Surface modifications of biometallic commercially pure Ti and Ti–13Nb–13Zr alloy by picosecond Nd:YAG laser

The effects of picosecond Nd:YAG laser irradiation on chemical and morphological surface characteristics of the commercially pure titanium and Ti–13 Nb–13 Zr alloy in air and argon atmospheres were studied under different laser output energy values. During the interaction of laser irradiation with the investigated materials, a part of the energy was absorbed on the target surface, influencing surface modifications.Laser beam interaction with the target surface resulted in various morphological alterations, resulting in crater formation and the presence of microcracks and hydrodynamic structures. Moreover, different chemical changes were induced on the target materials' surfaces, resulting in the titanium oxide formation in the irradiation-affected area and consequently increasing the irradiation energy absorption. Given the high energy absorption at the site of interaction, the dimensions of the surface damaged area increased. Consequently, surface roughness increased.The appearance of surface oxides also led to the increased material hardness in the surface-modified area. Observed chemical and morphological changes were pronounced after laser irradiation of the Ti–13 Nb–13 Zr alloy surface.     

Interface microstructure and formation mechanism of ultrasonic spot welding for Al–Ti dissimilar metals

The present study focuses on interface microstructure and joint formation. AA6061 aluminum alloy(Al) and commercial pure titanium(Ti) joints were welded by ultrasonic spot welding(USW). The welding energy was 1100–3200 J. The Al–Ti joint appearance and interface microstructure were observed mainly via optical microscopy and field emission scanning electron microscopy. Results indicated that a good joint can be achieved only with proper welding energy of 2150 J. No significant intermetallic compound(IMC) was found under all conditions. The high energy barriers of Al–Ti and difficulties in diffusion were the main reasons for the absence of IMC according to kinetic analysis. The heat input is crucial for the material plastic flow and bonding area, which plays an important role in the joint formation.     

Saturation phenomenon of Ce and Ti in the modification of Al–Zn–Si filler metal

Cerium and titanium were added to an Al–42Zn–6.5Si brazing alloy, and the subsequent microstructures of the brazing alloy and the 6061 Al alloy brazing seam were investigated. The microstructures of filler metals and brazed joints were characterized by scanning electron microscopy and X-ray energy dispersion spectrometry. A new Ce–Ti phase formed around the silicon phase in the modified filler metal and this saturation phenomenon was analyzed. Interestingly, following brazing of the 6061 alloy, there is no evidence of the Ce–Ti phase in the brazing seam. Because of the mutual solubility of the brazing alloy and base metal, the quantity of the solvent increases, and the solute Ce and Ti atoms assume an undersaturated state.     

Characterization of Cu-Ti powder metallurgical materials

Powder metallurgical Cu-Ti alloys with different titanium additions produced by hot pressing were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction analysis, and hardness, wear and bending tests. The addition of titanium to copper caused the formation of different intermetallic layers around titanium particles. The titanium content of the intermetallics decreased from the center of the particle to the copper matrix. The hardness, wear resistance, and bending strength of the materials increased with increasing Ti content, whereas strain in the bending test decreased. Worn surface analyses showed that different wear mechanisms were active during the wear test of specimens with different chemical compositions. Changes in the properties of the materials with titanium addition were explained by the high hardness of different Cu-Ti intermetallic phases.     

Microstructural study and numerical simulation of phase decomposition of heat treated Co–Cu alloys

The influence of heat treatment on the phase decomposition and the grain size of Co–10 at% Cu alloy were studied. Few samples were aged in a furnace for either 3 or 5 h and then quenched in iced water. The materials and phase compositions were investigated using energy dispersive spectrometry and X-ray diffraction techniques. X-ray diffraction analysis showed that the samples contained Co, Cu, Cu O, Co Cu2O3, Co Cu O2 phases in different proportions depending on the heat treatment regimes. The formation of dendrite Co phase rendered the spinodal decomposition while the oxidations prevent the initiation of the spinodal decomposition even for a deep long aging inside the miscibility gap.Since the Bragg reflections from different phases of Co–Cu alloy significantly overlap, the crystal structural parameters were refined with FULLPROF program. The shifts in the refined lattice constants(a, b and c), the space group and the grain size were found to be phase- and heat treatment-dependant. Two-dimensional computer simulations were conducted to study the phase decomposition of Co–Cu binary alloy systems.The excess free energy as well as the strain energy, without a priori knowledge of the shape or the position of the new phase, was precisely evaluated. The results indicate that the morphology and the shape of the microstructure agree with SEM observation.     

Effects of solidifi cation cooling rate on the corrosion resistance of Mg – Zn–Ca alloy

This study was carried out to investigate the effect of solidification cooling rate on the corrosion resistance of an Mg–Zn–Ca alloy developed for biomedical applications. A wedge shaped copper mould was used to obtain different solidification cooling rates. Electrochemical and immersion tests were employed to measure the corrosion resistance of Mg–Zn–Ca alloy. It was found that increasing cooling rate resulted in a significant improvement in the corrosion resistance of the Mg–Zn–Ca alloy. The findings were explained in terms of solidification behaviour in association with the change in solubility of the alloying elements, microstructural homogeneity and refinement and chemical homogeneity as well as the increased cooling rates.     

Effect of thermo-mechanical treatment on mechanical and elastic properties of Ti–36Nb–5Zr alloy

The evolutions of phase constitutions and mechanical properties of a β-phase Ti–36Nb–5Zr(wt%) alloy during thermo-mechanical treatment were investigated. The alloy consisted of dual(β t α″) phase and exhibited a double yielding phenomenon in solution treated state. After cold rolling and subsequent annealing at 698 K for 20 min, an excellent combination of high strength(833 MPa) and low modulus(46 GPa) was obtained. The high strength can be attributed to high density of dislocations, nanosized α phase and grain refinement. On the other hand, the low Young's modulus originates from the suppression of chemical stabilization of β phase during annealing, which guarantees the low β-phase stability. Furthermore, the single-crystal elastic constants of the annealed Ti–36Nb–5Zr alloy were extracted from polycrystalline alloy using an in-situ synchrotron X-ray technique. The results indicated that the low shear modulus C44 contributes to the low Young's modulus for the Ti–36Nb–5Zr alloy, suggesting that reducing C44 through thermo-mechanical treatment might be an efficient approach to realize low Young's modulus in β-phase Ti alloys. The results achieved in this study could be helpful to elucidate the origin of low modulus and sheds light on developing novel biomedical Ti alloys with both low modulus and high strength.     

Nd–Mg–Ni alloy electrodes modified by reduced graphene oxide with improved electrochemical kinetics

To improve the electrochemical kinetics of Nd–Mg–Ni alloy electrodes, the alloy surface was modified with highly conductive reduced graphene oxide(rGO) via a chemical reduction process. Results indicated that rGO sheets uniformly coated on the alloy surface, yielding a threedimensional network layer. The coated surfaces contained numerous hydrophilic functional groups, leading to better wettability of the alloy in aqueous alkaline media. This, in turn, increased the concentration of electro-active species at the interface between the electrode and the electrolyte, improving the electrochemical kinetics and the rate discharge of the electrodes. The high rate dischargeability at 1500 mA·g~(–1) increased from 53.2% to 83.9% after modification. In addition, the modification layer remained stable and introduced a dense metal oxide layer to the alloy surface after a long cycling process. Therefore, the protective layer prevented the discharge capacity from quickly decreasing and improved cycling stability.     

Microstructural characterization and hydrogenation performance of Zr_xV_5Fe(x=3-9) alloys

Zr_xV_5 Fe(x=3,5,7,8,9) alloys were designed to investigate the influence of Zr addition on hydrogenation performance.The alloys were prepared by arc melting and then annealed at 1273 K for 168 h.The results showed that the alloys were composed of α-Zr and C15-ZrV2 phases.The cell volume of C15-ZrV_2 phase firstly increased and then decreased as the content of Zr increased,while the reversed trend was found for the cell volume of α-Zr phase,which was related to the stoichiometric ratio of elements.α-Zr phase distributed in C15-ZrV2 phase matrix in Zr_xV_5 Fe(x=5,7,8,9) alloys,among which Zr7 V5 Fe alloy showed the best distribution.The PCT curves of the alloys under 623 K,673 K and 723 K showed that the hydrogen absorption plateau pressure of the phases in different alloys decreased gradually with the increasing content of Zr.However C15-ZrV2 phase in Zr7 V5 Fe alloy had the lowest hydrogen absorption plateau pressure at room temperature,which was consistent with the change tendency of the corresponding cell volume.Moreover,the kinetic curves of hydrogen absorption at 623 K revealed that Zr7 V5 Fe alloy with the smallest average particle size and the largest phase boundary area showed the fastest hydrogen absorption kinetics.Compared with other four alloys(including St707 alloy),Zr_7 V_5 Fe alloy is more suitable for the use of getter.     

Microstructure and properties of Cu–Ti–Ni alloys

The effects of Ni addition and aging treatments on the microstructure and properties of a Cu–3Ti alloy were investigated. The microstructure and precipitation phases were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy; the hardness, electrical conductivity, and elastic modulus of the resulting alloys were also tested. The results show that Ni addition increases the electrical conductivity and elastic modulus, but decreases the hardness of the aged Cu–3Ti alloy. Within the range of the experimentally investigated parameters, the optimal two-stage aging treatment for the Cu–3Ti–1Ni and Cu–3Ti–5Ni alloy was 300°C for 2 h and 450°C for 7 h. The hardness, electrical conductivity, and elastic modulus of the Cu–3Ti–1Ni alloy were HV 205, 18.2% IACS, and 146 GPa, respectively, whereas the hardness, electrical conductivity, and elastic modulus of the Cu–3Ti–5Ni alloy were HV 187, 31.32% IACS, and 147 GPa, respectively. Microstructural analyses revealed that β′-Ni3 Ti and β′-Cu4 Ti precipitate from the Cu matrix during aging of the Cu–3Ti–5Ni alloy and that some residual Ni Ti phase remains. The increased electrical conductivity is ascribed to the formation of Ni Ti, β′-Ni3 Ti, and β′-Cu4 Ti phases.     

Experimental Study on the Milling of a Ti Beta 21S

Ti Beta 21S (Ti-15Mo-2.7Nb-3Al-0.2Si) was devel op ed by TIMET in 1989. It is a metastable beta titanium alloy that offers subs tantial weight reductions over other engineering materials. Compared with common beta Ti alloys, it offers the high specific strength, good cold formability, im proved oxidation resistance, elevated temperature strength, creep resistance, an d thermal stability. Besides the common characters of titanium alloy, such as po or heat diffusivity, low elastic modulus, Ti Beta 21S has ...     

Effect of trace Ce and B additions on the microstructure of Nb-3Si-22Ti alloys

The effects of trace Ce and B additions on the microstructure Nb-22Ti-3Si alloys were studied. The microstructure of the alloys was observed by scanning electron microscope (SEM), and their phase compositions were analyzed with X-ray diffraction (XRD) and Electro-Probe micro-analyzer (EPMA). The distributions of the elements were detected by Spectrum analyzer. The interface of the phases in the alloys was investigated by transmission electron microscopy (TEM). The results indicated that two phases of Nbss and Nb3Si presented in Nb-22Ti-3Si, Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys. The segregation of Ti at the interface between Nbss and Nb3Si was promoted and the volume fraction of silicides in the alloy increased with the trace B and Ce addition to the Nb-22Ti-3Si alloy respectively. And there was no single and definite orientation relationship between Nb3Si and Nbss in Nb-22Ti-3Si, Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys. Compared with the Nb-22Ti-3Si alloy, the Nbss superlattice structure was found in Nb-22Ti-3Si-0.2Ce and Nb-22Ti-3Si-0.2B alloys.     

Macrosegregation and the underlying mechanism in Ti-6.5Al-1.0Cr-0.5Fe-6.0Mo-3.0Sn-4.0Zr alloy

A novel method for the analysis of composition distribution of titanium alloys over a large area(64 mm × 72 mm) was investigated by exploring the original position statistic distribution based on spark spectrum(OPA-SS) in Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0-Sn-4.0 Zr titanium alloy. The results showed that OPA-SS could characterize the distribution of elements in different positions on the titanium alloy. The macrosegregation of Sn was the most pronounced, with a statistic segregation degree higher than 18%; the macrosegregation of Mo followed with a statistic segregation degree of 10%; the macrosegregation of Al and Fe was relatively milder,lower than 8%. The main reason for the macrosegregation state of the as-cast Ti-6.5 Al-1.0 Cr-0.5 Fe-6.0 Mo-3.0 Sn-4.0 Zr alloy can be the solute redistribution during liquid solidification and the diffusion rate of each element in the solid phase.     

Effect of trace Zn, P and Mg additions on microstructure and mechanical properties of Nb-Si-Ti alloys

The effects of Zn,P and Mg additions on the microstructure and mechanical properties of Nb-22Ti-3Si alloys were studied. The phases of Nbss and Nb_3Si presented in Nb-22Ti-3Si(AC1),Nb-22Ti-3Si-0.2Zn(AC2) and Nb-22Ti-3Si-0.2Mg alloys(AC3). The Nb-22Ti-3Si-0.2P(AC4) alloy consisted of Nbss,Nb_3Si network and eutectic cell of Nbss/α-Nb_5Si_3.By the addition of Zn,the Nb_3Si network was broken and the volume fraction of Nbss increased from 92%to 96%.The values of fracture toughness of the alloy AC2 at ambien...     

Static coarsening of titanium alloys in single field by cellular automaton model considering solute drag and anisotropic mobility of grain boundaries

Static coarsening is an important physical phenomenon that influences microstructural evolution and mechanical properties. How to simulate this process effectively has become an important topic which needs to be dealt with. In this paper, a new cellular automaton (CA) model, which considers the effect of solute drag and anisotropic mobility of grain boundaries, was developed to simulate static grain coarsening of titanium alloys in the beta-phase field. To describe the effect of the drag caused by different solute atoms on coarsening, their diffusion velocities in beta titanium were estimated relative to that of titanium atoms (Ti). A formula was proposed to quantitatively describe the relationship of the diffusion velocity of Ti to that of solute atoms; factors influencing the diffusion velocity such as solute atom radius, mass, and lattice type were considered. The anisotropic mobility of grain boundaries was represented by the parameter c0, which was set to 1 for a fully anisotropic effect. These equations were then implemented into the CA scheme to model the static coarsening of titanium alloys Ti-6Al-4V, Ti17 (Ti-5Al-4Mo-4Cr-2Sn-2Zr, wt%), TG6 (Ti-5.8Al-4.0Sn-4.0Zr-0.7Nb-1.5Ta-0.4Si-0.06C, wt%) and TA15 (Ti-6Al-2Zr-1Mo-1V, wt%) in the beta field. The predicted results, including coarsening kinetics and microstructural evolution, were in good agreement with experimental results. Finally, the effects of time, temperature, and chemical composition on grain coarsening and the limitations of the model were discussed.     

Effect of oxygen on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr alloy

The influence of oxygen content on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr (at%) alloy in as-cast and cold-rolled states was investigated systematically in this paper. It is found that the alloy containing oxygen element is only composed of a single β phase, while the alloy without oxygen element consisted of β and α″ phases. Although the grain size becomes larger, the elastic deformation ratio, strength, and hardness of the alloy are all increased with an increase of oxygen content. The as-cast alloy has excellent plastic deformation ability, but the cold-rolled alloy containing oxygen element exhibits brittle characteristics. A conclusion can be drawn that oxygen element can stabilize β phase, inhibit the phase transformation from β to α″, and furthermore help to increase the strength and elastic deformation ability of the alloy.     

Zr77.1Cu13Ni9.9非晶合金破片侵彻LY12铝合金及TC4钛合金靶板毁伤后效及机理对比研究

锆基非晶合金是极具发展潜力的含能结构材料,由其制备的破片侵彻不同材质装甲时,会表现出显著不同的毁伤效果.本研究中利用弹道枪发射装置,针对Zr_77.1Cu₁₃Ni_9.9非晶合金破片,以1 200 m/s速度分别侵彻8 mm厚LY12铝合金和TC4钛合金屏蔽靶,结合高速摄影技术比较了破片碎裂形成碎片云并造成毁伤后效的过程;同时基于FEM/SPH自适应耦合法,再现了破片对两类屏蔽靶开坑、稳定侵彻、穿透等系列阶段,以及碎片云形成的复杂物理过程,揭示了其对后效靶的毁伤机理.结果表明,由于TC4钛合金相比LY12铝合金具有更高的强度,穿透TC4屏蔽靶所需的时间更长,且靶板内最大等效应力是后者的3倍左右;破片在侵彻TC4屏蔽靶时与靶板间发生了更强的相互作用,使得破片前端出现更大面积的高应变区域,由此导致破片发生了更严重的破碎并产生分布范围更大的碎片云,从而在后效靶上产生更大面积的损伤.     

Microstructure and property of the Ti-24Al-15Nb-1.5Mo/TC11 joint welded by electron beam welding

The Ti-24Al-15Nb-1.5Mo alloy, in the as-forged and heat-treated states, was joined to the as-forged TC 11 titanium alloy by electron beam welding with the heat inputs of 135 and 150 kJ/m. Then the microstructure and property of the Ti-24Al-15Nb-1.5Mo/TC 11 welding interface were investigated. The results show that the phase constitution of the weld is not related to the heat input, and is mainly composed of α' phase. Moreover, the intermetallic phases of TiEAlNb, MoNb, Nb₃Al, and TiAl₃ are formed in the weld zone. Therefore, the microhardness value of the weld zone is higher than that of the other portions in the same sample. The profile of the weld is asymmetrically fimnel-like. The grain sizes of the weld and its heat-affected zones are increased with increasing heat input. There is an obvious difference in the element content of the welding interface; only the alloying elements in the fusion zone reach a new balance during solidification.     

钛合金表面织构的光纤激光加工多参数耦合研究

针对钛合金作为生物医用材料具有耐磨性差、表面容易划伤等缺点,采用光纤激光表面织构提高其抗磨性能.因诸多激光工作参数共同制约其加工效率,对钛合金TC4进行多参数耦合实验研究,提出了一套适用于凹坑形和凹槽形两种表面图案的理想工作参数组.实验结果表明,该参数组能有效地提高表面织构的精度和速度.