Using Variant Selection to Facilitate Accurate Fitting of \u03b3\u2033 Peaks in Neutron Diffraction

R Y Zhang,J Li,S Paul,H B Dong,B Nenchev,S Kabra,J F Kelleher,Z N Bi,T L Lee,H L Qin,J Zhang

doi:10.1007/s11661-019-05393-9

Abstract

γ″ diffraction peaks are hard to discern in neutron/X-ray diffraction patterns, hindering studies on the γ″-strengthened superalloys using in-situ diffraction. In this study, we propose a variant selection method to increase the intensity of γ″ peaks and to facilitate accurate fitting. The specific variants of γ″ are controlled by applying a 300 MPa tensile stress during aging at 790 °C for 5 hours. The interaction energy between the applied stress and the transformation strain of each γ″ variant differs, leading to an increase in the amount of the variants with a greater energy reduction at the expense of other variants. The enhanced variants result in greater γ″ peak intensities in neutron diffraction patterns, allowing both the Pawley refinement and single peak fitting to be performed. Lattice parameters of γ″ and γ phases, and lattice misfit between the two phases and volume fraction of γ″ are acquired. The uncertainties associated with the fitting maintain an acceptable level corresponding to 150 microstrains. The proposed variant selection method shows potential for studying the role of γ″ phase in Ni-base superalloys.

Highlights

IN-SITU neutron/synchrotron diffraction techniques have been commonly used in studies of engineering materials by measuring the lattice spacings of the major constituent phases.[1,2,3,4,5,6] Such techniques have become important approaches when investigating the role/behavior of c¢ phase in Ni-base superalloys[6,7,8,9,10] since the successful separation of the overlapping c–c¢ through the deconvolution method was first reported by Stone et al.[6]
The variant selection method proposed in this study shows a promising method that may be employed in in-situ neutron diffraction experiments to study mechanical properties related to c¢¢ phase in c¢¢strengthened Ni-base superalloys
A variant selection method is developed to facilitate the quantitative analysis of c¢¢ peaks in neutron diffraction on Inconel 718 (IN718)

Summary

Introduction

IN-SITU neutron/synchrotron diffraction techniques have been commonly used in studies of engineering materials by measuring the lattice spacings of the major constituent phases.[1,2,3,4,5,6] Such techniques have become important approaches when investigating the role/behavior of c¢ phase in Ni-base superalloys[6,7,8,9,10] since the successful separation of the overlapping c–c¢ through the deconvolution method was first reported by Stone et al.[6] Regarding the c¢¢ strengthened Ni-base superalloys such as Inconel 718 (IN718), most of the reported in-situ diffraction experiments on these alloys have measured the lattice spacings of the c matrix phase but not the c¢¢ phase. The role/behavior of c¢¢ phase in these alloys has rarely been studied using in-situ diffraction due to the difficulties in analysis of gamma double prime peaks.

Methods

Results

Discussion

Conclusion