Energy Materials 2017: Materials for Coal-Based Power: Session V
Sponsored by: Chinese Society for Metals
Program Organizers: Jeffrey Hawk, U.S. Department of Energy, National Energy Technology Laboratory; Zhengdong Liu, China Iron & Steel Research Institute Group; Sebastien Dryepondt, Oak Ridge National Laboratory

Thursday 2:00 PM
March 2, 2017
Room: 12
Location: San Diego Convention Ctr

Session Chair: Jeffrey Hawk, U.S. Department of Energy, National Energy Technology Laboratory

2:00 PM  Invited
Alloy Design of Creep-resistant High Entropy Alloys for Elevated-Temperature Applications: Peter Liaw1; Haoyan Diao2; Chuan Zhang3; Fan Zhang3; Karin Dahmen4; 1The University of Tennessee; 2The University of Tennessee ; 3CompuTherm, LLC,; 4University of Illinois at Urbana–Champaign
    The creation and design of novel structural materials with enhanced creep-resistance has always been the goal of many scientists. The high-entropy alloy (HEA) concept has revolutionized alloy-design approaches, by employing the use of multi-principal elements in contrast to traditional alloys, based on one or two principal elements with small amount of alloying elements to achieve desired properties. HEAs have shown to be suitable materials for elevated-temperature applications. The fundamental studies on the AlxCoCrFeNi for use in boilers and steam and gas turbines at 760 C and 35 MPa has been performed. The creep behavior and related deformation mechanisms of HEAs has been studied using in-situ neutron diffraction. The thermodynamics and kinetics of NiAl precipitates and its strengthening effect, has also been investigated, through an integrated approach, coupling modeling [thermodynamic calculations and crystal-plasticity finite-element modeling (CPFEM)] and experiments, to identify HEAs that outperform conventional alloys for high-temperature applications.

2:40 PM  
Continued Development of a Cast Superalloy, IN740 for Advanced Power Generation Applications: Kyle Rozman1; Jeff Hawk1; Paul Jablonski1; 1National Energy Technology Laboratory
    The National Energy Technology Laboratory is developing advanced structural materials to be used in high temperature power generation applications. Wrought Inconel 740 has been code approved for use in boiler applications and subsequently was investigated for use as a casting. Homogenization and aging heat treatments were given to castings which modeled thick section components. Variations of chemistry aims were made to modify the secondary phases that formed during aging and thus improve ductility. For this presentation the tensile and creep results of the cast alloy was investigated. Excellent ductility in excess of 20% at 800oC was found in one heat. However, the creep ductility is rather poor, less than 5% for all heats, regardless of the applied stress or heat chemistry.

3:00 PM  Invited
Creep Behavior and Microstructural Stability in Cast γ' Strengthened Nickel Superalloys: Jeffrey Hawk1; John Sears2; Paul Jablonski1; 1U.S. Department of Energy, National Energy Technology Laboratory; 2AECOM
    A-USC power plants will see steam temperatures approaching 760C. Conventional 9% Cr martensitic steels will not work in this environment. Thus, Ni-based superalloys are considered both in the wrought and cast forms. Of particular interest is achieving thick-wall  strengthened nickel superalloys castings. Full size castings can be quite substantial and achieving uniform properties is critical for their use. NETL with the A-USC consortium addressed this problem by looking at solution and precipitation strengthened wrought variants but casting them into laboratory-scale ingots. Effort was expended to reduce segregation prior to subsequent heat treatments. One particular benefit of this approach was improved creep resistance. Mechanical property results on developing cast Haynes 282 and alloy 263 will discussed. The microstructures in the creep tested samples will be contrasted against the starting material.

3:35 PM Break

3:55 PM  
Design and Performance of Nickel-Base Alloys Strengthened by Eta Phase Precipitates: Walter Milligan1; Calvin White1; Paul Sanders1; John Shingledecker2; Daniel Purdy2; 1Michigan Technological University; 2Electric Power Research Institute
    Eta phase (Ni3Ti) forms naturally at long exposure times in alloys such as Nimonic 263 that are used in power generation systems. Eta forms at the expense of gamma prime, and is typically considered to be deleterious to performance. In this work, alloys were designed starting with Nimonic 263, but with modified chemistries designed to completely eliminate gamma prime and form eta instead. High temperature tensile and creep performance, along with deformation mechanisms, will be discussed.

4:15 PM  Invited
Materials and Manufacturing Challenges for Components of Supercritical CO2 Power Systems: Omer Dogan1; 1DOE National Energy Technology Laboratory
    Supercritical CO2 (sCO2) power systems are being developed for their superior power generation efficiency compared to the steam cycles. The higher efficiency is realized due to several factors such as high heat recuperation, recompression near liquid densities, and lack of phase change in the cycle. The other advantages of the sCO2 cycles include lower capital cost due to compact turbomachinery and simpler configurations, and lower environmental impact due to dry water cooling and ability to capture storage ready CO2 in direct cycles. Materials and manufacturing issues pose challenges in realizing these systems. Chemical and mechanical stability of materials in sCO2 power cycle environments have not been demonstrated sufficiently. The presentation will elaborate on the primary materials issues such as corrosion and fatigue crack growth behavior in sCO2 power cycle environments. Joining issues related to the high-temperature alloys used in sCO2 power systems will also be discussed.

4:50 PM  Invited
Micro Creep and Fatigue Behaviors in an Advanced Austenitic Stainless Steel: Guocai Chai1; 1Sandvik Materials Technology
    Micro deformation behaviors during the creep, fatigue and creep-fatigue interaction in an advanced austenitic stainless steel, Sanicro 25, has been studied in this paper. The creep tests have been done at temperature from 550C up to 800C for more than 80 000 hours. Different models have been used to evaluate the long-term creep strength. A creep rupture strength near 100MPa at 700C for 100 000h has been predicted. Creep mechanisms at different temperatures and loading conditions have been identified using TEM and SEM. The interactions between dislocations and precipitates are the main creep mechanism at temperature below 700C. For LCF, interaction and impingement between dislocation slip bands and grain or twin boundaries are the main mechanism with large strain range at high temperature. Finally, the influences of dwell time on the cyclic plastic deformation, precipitation behavior, recovery phenomena and local plasticity exhaustion have also been studied.