In β titanium alloys, the β stabilizers segregate easily and considerable effort has been devoted to alleviate/eliminate the segregation. In this work, instead of addressing the segregation problems, the segregation was utilized to develop a novel microstructure consisting of a nanometre-grained duplex (α+β) structure and micrometre scale β phase with superior mechanical properties. An as-cast Ti-9Mo-6W alloy exhibited segregation of Mo and W at the tens of micrometre scale. This was subjected to cold rolling and flash annealing at 820 oC for 2 and 5 mins. The solidification segregation of Mo and W leads to a locally different microstructure after cold rolling (i.e., nanostructured β phase in the regions rich in Mo and W and plate-like martensite and β phase in regions relatively poor in Mo and W), which play a decisive role in the formation of the heterogeneous microstructure. Tensile tests showed that this alloy exhibited a superior combination of high yield strength (692 MPa), high tensile strength (1115 MPa), high work hardening rate and large uniform elongation (33.5%). More importantly, the new technique proposed in this work could be potentially applicable to other alloy systems with segregation problems.

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Segregation mediated heterogeneous structure in a metastable β titanium alloy with a superior combination of strength and ductility

Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physico-chemical and mechanical surface interactions in a tribological contact. Electrochemical methods are well suited for the study of tribocorrosion phenomena because they allow one to simulate the corrosive effect of the environment by imposing a fixed potential. Furthermore, the measurement of the anodic current permits one to determine the amount of material removed by oxidation as opposed to mechanical wear. In the present paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented. The importance of controlling the mechanical parameters and the contact geometry is stressed, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.

Electrochemical methods in tribocorrosion: a critical appraisal

Fe-based bulk metallic glasses: Glass formation, fabrication, properties and applications

Microstructure evolution and superelastic behavior in Ti-35Nb-2Ta-3Zr alloy processed by friction stir processing

In this work, the thermal and electrical transport in an individual silver nanowire is characterized down to 35 K for in-depth understanding of the strong structural defect induced electron scattering. The results indicate that, at room temperature, the electrical resistivity increases by around 4 folds from that of bulk silver. The Debye temperature (151 K) of the silver nanowire is found 36% lower than that (235 K) of bulk silver, confirming strong phonon softening. At room temperature, the thermal conductivity is reduced by 55% from that of bulk silver. This reduction becomes larger as the temperature goes down. To explain the opposite trends of thermal conductivity (κ) ~ temperature (T) of silver nanowire and bulk silver, a unified thermal resistivity (Θ ~ T/k ) is used to elucidate the electron scattering mechanism. A large residual Θ is observed for silver nanowire while that of the bulk silver is almost zero. The same Θ ~ T trend proposes that the silver nanowire and bulk silver share the similar phonon-electron scattering mechanism for thermal transport. Due to phonon-assisted electron energy transfer across grain boundaries, the Lorenz number of the silver nanowire is found much larger than that of bulk silver and decreases with decreasing temperature.

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Temperature dependence of electrical and thermal conduction in single silver nanowire.

Formation of nanocrystalline β structure in metastable beta Ti alloy during high pressure torsion: The role played by stress induced martensitic transformation

Effect of W addition on the glass forming ability and mechanical properties of Fe-based metallic glass

Influence of sealing treatment on the corrosion resistance of Fe-based amorphous coatings in HCl solution

Mechanical and functional properties of ultrafine grained Al wires reinforced by nano-Al2O3 particles

A Ti40Zr25Cu12Ni3Be20 bulk metallic glass (BMG) was welded to a crystalline aluminum by the parallel plate explosive welding method. Experimental evidence and numerical simulation show that atomic-scale bonding between the BMG and the crystalline aluminum can be achieved, and the weldment on the BMG side can retain its amorphous state without any indication of crystallization in the welding process. Nanoindentation tests reveal that the interface of the explosive joints exhibits a significant increase in hardness compared to the matrix on its two sides. The joining of BMG and crystalline materials opens a window to the applications of BMGs in engineering.

Xianshun Wei

Papers

Formation of nanocrystalline β structure in metastable beta Ti alloy during high pressure torsion: The role played by stress induced martensitic transformation

Effect of W addition on the glass forming ability and mechanical properties of Fe-based metallic glass

Influence of sealing treatment on the corrosion resistance of Fe-based amorphous coatings in HCl solution

Mechanical and functional properties of ultrafine grained Al wires reinforced by nano-Al2O3 particles

Atomic-scale bonding of bulk metallic glass to crystalline aluminum