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In this research, a repetitive bending and straightening process was carried out on the Ti–3Al–4Cr–Mo alloy for 20 passes. The changes in mechanical properties of the titanium alloy before and after repetitive bending and annealing were studied. The microstructure evolution and deformation mechanism were analyzed. The results show that after the repetitive bending and straightening process, the microstructure of the Ti–3Al–4Cr–Mo alloy is obviously refined, and, simultaneously, the yield strength is significantly improved. After annealing at 850 °C, the plastic ductility of the material was improved. The combined effects of grain refinement and dislocation behavior were the main reasons for the improvement in mechanical properties of the Ti–3Al–4Cr–Mo alloy. Twinning rarely occurred during plastic deformation of the Ti–3Al–4Cr–Mo alloy. The fine grains strongly inhibited the formation of twins. In addition, a small amount of α to β phase transformation was observed during the repetitive bending and straightening process of the material, which may have been induced by strain accumulation. [ABSTRACT FROM AUTHOR]

Refractory multi-principal element alloys (RMPEAs) are promising candidate materials for use in high temperature structural applications and other extreme environments. Recent experiments and simulations have highlighted the unusual deformation behavior of an equiatomic MoNbTi alloy, which exhibits slip on higher order planes and sluggish edge dislocation mobility. In this work, we utilize micropillar compression and postmortem transmission electron microscopy to elucidate the orientation dependent deformation behavior of MoNbTi. Our results suggest that deformation in this system is largely mediated by kink-migration of screw dislocations, as evidenced by the presence of long screw dislocations and significant dislocation debris in postmortem observations, and the absence of twinning/anti-twinning asymmetry. Moreover, we report an unusual orientation dependence of the yield strength, owing to the high stress required to facilitate slip on {110} type planes. These results further demonstrate the unconventional plasticity in BCC RMPEAs, and provide experimental verification that kink-migration is the rate limiting feature in this alloy at low temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, molecular statics and molecular dynamics simulations of a/2<110> dislocation behavior for a model FCC Co 30 Fe 16.67 Ni 36.67 Ti 16.67 alloy are discussed. It is shown that the single FCC phase is elastically stable in this alloy. Local stacking fault energies for the FCC alloy are determined as a function of average composition. The core structure of a/2<110> screw and edge dislocations in the FCC Co 30 Fe 16.67 Ni 36.67 Ti 16.67 alloy is shown to be planar with significant variations in the Shockley partial splitting along the dislocation line (factor of ∼3) due to concentration fluctuations. The correlation lengths for dislocation line fluctuations in this alloy are determined and discussed. The critical stress to move both a/2<110> screw and edge dislocations at 0 K in the model FCC Co 30 Fe 16.67 Ni 36.67 Ti 16.67 alloy is of the order of 0.0025–0.005μ, where μ is the (111) shear modulus, and is significantly higher than that of pure FCC Ni. Molecular dynamics simulation results on the critical stress to move a/2<110> screw and edge dislocations in the model FCC concentrated solid solution alloy show that it decreases with increasing temperature, similar to solid-solution strengthened FCC metals. These molecular dynamics simulation results are in reasonable agreement with experimental tensile yield strength data for an analogous FCC concentrated solid solution alloy. It is also shown that local fluctuations in the concentration of solutes has a strong effect on the effective cross-slip activation energy of screw dislocations in the random alloy. [ABSTRACT FROM AUTHOR]