Search

Gradient nanograined Ti (GNG Ti) samples were produced by a surface rolling treatment. The mechanical properties were evaluated by microhardness and tensile tests. The results indicated that GNG Ti achieved an optimized combination of strength and ductility relative to the free-standing nano/ultrafine-grained Ti. The deformation and fracture mechanisms were studied using transmission electron microscope (TEM) and scanning electron microscope (SEM). As the grain size reduced from the coarse-grained (CG) matrix to the nano/ultrafine-grained (NG/UFG) layer, the transition from conventional plastic deformation mechanisms, such as dislocation activity and twinning deformation, to grain boundary-mediated deformation mechanisms, such as stress-inducing grain growth, was identified. At the early stage of tensile deformation, the microcracks were first initiated in the CG and deformed grain (DG) regions rather than in the NG/UFG region and the CG/DG interface had a deflection effect on crack propagation. After tensile failure, the fracture morphology showed a mixture of ductile dimples and shear band-like regions. [ABSTRACT FROM AUTHOR]

Different size effects and deformation mechanisms are revealed in α-titanium (Ti) single crystal nanopillars orientated for [112̄0] and [0001] based on molecular dynamics simulations. The strength–size relationship changes from “smaller is stronger” to “smaller is much weaker” when the width of nanopillars reduces from 19 nm to 3 nm. The “smaller is much weaker” is attributed to that the surface effect caused by a thermal vibration of surface atoms leads to the initiation and growth of surface dislocations. [ABSTRACT FROM AUTHOR]

The Charpy impact absorbed energy of a hot-rolled Ti–6Al–3Nb–2Zr–1Mo alloy plate with different sampling and notching directions was investigated. Strong anisotropic variations occurred in impact absorption energies due to difference of the α phase crystal orientation and microstructural characteristics along different directions. The higher crack propagation energy of the sampling-notching direction sample (RD-ND) resulted in an impact absorption energy of approximately 2.5 times larger than that of the TD-ND, TD-RD and RD-TD samples. Based on the analysis of the α crystal orientation and the TEM microstructure after impact deformation, it was found that the higher absorption energy of the RD-ND sample was attributed to the activities of a large number of { 10 1 ‾ 0 } ⟨ 1 2 ‾ 10 ⟩ prismatic slips and the resistance created by grain boundaries against crack propagation, which also resulted in the delamination of the impact fracture surface. Finally, the coupling effect of crystallographic texture and microstructural characteristics on the impact deformation mechanisms of the hot-rolled Ti–6Al–3Nb–2Zr–1Mo alloy was described. • A strong anisotropy of the impact energy in A hot-rolled Ti6321 alloy plate is observed due to the coupling effect of the microstructural characteristics and the crystal orientation of the α grains. • The RD-ND orientation sample exhibits the highest impact absorbed energy due to the activity of a large number of { 10 1 ‾ 0 } 1 2 ‾ 10 prismatic slips and the barrier effect of grain boundary on crack propagation during impact loading. • The coupling effect of crystallographic texture and microstructural characteristics on the impact deformation mechanisms were established. [ABSTRACT FROM AUTHOR]

High-temperature stability and strengthening mechanisms of high/medium-entropy alloys (HEAs/MEAs) have been studied for Ti-added FeCrV-based MEAs. Experimental results show that FeCrVTi x MEAs can maintain good high-temperature stability in chemical element, phase structure and mechanical property. A mixed-strengthening-mechanism model dominated by precipitation and fine-grain strengthening has been proposed by comparing experimental results and model calculations of the yield strength increments for the FeCrV-based MEAs owing to Ti addition. The calculated strength increments with this mixed-strengthening-mechanism model closely match the series experimental results. The excellent compressive fracture strain in the FeCrVTi x MEAs mainly comes from crack tip plasticity, and Ti addition not only enhances compressive strain by grain refinement, but also improves compressive strain by crack deflection and bridging. Based on this strengthening model, the content, size and distribution of precipitates can be designed and controlled to regulate and optimize the mechanical properties of HEAs/MEAs. Therefore, this study provides new approaches and ideas for the design and development of HEAs/MEAs with high strength and good ductility for advanced nuclear energy systems. [Display omitted] • A mixed-strengthening-mechanism model is proposed to explain well the yield strength increments of FeCrVTi x MEAs. • The mixed-strengthening-mechanism model provides new ideas and methods for the design and development of new materials. • The good fracture strain in FeCrVTi x mainly arises from grain refinement, crack deflection and bridging of Laves phase. [ABSTRACT FROM AUTHOR]