May_June_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 9 2 6 D ispatchable solar power genera- tion is one of the key building blocks for the 21st century grid, while the nuclear and fossil industries continue to demand improved effi- ciencies to remain competitive. Under- standing and exploiting the beha- vior of materials subjected to extreme environments such as radiation, elevated temperatures, andmechanical stresses is critical for achieving increased efficien- cies and energy production in the nu- clear, solar, and fossil energy systems. Fortunately, the material requirements of the specific hot section components fromthese three industries are similar: an extended stability alloy capable of oper- ating at 1000°C for up to 100,000 hours, either to extract themaximumamount of efficiency from the systemor tomake the system technologically feasible. The power generation systems in these sectors must withstand tempera- tures approaching or exceeding 1000°C. The higher temperature capabilities re- quired by specific components in those systems are either desired for basic fuel savings (fossil), output applications (nuclear cogeneration), or to make sys- tems technically achievable (solar). In all cases, the need for a material that is not only capable of reliable opera- tion at high temperatures but resistant to cyclic failure from greatly varying fatigue conditions demands an alloy of extraordinary microstructural stability. SUPERALLOY R&D The term superalloys refers to the group of metallic alloys that are es- pecially stable at high temperatures (>800°C) and are usually based on iron, titanium, cobalt, or nickel. The defining characteristic of these materials is the presence of two distinct phases referred to as γ and γ′ . They have proven out- standing resistance to high tempera- ture creep and fatigue/creep-fatigue cycling. Nickel-base γ - γ′ superalloys are commonly used in aerospace and land-based gas turbine engines and are accustomed to operating in extreme environments. Preliminary evaluations [1] of can- didate materials have focused on both Haynes 230 and Alloy 617, two renowned solid-solution strengthened Ni-base al- loys. Both have relatively high tempera- ture and strength capabilities and are not dependent on the strengthening ef- fect of the Ni 3 Al γ′ phase, which would potentially limit long-term use due to γ′ coarsening. The tradeoff for this lack of NEW NICKEL-BASE SUPERALLOYS WITHSTAND EXTREME TEMPERATURES Hot section components of next-generation energy systems call for superalloys that can handle the heat. Subhashish Meher Idaho National Laboratory, Idaho Falls Subhashish Meher analyzes the nanoscale chemical information in a nickel-base superalloy using a local electrode atomprobe instrument.