Microstructure and properties of a beta-solidifying TiAl-based alloy with different refiners

This study systematically compared the influences of yttrium（Y）,boron（B）,and carbon（C） on the microstructural refinement and properties of a Ti-43Al-5Nb alloy.The microstructural refinement effect in the TiAl alloy closely depends on the refiner used.The refinement effects of the three elements on colony size and lamellar thickness can be arranged as B 〉 Y 〉 C and Y 〉 C 〉 B,respectively.Moreover,a microstructure with a small grain size and ultra-fine lamellar spacing can be obtained by adding B and Y or B and C.The mechanical properties of TiAl alloy are also influenced by the refiners.TiAl alloys with proper B and Y contents exhibit favorable hot workability,tensile properties,and fracture toughness,whereas the C-containing alloy displays poor tensile properties and low fracture toughness.These results indicate that Y and B are more suitable microstructure refiners than C.This study may serve as a reference for practical alloying design.

Influence of Processing Parameters on Microstructural Evolution and Tensile Properties for 7075 Al Alloy Prepared by an ECAP-Based SIMA Process

A modified strain-induced melt activation（SIMA）process consisting of homogenization,equal-channel angular pressing（ECAP）and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors.The effects of both the homogenization and the number of ECAP passes,as well as the isothermal temperatures on the microstructural evolution,were investigated.The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation-recrystallization mechanism.Increasing the number of ECAP passes accelerates the recrystallization of strained grains,thus reducing the average grain size and improving the grain sphericity.Moreover,higher holding temperatures and prolonged soaking time can improve the growth of the solid grains.Two main coarsening mechanisms,viz.coalescence and Ostwald ripening,contribute to the growth of the solid grains simultaneously and independently.The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet,while the elongation of SIMA processed samples is much higher than that of as-received ones.Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.