Design of Novel Precipitate-Strengthened Al-Co-Cr-Fe-Nb-Ni High-Entropy Superalloys
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, MARTIN DETROIS, and SAMMY TIN
A series of non-equiatomic Al-Co-Cr-Fe-Nb-Ni high-entropy alloys, with varying levels of Co, Nb and Fe, were investigated in an effort to obtain microstructures similar to conventional Ni-based superalloys. Elevated levels of Co were observed to significantly decrease the solvus temperature of the c¢ precipitates. Both Nb and Co in excessive concentrations promoted the formation of Laves and NiAl phases that formed either during solidification and remained undissolved during homogenization or upon high-temperature aging. Lowering the content of Nb, Co, or Fe prevented the formation of the eutectic type Laves. In addition, lowering the Co content resulted in a higher number density and volume fraction of the c¢ precipitates, while increasing the Fe content led to the destabilization of the c¢ precipitates. Various aging treatments were performed which led to different size distributions of the strengthening phase. Results from the microstructural characterization and hardness property assessments of these high-entropy alloys were compared to a commercial, high-strength Ni-based superalloy RR1000. Potentially, precipitation-strengthened high-entropy alloys could find applications replacing Ni-based superalloys as structural materials in power generation applications. DOI: 10.1007/s11661-017-4399-9 The Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
NOVEL structural materials intended for use in power generation applications are continuously being developed and evaluated in an effort to lower their weight and cost for given performance requirements, and ultimately improve their efficiency. From advanced high-strength steels in service in power plants to Ni-based superalloys in turbine engines, the design of an optimal alloy begins with the selection of a principal, or a base, element, such as Fe or Ni, to which other property improving elements are added in significantly lower concentrations. In the past, this design process led to the development of alloys with targeted properties and microstructures in order to meet the demanding design requirements while limiting their weight and cost. In recent years, a novel class of multicomponent alloys, often referred to as high-entropy alloys (HEAs) or compositionally complex alloys (CCAs), has been developed based on the design strategy of high configurational entropy.[1] Essentially, they rely on the formation of a single solid-solution phase with multiple alloying
STOICHKO ANTONOV and SAMMY TIN are with the Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616. Contact e-mail: [email protected] MARTIN DETROIS is with ORISE, National Energy Technology Laboratory, 1450 Queen Ave SW, Albany, OR 97321. Manuscript submitted August 18, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
additions at near-equimolar ratios.[2] Therefore, unlike Fe, Ni, or Co-based alloys that contain one primary base element, at least five principal elements, with concentrations between 5 and 35 at. pct,[3] are added to the
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