Modelling ternary effects on antiphase boundary energy of Ni3Al

K.V Vamsi,S Karthikeyan,J.Y Guédou,J Choné

doi:10.1051/matecconf/20141411005

Abstract

The shearing of ordered γ′ precipitates by matrix dislocations results in the formation of antiphase boundaries (APB) in Ni-base superalloys. The APB energy is an important source of order-strengthening in disk and blade alloys where Ti and Ta substitute for Al in γ′. While the importance of APB energy is well-acknowledged, the effect of alloying on APB energy is not fully understood. In the present study, the effect of Ti and Ta additions on the {111} and {010} APB energies was probed via electronic structure calculations. Results suggest that at low levels of Ti/Ta, APB energies on either plane increases with alloying. However, at higher Ti/Ta levels, the APB energies decrease with alloying. These trends understood by accounting for nearest neighbour violations about the APB and additionally, invoking the effect of precipitate composition on the energy penalty of the violations. We propose an Environment Dependent Nearest Neighbour Bond (EDNNB) model that predicts APB energies that are in close agreement to calculated values.

Highlights

Ni-based disk and blade alloys exhibit excellent high temperature mechanical properties due to the presence of coherent γ precipitates in γ, the Ni-rich f.c.c matrix [1, 2]
The penalty associated with the creation of this planar fault is the primary source of the strength of the precipitate; higher the antiphase boundaries (APB) energy, higher is the strength of the precipitate [2,3,4]
While for APB(111), the increase and decrease are steeper for Ta additions, for APB(010) the increase is similar for Ti and Ta, whereas the decrease is steeper for Ta

Summary

Introduction

Ni-based disk and blade alloys exhibit excellent high temperature mechanical properties due to the presence of coherent γ precipitates in γ , the Ni-rich f.c.c matrix [1, 2]. The primary glide dislocation in γ matrix has a Burgers vector of 1/2 10-1 , and these dislocations are glissile on the {111} at all temperatures [2]. The penalty associated with the creation of this planar fault is the primary source of the strength of the precipitate; higher the APB energy, higher is the strength of the precipitate [2,3,4]. High temperature deformation of Ni-base superalloys involving shear of precipitates, is possible only at high stresses in both in disk and blade alloys [5,6,7,8]

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