Microstructural Change of Weld Interface in Ti/Al Friction Weld during Heat Treatment.

TLDR: In this paper, the microstructural change of a Ti/Al friction weld interface during heat treatment at 673K, 773k, and 873K was described, and it was shown that Si segregation took place before the formation of the Al3Ti phase.

Abstract: This paper describes the microstructural change of a Ti/Al friction weld interface during heat treatment at 673K, 773K, and 873K. TEM/EDS observations of a commercially pure Al/Ti weld confirmed that only the Al3Ti phase formed at the weld interface during heat treatment at 773K or 873K, while no intermetallic compound formed during heat treatment at 673K. The Al3Ti phase was composed of fine equiaxed grains nucleated at the interface boundary and grown up to a few microns in diameter during the heat treatment. Although the Si content was less than 0.12at% in the commercial Al/Ti weld, approximately 5at% Si was solved into the Al3Ti phase and a large amount of Si segregation, almost 20at%, was detected at the Ti/Al3Ti interface. No silicide formed during the heat treatment and the sugregation of Si was always observed. The observation of the specimen heat treated at 673K confirmed that Si segregation took place before the formation of the Al3Ti phase. The faster growth rate of the Al3Ti phase in the highly pure Al/Ti weld at 873K strongly suggested that the Si segregation retarded growth of the Al3Ti phase. The growth rate of the Al3Ti phase heat treated at 873K was in proportion to the square root of the holding time in the early stage of the heat treatment up to 3.6ksec, while it was linearly proportional to the holding time in the latter stage of the heat treatment.