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 Nb 5Si 3 phases. All the Nbss/Nb 5Si 3 eutectic colonies aligned well along the growth direction of the DS specimens. A small amount of hex-Nb 5Si 3 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-Nb 5Si 3, which was determined as [ 111 ] Nb / / [ 22 4 ¯ 3 ] h and the two almost parallel planes of ( 1 1 ¯ 0 ) Nb / / ( 1 1 ¯ 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. ► 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.