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7169 |
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Brazing of titanium-bronze-bearings with high anti-friction performance and light-weight properties |
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Tobias Burgdorf-Nommsen / EMPA, Switzerland Hans Rudolf Elsener / Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland, Bastian Rheingans/ Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland, Jolanta Janczak-Rusch/ Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland, |
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Conventional bearings are manufactured by casting copper-based alloys into a steel backing material. Often, lead-containing copper-based alloys are used to provide the bearing with "emergency lubrica-tion" by lead particles in case lubrication is interrupted due to an oil-film rupture. This requires a very homogeneous distribution of lead in the copper matrix, even after joining to the steel backing. The development of bearings with optimized weight-to-strength-ratios requires the use of light metal (alloys) such as titanium instead of steel. However, casting of copper-based alloys into titanium back-ings leads to the formation of brittle Cu-Ti phases due to the very high casting temperatures ( >1000 °C), and therefore does not allow the production of high-performance bearings. In this situation, braz-ing appears as a suitable processing alternative. However, brazing of titanium and bronze is challeng-ing due to the generally very reactive joining behavior of titanium, the intense reactions between the two base materials and the significant difference in their CTE. In this work, the brazing of titanium to bronze was studied, focusing on strategies for the control of the residual stresses and of the formation of intermetallic phases. Different brazing designs and coating-interlayer systems were investigated to control the CTE mismatch, material interactions and interfacial reactions. Diffusion mechanisms and the evolution of the bond microstructure were analyzed by elec-tron microscopy and X-ray-based spectroscopy. Mechanical properties such as shear strength, tensile strength, hardness and impact strength were determined for various brazing systems. |