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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 1 7 2 5 B razing and repair of turbine blades and vanes, such as those in Fig. 1, is a subject of considerable inter- est, especially for Ni-base single-crystal (SC) superalloys. These materials offer a good balance of high-temperature me- chanical properties and resistance to the high-temperature environment, and are widely used in aeronautic and industrial gas turbine blades and vanes. Examples of Ni-base superalloys manufactured as single crystals includeDD, Ni 3 Al, andRene typealloys [1] . Traditional brazingmethods must be fine-tuned in order not to alter the microstructure of the SC superalloy. Due to the high-temperature, high-corro- sion environment to which turbine parts are exposed, nickel-base brazing materi- als are favored due to their high melting temperature and oxidation resistance. High-temperature brazing materials such as BNi-2 typically contain a melting point depressant (MPD) such as boron or sili- con. The drawback of MPDs is that they NANOBRAZING FOR TURBINE BLADE AND VANE REPAIR Nanobrazing is de‘ned as an innovative brazing technique using nanomaterials as the ‘ller materials. Incorporating nanobrazing into conventional brazing technologies creates a new frontier for repairing turbine blades and vanes. Anming Hu, Denzel Bridges, and Suhong Zhang, University of Tennessee, Knoxville Zhili Feng, Oak Ridge National Laboratory, Tennessee potentially can form brittle, hard sili- cide and boride phases in the base mate- rial and brazing material, which can de- teriorate long-term mechanical stability and reliability. Several brazing processes and techniques, such as laser and furnace brazing, have been developed. Laser brazing is often used for fabrication in the automotive and aerospace in- dustries due to its high manufacturing speed and small heating area, which helps ensure that most of the base ma- terial is unaffected by the brazing pro- cess. Furnace brazing is conducted in either an inert gas or vacuum environ- ment. Long holding times in furnace brazing enables completing certain brazing steps. For example, sufficient holding time for MPD-containing braz- ing alloys allows the MPD to diffuse a long distance into the base material, which helps prevent MPD segregation and brittle phase nucleation [2] . Certain annealing procedures also require long holding times. Transient liquid phase (TLP) bond- ing, a diffusion brazing process de- veloped to increase the remelting temperature and ductility of joints, is primarily used with furnace brazing. TLP bonding makes use of isothermal solidification and sufficient diffusion of an MPD to prevent brittle intermetallic formation during cooling. Boron-con- taining filler metals are the preferred choice for TLP processes due to the high diffusivity of boron [3] . During the process, four main stages that occur as the joint is heated above the filler met- al’s melting point include: (1) dissolu- tion of the filler metal, (2) melting and homogenization of the filler metal, (3) MPD diffusion-controlled isothermal solidification, and (4) further solid state diffusion. Full isothermal solidification and joint homogenization can take sev- eral hours to complete, so the process Nanobrazing Acronym Guide CSNW – core-shell nanowire HEA – high-entropy alloy MPD – melting point depressant NP – nanopaste NW – nanowire SC – single crystal TLP – transient liquid phase WGB – wide-gap brazing Fig. 1 — Two-blade component for high pressure turbines (le ), and three-blade component for low pressure turbine engines (right).