The Effect of Sulphide Corrosion on P/M Ni-Base Superalloys
VV750P VV750PD, VV751P and EP741NP superalloys were tested on specimens cut from four gas-turbine engine disks showing strength of 1500 MPa. All of the alloys offer sulphide corrosion resistance at test temperatures up to 650 °C. However, kinetics of light corrosion development in corrosion resistant field depends on chemical composition of the superalloys. In this temperature field VV750P superalloy corrodes with a weight loss, while VV750PD, VV751P and EP741NP super-alloys corrode with an increase in weight due to oxide film formation. Low-cycle fatigue resistance at 650 °C has been investigated both in the initial state and after application of a salt layer on working surface. Low-cycle fatigue resistance of VV751P superalloy in the case of simultaneous attack of the corrosive layer grows by 80 % due to oxide film formation. A possible mechanism of sulphide corrosion attack is investigated with the use of X-ray diffractometry, scanning electron microscopy and X-ray microanalysis.