Historically, engineers and their designs have been limited by what could be manufactured using conventional methods. The need for increased performance, efficiency, and thermal stability of mechanical systems is increasing demand for highly complex metal components made from specialty alloys. Conventional manufacturing is not a viable option to fabricate these complex components and/or materials and metal additive manufacturing processes are required to fill the demand. A portion of this demand is filled by finding new applications and manufacturing processes for existing materials. The dual phase, β and γ/γ′ [where β = NiAl, γ = Ni(Co, Cr), and γ′ = Ni3Al], MCrAlY (M = Ni and/or Co) family of superalloys exhibit several beneficial high-temperature (>1000 °C) strength and corrosion resistance properties which makes them ideal candidates for protecting components from harsh environments where a combination of high temperature corrosion, abrasion, and extreme loading are encountered. These alloys are difficult to manufacture by any process and can currently only be manufactured as thin coatings using particle spray, vapor deposition, or laser cladding techniques. While prior studies report laser fabrication of these materials in coating and cladding configurations, bulk structures have not been realized. MCrAlY alloys have been traditionally limited to coating applications due their propensity to hot crack during bulk manufacturing. Although aluminum is necessary for corrosion resistance in MCrAlY alloys, it also promotes the formation of β-NiAl intermetallic phases which cause microstructure embrittlement and increase an alloys susceptibility to brittle cracking induced by thermo-mechanical fatigue. This tendency to crack from thermo-mechanical fatigue is of importance for additive manufacturing processes because thermal gradients and stresses are constantly changing within a deposition during fabrication. In order to fabricate bulk, complex structures from difficult to process materials in a reasonable amount of time, an additive manufacturing process such as directed energy deposition (DED) must be used. DED is a good candidate for this application because it is a freeform additive manufacturing process which features high deposition rates, relatively good dimensional accuracy, build volumes on the order of tens or hundreds of centimeters, and the ability to process difficult materials. This dissertation investigates the feasibility of fabricating bulk structures from an alumina forming NiCoCrAlY superalloy (tradename “Amdry 386”) using laser-DED, and develop heat treatments necessary to improve the structural integrity of laser-processed MCrAlY components.
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