Microstructural characterization and oxidation resistance of multicomponent equiatomic CoCrCuFeNi–TiO high-entropy alloy

CoCrCuFeNi–TiO was prepared by arc melting of the pure elements and Ti_2CO powder under an Ar atmosphere. Both CoCrCuFe Ni and CoCrCuFeNi–TiO alloys are composed of a face-centered cubic(fcc) solid solution, whereas the alloys of CoCrCuFeNi–TiO are basically composed of an fcc solid solution and TiO crystals. The microstructures of CoCrCuFeNi–TiO are identified as dendrite and interdendrite structures such as CoCrCuFeNi. The morphology of TiO is identified as an equiaxed crystal with a small amount of added Ti_2CO. By increasing the amount of Ti_2CO added, the TiO content was dramatically increased and part of the equiaxed crystals changed to a dendrite structure. A test of the oxidation resistance demonstrates that the oxidation resistance of CoCrCuFeNi–TiO is better than that of CoCrCu Fe Ni. However, as the TiO content increases further, a corresponding decrease is observed in the oxidation resistance.

Microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys

The microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys were studied by TEM and EBSD.The results showed that an increase in the tool rotation speed(300−700 r/min)led to a decrease in the defect area(from 10.5 mm2 to zero),whereas the defect area demonstrated the opposite trend(increased to 1.5 mm2 from zero)upon further increasing the rotation speed(700−1200 r/min).The types of defects were transformed from tunnel defects to fusion defects as the rotational speed increased.The coarse Mg2Si dendrites were broken and fine particles(smaller than 10mm)formed in the weld nugget(WN).The amount of low-angle grain boundaries increased significantly from 57.7%to 83.6%,which was caused by an increase in the content of the deformed structure(from 1.7%to 13.6%).The hardness,ultimate tensile strength(UTS)and elongation were all greatly improved for the weld nugget.The hardness values of the WNs had the following order:R300<R1200<R500<R900<R700.The UTS and elongation had the following order:BM(base material)<R300<R1200<R500<R900<R700.The UTS and the elongation for the WN were increased by one and three times,respectively.