Investigation on tribological behaviour of diesel engine exhaust valve dry sliding against valve seat

A high-chromium alloy with 2Cr32Si2MnMo2 available for diesel engine valve seats was fabricated by centrifugal casting to improve valve seat quality. The friction and wear performances of the valve seat dry sliding against an exhaust valve were measured using a SRV testing machine. The test procedures include temperature and load sensitivities and wear. The test temperatures ranged from 100 ℃ to 280 ℃ and loads from 50 to 125 N. The friction and wear of the valve seat were found to decrease first and then increase with the increment of temperature or load. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses revealed the tribofilms contained more friction-increasing Cr₂O₃ and the wear mechanism was a complicated combination of two-body abrasion, three-body abrasion and oxidation. The strong adhesion between the valve and its seat arrested the relative sliding, but with loads going up to 150 N. In most cases, the valve had unexpectedly higher wear resistance than that of its seat over the temperature range, which is ascribed to adhesion to the tribofilms.