Diffusion Bonding of γ(TiAl) Alloys: Influence of Composition, Microstructure, and Mechanical Properties

Abstract

The metallurgical factors governing the solid-state diffusion bonding of TiAl alloys have been characterized using scanning electron microscopy together with energy-dispersive X-ray (EDX) spectroscopy and electron backscattered diffraction (EBSD) analysis. The investigations were performed on TiAl alloys with various compositions and microstructures, which had been thoroughly mechanically characterized. The process zone of the bonds typically consists of a fine-grained layer of a 2 (Ti 3 Al) phase at the former contact plane, followed by relatively large, defect-free c(TiAl) grains and a region of deformed parent material. The evolution of the process zone involves phase transformation and recrystallization processes, which are triggered by asperity deformation at the contact plane and the unavoidable contamination of the diffusion couple with oxygen and nitrogen. The structural details depend on the alloy composition and the bonding conditions. In the final section of the article, technical aspects, including the tensile strength of diffusion bonds, will be discussed.

Low‐Temperature Brazing of Titanium Using Al‐Based Filler Alloys

“…It was concluded by Buque and Appel [82] that the unavoidable contamination of the diffusion couple with oxygen leads to the formation of a thin layer of α 2 -Ti 3 Al phase. Similar result was found by Herrmann and Appel [83] for various two-phase gamma-based titanium aluminides, even considerably higher vacuum was used.…”

“…e resulted strengths using Al-Mg filler alloys were relatively high (82)(83), while the produced joint using Al-Si filler alloy was characterized by inferior quality with a continuous layer of silicide detected along the interface.…”

Recrystallization Behavior at Diffusion Bonding Interface of High Nb Containing TiAl Alloy

“…The diffusion bonding technique appears to be the most promising in comparison with other welding techniques due to the sound joining with low residual stresses at the interface and excellent oxidation resistance. [7,8] However, joining g-TiAl alloys by diffusion bonding needs a combination of high bonding temperatures and pressures, [9] which not only leads to high production cost but also is harmful for TiAl base. The modern diffusion bonding technology requires low temperatures, low pressures, and short holding times in order to avoid undesired phase transformations, large deformations, and grain coarsening for the engineering applications.…”

Role of vacancies in work hardening and fatigue of TiAl alloys

“…The resulting locking of the dislocations may impede defect annihilation. The locking effect of defect atmospheres disappears at about 750 K. Thus, above this temperature intensive dynamic recovery and recrystallization probably develop, which is eventually manifested in work softening (Herrmann and Appel, 2009).…”