Investigation of strengthening mechanism in Ni–38Cr-3.8Al alloy with fine lamellar structure by in situ neutron diffraction analysis

Abstract

The strengthening mechanism of Ni–38Cr-3.8Al (mass%) alloy with fine lamellar structure composed of the γ/γ' and α-Cr layers, which is formed by discontinuous precipitation, was examined by in situ neutron diffraction analysis. The contribution of each constituent phase on the deformation behavior could be separated by the in situ analysis. The plastic deformation occurred preferentially in the γ and γ' phases, while the α-Cr phase deformed more elastically even beyond the yield point of the γ and γ' phases, which is similar to the cementite in pearlite of a steel. Fine nano-lamellar structure formed by the discontinuous precipitation is found to be mainly responsible for high strength of the alloys, while the influence of the γ' precipitates on strength is likely to be small. Furthermore, the strengths of the α-Cr and γ phases in the lamellar structure increased linearly with increasing inverse square root of the width of the α-Cr and the γ phases, and therefore, the strengthening mechanism of this alloy is consistent with the Hall-Petch relationship of fine lamellar structure.