Search

In this study, the deformation behavior of a near-β Ti-17 titanium alloy under uniaxial tension was investigated using electron backscatter diffraction (EBSD) and tensile tests with in situ scanning electron microscope (SEM) observation. It is found slip mode is the main deformation mechanism in primary α grains of Ti-17 during the tensile test. Slip systems activated were identified by performing calculations on EBSD orientation data. The results show that all the three slip systems with a -type Burgers vector, i.e. basal, prism and 1st-order pyramidal slip, could be activated in the primary α grains of Ti-17, but no a+c -type slip (2nd-order pyramidal slip) activated is observed. Analysis reveals that basal and prism slips are the dominating slip mode, while 1st-order pyramidal slip acts as a subsidiary or deviated slipping mode. For the equivalent slip systems, Schmid factor dominates the slip behavior, while for the non-equivalent slip systems, critical resolved shear stress (CRSS) must be taken into account. It is proved that CRSS for a+c -type slip is much larger than that for a -type slips (basal and prism slips) in Ti-17 alloy (at least 2.5 times that for basal slip). a -type slip remains the easiest slip to be activated even in the condition favoring a+c -type slip and suppressing a -type slip (an angle of ~10° between the tensile axis and c -axis). [ABSTRACT FROM AUTHOR]

By adjusting the particle size of Ti6Al4V(TC4) powders and the distribution of boron particles, a high-performance heterogeneous network structure titanium matrix composites were fabricated through the spark plasma sintering (SPS) technique. In the present work, TiB whisker (TiBw) are in situ synthesized around the boundaries of the small size TC4 (STC4) particles, and formed into a TiBw network structure. The STC4 particles of the network surround the larger size TC4 (LTC4) particles to form a new heterogeneous network structure similar to the shape of a sunflower. The heterogeneous network structure consisted of coarse grain zones (LTC4) and fine grain zones (TiB/STC4) is formed in the microstructure. In light of tensile results, the tensile strength and ductility of TiB/TC4 composites with heterogeneous network structure are about 987.5 MPa and 11.5 %, respectively, which are 16.6 % and 35.3 % higher than those of TC4 alloy. The improvement of mechanical properties is mainly due to the interface strengthening mechanism of heterogeneous network structure and the hindrance and pinning mechanism of reinforcements to dislocation movement. The improvement of ductility depends on the inhibition of crack propagation by the heterogeneous network structure and the existence of high ductility coarse grain zone. [Display omitted] • A titanium matrix composite with heterogeneous network structure was prepared successfully. • Heterogeneous network structure composite achieves the matching of strength and ductility. • The improvement of the strength and ductility is attributed to the fracture mechanism of the heterogeneous network structure. [ABSTRACT FROM AUTHOR]

To improve the wear resistance of titanium alloy, the WC-reinforced composite coatings were prepared on Ti-6Al-4V substrate by laser cladding. The effect of linear energy density (LED: 73.3 J·mm−1-283.3 J·mm−1) on the microstructure, microhardness and wear resistance of the composite coatings were investigated. The evolution of WC during laser cladding was revealed and discussed. It is found that the WC is dissolved by the forms of releasing W and C with increasing LED, and grows into specific shapes according to the Lifshitz-Slyosov-Wagner model. As the LED increases, the retention index of WC decreases (0.91–0.80) and the grain size increases (1.89 μm–5.81 μm) in the composite coating. The microstructure differences lead to the microhardness and brittleness increasement of composite coating. Compared with the Ti-6Al-4V substrate, the maximum microhardness improvement and wear mass loss reduction are 5 times and 25 times by varying LED. The main wear mechanism of composite coatings is abrasive wear. However, additional forms of wear mass loss such as adhesive wear and WC peeling can occur due to LED variation, and further leads to the difference in wear resistance. It is expected that the evolution of WC, which can regulate the microstructure will provide an effective theoretical foundation for the wear-resistance improvement of the laser cladding coatings. [Display omitted] • The evolution process and growth mechanism of WC during laser cladding are revealed. • The effect of linear energy density on the microstructure is summarized. • The WC grows into a specific shape along the habit plane by atomic migration. • The evolution of WC and wear performance response of WC-Co-Cr coating is elucidated. [ABSTRACT FROM AUTHOR]

As light alloys have inherent friction and corrosion problems, an appropriate ceramic coating is often needed to resolve these problems in tribological and corrosive environments. In this work, the optimized pore structure of MoS 2 /Al 2 O 3 self-lubricating ceramic coating was designed by in-situ synthesis of MoS 2 combined with plasma electrolytic oxidation (PEO) and regulating the duty cycle. The evolution of pore structure was investigated by X-ray computed tomography. It is found that the power supply delivers more energy in each cycle as the duty cycle increases, resulting in larger discharge channels and ejecting more molten material. The change of the pore shape from connected to isolated and the decreasing of porosity through decreasing the duty cycle, which was caused by the narrowing of discharge channel and reduction of molten oxide ejection are acquired. The isolated pores structure is conducive to superior corrosion resistance, which can blocks the penetration of corrosive medium. Additionally, MoS 2 /Al 2 O 3 coating exhibit a 75% reduction in coefficient of friction over traditional PEO coatings. This coating preparation approach is expected to provide a newly strategy to optimize the pore structure of the self-lubricating ceramic coating by regulating electrical parameters. • MoS 2 /Al 2 O 3 self-lubricating ceramic coatings were elaborated during PEO of aluminium. • Coating with optimized pore structure was achieved by regulating duty cycle. • The optimized pore structure has a significant positive correlation with corrosion resistance. • Ceramic coatings with excellent antifriction and corrosion properties were obtained simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] • A toughened ZrO 2 /MgO nanocomposite coating is in-situ synthesized during the plasma electrolytic oxidation process (PEO). • The ZrO 2 /MgO toughening behavior occurs with dislocation slipping and pinning caused by semicoherent interface lattice distortion. • The toughness (K IC) of the ZrO 2 /MgO nanocomposite coating is 2.7 times that of the traditional PEO coating. Ceramic coatings are in general a kind of brittle material because they are predominantly made up of ionic crystals that avoid dislocation motion caused by lattice distortion. In this regard, a remarkable toughened ZrO 2 /MgO nanocomposite coating is obtained by the plasma electrolytic oxidation (PEO) process and in-situ synthesized ZrO 2 with quantitative control approach. It is revealed that the toughening behavior of the ZrO 2 /MgO coating is related to the coordination and diversion of lattice distortion at the metallic oxide interface, which induces distinct dislocation motion at the interface. The semicoherent interface between m-ZrO 2 and MgO is verified to act as a buffer to realize toughening of the nanocomposite coating through dislocation slipping induced by lattice coordinated distortion. Simultaneously, significant interfacial lattice distortion transfer and dislocation pinning are discovered at the semicoherent interface between t-ZrO 2 and MgO, which are beneficial to toughness enhancement of the nanocomposite coating. The results indicate that the toughening effect occurs along with dislocation slipping and pinning caused by lattice distortion of the ZrO 2 /MgO semicoherent interface, which enables the toughness of novel nanocomposite coating to reach 2.7 times of the traditional PEO coating. [ABSTRACT FROM AUTHOR]

The evaluation of a chiral Schiff base ligand in the zinc-catalyzed asymmetric addition of 1-ethynylcyclohexene to both aromatic and heteroaromatic ketones is reported (with up to 83% enantioselectivity and up to 88% isolated yield).