Date of Award

2009-01-01

Degree Name

Master of Science

Department

Metallurgical and Materials Engineering

Advisor(s)

Shailendra K. Varma

Abstract

Materials for high temperature applications, such as jet engines, gas turbines and turbine blades, require a balanced combination of physical and chemical properties to withstand the aggressive environments in which they are utilized. Some of the properties required are high strength, low density, high melting point and good oxidation resistance at elevated temperatures [1-3]. For this reason, the microstructure and oxidation behavior of the Nb-20Mo-15Si-5B-20Cr alloy (at.%) has been studied as a potential candidate to replace Nickel-based alloys currently used in the aerospace industry.

Short term oxidation (STO) and long term oxidation (LTO) studies have been performed in air for this alloy over a temperature range from 700°C to 1400°C, for 24 and 168 hours respectively. Oxidation curves for this alloy were obtained by plotting the mass gain per unit area as a function of temperature and time to determine its oxidation resistance. Microstructure of the alloy and oxidized products were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). According to results, the microstructure is composed of BCC solid solution (α), tetragonal Nb5Si3, Nb3Si, hexagonal Laves phase NbCr2 and eutectic like microconstituent α, Nb3Si and NbCr2. The oxidation products at 700 to 1300°C show the presence of Nb2O5, SiO2, CrNbO4, among others. The parabolic and linear oxidation rate constants values indicate that the studied alloy is competitive when compared to the values for Nb-based alloys reported by different authors.

Language

en

Provenance

Received from ProQuest

File Size

84 pages

File Format

application/pdf

Rights Holder

Julieta Angelica Ventura

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