Diffusion vacuum brazing of TiAl48Cr2Nb2 casting alloys based on TiAl (γ) intermetallic compound using Ag-Cu-Ti braze alloy

Fast-developing such advanced industries as aviation, automotive and power-generation are increasing demand for new engineering materials which could resists such extreme operation conditions as high operating temperature, considerable stresses or operation in fume-affected environment. Highly desirable properties of such materials should include high hardness and strength, corrosion resistance (also when exposed to aggressive fumes) but also, first of all, low density. However such materials also requirements engineering methods to ensure obtain of good sound joints. Results in growing interest in modern engineering materials characterised by increasingly better operational parameters combined with a necessity to obtain joints of such materials representing good operation properties create important research and technological problems of today. These issues include also titanium joints or joints of titanium alloys based on intermetallic compounds. Brazing is one of the basic and sometimes even the only available welding method used for joining the aforesaid materials in production of various systems, heat exchangers and, in case of titanium alloys based on intermetallic compounds, turbine elements and space shuttle plating etc. This article presents the basic physical and chemical properties as well as the brazability of alloys based on intermetallic compounds. The work also describes the principle and mechanisms of diffusionbrazed joint formation as well as reveals the results of metallographic and strength tests involving diffusion-welded joints of TiAl48Cr2Nb2 casting alloy based on TiAl (g) phase with the use of sandwich-type layers of silver-copper-titanium based filler metal (Ag-63%; Cu-35,5%; Ti-2%). Structural examination was performed by means of light microscopy. Furthermore, the article reveals the results of shear strength tests involving the aforementioned joints. Obtained mechanical test results of TiAl48Cr2Nb2 joints brazed with usage of three/different filler metal alloys ware compared.