Crystal Plasticity Finite Element Study of Incompatible Deformation Behavior in Two Phase Microstructure in Near β Titanium Alloy

基于晶体塑性模型,研究了近β钛合金中(α+β)两相组织的不协调变形行为。首先,双晶体模型的计算结果表明(α+β)两相组织中的塑性变形是不协调的,而且α相的变形行为与晶体取向和加载方向密切相关。另外,通过耦合三维Voronoi几何模型,探讨了近β钛合金中球状初生α相对宏观力学响应的影响。利用该CPFE-VT数值模型,研究发现α相与β相的不协调变形导致了合金强度随α相体积分数的增加而成线性降低。此外,β基体中α相的分布对合金应力-应变响应也有较大的影响。针对具有两相组织的近β钛合金建立的晶体塑性有限元模型为钛合金组织控制技术的发展以及性能预测提供了重要的途径。     

Kinetic Study of Phase Transformations in Zr-Cr-Fe Alloy

ＫｉｎｅｔｉｃＳｔｕｄｙｏｆＰｈａｓｅＴｒａｎｓｆｏｒｍａｔｉｏｎｓｉｎＺｒ－Ｃｒ－ＦｅＡｌｌｏｙＳｕｎＸｉｃｈｅｎａｎｄＤｅｒｅｋＯ．Ｎｏｒｔｈｗｏｏｄ（孙喜臣）（ＤｅｐａｒｔｍｅｎｔｏｆＭｅｃｈａｎｉｃａｌＥｎｇｉｎｅｅｒｉｎｇＵｎｉｖｅｒｓｉｔ...     

Improvement of Strength in 2024 Al Alloy by Enhanced Solution Treatment

In present paper, the effect of enhanced solution on mechanical properties and aging behavior in a commercially available 2024A1 alloy were investigated using tension test and scanning electron microscopy. Differential scanning calorimeter (DSC) was used to measure the incipient melting behavior and then determine the technology parameter of enhanced solution heat treatment for high strength. The results show that an appropriately enhanced solution treatment can make final solution temperature higher than that of the conventional solution temperature and improves second phase solution without the formation of overheated microstructure. As the results, both the strength especially the yield strength and the resistance to over aging can be improved considerably without a large deterioration to tensile ductility.     

Electrochemical Study on Formation of Dy-Ni Alloy in Molten Chlorides

ＥｌｅｃｔｒｏｃｈｅｍｉｃａｌＳｔｕｄｙｏｎＦｏｒｍａｔｉｏｎｏｆＤｙ－ＮｉＡｌｌｏｙｉｎＭｏｌｔｅｎＣｈｌｏｒｉｄｅｓＴｏｎｇＹｅｘｉａｎｇ；ＬｉｕＧｕａｎｋｕｎ；ＹａｎｇＱｉｑｉｎ；ＨｏｎｇＨｕｉｃｈａｎ，（童叶翔）（刘冠昆）（杨绮琴）（洪惠婵）...     

Design of DLC/Titanium Alloy Bio-Functionally Gradient Coat

１ＩｎｔｒｏｄｕｃｔｉｏｎＭａｎｙｏｆｔｈｅｏｒｔｈｏｐｅｄｉｃｃｏｍｍｕｎｉｔｉｅｓｎｏｗｂｅｌｉｅｖｅｔｈａｔｔｈｅｌｏｎｇｔｅｒｍｆａｉｌｕｒｅｏｆｗｈｏｌｅｈｉｐａｎｄｋｎｅｐｒｏｓｔｈｅｓｅｓｉｓｄｉｒｅｃｔｌｙｏｒｉｎｄｉｒｅｃｔｌｙ...     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

Effect of Diffusivity on the Pseudospinodal Decomposition of the γ′ Phase in a Ni-Al Alloy

The effect of diffusivity on pseudospinodal decomposition of γ′ (Ni₃Al) phase precipitation was investigated in a Ni-Al alloy using the diffuse interface phase field model. The γ′ phase microstructure, coarsening dynamics and interfacial composition width between the γ and γ′ phases were studied as a function of the diffusivity magnitude. Increasing the diffusivity results in a reduced number of γ′ nuclei, and accelerated growth and coarsening of the γ′ phase. The cube of the γ′ average radius versus time shows a linear relation during coarsening, and the Al concentration in the γ matrix follow the relations \(\Delta c_{\text{Al}}^{\gamma } \sim t^{ - 1/ 3}\) regardless of the diffusivity magnitude. The γ/γ′ interfacial composition width decreases with increased diffusivity and average radius. An obvious Al concentration depleted region is present at the γ/γ′ interface during the nucleation and growth stage of γ′ phase indicates that growth occurs by down-hill diffusion in the matrix γ phase. That combined with the gradual increase in γ′ composition demonstrates that pseudospinodal decomposition is the transformation mechanism.     

Surface Characterization of Laser Surface Melted NiTi Shape Memory Alloy in Hanks'''' Solution

LASER processing is a relative new surfaceengineering technique for improving the surfaceperformance of metal materials.Both themicrostructure and the distribution of elements in therapidly resolidified surface layer resulted from lasersurface melting(LSM)can be greatly modified.Manycommercially used biomaterials such as Ti-6Al-4V,austenitic stainless steel and titanium were processedby laser,which consequently resulted in improvedcorrosion resistance and biocompatibility.Our previousstudy…     

Study of Snap-acting Two Way Shape Memory Effect in NiTi Alloy

Snap-acting transformation and snap-acting two way shape memory(TWSM)effect have been obtained in NiTi alloy usingthe constrained effect of stress on the driving force of TWSM element.The TWSM strain of the snap-acting element made ofNi_(51)Ti_(49) alloy finishes abruptly at an acertain temperature without any additional mechanism,within an interval less than 1 ms.Athermodynamic model is presented to account for these observations.     

Electrochemical Behavior of Biomedical Titanium Alloys Coated with Diamond Carbon in Hanks’ Solution

Biomedical implants in the knee and hip are frequent failures because of corrosion and stress on the joints. To solve this important problem, metal implants can be coated with diamond carbon, and this coating plays a critical role in providing an increased resistance to implants toward corrosion. In this study, we have employed diamond carbon coating over Ti-6Al-4V and Ti-13Nb-13Zr alloys using hot filament chemical vapor deposition method which is well-established coating process that significantly improves the resistance toward corrosion, wears and hardness. The diamond carbon-coated Ti-13Nb-13Zr alloy showed an increased microhardness in the range of 850 HV. Electrochemical impedance spectroscopy and polarization studies in SBF solution (simulated body fluid solution) were carried out to understand the in vitro behavior of uncoated as well as coated titanium alloys. The experimental results showed that the corrosion resistance of Ti-13Nb-13Zr alloy is relatively higher when compared with diamond carbon-coated Ti-6Al-4V alloys due to the presence of β phase in the Ti-13Nb-13Zr alloy. Electrochemical impedance results showed that the diamond carbon-coated alloys behave as an ideal capacitor in the body fluid solution. Moreover, the stability in mechanical properties during the corrosion process was maintained for diamond carbon-coated titanium alloys.     

Study On the Tribological Behavior of the Arc-added Glow Discharge Plasma Non-hydrogen Carburization On Titanium Alloy Surfaces

This paper introduces a new titanium alloys surface strengthening treatment by using the arc-added glow discharge plasmas non-hydrogen carburization technique. High purity and high strength graphite is selected as cooling cathode arc source for supplying carbon atoms and particle, which migrate to the titanium alloy(Ti6Al4V) surface and form modified layer. Thus, the hydrogen embrittlement is avoided while the tfibological behavior of the titanium alloy surface is improved in the respects of anti-friction and anti-wear ability.The tribological behavior of the modified layer under dry sliding against SAE52100 steel was evaluated on a ball-on-disc test rig. The results showed that the modified layer obtained a thickness of 30μm at 980℃, 30minutes. The microhardness of the Ti6Al4V alloy surface attained 936 HV, which was much larger than that of the Ti6AI4V alloy. The Ti6AI4V alloy was characterized by adhesion wear and scuffing under dry sliding against the steel, while the surface modified layer experienced much abated adhesion wear and scuffing under the same testing condition. This could be attributed to the carbon dement with different modalities exists in the modified layer.The modified layer showed good friction-reducing and fair anti-wear ability in dry sliding against the steel. Using the SEM,XRD and XPS, the phase structure and morphology of the carburization modified layer was analyzed.     

Study on Electrochemical Formation of Neodymium-Iron Alloy

The cyclic voltammetry was used to investigate the electrode processes of Nd(Ⅲ)reduced on iron electrode and Nd(Ⅲ),Fe(Ⅱ)reduced on molybdenum electrode in molten chlorides.The Nd-Fe and Nd-rich RE-Fe alloys contained rare earth up to90wt% were prepared by consumable cathode and electrolytic codeposition.The mechanism of electrochemical formation ofNd-Fe alloy had been discussed.     

Study of the Structure of Oxide Interface in the Pt-Rh Alloy by AP-FIM

This paper reports the study of structure of oxide interface in Pt-Rh alloy by atom probe field ion micro-scope (AP-FIM) which is well suited for the study of atom distribution with atomic scale at the surface and in-terface of alloy. AP depth profiles show that oxide interface exist in the Pt-Rh alloy which consists of PtO,RhO, PrO_2 and RhO_2 . The mechanism of oxidation of the alloy is considered as that first oxygen moleculesadsorbed on-to the surface of alloy then dissociate into oxygen atoms (0_2→2O). Consequently oxygen atomsdiffuse into interior through grain boundary forming oxide (M+O→MO). When the concentration of oxygencontinuously increases the dioxide (MO+O→-MO_2) forms.     

Effect of Cooling Rate on SCC Susceptibility of β-Processed Ti–6Al–4V Alloy in 0.6M NaCl Solution

The effects of cooling rate on the stress corrosion cracking (SCC) susceptibility of β-processed Ti–6Al–4V (Ti64) alloy, including BA/S specimen with furnace cooling and BQ/S specimen with water quenching, were investigated in 0.6M NaCl solution under various applied potentials using a slow strain rate test technique. It was found that the SCC susceptibility of β-processed Ti64 alloy in aqueous NaCl solution decreased with fast cooling rate, which was particularly substantial under an anodic applied potential. The micrographic and fractographic analyses suggested that the enhancement with fast cooling rate was related to the random orientation of acicular α platelets in BQ/S specimen. Based on the experimental results, the effect of cooling rate on the SCC behavior of β-processed Ti64 alloy in aqueous NaCl solution was discussed.     

In Vitro Corrosion Behavior and Apatite Growth of Oxygen Plasma Ion Implanted Titanium Alloy β-21S

Titanium alloy beta 21S was implanted with oxygen ions by plasma immersion ion implantation. The implanted surface was characterized by micro-Raman, XPS and FESEM before and after potentiodynamic polarization and electrochemical impedance studies in Hanks’ solution and after incubation in Hanks’ solution for 1 and 7 days. The investigations show that the native oxide on the sample is replaced by a compact oxide by implantation and the new oxide layer behaves in a different way in that a two layer model is required to explain the observed electrochemical impedance data. The analysis of layers formed in the electrochemical studies and after incubation in Hanks’ solution by XPS and FESEM shows that the new oxide surface is capable of inducing apatite growth on it.     

Study of Dislocation Boundary Structure in Al–Li Alloy During Bending

The dislocation boundary structures of 2060-T8 alloy during bending were investigated by backscattered electron imaging, electron backscattered diffraction, and misorientation axes maps. Experimental result shows that typical dislocation boundary structures, which depend on grains' orientation, are formed in grains during bending. The microstructure of type A is mainly observed in grains near brass, copper, and Goss orientations; microstructure of type B is mainly found in grains near S orientation; microstructure of type C is mainly seen in grains near Cube orientation. The angle between geometrically necessary boundaries(GNBs) and force axis is in the range of-45° to-30° and 30° to 45°.Most of the GNBs are approximately parallel to the trace of {111} slip planes which are identified by Schmid factor analysis.     

Surface Characterization of Laser Surface Melted NiTi Shape Memory Alloy in Hanks＇ Solution

The surface of Ti-50.8Ni at% shape memory alloy was melted by an Nd-YAG laser. The Ti/Ni and Ti^4 / Tiatomic concentration ratios at the surface were changed significantly. The Ni ion release rate of the laser melted surface was much lower than that of the mechanical polished samples. A calcium-phosphorous layer with high Ca/P ratio was detected after immersion in Hanks‘ solution.