Microstructure and mechanical behavior of Ti−Cu alloys produced by semisolid processing

The mechanical properties of Ti−Cu alloys processed via thixoforming were evaluated.Ti−Cu(25,27,and 29 wt.%Cu)ingots were produced via arc melting,homogenization at 950℃ for 24 h,and hot-forging at 900℃,followed by thixoforming at a speed of 8 mm/s after isothermal heat treatment at 1035℃ for 300 s.The thixoformed alloys exhibited good mechanical strength,limited plasticity under tensile loading,and reasonable plasticity under compressive loading.The mechanical strength and plasticity decreased as the Cu content increased as a result of the increasing volume fraction of the peritectic Ti_(2)Cu phase(transformed liquid),which exhibited a lower strength and plasticity than theα+Ti_(2)Cu regions(transformed solid).These findings indicated that the trade-off between the mechanical properties and semisolid processability is largely governed by the Cu content.

Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys

High-entropy alloys can be compelling raw materials for semi-solid applications.In the present study,the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi(x=0,1,2,3)alloys was investigated.Arc-melted samples were cross-rolled at room temperature and then isothermally treated at 1175℃in the semi-solid state for 300 s.Microstructural characterization showed that the alloys containing Cu were formed by two fcc phases.Notably,the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich phase.During solidification,this phase,which is the last to form,nucleates and epitaxially grows on the Cu-lean phase.All the studied CoCrCuFeNi alloys exhibited the same melting behavior.The Cu-rich phase melts at approximately 1120℃,whereas the Culean phase melts at approximately 1350℃,providing a suitable processing temperature range of more than 200℃.The semi-solid microstructures were considerably refined and globular regardless of the alloy composition,being suitable for semi-solid processing.Furthermore,each fcc phase exhibited roughly the same composition under the different processing conditions.The Cu content in the Cu-lean phase was approximately 10 at.%,while Co,Cr,Fe,and Ni were in an approximately equiatomic ratio.Meanwhile,the Cu content was between 80 at.%and 86 at.%in the Cu-rich phase.The isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature(1300℃)only caused the globules to coarsen.In conclusion,this work showed that these alloys can be potential candidates for semi-solid processing.