Improved Tensile Properties of Micro-grain Casting K447A Alloy

Micro-grain K447A superalloy with grain refined to 54 μm and yield strength up to 1022 MPa has been successfully fabricated in this work, whose strength is 200 MPa higher than that of conventional casting K447A. Owing to the bimodal distribution of γ′, two dislocation mechanisms act simultaneously at the initial stage of plastic deformation. That is, dislocations cut γ′ with radius less than 100 nm but bypass γ′ over 100 nm. Based on the deformation mechanisms of γ′ with different sizes, a frequency-weighted precipitation strengthening calculation method has been proposed to predict the contribution of precipitation strengthening accurately. Yield strength predicted by this method is in good agreement with experimental results with maximum error of 4.0 pct. Strength calculation indicates that micro-grain casting process improves the yield strength mainly by increasing the volume fraction of γ′ from 34.2 to 51.6 pct and reducing the grain size from 5 mm to 54 μm, compared with the conventional one.