Electron Beam Melting of Niobium Alloys from Blended Powders.

Jameson P Hankwitz,Christopher Ledford,Timothy J Horn,Christopher Rock,Scott O’Dell

doi:10.3390/ma14195536

Abstract

Niobium-based tungsten alloys are desirable for high-temperature structural applications yet are restricted in practice by limited room-temperature ductility and fabricability. Powder bed fusion additive manufacturing is one technology that could be leveraged to process alloys with limited ductility, without the need for pre-alloying. A custom electron beam powder bed fusion machine was used to demonstrate the processability of blended Nb-1Zr, Nb-10W-1Zr-0.1C, and Nb-20W-1Zr-0.1C powders, with resulting solid optical densities of 99+%. Ultimately, post-processing heat treatments were required to increase tungsten diffusion in niobium, as well as to attain satisfactory mechanical properties.

Highlights

We explore the feasibility of utilizing blended powders in electron beam powder bed fusion (EB-PBF) for the fabrication of Nb alloys with a range of W content (0–20 wt%); Nb-1Zr, Nb-10W-1Zr0.1C, and Nb-20W-1Zr-0.1C
The research presented in this study demonstrates that highly dense Nb-1Zr, Nb-10W1Zr-0.1C, and Nb-20W-1Zr-0.1C particles can be fabricated through EB-PBF via bimodal dissimilar powder blending followed by spheroidization
W powder segregation in the feedstock prevented effective alloying with Nb-1Zr, leading to unmelted W

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Niobium (Nb)-based refractory alloys are of significant interest for high-performance components in extreme environments, such as the STAR thruster [1] and leading edge heat pipes for aerospace vehicles [2]. Nb does not possess sufficiently high mechanical properties at elevated temperatures (>1000 ◦ C) for these applications. This includes cold-worked Nb, which achieves greater tensile strengths than annealed Nb, up to 585 MPa [3], but does not retain increased strengths at high temperatures (600 ◦ C, according to Barlett et al.) [4,5]. Nb readily oxidizes above 400 ◦ C—at which point, oxygen embrittlement and large residual stress formation occur, resulting in reduced creep strength [6,7]

Methods

Discussion

Conclusion