Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys

Bao-Ping Wu,Zhen Wang,Jian-Xin Dong,Yan-Bin Wang,Lin-Han Li,Jun-Tao Li,Jian-Tao Wu,Xing-Fu Chen

doi:10.1007/s12613-014-1017-3

Abstract

Abstract This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. With increasing boron content in the as-cast alloys, there is an increase in the fraction of the γ′/γ eutectic and block borides precipitate around the γ′/γ eutectic. At a high boron content of 0.03wt%, there is precipitation of lamellar borides. Upon heat treatment, fine block borides tend to precipitate at grain boundaries with increasing boron content. Overall, the rupture life of the directionally solidified superalloy is significantly improved with the addition of nominal content of boron. However, the rupture life decreases when the boron content exceeds 0.03wt%.

Highlights

This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy
The rupture life of alloy D decreases and its fracture mode transforms from transgranular to mixed transgranular and intergranular fracture (Fig. 7). This indicates that the addition of excess boron will lead to the formation of lamellar borides at grain boundaries, which in turn will make the interfaces brittle and decrease the rupture life
This paper investigates the effect of boron addition on the microstructure and properties of directionally solidified alloys

Summary

Introduction

This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. Several studies have reported the effects of boron addition on the microstructure and properties of Ni-based alloys, such as Ni3Al [5 10]. According to these studies, boron segregation at grain boundaries increases the cohesion or decreases the grain boundary diffusivity. To the best of our knowledge, studies on the effect of boron on the microstructure and properties of directionally solidified alloys have been rarely reported in the literature. The average areal eutectic fraction, Aa, is representative of the volume fraction, Ve: Ve

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