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793 |
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Poster Presentation Fügen von Leichtmetallen Joining of light weight metals |
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PRODUCTION OF TITANIUM BRAZED JOINTS IN AIR |
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Svitlana Maksymova / Paton Electctric Welding Institute, Ukraine Victor Khorunov / Paton Electric Welding Institute, Ukraine Bogdan Stefaniv/ Paton Electric Welding Institute, Ukraine |
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It is a known fact that brazing of titanium-base alloys involves difficulties associated with high reactivity of titanium with respect to all atmospheric gases (O2, N2, H2). These difficulties can be successfully overcome using the technology of brazing in vacuum or inert atmosphere. Joining of titanium to other metals involves even more serious difficulties, as titanium forms intermetallics of high chemical and thermal stability when joined to the majority of metals. In this case the use of vacuum or inert atmospheres does not solve the problem of producing sound joints. Special approaches are required in this case. In this study the authors investigated the possibility of producing brazed joints in pseudo-alpha titanium alloys in air using fluxes and flame heating. The special procedure for deposition of a barrier coating on titanium alloy was developed, allowing discontinuities, separations and crack to be avoided. Microstructure, chemical heterogeneity and mechanical properties of brazed joints in titanium alloys in similar (titanium + titanium) and dissimilar (titanium + stainless steel) combinations were studied. Microstructure of a brazed joint made by using a commercial silver filler alloy PSr40 is sufficiently homogeneous and consists of silver- and copper-base solid solutions and eutectic. Dendrites of the copper-base solid solution solidify in a direction normal to the substrate both on the side of stainless steel and on the side of a nickel coating. Under the optimal brazing conditions the coating does not fracture. It does not only protect titanium from oxidation but also provides shear strength of the titanium + titanium brazed joints at a level of 259-271 MPa. In brazing of titanium alloy to stainless steel the joints have shear strength of 295-403 MPa. The developed brazing technology allows joining of titanium alloys to each other and to stainless steel in air using both standard commercial filler alloys and fluxes, and new cadmium-free filler alloys of the Ag-Cu-Zn-Sn system developed by the authors. |