Titanium alloys are widely used in the field of orthopaedics, however, poor tribological performance arising from the low shear resistance and weak protection of the oxide layer limits their applicability. In this work, the tribocorrosion behaviour of novel beta and alpha + beta biomedical titanium alloys were studied in bovine serum solution under open circuit potential. Ti-5Mo-Fe-3Sn and Ti-6Al-4V ELI alloys were found to have the capability to repassivate when testing at a slower sliding speed. Scanning and transmission electron microscopy results revealed that the repassivation was mainly associated with the greater tribofilm formation on the worn surface, rather than an oxide film. The tribolayer performed as a solid lubricating film, which stabilised the coefficient of friction.

Cold spray (CS) coating technique is being studied as a potential solution for repairing aircraft Ti-6Al-4V components. This work is focused on the restoration of damaged components due to wear induced by vibrations. It is known that Ti-6Al-4V CS deposition shows difficulties to obtain non-porous coatings due to the high strength of this material, that is detrimental for wear resistance. In this sense, performing a post-heat treatment leads to lower porosity CS Ti-6Al-4V coatings and improves their mechanical properties, and thus, a better tribological behaviour is also expected. Therefore, the objective of this study was to determine the effect of a post-heat treatment on the wear resistance of Ti-6Al-4V coatings deposited by the CS technique. Ti-6Al-4V CS coatings were used, which have been sprayed with nitrogen as process gas at a temperature of 1100 degrees C and a pressure of 50 bar. The coatings were subjected to a solution heat treatment followed by a precipitation heat treatment. Oscillating and unidirectional sliding wear experiments were conducted on the coatings at room temperature and at 450 degrees C. A pin on disc configuration was used with a bearing steel counterbody. The results were compared to those obtained on the substrate (which represents the material to be repaired) and on the as-sprayed coating, which were derived from a previous work. The heat treated coating presented improved wear behaviour as compared to the substrate as well as to the as-sprayed coating, particularly during the high temperature tests. Wear at high temperature was dominated by material transference from the counterbody to the Ti-6Al-4V coating.

This article presents a microstructural study on the role of incipient residual stress relaxation in TiC-particulate/SiC-matrix ceramic composite toughened by thermal expansion mismatch and phase transformation toughening. Exhaustive microstructural studies was undertaken using scanning electron microscopy and transmission electron microscopy following a wear test. It was found that the superposition of hydrostatic tensile stress induced at the surface following the sliding contact on the inherent residual stresses locked in the composite led to a relaxation and/or reduction in the residual stresses. Stress relaxation presented a wider implication for the tribological properties of this ceramic matrix composite (CMC) in the form of a grain-scale rippling microstructural phenomena.

MAX phase composites Ti3SiC2?TiCx and Ti3SiC2?(TiCx + TiC) were synthesized and consolidated via a powder metallurgy spark plasma sintering (SPS) technique. The bulk compositions and microstructural evolution of the resulting SPS discs were analyzed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy (SEM) paired with an energy-dispersive spectroscopy (EDS) system. The tribological behavior of the synthesized discs was investigated at room temperature under dry sliding conditions using an Al2O3 ball by employing a ball-on-disc tribometer configuration. Postmortem analyses of the worn surfaces showed that the Ti3SiC2 MAX phase exhibited intrinsic self-lubricating behavior due to the evolution of easily sheared graphitic carbon at the sliding surface. The addition of stoichiometric TiC delayed the oxidation kinetics of Ti3SiC2, which favors the evolution of graphitic carbon in lieu of rutile and oxycarbide films. Thus, this work shows comprehensively the existence of an intrinsic self-lubricating behavior of Ti3SiC2 and the important role of secondary-phase TiC in the Ti3SiC2 matrix in its tribological behavior. The wear mechanisms in both composites are dominated by tribo-oxidation triggered by frictional heating. This is then followed by deformation-induced wear upon friction transition.

In this work, we report the synthesis, deformation and tribological behaviour of a novel Ti3AlC2 – Ti2AlC MAX phase composite metallo-ceramic. The dual MAX phase composite was synthesized by spark plasma sintering (SPS) under a vacuum environment using Ti, Al, and C precursor powders. The layered composite deformation mechanism and tribological behaviour were studied and analyzed by SEM, TEM, and Raman spectroscopy. The transition in friction and wear as well as the operative wear mechanisms involved were further discussed. Detailed analyses of the worn surface showed that Ti3AlC2 – Ti2AlC dual MAX phase composite is intrinsically self-lubricating.

Due to internal processing defects, bulk nanostructured Mg alloys have high strength but extremely poor ductility. A novel and facile process was designed and in-situ powder casting was initiated during spark plasma sintering. This process significantly reduced processing induced defects, enhanced inter-particle bonding and introduced significant precipitation without extra ageing treatment, leading to improvement of the compressive strength and ductility. The compressive strain of bulk sample consisting of pure cryomilled powder was 3.6% with an ultimate strength of 500 MPa, while cryomilled powder mixed with eutectic Mg-Zn alloy powder obtained a compressive strain of 6.6% and ultimate strength of 506 MPa. The ductility of the sample with mixed powder was increased by 83% without any sacrifice of strength compared to the sample consisting of only pure cryomilled powder. (C) 2018 Elsevier B.V. All rights reserved.

Artificial multiferroic structures are of great interest as they combine two or more functionalities together. One example of these structures is magnetostrictive films grown on top of piezoelectric substrates; allowing the magnetisation hysteresis loop of the magnetostrictive film to be manipulated using an electric field across the structure rather than a magnetic field. In this paper, we have studied the multiferroic structure NiFe/FeCo/Ti/Pb(Mg1/3Nb2/3)-PbTiO3 (PMN-PT) as a function of the electric and magnetic field. Soft magnetostrictive bilayer films (NiFe/FeCo) are studied, as often applications require soft magnetic properties (small coercive and anisotropy fields) combined with larger magnetostrictive constants. Unfortunately, FeCo films can have coercive fields that are too large, while NiFe films' magnetostriction constants are almost zero; thus, combining the two together should produce the 'ideal' soft magnetostrictive film. It was found that the addition of a thin NiFe film onto the FeCo film reduced the coercive field and remnant magnetisation on the application of an applied voltage in comparison to just the FeCo film. It was also determined that for the NiFe/FeCo bilayer the magnetisation switchability was similar to 100% on the application of 8 kV cm(-m), which was higher than the monolayer FeCo films at the same applied field, demonstrating improvement of the multiferroic behaviour by the soft magnetic/magnetostrictive bilayer.

LiCoMnO4 was made at 550 °C in 2 h using a novel biotemplating synthetic methodology. High temperature heat treatment under flowing N2 was then used to prepare the cation-disordered rock salt, LiCoMnO3. We demonstrate for the first time that both phases can operate as conversion anodes in lithium-ion batteries, operating at ~ 0.7 V with specific capacities of ~ 400 mAh g-1. We also demonstrate that 1,3-propane sultone can be used as an electrolytic additive to provide a modest boost to specific capacity in cells cycled at high potentials with LiCoMnO4 as the cathode.

In this paper, the thermal stability of cryomilled nanocrystalline (NC) AZ31 powder was evaluated by annealing at elevated temperature ranging from 350 to 450 °C. The results show the NC AZ31 powder exhibited excellent thermal stability during short anneals at 350–450 °C, and the mechanisms were investigated in detail. There were two separate growth stages with a transition point at around 400 °C. More specifically, between 350 and 400 °C, NC Mg grains were stable at approximately 32 nm, even after 1 h annealing. At 450 °C, the nano grains grew to 37 nm in the first 5 min and grew quickly to approximately 60 nm after 15 min. However, the grain growth was limited when the annealing time was increased to 60 min. The average grain size remained stable less than approximately 60 nm even after long anneals at temperatures as high as 450 °C (0.78 T/TM), indicating an outstanding degree of grain size stability. This excellent thermal stability can be mainly attributed to solute drag and Zener pinning.

Recrystallised grain nucleation, grain growth and corresponding texture evolution in a cold-rolled rare earth containing WE43 Mg alloy during annealing at 490 degrees C was fully tracked using a quasi-in-situ electron backscatter diffraction method. The results show nucleation sites, such as double twins, can weaken the deformed texture and for the first time provide direct evidence that recrystallised grains originating from double twins can form the rare earth texture during annealing. Precipitation and recrystallisation occurred concurrently during most of the annealing period, with precipitates forming preferentially along prior grain and twin boundaries. These precipitates effectively retard the recrystallisation due to particle pinning leading to an excessively long time for the completion of recrystallisation. A large portion of recrystallised grains were observed to have (0001) poles tilted 20-45 away from the normal direction. The RE texture emerges during the nucleation of recrystallised grains and is maintained during subsequent uniform grain growth, which results in a stable RE texture being developed as recrystallisation progresses. The uniform grain growth could be attributed to solute drag suppressing the grain boundary mobility of those grains that had recrystallised with a basal texture and precipitate pinning restricting potential orientated grain growth. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.

DLC coatings and nanostructured carbon coating have been successfully used to prevent against wear and corrosion. Their thermal stability and internal stress have been improved by the addition of transition metals. This work characterizes the surface morphology against two different materials and growth mechanisms of an hydrogen-free carbon coating doped with a W–Mo. The wear resistance is evaluated under dry and room temperature by a set of pin on disc tests at different load and against two different counterfaces, Al2O3 and stainless steel 440C. The as-deposited and worn surfaces were characterized by electron microscopy techniques, interferometry, nanoindentation and Raman spectroscopy. The as-deposited coating presented a hardness of 14GPa and an elastic modulus of 179GPa with a dense surface finished and a columnar structure. The average friction coefficient was between 0.15 and 0.25, with almost no wear on the counterfaces. The W–Mo doped DLC coating showed high resistance against wear with wear rates between 3.79×10−8 mm3N−1m−1 and 2.65×10−7mm3N−1m−1 due to its Mo–W carbide content in the amorphous matrix. A major presence of carbides prevent from adhesion to the counterface by reducing the number of dangling bonds.

Precipitation along twin boundaries and dissolution in a cold-rolled Mg-Y-Nd alloy was directly observed for the first time during annealing at 490 degrees C Precipitation occurred concurrently with recrystallization and the combined effect of precipitation and solute segregated to twin boundaries modified the recrystallization behaviour. Precipitates later dissolved into the matrix at the point where full recrystallization was nearly complete. The precipitates and higher solute concentration along original twin boundaries hindered grain growth of newly formed recrystallized grains. Even where twin boundaries had been consumed by recrystallization, the size of recrystallized grains were still controlled by the pre-existing twin boundaries. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.

The manipulation of the strain-mediated magnetoelectric (ME) coupling strength is investigated by inserting a thin Ti layer (0–10 nm) between a 50 nm Co50Fe50 layer and a (011) oriented lead magnesium niobate-lead titanate (PMN-PT) substrate. A record high remanence ratio (Mr/Ms) tunability of 100% has been demonstrated in the 50 nm CoFe/8 nm Ti/PMN-PT heterostructure, when a total in-plane piezoelectric strain of −1821 ppm was applied at an electric field (E-field) of 16 kV/cm. The ME coupling strength is gradually optimized as the Ti layer thickness increases. Magnetic energy calculation showed that with increasing Ti layer thickness the uniaxial magnetic anisotropy energy (Euni) was reduced from 43 ± 1 kJ/m3 to 29.8 ± 1 kJ/m3. The reduction of Euni makes the strain effect dominant in the total magnetic energy, thus gives an obvious enhanced ME coupling strength.

The transformation on heating LiCoMnO 4 , with a spinel structure, to LiCoMnO 3 , with a cation-disordered rock salt structure, accompanied by loss of 25% of the oxygen, has been followed using a combination of diffraction, microscopy and spectroscopy techniques. The transformation does not proceed by a topotactic mechanism, even though the spinel and rock salt phases have a similar, cubic close-packed oxygen sublattice. Instead, the transformation passes through two stages involving, first, precipitation of Li 2 MnO 3 , leaving behind a Li-deficient, Co-rich non-stoichiometric spinel and, second, rehomogenization of the two-phase assemblage, accompanied by additional oxygen loss, to give the homogeneous rock salt final product; a combination of electron energy loss spectroscopy and X-ray absorption near edge structure analyses showed oxidation states of Co 2+ and Mn 3+ in LiCoMnO 3 . Subsolidus phase diagram determination of the Li 2 O-CoO x -MnO y system has established the compositional extent of spinel solid solutions at approximately 500°C.

The precipitates formed in a new series of FeMn maraging steels when aged at 500°C were identified as the L21-ordered Ni2TiAl phase. The precipitate formed a coherent-coplanar microstructure analogously to γ/γ' Ni-based superalloys and maintained a high number density and homogeneous dispersion within α′-martensite matrix even after aging for 10,080min. An increase in the Mn content of the alloy led to faster precipitation kinetics and thus rapid hardening kinetics.

Bulk nanostructured magnesium alloy AZ31 has been produced by spark plasma sintering at four different temperatures from 350 to 450 degrees C. The effect of sintering temperature on microstructural evolution and compression behaviour was studied in detail. It was concluded that the sample consolidated at 400 degrees C exhibited the highest strength. Higher sintering temperature (450 degrees C) improved the compressive strain of the bulk sample but at the sacrifice of strength. However, samples consolidated at 350 degrees C displayed brittle behaviour with low strength. All consolidated samples had a bimodal microstructure with nanocrystalline and coarse grains. The nanocrystalline microstructure formed by cryomilling was retained after consolidation and a maximum microhardness was approximately 150 HV. The bulk samples consolidated at 400 degrees C with an average grain size of 45 nm showed exceptional average true compressive yield strength of 400.7 MPa, true ultimate compressive strength of 499.7 MPa, which was superior to published results for most of conventional magnesium alloys. Although nanostructured materials usually have high strength but poor ductility, the material in this study exhibited high strength and a true compressive strain of 0.036. (C) 2016 Elsevier B.V. All rights reserved.

The microstructural evolution in a set of Mn-based maraging steels (7–12 wt% Mn) when aged at 460–500 ºC for various durations up to 10,080 min and the influences on mechanical properties are systematically investigated. The improved yield strength of peak-aged samples is attributed to the formation of Ni2TiAl precipitates and the precipitation strengthening is governed by Orowan mechanism. Segregation of Mn at grain boundaries in the initial aging stage resulted in severe intergranular brittleness. During further aging, accumulated Mn segregation leading to the formation of ductile lath-like reverted austenite removed the embrittlement and significantly improved the ductility. In the overaged condition, the steady work hardening after yielding compensates the loss of yield strength resulting from the coarsening of precipitates and softening of α′-martensite matrix. There was only limited evidence of the TRIP effect in the reverted austenite, indicating that work hardening was associated with other deformation mechanisms. Increasing the aging temperature or the Mn content of alloy that promotes austenite reversion was demonstrated to accelerate the improvement of ductility.