CHANGING OF THE CONSTITUENTS AND MICROSTRUCTURE AT DISSIMILAR ALLOY TC11/Ti-22Al-25Nb WELDING INTERFACE

摘要

The operation temperature is higher, the temperature gradient and stress gradient of compressor disk is greater for aero-engine with great ratio of thrust to weight (or T/W). The disk that is made of unitary material is not to meet the demand. So the disk made of dissimilar alloy can come true. However, the strength of joint interface of dissimilar alloy is controlled by its structure constituents and microstructure. So it is very important to research the changing of constituents and microstructure at joint interface of dissimilar alloy during hot working and thermal exposure. Changing of the constituents and microstructure at TC11/Ti-22Al-25Nb dual-alloy welded interface gone through near thermal forging, heat treatment and thermal exposure has been investigated. The fusion zone of dual-alloy joint welded by EBW is composed of β phase. After deformation and heat treatment, new phases are precipitated which the types influenced by the deformation temperatures. As deformation temperature rose, the O phase (based on Ti2AlNb with Cmcm symmetry) become more slender. Under thermal exposure, O phases in fusion zone grow up. As exposed at 700°C, the O phases coarsen obviously, and the thickness of O phase achieves 0.095μm. Meanwhile, the grain boundaries become thick and α2 phase precipitates in the grain boundaries. The constituents of fusion zone have been changed during thermal exposure, Al and Nb contents are basically unchanged while the Ti content decreases.