R.P. Liu

Development of a new β Ti alloy with low modulus and favorable plasticity for implant material.

One of the most important development directions of the Ti and its alloys is the applications in medical field. Development of new Ti alloys with low elastic modulus and/or favorable biocompatibility plays an important role for promoting its application in medical field. In this work, a new β Ti alloy (Ti-31Nb-6Zr-5Mo, wt.%) was designed for implant material using d-electron alloy design method. Microstructure and tensile properties of the designed alloy after hot rolling (HR) and solution followed by aging treatments (SA) were investigated. Results show that the designed alloy is composed of single β phase. However, microstructural analysis shows that the β phase in the designed alloy separates into Nb-rich and Nb-poor phase regions. The Nb-rich regions in HR specimen are typical elongated fiber texture, but are equiaxed particles with several micrometers in SA specimen. Tensile results show that the designed alloy has low Youngs modulus of 44 GPa for HR specimen and 48 GPa for SA specimen which are very close to the extreme of Youngs modulus of bulk titanium alloys. At the same time, the designed alloy has favorable plasticity in term of elongation of 26.7% for HR specimen and 20.6% for SA specimen, and appropriate tensile strength over 700 MPa. In short, the designed alloy has low elastic modulus close to that of bone and favorable plasticity and strength which can be a potential candidate for hard tissue replacements.

Effect of Voronoi volume on fluctuation at initial deformation of amorphous alloys

Quasi-static compressive behaviors of three amorphous alloys (Cu 50Zr50, Pd80Si20, and Ni 67Zr33) are investigated via molecular dynamics simulations. Compared to the crystalline counterpart, when the strain is below 1%, significant fluctuations can be observed in the stress-strain curves. Further analysis of the simulated data indicates that the fluctuations are associated with the variations of Voronoi volume. A gradient reduction model is proposed to explain the process of the evolution of Voronoi volume at the initial stage of the deformation.

Dynamic precipitation of Al–Zn alloy during rolling and accumulative roll bonding

In this study, cold rolling was performed on a binary Al–20 wt%Zn alloy and dynamic precipitation identified for the first time in Al alloys under cold rolling. Zn clusters formed after application of 0.6 strain, and the Zn phase precipitated upon further increasing strain. Both grain refinement and rolling-induced defects are considered to promote Zn precipitation. The hardness of Al–Zn alloy initially increased with strain up to a strain of 2.9 and then decreased with increasing rolling strain. Dynamic precipitation greatly affects the strengthening mechanism of the rolled Al–Zn alloy under various strains.

Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under high pressure examined by in situ synchrotron radiation x-ray diffraction

Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under high temperature and high pressure has been investigated by in situ synchrotron radiation x-ray diffraction. The onset temperature of crystallization was found to increase with pressure, but with a sudden drop at about 5.6GPa. Though the primarily precipitated phase is the same at different pressures, the sequences of the following phase precipitation are different.

Stability and electronic structure of ordered Si0.75Ge0.25C alloy

Calculations are performed on the stability and electronic structure of an ordered Si0.75Ge0.25C alloy within the generalized gradient approximation using the first-principles method. The alloy is stable at zero pressure and temperature, with its lattice constant 4.34 A close to that of cubic SiC and bulk modulus 223 GPa. An analysis of the band structure and density of states shows the cubic alloy to be an indirect semiconductor with a wider band gap compared to SiC and therefore is a candidate material that can function in heterostructure applications. When combined with cubic SiC to form heterostructure bipolar transistors, an enhancement coefficient 2×104 for current gain β would be expected relative to the SiC homojunction bipolar junction transistors at room temperature.

Tribological properties of plasma-nitrided AISI 4340 steel in vacuum

Tribological properties of nitrided AISI 4340 steel are evaluated using ball-on-disk tribometer in vacuum. Optical microscopy and Vickers hardness tester are used to analyse compound layer thickness and case depth. X-ray diffraction is used to observe the presence of different constituents of nitrided surface before and after the wear tests. The wear mechanisms are investigated by microscopic observations of the worn surface using scanning electron microscopy. At 200 rpm, mild adhesive wear forms the main wear mechanism under the lower load. With increasing the normal load, the dominant wear mechanism changes to mild plastic deformation and abrasive wear. At 600 rpm, the wear mechanisms vary from the mild plastic deformation to severe plastic deformation, abrasive wear and even delamination with increasing the normal load.

Effects of minor addition on glass forming ability: Thermal versus elastic criteria

The effect of partial substitution of Zr by Al in Zr35−xTi30Cu7.5Be27.5Alx (x≤10) alloys on the glass forming ability (GFA) is studied. The thermal and the elastic criteria in evaluating the GFA of the alloys are examined. The calorimetric quantities are measured to determine the width of the supercooled liquid region ΔTx and γ indexes. Parallel studies are performed to measure the elastic moduli with the emphasis of the ratio of the shear to the bulk modulus G/B. The addition of Al is found to have remarkable influence on the GFA of the alloys. While ΔTx and γ decrease with the deterioration of the GFA, G/B is observed to decrease as well, contrasting with the general tendency among various glass forming metallic systems. The thermal and elastic criteria of GFA are discussed.

Pressure effect on crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass prepared by shock-wave quenching

Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) prepared by shock-wave quenching under high-temperature and high-pressure has been examined by in situ synchrotron radiation x-ray diffraction. The first precipitated phase is found to be the same at different pressures, but the subsequent phase precipitation sequences are different. The crystallization temperature of the BMG increases with pressure, but with a sudden drop at about 6.0 GPa. The different phase precipitation sequences and the sudden drop in the crystallization temperature can be explained by complex pressure effects on the atomic configuration of the BMG.

Microstructural evolution and densification of Fe80P11C9 metallic glass under high pressure

Abstract The structural evolution of Fe80P11C9 metallic glass was investigated by X-ray diffraction with synchrotron radiation under high pressure up to 32 GPa at room temperature. The diffraction data, structure factor and pair distribution function show no indication of phase transition. The positions of the first sharp diffraction peak q1 are increasing and scale with pressure. The nearest neighbour distance r1 decreases with increasing pressure. After decompression, q1 and r1 do not revert to normal levels at ambient pressure. The results indicate that microstructural relaxation occurs during pressure progress. The annihilation of free volumes and reduction of voids in the amorphous matrix increase the packing density of amorphous alloys. The present study demonstrated that high pressure induces a ‘highly ordered’ glass state and densification of metallic glass.

Study of internal stress of amorphous Ni–W alloy films

Abstract The present paper introduces the effect of W content, pH, current density, pulse ratio and stress reducers on the internal stress of Ni–W alloy films in the system of citrate amine HEDP. Morphologies of Ni–W alloy films were also investigated. The results showed that the internal stress was closely related to W content of alloy films. pH had an important effect on the internal stress of amorphous Ni–W alloy films and there were some cracks in the electrodeposits surface when pH value was in the range 5·5–6·0. Internal stress varied obviously with different current densities, however there were no obvious cracks in amorphous Ni–W alloy films. Internal stress was affected slightly by pulse ratio and stress reducers, and morphologies of amorphous Ni–W alloy films had little change with different pulse ratios and stress reducers.