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796 |
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Poster Presentation Fügen von Hochleistungswerkstoffen Joining of high performance materials |
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STRUCTURE AND PROPERTIES OF INTERMETALLIC ALLOYS BRAZED JOINTS |
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Svitlana Maksymova / Paton Electctric Welding Institute, Ukraine Victor Khorunov / Paton Electric Welding Institute, Ukraine Svitlana Maksymova/ Paton Electric Welding Institute, Ukraine |
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The paper presents results of investigations of brazed joints in intermetallic alloy -TiAl: Ti-45Al-2Nb-2Mn+0.8 vol. % TiB2. The alloy is a good candidate for application in aircraft engineering for manufacture of components of a hot section of gas turbine engines. It can compete with high nickel alloys in heat resistance characteristics at a temperature of 700-750 oC, having substantial advantages in specific weight (3.8 g/cm3 against 8.9 g/cm3 for nickel). Brazing of butt and overlap joints was performed in vacuum using standard and experimental filler alloys of the Ti-Zr-Cr, Ti-Zr-Fe, Ti-Zr-Mn, Ti-Hf-Fe and Ti-Zr-Cu-Ni systems. The resulting joints were examined by optical and scanning microscopy, and by X-ray microanalysis. Tensile strength of the joints at 20 and 700 oC and long-time strength at 700 oC under a load of 140 and 200 MPa were evaluated. Structure, chemical heterogeneity and strength of the brazed joints was found to depend upon many factors, including the brazing temperature, time of holding at this temperature, and brazing filler alloy composition. At the optimal filler alloy composition and brazing temperature the seam metal is enriched with elements of the base metal, and a lamellar structure characteristic of the base metal is formed in some regions of the seam. The best results were obtained when using filler alloys of the Ti-Zr-Fe and Ti-Zr-Mn systems. Strength of the butt joints brazed with these alloys is close to that of the base metal both at room and 700 oC temperatures. Specimens tested to long-time strength at 700 oC did not fracture after holding for 483 and 500 hours under a load of 140 MPa, nor did they fracture after holding for 499 and 300 h under a load of 200 MPa. |