Microstructure evolution and room temperature deformation of a unidirectionally solidified Nb-22Ti-16Si-3Ta-2Hf-7Cr-3Al-0.2Ho (at.%) alloy

Unidirectional solidification (DS) experiments were performed on a Nb-22Ti-16Si-3Ta-2Hf-7Cr-3Al-0.2Ho (at.%) alloy and the growth rates were selected as 6, 10 and 16 mm/h, respectively. The effect of solidification rates on the microstructure development and room temperature deformation was investigated. The DS alloys were mainly composed of Nb solid solution (Nbss) and Nb5Si3 phases. All the Nbss/Nb5Si3 eutectic colonies aligned well along the growth direction of the DS specimens. A small amount of hex-Nb5Si3 phase was identified as intergranular phase when observed from the transverse section of the DS specimens. There was an orientation relationship between Nbss and hex-Nb5Si3, which was determined as [111]Nb//[224¯3]h and the two almost parallel planes of (11¯0)Nb//(11¯00)h with an include angle about 2.2°. The DS alloys showed improved room temperature compressive strength and fracture toughness as compared with the casting alloy.

Research highlights
► RT yield strength and fracture toughness were improved by unidirectional solidification.
► Mixed fracture mode in the DS alloy but transgranular cleavage in the cast alloy.
► There is a OR between Nbss & hex-Nb5Si3: (110)Nb//(1-100)h //[110]Nb//[11-26]h.