High-strength Ti-Al-V-Zr cast alloys designed using α and β cluster formulas

Ti-Al-V-Zr quaternary titanium alloys were designed following α-{[Al-Ti₁₂](AlTi₂)}_17−n+β-{[Al-Ti₁₂Zr₂](V₃)}_n, where n=1–7 (the number of β units), on the basis of the dual-cluster formula of popular Ti-6Al-4V alloy. Such an alloying strategy aims at strengthening the alloy via Zr and V co-alloying in the β-Ti unit, based on the original β formula [Al-Ti₁₄](V₂Ti) of Ti-6Al-4V alloy. The microstructures of the as-cast alloys by copper-mold suction-casting change from pure α (n=1) to α+α′ martensite (n=7). When n is 6, Ti-5.6Al-6.8V-8.1Zr alloy reaches the highest ultimate tensile strength of 1,293 MPa and yield strength of 1,097 MPa, at the expense of a low elongation of 2%, mainly due to the presence of a large amount of acicular α′ martensite. Its specific strength far exceeds that of Ti-6Al-4V alloy by 35%.

     

Effects of Sc,Zr and Ti on the microstructure and properties of Al alloys with high Mg content

The effects of trace Sc, Zr, and Ti on the microstructure and hardness of Al alloys with high Mg content (Al-6Mg, Al-8Mg, and Al-10Mg) were studied by optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brinell hardness. The grain size of the as-cast alloys was refined by the addition of Sc and Zr, and it was further refined by the addition of Ti. With the same contents of Sc, Zr, and Ti, an increase in Mg content was beneficial to the refinement due to the solution of Mg into α-Al. The refined microstructures of the as-cast alloys were favorable for Brinell hardness. Addition of Sc, Zr, and Ti to the Al-10Mg alloy results in the improvement of peak hardness and it is about 45% higher than that of the Al-10Mg alloy, which is due to fine precipitations of Al₃(Sc_1−x Zr _x ), Al₃(Sc_1−x Ti _x ), and Al₃(Sc_1−x−y Zr _x Ti _y ).     

Effects of Fabrication Parameters on Interface of Zirconia and Ti-6Al-4V Joints Using Zr55Cu30Al10Ni5 Amorphous Filler

ZrO₂ was brazed to Ti-6Al-4V using a Zr₅₅Cu₃₀Al₁₀Ni₅ (at.%) amorphous filler in a high vacuum at 1173-1273 K. The influences of brazing temperature, holding time, and cooling rate on the microstructure and shear strength of the joints were investigated. The interfacial microstructures can be characterized as ZrO₂/ZrO_2?x  + TiO/(Zr,Ti)₂(Cu,Ni)/(Zr,Ti)₂(Cu,Ni,Al)/acicular Widmanstäten structure/Ti-6Al-4V. With the increase in the brazing temperature, both the thickness of the ZrO_2?x  + TiO layer and the content of the (Zr,Ti)₂(Cu,Ni) phase decreased. However, the acicular Widmanstäten structure gradually increased. With the increase in the holding time, the (Zr,Ti)₂(Cu,Ni) phase decreased, and the thickness of the (Zr,Ti)₂(Cu,Ni) + (Zr,Ti)₂(Cu,Ni,Al) layer decreased. In addition, cracks formed adjacent to the ZrO₂ side under rapid cooling. The microstructures produced under various fabrication parameters directly influence the shear strength of the joints. When ZrO₂ and Ti-6Al-4V couples were brazed at 1173 K for 10 min and then cooled at a rate of 5 K/min, the maximum shear strength of 95 MPa was obtained.     

Effect of Zr on microstructure and mechanical properties of binary TiAl alloys

Ti43Al and Ti47Al alloys with different contents of zirconium were prepared by non-consumable vacuum arc melting furnace. The microstructure and mechanical properties were investigated. The results showed that Zr had no obvious effect on microstructure morphology of Ti43Al, while that of Ti47Al was modified from dendrites into equiaxed grains. The addition of Zr could refine the grains. Zr promoted the formation of γ phase significantly and the solubility values of Zr in γ phase were 12.0% and 5.0% (molar fraction) in Ti43Al and Ti47Al, respectively. Zr-rich γ phase mainly formed through β→γ in Ti43Al?xZr (molar fraction, %) and β→α→γ in Ti47Al?xZr (molar fraction, %). Fine-grain strengthening and solution strengthening were beneficial to improving the compressive strength while severe micro-segregation was detrimental to compressive properties. Large solubility of Zr was bad for ductility of alloys as well. The maximum compressive strengths of Ti43Al?xZr and Ti47Al?xZr were 1684.82 MPa (x=5.0%) and 2158.03 MPa (x=0.5%), respectively. The compressive strain fluctuated slightly in Ti43Al?xZr and reached the maximum value of 35.24% (x=0.5%) in Ti47Al?xZr. Both alloys showed brittle fracture.     

Low-melting-point titanium-base brazing alloys—part 1: Characteristics of two-, three-, and four-component filler metals

The melting point, microstructure, phase, and electrochemical behavior of Ti-21Ni-15Cu alloy, together with two-, three-, and four-component low-melting-point titanium-base brazing alloys, are presented in this paper. Five filler metals were selected for the study, in which melting points were measured by differential thermal analysis, phases identified by x-ray diffractometry, and corrosion behaviors tested by potentiodynamic polarization. The experimental results show that the three-component Ti-15Cu-15Ni and the newly developed Ti-21Ni-14Cu alloys exhibit the combination of lower melting point and superior corrosion resistance compared to the two-and four-component titanium alloys, 316L stainless steel, and a Co-Cr-Mo alloy in Hank’s solution at 37 °C. On a short time basis, the presence of Ti₂Ni and Ti₂Cu intermetallics in the Ti-15Cu-15Ni and Ti-21Ni-14Cu alloys should not be preferentially dissolved in galvanic corrosion with respect to the dissimilar Ti-6Al-4V alloy.     

Microstructure and mechanical properties of laser melting deposited Ti2Ni3Si/NiTi Laves alloys

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions ofNi-39Ti-11Si and Ni-42Ti-8Si （%, mole fraction, the same below）, respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-llSi alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.     

Influence of Zr content on microstructure and mechanical properties of implant Ti–35Nb–4Sn–6Mo–xZr alloys

The influence of Zr content on the microstructure and mechanical properties of implant Ti–35Nb–4Sn–6Mo–xZr (x=0, 3, 6, 9, 12, 15; mass fraction) alloys was investigated. It is shown that Ti–35Nb–4Sn–6Mo–xZr alloys appear to have equiaxed single β microstructure after solution treatment at 1023 K. It is found that the grains are refined first and then coarsened with the increase of Zr content. It is also found that Zr element added to titanium alloys has both the solution strengthening and fine-grain strengthening effect, and affects the lattice parameters. With increasing the Zr content of the alloys, the strength increases, the elongation decreases, whereas the elastic modulus firstly increases and then decreases. The mechanical properties of Ti–35Nb–4Sn–6Mo–9Zr alloy are as follows: σ_b=785 MPa, δ=11%, E=68 GPa, which is more suitable for acting as human implant materials compared to the traditional implant Ti–6Al–4V alloy.     

Zr对Ni3Al晶界及力学性能的影响

对不同Ｚｒ含量Ｎｉ３Ａｌ的力学性能及晶界的研究结果表明：随Ｚｒ含量的增加，合金的屈服强度和抗张强度不断提高；当Ｚｒ≤０．７ａｔ．－％时，塑性随Ｚｒ含量的增加而提高；但Ｚｒ含量达１．２ａｔ．－％时，Ｚｒ的增塑效果下降．Ａｕｇｅｒ能谱分析表明：Ｚｒ在晶界有偏聚，偏聚因子约为３．断口观察显示：不含Ｚｒ或Ｚｒ含量为１．２ａｔ．－％的Ｎｉ－２４．０Ａｌ合金均为沿晶断裂，其余含Ｚｒ合金的断裂方式为穿晶、沿晶混合断裂．这表明：含Ｚｒ的Ｎｉ３Ａｌ塑性和Ｚｒ在晶界的偏聚有密切关系．     

Effect of brazing temperature and brazing time on the microstructure and tensile strength of TiAl-based alloy joints with Ti-Zr-Cu-Ni amorphous alloy as filler metal

An amorphous Ti-37.5Zr-15Cu-15Ni (wt.%) ribbon fabricated by vacuum arc remelting and rapid solidification was used as filler metal to vacuum braze TiAl alloy (Ti-45Al-2Mn-2Nb-1B (at.%)). The effects of brazing temperature and time on the microstructure and strength of the joints were investigated in details. The typical brazed joint major consisted of three zones and the brazed joints mainly consisted of α_2-Ti₃Al phase, α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase. When the brazing temperature varied from 910 °C to 1010 °C for 30 min, the tensile strength of the joint first increased and then decreased. With increasing the brazing time, the tensile strength of the joint increased. The maximum room temperature tensile strength was 468 MPa when the specimen was brazed at 930 °C for 60 min. All the fracture surfaces assumed typical brittle cleavage fracture characteristic. The fracture path varied with the brazing parameter and cracks preferred to initiate at (Ti, Zr)₂(Cu, Ni) phase and propagation path were mainly determined by the content and distribution of α-Ti phase and (Ti, Zr)₂(Cu, Ni) phase.     

High-Temperature Oxidation Behavior of Ti-22Al-27(Nb, Zr) Alloys

研究了Ti2Al Nb基合金Ti-22Al-(27-x)Nb-x Zr(x=0,1,6,at%)在650~800℃的氧化行为。采用XRD和SEM等测试技术对此温度区间形成的氧化层特征进行了分析。结果表明,相比Ti-22Al-27Nb,含锆合金具有较好的抗氧化性能。Ti-22Al-(27-x)Nb-x Zr合金在650℃氧化100 h,主要氧化产物为Ti O2,而在800℃氧化100 h,Ti O2,Al2O3和Al Nb O4为主要产物,但是在Ti-22Al-21Nb-6Zr合金中还有Zr O2生成。Ti-22Al-26Nb-1Zr合金具有优异抗氧化性能,归因于氧化产物细化形成了致密的氧化层,而Ti-22Al-21Nb-6Zr合金,虽然在800℃也形成了较多Al2O3,但是氧化层中的Zr O2为氧的快速扩散提供通道,进而导致该合金氧化增重明显。     

Effect of Ti and Zr elements with equal mass ratio on microstructure and corrosion resistance of Zn-11Al-3Mg alloy

In this study, the effect of Ti and Zr elements with equal mass ratio on microstructure and corrosion resistance of Zn-11Al-3Mg alloy was investigated. The microstructure was significantly refined and Al-rich phase transformed from dendrite to petal-like with the addition of Zr and Ti elements, due to the Al₃(Ti_xZr_{1 − x}) phase as the nucleation substrate. The corrosion resistance of Zn-11Al-3Mg-x(Ti,Zr) alloy was effectively improved. Moreover, the corrosion products of Zn-Al-Mg alloy were not changed by the addition of Ti and Zr, which are mainly composed of Zn₅(OH)₈Cl₂·H₂O and Zn₆Al₂(OH)₁₆CO₃·4H₂O.     

Ni含量对Cu-xNi-3Ti-0.1Zr合金组织和性能的影响

采用真空熔炼并经均匀化退火、热轧、固溶、冷轧和时效处理工艺制备Cu-xNi-3Ti-0.1Zr(x=2、4、6)合金,通过X射线衍射仪、光学显微镜和扫描电镜对合金的析出相进行表征和分析。结果表明,Ni的加入能够显著提高合金的导电率,且对其硬度的影响也同样显著。Ni在Cu-xNi-3Ti-0.1Zr合金中主要以CuNiTi相存在;Ni的加入导致合金中大量CuNiTi相的析出,降低了基体中Ti的固溶度,使合金的晶格畸变程度降低,从而提高了合金的导电率。但随着Ti的析出,Ti对合金的强化效果减弱,从而导致合金的硬度降低。在本试验工艺下,Cu-xNi-3Ti-0.1Zr(x=2、4、6)合金在500 ℃时效的峰值硬度分别为295、231、201 HV0.5。     

Grain refinement of AZ31 magnesium alloy by new Al-Ti-C master alloys

New Al₄C₃-containing Al-Ti-C master alloys (Al-0.6Ti-1C and Al-1Ti-1C) were developed by introducing Ti element into Al-C melt using melt reaction method, in which most of the TiC particles distribute around Al₄C₃ particles. It is believed that most of the C firstly reacts with Al melt and form Al₄C₃ particles by the reaction Al(l)+C(s)→Al₄C₃(s), and after adding Ti into the Al-C melt, the size of Al₄C₃ particles is decreased and the distribution of Al₄C₃ is improved through the reaction Ti(solute)+Al₄C₃(s)→TiC(s)+Al(l). With the addition of 1% Al-1Ti-1C master alloy, the average grain size of AZ31 is reduced sharply from 850 μm to 200 μm, and the grain morphology of α-Mg transits from a fully-developed equiaxed dendritic structure to a petal-like shape. Al-C-O-Mn-Fe compounds are proposed to be potent nucleating substrates for primary Mg. Appropriate addition of Ti is believed to increase the grain refinement efficiency of Al₄C₃-containing Al-Ti-C master alloys in AZ31 alloy.     

Behaviors of interfacial elements during the brazing of SiO2 glass ceramic to Ti-6Al-4V with AgCu/Ni interlayer

AgCu/Ni composite interlayer was used to join SiO₂ glass ceramic to Ti-6Al-4V alloy successfully, obtaining the largest joint shear strength 110MPa. Ag, Cu and Ni in the interlayer and Ti in the Ti-6Al-4V alloy affect the joint formation and interfacial products significantly. To understand the joint formation process better, behaviors of elements Ag, Cu, Ni and Ti during the brazing of SiO₂ glass ceramic to Ti-6Al-4V alloy were investigated in the present work. Active element Ti is the most important component in the joining, realizing the metallurgical bonding of SiO₂ glass ceramic to braze alloy. Cu together with Ni reacts to Ti in the base material by Ti-Cu-Ni ternary eutectic reaction, which is beneficial for reducing the massive Ti-Cu and/or Ti-Ni brittle intermetallic compounds on the joint interface. Dispersion of Ag decreases the brittleness of the whole joint effectively.     

Thermodynamics of Selected Ti-Al and Ti-Al-Cr Alloys

Two alloys in the Ti-Al system (Ti-45 a/o Al,Ti-62Al) and three alloys in the Ti-Al-Cr system(Ti-47Al-2Cr, Ti-47Al-13Cr, Ti-51Al-12Cr) were selectedfor a thermodynamic study because of interest in their high-temperature oxidation behavior. Activitiesof Al and Ti were measured using a twin Knudsen-cellassembly with one cell acting as an internal standard.For the Ti-45Al alloy, Al activity was also measured with an EMF technique. The Ti-Al-Cr data wereconsistent with the Al and Ti activities expected fromthe adjacent binary Ti-Al phase fields. Implications ofthis work on oxidation properties arediscussed.     

Ti811和TC4合金的热盐应力腐蚀行为研究

研究了Ti811(Ti-8Al-1Mo-1V)和TC4(Ti-6Al-4V)两种钛合金对热盐应力腐蚀(HSSC)的敏感性.结果表明:Ti811合金对HSSC非常敏感,在相同条件下其热盐应力腐蚀临界应力(σHSSC)明显低于TC4合金,且低于同温度的蠕变强度,而TC4合金的σHSSC高于同温度的蠕变强度;两种合金在HSSC暴露过程中,明显遭受到盐腐蚀,腐蚀产生的氢扩散到基体中,致使合金发生脆化,从而降低合金的室温塑性.     

Effect of Nb on oxidation behavior of high Nb containing TiAl alloys

The isothermal oxidation behavior of Ti-45Al-8Nb and Ti-52Al-8Nb alloys at 900 °C in air was investigated. The early oxidation behaviors were studied by using XPS and AES. And the microstructure and the composition of the oxidation scale were studied by using XRD and SEM. The results show that the oxidation behavior of TiAl alloy is significantly improved by Nb addition. Nb substitutes for Ti in TiO₂ as a cation with valence 5, and thus to suppress TiO₂ growth. The (Ti,Nb)O₂-rich layer is a dense and chemically uniform which is more protective than the TiO₂ layer. Nb addition also lowers the critical Al content to form an external alumina. Nb₂Al phase is formed in the metallic matrix at the oxide–metal interface on the high Nb containing TiAl alloys.     

Microstructure and tensile properties of isothermally forged Ni–43Ti–4Al–2Nb–2Hf alloy

NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope （SEM）, X-ray diffraction （XRD）, and tensile tests. Results show that the micro- structure of as-forged Ni-43Ti--4AI-2Nb-2Hf alloy con- sists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. The tensile strengths of Ni-43Ti-4A1-2Nb-2Hf alloy are dramatically increased compared with the ternary Ni-46Ti-4A1 alloy. At room temperature and 650℃, the yield stress of Ni--43Ti-4Al- 2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, which are 30 % and 150 % higher than those of Ni--46Ti- 4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.     

Oxygen effects on the mechanical properties and lattice strain of Ti and Ti-6Al-4V

The effects of oxygen on the mechanical properties and the lattice strain of commercial pure CP) Ti and Ti-6Al-4V alloys are discussed here in terms of the Vickers hardness, tensile strength and elongation. The Vickers hardness and tensile strength of the CP Ti and the Ti-6Al-4V alloys increased with an increase in the oxygen concentration. On the other hand, the elongation of the CP Ti decreased considerably as the oxygen concentration increased, while that of the Ti-6Al-4V alloys gradually decreased as the oxygen concentration increased. Thus, the oxygen concentration has a greater effect on the mechanical properties of CP Ti compared to its effects on the Ti-6Al-4V alloy. This can be explained in terms of the difference in the solid solution effect of oxygen between the CP Ti and the Ti-6Al-4V alloy. Where, the mechanical properties of Ti-6Al-4V alloy were previously affected by an earlier lattice expansion caused by an increment in the c/a ratio of the Ti-6Al-4V during the Al and V alloying process.     

Thermodynamic modeling and composition design for the formation of Zr–Ti–Cu–Ni–Al high entropy bulk metallic glasses

This work explores the idea of predicting metallic glass forming composition in a multi component alloy for which an equilibrium phase diagram is yet to be deciphered. Deep eutectic regions in a quaternary alloy (Zr–Ti–Cu–Ni) have been extrapolated to the quinary Zr–Ti–Cu–Ni–Al system for designing a potential bulk glass forming composition. P_HSS parameter which is the product of mixing enthalpy, mismatch entropy and configurational entropy of an alloy, has been utilized for thermodynamic modeling. P_HSS values are computed through substitution of Al into the each of the fifteen quaternary eutectics that have been reported in the literature in the Zr–Ti–Cu–Ni system. A good correlation of P_HSS range between modeled alloys and established glass formers indicates the subtle efficacy of this method for high entropy amorphous alloy design through a rationale thermodynamic approach.