Semester

Summer

Date of Graduation

2019

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Bruce S. Kang

Committee Co-Chair

Jacky C. Prucz

Committee Member

Jacky C. Prucz

Committee Member

Kenneth H. Means

Abstract

The capabilities of Additive Manufacturing (AM) techniques has grown rapidly in recent years, however, current available metal powders for AM processes, such as Powder Bed Fusion and Directed Energy Deposition, are limited and primarily fabricated through atomization processes; the atomization process is capable of producing metal powders 15 µm to 150 µm in size, uniform size distribution, and spherical shape. Despite the advantages of atomization process, iron or nickel-based Oxide Dispersion Strengthened (ODS) powders, with nanocrystalline microstructure, cannot be produced with the atomization process because of the high temperature of yttrium (III) oxide (Y2O3, 2425 °C) compared to iron (Fe, 1538 °C), nickel (Ni, 1668 °C), chromium (Cr, 1907 °C) and aluminum (Al, 660 °C), thus, uniform dispersion of Y2O3 is problematic for ODS powders. In this work, a combination of Mechano-Chemical Bonding (MCB) process and Mechanical Alloying (MA) by planetary ball milling (BM) will be implemented to produce ODS powders suitable for AM applications. The MCB process fractures and uniformly disperse the Y2O3 nanoparticles and the nanoparticles are bonded on the surface of the master particles (Ni and Cr). Also, the MA process, because of the constant fracturing and cold-welding of the elemental particles, produces alloyed ODS powders with uniform size distribution, near spherical shape, and nanocrystalline microstructure.

The objectives of this research work (1) adjust the processing parameters for the MCB+BM technique and investigate the effects of the process parameters on the size, morphology, and microstructure of the ODS powders and (2) use Ni-based ODS powder particles with optimal shape, size, size distribution, and microstructure on Laser Engineering Net Shaping (LENS) AM machine.

Ni-based ODS powder particles nearly spherical in morphology, average particle size of 15 μm, uniform size distribution, uniform distribution of Y2O3, existence of the strength-hardening precipitate, and nanocrystalline microstructure were produced. The resultant Ni-based ODS powder particles were successfully used on a LENS AM machine to produce coupon specimen. The coupon specimen microstructure contains γ-NiAl matrix and γ’-Ni3Al strength hardening phase.

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