Effect of rhenium and cobalt additions on the microstructure and gamma prime phase stability of vacuum arc melted modified nickel-based superalloys grade MGA 1400

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Abstract
The effect of rhenium and cobalt additions on the microstructure and gamma prime phase stability of modified nickel-based superalloy, grade MGA1400 by means of a vacuum arc melting method with different contents of rhenium (Re) and cobalt (Co) was investigated. After being subjected to heat treatment, the size of the gamma prime particles was slightly reduced with increasing rhenium content. Then, the alloys were exposed at a temperature of 1173 K for 1800 ks. The results showed that increasing the rhenium addition leads to a slower coarsening rate of the gamma prime particles. Furthermore, the shape of the gamma prime particles changed to a more cubic shape. However, an excessive rhenium content (>1.21 wt.-%) promotes the formation of a topologically close-packed phase after a 360 ks exposure at 1173 K. It can be concluded that an increase in rhenium content can result in a lower coarsening rate of the gamma prime particles. The cobalt addition is beneficial for impeding or slowing the precipitation of topologically close-packed phases at an elevated temperature.

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