關鍵字: 輕量化中熵合金、非等原子比合金、微量元素摻雜、熱機處理;This study was based on a previously developed Ti70 Ti-rich lightweight medium-entropy alloy. Minor amounts of boron were added to improve the mechanical properties of the alloys. Therefore， a series of (Ti70(AlCrZrV)30)100-xBx alloys (x = 0， 0.05， 0.1， 0.2， and 0.3) was successfully fabricated by vacuum arc melting and drop casting. The modified alloys were analyzed to evaluate the effects of boron addition on their microstructure and mechanical properties.
X-ray Spectra results revealed that all the (Ti70(AlCrZrV)30)100-xBx alloys maintained as a single BCC phase in as-cast and after thermomechanical treatment. In addition， the diffraction peaks shifted slightly as the boron content increased. Optical microscopy showed that the average grain size of the alloys decreased significantly with increasing boron content， from 145 μm in the Ti70B0 alloy to 37 μm in the Ti70B0.2 alloy. Scanning electron microscopy further revealed that the formation of the precipitates along the grain boundaries in the Ti70B0.2 and Ti70B0.3 alloys. In mechanical properties analysis， the Ti70B0.2 alloy exhibited a yield strength of 1096 MPa and an elongation of 15.2 %. The yield strength was approximately 17% higher than the Ti70B0 alloy. In addition， it also could be noticed that the morphology of the fracture surfaces on the tensile specimens were changed from dimple structure to cleavage surface due to the mechanical properties had been changed from ductile to brittle.
The (Ti70(AlCrZrV)30)100-xBx alloys underwent thermomechanical treatment. After conducted with thermomechanical treatment， the alloys exhibited higher strength with the boron content increased. Boron addition was also found to delay the recrystallization behavior， resulting in different degrees of recrystallization ratio among the alloys annealing to same temperature. Among of all， the Ti70B0.2 alloy annealed at 800 °C exhibited the best overall mechanical performance among the (Ti70(AlCrZrV)30)100-xBx alloys， achieving a yield strength of 1255 MPa while maintaining an elongation of 15.4%.
Keyword: Lightweight medium-entropy alloys， Non-equiatomic alloy， minor element doping ， thermo-mechanical treatment
