Diffusion Bonding of FGH 98 and CoCrNi-Based Medium-Entropy Alloy: Microstructure Evolution and Mechanical Tests

Yajie Du,Jiangtao Xiong,Yipeng Chen,Zhaoxi Li,Jihong Dong,Shiwei Li,Jinglong Li

doi:10.3390/cryst11101158

Abstract

The superalloy FGH98 was successfully diffusion bonded (DB) with medium-entropy alloy (MEA) Al3Ti3(CrCoNi)94 using pure Ni as the interlayer at a temperature range of 1050–1170 °C for 1 h under 5 MPa. The microstructure and mechanical properties of joints were investigated. The diffusion bonding seam was composed of an interlayer zone (IZ) and two diffusion-affected zones (DAZ). The IZ and DAZ beside the FGH98 consisted of cubic Ni3(TiAl)-type γ′ phases due to the diffusion of Ti and Al atoms. Meanwhile, the DAZ adjacent to the MEA consisted of spherical γ′ phases. Both of the γ′ phases with different morphology kept the coherent relationship with the matrix. Moreover, increase of bonding temperature led to the morphology of interlayer γ′ phase to transform from sphere to cube. Due to the strengthening effect of a mass of γ′ phase distributed evenly in IZ and the DAZ beside the FGH98, the microhardness and Young’s modulus of these two zones were higher than that of DAZ near the MEA. The maximum shear strength of DB joint, 592 MPa, was achieved in the joint bonded by 1150 °C, which was the typical ductile fracture feature confirmed by the shear dimples.

Highlights

The medium-entropy alloys (MEAs), especially the MEAs with face-centered-cubic structure are currently receiving extensive attention due to their unique composition, microstructure and superior properties, such as excellent ductility, good corrosion resistance and high radiation tolerance [1,2,3,4,5]
The MEA Al3Ti3(CrCoNi)94 consisted of fcc phase and the Ni3Al-type γ phases precipitated in matrix, which was similar to the result of Reference [15]
When the temperature increased to 1100 ◦C (Figure 2b), the grain size of Zone I was almost unchanged compared to Figure 2a

Summary

Introduction

The medium-entropy alloys (MEAs), especially the MEAs with face-centered-cubic (fcc) structure are currently receiving extensive attention due to their unique composition, microstructure and superior properties, such as excellent ductility, good corrosion resistance and high radiation tolerance [1,2,3,4,5]. The ternary CoCrNi MEA with single phase exhibits excellent strength-ductility trade-off due to the twining-induced plasticity (TWIP) effect and high work hardening capability [6,7]. In order to overcome the surplus ductility and resultant insufficient strength of single phase MEAs, Y.L. Zhao et al [8] have added the strong γ formers Ti and Al into the CoCrNi-based MEAs, promoting the precipitation of nano-scale Ni3(Al, Ti)-type γ. The yield strength significantly increased without sacrifice of ductility, owing to the effect of precipitation hardening. The superior strength-ductility combination endows the nanoparticle-reinforced CoCrNi-based MEAs great potential for engineering applications [9], especially for the structural materials with extreme requirements. As is well known, welding technology, a processing method of assembling individual parts into structural parts, is an essential link in promoting materials to practical engineering application

Methods

Results

Conclusion