On effect of salt deposits on oxidation behaviour of CMSX-4 above 1000°C

Abstract

Whereas the effect of contaminants in causing hot corrosion has been extensively studied at temperatures up to 1000°C, this paper describes a systematic study of the effects of various salt deposits on the cyclic oxidation of CMSX-4** in air at temperatures above 1000°C. The alloy was tested both in the bare and in the platinum aluminised (Pt-Al) coated conditions and variables included temperature, salt concentration, and sulphur level of the original alloy. It was found that salt deposition at very moderate levels, re-applied at regular intervals, significantly increased the initial weight gain and decreased the time to first spallation despite the rapid loss of the salt through evaporation in the first heating up cycle subsequent to salt deposition. The degraded microstructure of the specimens tested with salt resembled closely that of blades having experienced engine service conditions. Hence, cyclic oxidation with the addition of salt offers an accurate, flexible, reproducible and above all realistic method of assessing the life of turbine components.