Oxidation behavior of laser clad nickel-aluminum-chromium-hafnium alloys
Ribaudo, Carl Robert
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https://hdl.handle.net/2142/19888
Description
Title
Oxidation behavior of laser clad nickel-aluminum-chromium-hafnium alloys
Author(s)
Ribaudo, Carl Robert
Issue Date
1991
Doctoral Committee Chair(s)
Mazumder, Jyotirmoy
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
Controversy regarding the mechanism(s) responsible for the retention of alumina scales formed on NiAlCr alloys containing reactive elements remains. Laser cladding is the process where a mechanical mixture of powders is rapidly melted and fused to a solid substrate using a CO$\sb2$ laser. The effects of laser cladding upon scale retention on NiAlCrHf alloys after cyclic and isothermal exposure to air were investigated. The stress developed in the scale during cooling after exposure was estimated using a thermoelastic model. Additions of up to $\approx$2${1\over2}$ wt % Hf increasingly promote retention of scales grown at 1200$\sp\circ$C. Laser clad samples containing $\approx$2${1\over2}$ wt % Hf retained almost intact scales. The improvement in scale retention is due to improved toughness in scales containing hafnia-rich polycrystallites possibly via microcracking initiated by anisotropic thermall contraction of the hafnia. Laser cladding provides a large concentration of $\approx$1$\mu$m Hf-rich particles that are precursors of the hafnia in the scale as well as a fine dendrite spacing that reduces the mean free distance between particles.
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