| Abstract Scope |
Crack repair of gas turbine engine components via diffusion brazing was developed and commercialized in the late 1960s. As a result of cracks being greater than 0.1mm, it earned the moniker of wide gap diffusion brazing. This process involved mixing a superalloy powder with a braze filler metal, with B (Boron) as the melt-point depressant. Five decades later, this process is still extensively utilized with tensile strengths of the crack repair approaching that of the base metal, stress rupture strengths approaching 80% to 90% of the base metal, low cycle and high cycle fatigue varying from 70% to 80% of the base metal's properties. The reason why the diffusion braze repair does not achieve creep and fatigue properties equivalent to that of the base metal is attributed to the presence of brittle intermetallic boride phases. In an attempt to mitigate the effects of brittle boride and silicide phases, the following developments have occurred: The diffusion brazing time has been increased, in fact the entire braze thermal cycle has evolved. The superalloy powder mixed with the braze filler metal has evolved. Ø Other elements are added to the braze filler metal to decrease the size of the boride phases. Other melt-point depressants, such as Zr, Hf, Ti, and Ge, have been introduced instead of B or Si. Use of high entropy braze filler metals containing no melt-point depressants. Use of nanoparticles containing no melt-point depressants. This presentation will not only provide a brief overview of the original concepts and current practices in the field of diffusion brazing, but also highlight the importance of new developments involving multi-principal element braze alloy (high entropy alloy) and nano-sintering. Furthermore, this paper will highlight engine run data from wide gap brazed joints after multiple 24,000 hours of service exposure. |