Morphology transformation of primary strip α phase in hot working of two-phase titanium alloy

Microstructural development in hot working of TA15titanium alloy with primary stripαstructure was investigated withthe aim to globularizeαstrips.Results show that the mechanisms of morphology transformation are the same to the spheroidizationmechanisms of lamellar structure.Boundary splitting and termination migration are more important than coarsening due to the largesize of stripα.Theαstrips are stable in annealing due to the unfavorable geometrical orientation of intra-αboundaries,the largethickness of strip and the geometrical stability ofαparticles.Predeformation and low speed deformation accelerate globularization ofαstrips in the following ways:direct changing of particle shape,promotion of boundary splitting and termination migration byincreasing high angle grain boundaries and interfacial area,promotion of coarsening by forming dislocation structures.Largepredeformation combined with high temperature annealing is a feasible way to globularize stripα.

Deformation banding in β working of two-phase TA15 titanium alloy

To study deformation banding inβworking of TA15titanium alloy,hot simulation compression experiments were carried out on a Gleeble3500thermal simulator,and the microstructure was investigated by optical microscopy(OM)and electron backscattered diffraction(EBSD).It is found that inβworking of TA15titanium alloy,deformation banding is still an important grain refinement mechanism up to temperature as high as0.7Tm(Tm is the melting temperature).Boundaries of deformation bands(DBBs)may be sharp or diffusive.Sharp DBBs retard discontinuous dynamic recrystallization(DDRX)by prohibiting nucleation,while the diffusive ones are sources of continuous dynamic recrystallization(CDRX).Deformation banding is more significant at high strain rate and large initial grain size.The average width of grain subdivisions is sensitive to strain rate but less affected by temperature and initial grain size.Multi-directional forging which produces crossing DDBs is potential to refine microstructure of small-size forgings.

Current development of body-centered cubic high-entropy alloys for nuclear applications

High-entropy alloys greatly expand the alloy design range and offer new possibilities for improving material performance.Based on the worldwide research efforts in the last decade,the excellent mechanical properties and promising radiation and corrosion resistance of this group of materials have been demonstrated.High-entropy alloys with body-centered cubic(BCC)structures,especially refractory high-entropy alloys,are considered as promising materials for high-temperature applications in advanced nuclear reactors.However,the extreme reactor conditions including high temperature,high radiation damage,high stress,and complex corrosive environment require a comprehensive evaluation of the material properties for their actual service in nuclear reactors.This review summarizes the current progress on BCC high-entropy alloys from the aspects of neutron economy and activation,mechanical properties,high-temperature stability,radiation resistance,as well as corrosion resistance.Although the current development of BCC high-entropy alloys for nuclear applications is still at an early stage as the large design space of this group of alloys has not been fully explored,the current research findings provide a good basis for the understanding and prediction of material behaviors with different compositions and microstructures.Further in-depth understanding of the degradation mechanisms and characterization of material properties in response to conditions close to reactor environment are necessary.A critical down-selection of potential candidates is also crucial for further comprehensive evaluation and engineering validation.