Performance and microstructure of TC4 titanium alloy subjected to deep cryogenic treatment and magnetic field

Abstract

In this paper, mechanical properties, scanning electron microscopy, electron backscatter diffraction (EBSD),X ray diffraction (XRD) and transmission electron microscopy (TEM)techniques were combined to investigate the performance and microstructure of TC4 titanium alloy subjected to sole deep cryogenic treatment (DCT) and coupled static magnetic field and deep cryogenic treatment (MDCT) with different processing time. It showed that both the DCT and MDCT samples arrived at the optimal properties when the processing time was 12 h, and the tensile strength and elongation of the DCT12 sample increased by 2.57% and 8.06% respectively in comparison to the untreated sample, while that of MDCT12 sample increased by 3.01% and 11.29%. In DCT samples, the (110) crystal plane has transformed toward (100) and (101). However, the (002) crystal plane of MDCT sample showed the preferred orientation. In addition, the EBSD results showed that both the sole DCT and MDCT promoted the transformation of α→β in titanium alloy, and sole DCT weakened the texture of {0001} direction, while MDCT strengthened it. The change of microstructure was attributed to the grain rotation caused by the effect of cold compression force and magnetic driving force. TEM images revealed that the dislocation density of the DCT sample increased obviously in comparison to the untreated sample, together with the apparent tangling. As for the MDCT sample, the dislocation density increased further, nevertheless, the tangling phenomenon decreased to some extent and the distribution tended to be well-aligned.