The effect of cooling rate on the γ′ composition, morphology and corrosion behaviour of IN738LC

The influence of gamma' size and composition on the corrosion behaviour of IN738LC superalloy was investigated while maintaining a monomodal microstructure. Experimental results showed that smaller precipitates (similar to 50 nm), obtained by a rapid water quench (3000 degrees C/min), were spherical with an Al content of 6.2 wt.-%. Slower-cooled specimens (2.5 degrees C/min) exhibited larger cuboidal shaped gamma' precipitates (similar to 800 nm) with reduced Al content (4.5 wt.%). Furthermore, a negative influence on the corrosion resistance of IN738LC was found with increasing rate of cooling, which is attributable to an increase in volume fraction and Al content of the gamma' precipitates.