Integrated Computational Alloy Design of Nickel-Base Superalloys
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CONVERSION efficiency of gas turbine engines increases with an increased turbine entry temperature,[1] which is attainable by availability of materials durable at high temperatures. A good combination of creep resistance, microstructure stability, and corrosion/oxidation resistance provided by Ni-base superalloys, makes them unsurpassed candidates as hot section turbine engine materials. The high-temperature durability of these alloys are achieved by a high-volume fraction of a strengthening gamma-prime (c¢) precipitate phase with an ordered face-centered cubic crystal structure embedded in a disordered face-centered cubic gamma (c) matrix.[1–3] Lightweight silicide-, nitride-, and aluminide-based ceramics and intermetallics are aimed
M. MONTAKHAB and E. BALIKCI are with the Department of Mechanical Engineering, Bogazici University, 34342 Istanbul, Turkey. Contact e-mail: [email protected] Manuscript submitted December 31, 2018. Article published online May 13, 2019 3330—VOLUME 50A, JULY 2019
to substitute for superalloys in turbine engines due to their lower density and higher temperature capability. However, their application is limited by their brittle nature.[4] Therefore, designing superalloys with increased temperature capability, improved life, and reduced density is of a crucial importance in aerospace and power industries. A significant improvement has been achieved over the many years in the high-temperature performance of Ni-base superalloys despite an Edisonian alloy development approach that relies on extensive experimentation in various stages of the alloy development from a concept to a validated part.[5] More than 10 alloying elements are present in superalloys, which makes the traditional experimental alloy design methods very time consuming and costly. As a result, the alloy development cycle is far behind the product development cycle. The materials community has decided to overcome this via the Materials Genome Initiative (MGI) and Integrated Computational Materials Engineering (ICME).[6] Computational methods reduce the materials development cycle to keep pace with very fast developing product design and development and hence enable
METALLURGICAL AND MATERIALS TRANSACTIONS A
development of new alloys to meet cost/performance requirements.[7] These methods should consider several parameters that are interlinked in a complex way. A partial list of these parameters can include the size, distribution, and volume fraction of the precipitates, the ordered nature of the precipitates, lattice misfit between the precipitates and the matrix, temperature, stress, and environmental conditions. Recently, a number of software are developed to model thermodynamics, diffusion, microstructure, and mechanical properties.[8–10] The existing software for mechanical properties is based on simplified empirical approaches, and so they are unable to make a full correlation between influencing parameters.[11,12] Mechanical properties depend not only on the atomic bonding and the atomic/molecular arrangement, bu
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