Materials Engineering, Hanyang University, Gyeonggi, 426–791, Korea.     

In situ synchrotron diffraction of the electrochemical reduction pathway of TiO2

Despite over ten years of work into the low-cost electrowinning of Ti direct from the oxide, the reduction sequence of TiO₂ pellets in molten CaCl₂ has been the subject of debate, particularly as the reduction pathway has been inferred from ex situ studies. Here, for the first time white beam synchrotron X-ray diffraction is used to characterize the phases that form in situ during reduction and with ～100 μm resolution. It is found that TiO₂ becomes sub-stoichiometric very early in reduction, facilitating the ionic conduction of O ions, that CaTiO₃ persists to nearly the end of the process and that, finally, CaO forms just before completion of the process. The method is quite generally applicable to the in situ study of industrial chemical processes. Implications for the industrial scale-up of this method for the low-cost production of Ti are drawn.     

DC magnetization investigations in Ti1−xMnxO2 nanocrystalline powder

In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti_1−xMn_xO₂ (x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO₂ when x ≤ 0.05 and a mixture of anatase and rutile TiO₂ along with the signature of Mn₃O₄ phase for x > 0.05. Magnetic measurements exhibited the presence of ferromagnetic ordering at room temperature in samples having either small fraction of Mn or no Mn at all. This ferromagnetic signature is accompanied with paramagnetic contribution which is found to dominate with increase in Mn concentration. The Ti_1−xMn_xO₂ sample having highest Mn concentration of x = 0.15 showed nearly paramagnetic behavior. However, at low temperatures, additional ferrimagnetic ordering arising due to Mn₃O₄ (T_C = 42 K) is evidenced in the doped samples. Consistent with the XRD investigations, the isofield DC-magnetization measurements under field cooled and zero field cooled (FC-ZFC) histories corroborated the presence of Mn₃O₄ phase. Also, distinct thermomagnetic irreversibility has been observed above 42 K. These results are suggestive of presence of weak ferromagnetic ordering possibly due to defects related with oxygen vacancies.