On the hot isostatic pressing of Inconel 625 structures built using laser powder bed fusion at higher layer thickness

Saurav Kumar Nayak,Vesangi Anil Kumar,Arackal Narayanan Jinoop,Dineshraj Subburaj,Kushvinder Singh Bindra,Rashmi Singh,Christ Prakash Paul

doi:10.1007/s00170-022-08960-4

Abstract

This paper reports the effect of hot isostatic pressing (HIP) on the porosity, microstructure and mechanical properties of laser powder bed fusion (LPBF) IN625 structures built at a higher layer thickness of 100 µm. It is observed that the process-induced pores/voids of volume fraction (Vf) 0.43% in as-built IN625 structures are reduced significantly to ~ 0.01% after HIP treatment. The microstructure is changed from fine columnar dendrites to coarse equiaxed dendrites. The microstructural analysis of as-built structures reveals the presence of cellular/dendritic growth along with elemental segregation of Nb, Si and C and precipitation of Nb-rich carbides, whereas coarse recrystallized microstructure along with elemental segregation of Si and precipitation of Nb, Mo and Cr rich carbides is observed in hot isostatic pressed (HIP) samples. HIP structures exhibit lower tensile strength, higher ductility and lower anisotropy as compared to LPBF built structures. There is a reduction in the Vickers micro-hardness of IN625 samples after HIP, and the values are observed to be similar to their conventional counterparts. Further, an increase in the energy storage capacity of the material is observed after HIP treatment through Automated Ball Indentation (ABI®) studies. The study paves a way to develop ~ 100% dense, defect-free and isotropic engineering components using LPBF.

Highlights

Ni-based superalloys are the preferred choice of deployment in applications involving extreme duty conditions due to high mechanical strength, corrosion resistance, oxidation resistance and creep strength at elevated temperature 1,2
One of the issues associated with the use of Inconel 625 (IN625) for many engineering applications is its difficulty in machining due to work-hardening during metal-cutting operation
As the present work is focused on higher layer thickness, Laser Powder Bed Fusion (LPBF) built samples have predominantly irregular porosity because of the following phenomena

Summary

Introduction

Ni-based superalloys are the preferred choice of deployment in applications involving extreme duty conditions due to high mechanical strength, corrosion resistance, oxidation resistance and creep strength at elevated temperature (up to ~ 0.7 times of the melting point) 1,2. Machining of IN625 block needs machining parameters in narrow window and selection of appropriate tools for circumventing the effect of work hardening and chatter; for reduction of residual stress build-up during machining; and for slowing down the wear of the tools and machines[4]. It necessitates adopting advanced manufacturing techniques, like – additive manufacturing for building near-net-shaped engineering components and avoiding excessive machining of IN625. There are many additive manufacturing techniques including laser directed energy deposition[9,10], laser powder bed fusion 11, electron beam-based additive manufacturing[12], and wire-arc based additive manufacturing 13 that can be deployed for these applications

Methods

Results

Conclusion