Oxidation, Creep and Fatigue Properties of Bare and Coated 31V Alloy

Increasing the efficiency of natural gas reciprocating engines will require materials with better mechanical and corrosion resistance at high temperatures. One solution to increase the lifetime of exhaust valves is to apply an aluminide coating to prevent corrosion assisted fatigue cracking, but the impact of the coating on the valve material mechanical properties needs to be assessed. In addition to cyclic oxidation testing in dry and humid air at 800°C, creep and high cycle fatigue (HCF) testing were conducted at 816°C on bare and slurry or pack-coated 31V alloy. The coated and bare creep specimens exhibited very similar creep rupture lives, as long as the specimens were annealed according to the 31V standard heat treatment before testing. The HCF behavior of the pack-coated alloy was close to the behavior of the bare alloy, but fatigue lifetimes of slurry-coated 31V specimens had higher variability. Aluminide coatings have the potential to improve the valve performance at high temperature, but the coating deposition process needs to be tailored for the substrate standard heat treatment.