The site occupancies of alloying elements in TiAl and Ti3Al alloys

The site occupancies of V, Cr, Mn, Fe, Ni, Zr, Nb, Mo, Ta, Ga and Sn (1–5 at.%) in TiAl alloys with different compositions, and in Ti₃Al with the compositions of Ti–26 at.%Al–(1–2 at.%)X, were measured by the atom location channelling enhanced microanalysis (ALCHEMI) method. For TiAl alloys, the results show that Zr, Nb and Ta atoms invariably occupy Ti sites, while Fe, Ni, Ga and Sn atoms occupy Al sites, the alloy composition having no significant influence on their site preference. By contrast, the site preference of V, Cr, and Mn changes considerably with alloy composition (the Ti/Al ratio in particular), the probability of these elements substituting for Ti decreasing in the above order. For quaternary Ti–Al–V–Cr alloys, the site occupancies of V and Cr do not show much mutual influence. In general, with increasing atomic number, elements in the same period show increasing tendency to substitute for Al, as is the tendency to substitute for Ti for elements in the same group of the periodic table. For Ti₃Al alloys, Ga and Sn atoms occupy Al sites, while V, Cr, Mn, Zr, Nb, Mo and Ta atoms occupy Ti sites, the site preference of V, Cr, Mn and Mo in TiAl alloys being different from that in Ti₃Al. The experimental results are interpreted in terms of a Bragg–Williams-type model and bond-order data obtained from electronic structure calculation. Qualitative agreement between the model and measurements is reached.     

Microstructure and properties of novel quinary multi-principal element alloys with refractory elements

Five equiatomic alloys(Ti Zr Hf VNb, Ti Zr Hf VTa, Ti Zr Nb Mo V, Ti Zr Hf Mo V and Zr Nb Mo Hf V) composed of five elements with high melting temperature, respectively were prepared by arc-melting to develop a novel high temperature alloy. The five alloys exhibit different dendritic and interdendritic morphologies. The Ti Zr Hf VNb, Ti Zr Hf VTa and Ti Zr Nb Mo V alloys formed disordered solid solution phases with body-centered cubic structure, and exhibited high compressive strength and good plasticity. The Ti Zr Hf Mo V and Zr Nb Mo Hf V alloys are composed with Laves phase(Hf Mo2) and disordered solid solution phases with body-centered cubic structure. The Ti Zr Hf Mo V and Zr Nb Mo Hf V alloys are harder and more brittle than the other three alloys due to the existence of hard and brittle Laves phases. At high temperatures, the strength decreases to below 300 MPa for the Ti Zr Hf VNb and Ti Zr Hf Mo V alloys. Solution strengthening is the primary strengthening mechanism of the Ti Zr Hf VNb, Ti Zr Hf VTa and Ti Zr Nb Mo V alloys, and brittle Laves phase is the main cause for the low ductility of the Ti Zr Hf Mo V and Zr Nb Mo Hf V alloys.     

High strength Mo/Ti6Al4V diffusion bonding joints: Interfacial microstructure and mechanical properties

Joining Mo to Ti6Al4V is of great interest for applications in the weaponry and aerospace fields. In this work, a diffusion bonding technique is developed to bond a MoZr alloy and Ti6Al4V using a Cr-Ni-Ti-Si composite interlayer. The formation of the interlayer ensured that crack-free bonds were obtained. The mechanical properties and microstructure of the interface were examined. The results show that as the temperature was raised, the thickness of the diffusion layer increased and Kirkendall voids formed on the Mo alloy side. At the Mo/Cr-Ni-Ti-Si interface, a diffusion layer formed as Cr, Ni, Si and Mo dissolved into Ti to form a substitutional solid solution. As a result, the lattice constant of Ti reduced. For diffusion bonding between Mo and Ti6Al4V, a maximum tensile strength of 369 MPa was attained while a processing temperature of 950 °C was used. Ductile fractures were observed at the Mo/Ti6Al4V joints, primarily in Mo adjacent to the Mo/Cr-Ni-Ti-Si interface. The findings in this study open up new possibilities for the use of Cr-Ni-Ti-Si composite interlayer to bind Mo alloys to Titanium alloys.     

快凝Al－Fe－M－Si合金的显微结构对熔体热历史的敏感性

研究了不同成分的快凝Ａｌ－Ｆｅ－Ｍ－Ｓｉ（Ｍ＝Ｔｉ，Ｎｂ，Ｃｒ＋Ｍｏ，Ｗ）合金显微结构对熔体热历史的敏感性．结果表明：在相同熔体热历史条件下，不同成分的快凝Ａｌ－Ｆｅ－Ｍ－Ｓｉ合金的显微结构有着明显差别；在１３２３Ｋ，５ｍｉｎ至１５２３Ｋ，５ｍｉｎ的熔体热历史制度范围内，只有快凝Ａｌ－Ｆｅ－Ｗ－Ｓｉ合金显微结构对熔体热历史比较敏感．作者认为合金过热熔体的微观不均匀区的大小是影响快凝Ａｌ－Ｆｅ－Ｍ－Ｓｉ合金显微结构对熔体热历史的敏感性的主要因素．     

High-Temperature Oxidation Behavior of Refractory High-Entropy Alloys: Effect of Alloy Composition

The high-temperature oxidation behavior of a new family of refractory high-entropy alloys (HEAs) with compositions of W–Mo–Cr–Ti–Al, Nb–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al was studied at 1000 and 1100 °C. Based on these equimolar starting compositions, the main incentive of this study was to select the most promising alloy system whose properties may then be successively improved. Despite the high amount of refractory elements, Ta–Mo–Cr–Ti–Al showed good oxidation resistance at 1000 and 1100 °C. Moderate values of mass gain and complex oxidation kinetics were observed for the W- and Nb-containing HEAs. These alloys formed inhomogeneous oxide scales possessing regions with thick and porous layers as well as areas revealing quite thin oxide scales due to the formation of discontinuous Cr- and Al-rich scales. The most promising behavior was shown by the alloy Ta–Mo–Cr–Ti–Al which followed the parabolic rate law for oxide growth due to the formation of a thin and compact Al-rich layer.     

合金元素Cr对钛合金燃烧行为的影响

以直流电弧激发燃烧法（ＤＣＳＢ）点燃钛合金,探讨了合金元素Ｃｒ对钛合金燃烧行为的影响,结果表明,合金元素Ｃｒ含量高于１０％可改善钛合金的阻燃性能,大于１５％效果更明显,而Ｔｉ－Ｃｒ二元合金不具有阻燃性能,原因在于,Ｔｉ－Ｃｒ合金燃烧产物表面均开裂多孔,Ｔｉ－（〈１０％）Ｃｒ合金的燃烧产物与基体界面亦如此,不可能阻止氧向基体内扩散,而Ｔｉ－（〉１０％）Ｃｒ合金的燃烧产物与基体的界面富积Ｃｒ,氧化物比     

快凝Al—Fe—M—Si合金的显微结构对熔体热历史的敏感性

研究了不同成分的快凝Ａｌ－Ｆｅ－Ｍ－Ｓｉ合金显微结构对熔体热历史的敏感性；结果表明；在相同熔体热历史条件下，不同成分的快凝Ａｌ－Ｆｅ－Ｍ－Ｓｉ合金的显微结构有着明显差别。     

Cr、V在Ti-Al系合金中合金化效应的理论研究

采用第一性原理赝势平面波方法研究了合金元素Cr、V对Ti-Al系合金电子结构的影响,计算了含Cr、V的Ti-Al系合金的总能量、结合能、力学性能、电荷密度、态密度,从理论上解释了在Ti-Al系合金中固溶合金元素Cr、V后其性能得到改善的原因。计算结果表明,随着合金元素Cr(0～25at%)、V(0～25at%)含量的增加,合金的结合能绝对值逐渐增大,结构稳定性逐渐增强;切变模量G和杨氏模量E都逐渐增大,但提高的幅度逐渐减小。原因主要是固溶的Cr使合金中Cr3d、Al3p和Ti3d电子相互杂化,V使合金中V3d、Ti3d和Al3p电子相互杂化,合金的结合能力增强。     

合金元素对典型阻燃钛合金燃烧行为的影响

阻燃钛合金是飞机发动机核心部件中的重要材料，由于钛合金燃烧过程难以控制，燃烧参数难以获得加大了研究难度。论文以典型阻燃钛合金Ti40和Ti14为研究对象，利用高速摄影在不同氧分压环境下通过直流点火研究其燃烧行为，探索其燃烧过程中的氧扩散过程，明确合金元素对阻燃行为的影响 。研究发现两种合金燃烧后均形成分层结构，Ti40合金中Cr和V元素向外扩散，和氧反应生成Cr2O3/V2O5，密度高于TiO2的密度，Ti原子很难通过Cr2O3向外扩散与氧反应，提高燃烧表面致密度，抑制氧的扩散；而对于Ti14合金，共析反应生成大量的液相，富Cu相包裹Ti相球化晶粒形成Cu元素富集层，隔离氧并减少钛与氧的接触，从而降低氧向基体的扩散速率，同时Cu相的包裹作用增加氧扩散的距离，氧需要更多的能量扩散与Ti接触并反应，从而抑制了反应的发生。     

Electrochemical stability and surface analysis in evaluation fluoride effect on new bioalloy Ti7Al3V2Mo2Fe used in dentistry

The aim of this study is focused on the effect of fluoride concentration on the corrosion behavior of Ti7Al3V2Mo2Fe alloys uncoated/coated in artificial saliva. Ti7Al3V2Mo2Fe alloys were covered by chemical methods with hydroxyapatite to enhance the osteointegration of implants materials. The stability of Ti7Al3V2Mo2Fe alloys uncoated/coated in artificial saliva with/without fluoride ions was studied by electrochemical techniques (open circuit potential, cyclic voltammetry, and linear polarization). On the covered samples, dissolution test in simulated body fluids and wettability test were performed. Investigations regarding the sample surface modifications were made by atomic force microscopy and Fourier transform infrared spectroscopy. The results show that the corrosion resistance of Ti7Al3V2Mo2Fe in solution containing fluoride decreases in comparison with that in a solution not containing fluoride. Significant changes appear at a concentration larger than 0.05 M. The coating has a positive effect on corrosion resistance of metallic substrate in the fluoride presence acting as a semi‐mechanical barrier.     

Einfluß von Calcium sowie Cer auf das Oxidationsverhalten hochwarmfester Nickelbasislegierungen

Influence of calcium and cerium on the oxidation behaviour of high temperature strength nickel base alloys Thermogravimetric investigation into the behaviour of Ni alloys having various Al, Co, Cr, Mo, Nb, Ta, Ti, V, W, and Zr contents; the investigations were carried out at temperatures between 800 and 1200°C; the influence of minor additions of Ca and Ce has been studied simultaneously. It turns out, that the improvement of scale adhesion which can be obtained by these additions is limited to a certain temperature range; above specific upper temperature limits the alloying additions lose their efficiency. From among the alloys investigated Inconel 713C turns out to be the alloy having the highest scaling resistance under these conditions. The scale layers formed are very thin and have excellent adhesion properties.     

Effects of Microstructural Factors on Adiabatic Shear Behaviors of Ti6441 Alloys

针对Ti-6Al-4V-4Zr-Mo(Ti6441)合金采用不同的热处理工艺得到等轴和片层2种微观组织,使用分离式Hopkinson Bar技术对2种组织的试样进行动态剪切试验,研究微观组织对该合金绝热剪切敏感性的影响。结果表明:相同加载条件下,片层组织绝热剪切敏感性较等轴组织低;2种组织动态强度接近,但片层组织较等轴组织具有更好的动态延展性;片层组织试样中的绝热剪切带出现分叉现象,从而可以消耗更多的变形能。     

Ti0.9Zr0.2Mn（1.8—x）MxV0.2（M=Ni,Cr;x=0,0.2）合金的贮氢性能

研究了Ti0.9Zr0.2Mn(1.8-x)MxV0.2(M=Ni,Cr;x=0,0.2)合金的晶体结构与贮氢性能。结果表明,Ti0.9Zr0.2Mn1.6Ni0.2V0.2和Ti0.9Zr0.2Mn1.6Cr0.2V0.2的贮氢量达到240mL/g。合金的主相均为C14 Laves相,镍,铬的取代使点阵常数和晶胞体积增大,P－C－T曲线的滞后降低,压力平台的倾斜度增加。     

V-Ti-Cr-Fe合金的储氢性能研究

研究了V（30％）-Ti（15％～55％）-Cr（7％～43％）-Fe（2％～18％）（原子分数，下同）四元合金的储氢性能。结果表明：V-Ti-Cr-Fe四元合金的吸氢量与有效吸氢量主要由Ti／（Cr＋Fe）比决定，当Ti／（Cr＋Fe）=1时，合金具有最好的吸放氢性能。随着Ti／（Cr＋Fe）比升高，合金的晶格常数增大，氢化物的生成焓增大，放氢平台压力降低。在298K时，V30Ti35Cr25Fe10合金的吸氢量达到3．6％（质量分数，下同），有效吸氢量达到2．0％。     

Nickel-Based Single-Crystal Superalloys (Ni,Co)-Al-(Ta,Ti)-(Cr,Mo, W) Designed by Cluster-Plus-Glue-Atom Model and Their 1000 h Long-Term Ageing Behavior at 900 degrees CEI北大核心CSCD

It has been pointed out recently that the compositions of industrial alloys are originated from cluster-plus-glue-atom structure units in solid solutions. Specifically for nickel-based superalloys, after properly grouping the alloying elements into Al, Ni-like ((Ni) over bar, including Ni, Co, Fe, Re, Ru and Ir), gamma '- forming Cr-like ((Cr) over bar (gamma '), including Ta, Ti, V, Nb), and gamma-forming Cr-like ((Cr) over bar;(gamma), including Cr, Mo and W), the optimal formula for single-crystal superalloys has been established [Al-(Ni) over bar (12)] (Al-1(Cr) over bar (gamma ')(0.5)(Cr) over bar (gamma)(1.5)). In this work, the first generation single-crystal superalloys were investigated on the basis of the proposed formula, by using (Ni) over bar=(Ni and Co), (Cr) over bar (gamma ')=(Ta and Ti), and (Cr) over bar (gamma)=(Cr, Mo and W). Two series of alloys were designed, formulated respectively as group A: [Al-Ni11Co1] (Al1TaxTi0.5-xCr1W0.25Mo0.25), with x=0, 0.25 and 0.5 (the corresponding mass fractions of Ta and Ti are respectively 0Ta-2.65Ti, 4.82Ta-1.26Ti and 9,32Ta-0Ti), and group B: [Al-Ni12-yCo gamma](Al1Ta0.25Ti0.25Cr1W0.25MO0.25), with y=1.5, 1.75, 2 and 2.5 (the corresponding mass fractions of Co are respectively 9.43Co, 11Co, 12.57Co and 15.71Co). The single-crystal superalloys were prepared using selector technique. And then they underwent the following tests of incipient melting, standard heat treatment and 1000 h long term ageing at 900 degrees C. It is found that: (1) In group A, with increasing Ta content (decreasing Ti), all the incipient melting temperatures are increased to above 1330 degrees C, and to the highest value is between 1335 degrees C and 1340 degrees C for alloy 9.32Ta-0Ti; the gamma(')gamma(') lattice negative misfits after standard heat treatment are reduced from -0.262% (0Ta-2.65Ti) to -0.247% (9.32Ta-0Ti); the gamma(') coarsening tendency after long-term ageing is deduced, and alloy 9.32Ta-0Ti has the lowest coarsening rate (K=5.6x10(-5) mu(3)/h). (2) In group B, the Co content does not influence the incipient melting temperature (always above 1330 degrees C) and the coarsening rate of gamma(') after long-term ageing. The major role of Co is to increase the mean size of the gamma(') precipitates to about 0.55 pm and the gamma(') volume fraction to about 69% after the standard heat treatment. These two groups of alloys have their gamma(') coarsening rates approaching the level of third-generation single-crystal superalloys (K approximate to(2.08 similar to 3.82)*10(-5) mu m(3)/h).     

EFFECT OF HYDROGEN ON DISLOCATION VELOCITY-STRESS EXPONENTS OF Ti ALLOYS

<正> 1959年 Johnston 和 Gilman 提出位错运动速度 v 与有效应力 σ~*之间的经验公式为:V=B(σ~*)~(m*) (1)其中 B 是系数,m~*称为位错速度的应力指数。用应力弛豫法可以测定 m~*值,如下式所示:     

Relation Between the Microstructure and Properties of Commercial Titanium Alloys and the Parameters of Gas Nitriding

Titanium alloys are unique materials with an excellent combination of properties. However, their applications are limited due to low surface hardness. In the present work gas nitriding is performed with the aim of improving the surface properties of commercial titanium alloys. Four widely used titanium alloys, namely, Ti – 6% Al – 4% V, Ti – 6% Al – 2% Sn – 4% Zr – 2% Mo, Ti – 8% Al – 1% Mo – 1% V, and Ti – 10% V – 3% Fe – 3% Al, are studied. The process is performed in a nitrogen atmosphere at 950 and 1050°C for 1, 3, and 5 h. The resulting surface hardness exceeds the normal value for titanium alloys by a factor of 3 – 5 due to the change in the phase composition of the surface layer, yielding a solid solution of nitrogen in an α-Ti phase, a TiN nitride, and TiO₂ dioxide. The influence of the parameters of the treatment process and the chemical composition of the alloys on the phase composition, microstructure, microhardness, and thickness of the surface layer is analyzed. It is shown that nitriding of alloys with α- and (α + β)-structures at 1050°C yields surface layers with inhomogeneous composition and irregular thickness, whereas after nitriding at 950°C the surface layers are homogeneous and have high properties. Practical recommendations are given for choosing nitriding parameters for different alloys and variants of application are discussed.     

Effects of Cr and Fe Addition on Microstructure and Tensile Properties of Ti–6Al–4V Prepared by Direct Energy Deposition

The effects of Cr and Fe addition on the mechanical properties of Ti–6Al–4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior β phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti–6Al–4V resulted in a partially melted Ti–6Al–4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti–33Fe) and the Ti–6Al–4V powder, which induced the formation of a thick liquid layer surrounding Ti–6Al–4V. The ductility of Fe-added Ti–6Al–4V was thus poorer than that of Cr-added Ti–6Al–4V.     

Ti6Al4V合金渗镀Cr-Mo表面改性层组织结构及其耐磨特性研究

采用双层辉光离子渗技术在Ti6Al4V合金表面进行多元合金化,形成均匀致密的Cr-Mo合金渗层.通过GDOES、XRD等手段标定表层成分和相结构,借助显微硬度计和球盘磨损仪测试合金渗层的性能.结果表明:合金渗层中合金化元素Cr与Mo呈梯度分布,主要由化合物Cr_(1.93)Ti_(1.07)、Cr_2Ti、Cr_2Ti_4O_(11)等相构成;改性的Ti6Al4V合金表面硬度有较大程度的提高,抗磨损性能明显改善.     

Relationship between phase composition and corrosion resistanceof Ni-Ti-Nb based shape memory alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＮｉ Ｔｉ Ｎｂａｌｌｏｙｓ ,ｏｎａｃｃｏｕｎｔｏｆｔｈｅｉｒｓｈａｐｅｍｅｍ ｏｒｙａｎｄ ｐｈａｓｅｔｒａｎｓｆｏｒｍａｔｉｏｎｈｙｓｔｅｒｉｓｉｓ ,ｈａｖｅｂｅｅｎｐａｉｄａｔｔｅｎｔｉｏｎｂｙｒｅｓｅａｒｃｈｅｒｓｆｏｒｍａｎｙｙｅａｒｓａｎｄｐｒｏ ｐｏｓｅｄｆｏｒｖａｒｉｏｕｓａｐｐｌｉｃａｔｉｏｎｓ[1～ 5] .Ｔｈｅｒｅｓｕｌｔｓｓｈｏｗｔｈａｔｔｈｅｐｈａｓｅｔｒａｎｓｆｏｒｍａｔｉｏｎｈｙｓｔｅｒｉｓｉｓｄｕｅｔｏ β ＮｂｐａｒｔｉｃｌｅｓｉｎＮｉ Ｔｉｍａｔ…