Foreword
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Foreword Materials for High Temperature Applications: Next Generation Superalloys and Beyond Nickel-based superalloys possess an excellent combination of mechanical properties and environmental resistance at elevated temperatures, and have been widely used in challenging environments prevalent in aircraft engines and land-based power generation gas turbines, as well as in nuclear power systems and chemical plants. The ever-increasing demand for higher operating temperatures to achieve better fuel efficiency has been driving the development of the next generation of superalloys, in which the higher temperature capability has been achieved by increasing additions of refractory elements, optimizing processing conditions, and through the application of coatings. However, there is a strong need for materials that can make a disruptive change in temperature capability beyond that provided by current materials. The symposium ‘‘Materials for High Temperature Applications: Next Generation Superalloys and Beyond’’ was held during the 2017 TMS annual Meeting from February 27 to March 2, 2017 in San Diego, California, with the sponsorship from the TMS High Temperature Alloys Committee and TMS Refractory Metals Committee. The goal of this symposium was to discuss (i) challenges that current Ni-based superalloys are facing and (ii) the recent progress in the development of next generation of superalloys and high temperature material systems beyond Ni-based superalloys. The symposium was composed of a total of seven sessions covering current and next generation Ni-based superalloys, refractory metal-based materials, intermetallic-based materials, coatings, Ir-based alloys, and ceramics composites and emerging materials. The organizers would like to thank all the presenters and the participants for their excellent contribution to the success of this symposium. There were in total 60 oral presentations, including 2 keynote presentations and 18 invited presentations, and 6 poster presentations. This special issue presents selections of 10 high quality research papers submitted to this symposium. We would like to express our appreciation to Prof. Tresa Pollock, Principal Editor; Prof. Jonathan Cormier, Editor; and Ms. Karen Doyle, of Metallurgical and Materials Transactions A for their support in the publication of these papers in a single issue. The first paper by Mignanelli et al.[1] investigated the precipitation behavior in a new class of Ni-based superalloys strengthened by two superlattice intermetallic phases, c¢ (L12) and c¢¢ (D022), as a candidate next generation alloy system having temperature capability beyond IN718. A T-T-T diagram was constructed, and the stability of the c¢¢ phase against d phase was discussed. The formation of the c¢¢ precipitates were shown to contribute to age hardening of the alloy. Detor et al.[2] presented their Ni-based superalloy design approach to solve a unique issue associated with physically large components, such as land-based power generation gas turbine disks, in which the inability to achie
