Alloy Optimization for Enhanced Flexible Coupling Performance

Flexible couplings are becoming increasingly important in the design and performance of automotive exhaust systems. Higher temperatures, tighter emission requirements along with extended warranties and governmental demands for increased gas mileage are rendering typically selected coupling alloys marginally acceptable or, more often, unacceptable for a growing number of engine platforms. Requirements for longer life are demanding improvements in fatigue and corrosion properties over those of currently employed alloys. This paper describes the optimization of the fatigue properties of alloy 625 for use in automotive flexible couplings. The salt corrosion resistance of typically used 321SS is then compared to that of INCONEL* alloy 625LCF* and two other candidate flexible coupling alloys, INCOLOY* alloys 800 and 825. INCONEL alloy 625LCF is shown to meet the performance requirements of this critical exhaust system component.