Superalloys 2021: Additional Pre-Recorded Talks Available On Demand starting Monday
Program Organizers: Sammy Tin, University of Arizona; Christopher O'Brien, ATI Specialty Materials; Justin Clews, Pratt & Whitney; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Qiang Feng, University of Science and Technology Beijing; Mark Hardy, Rolls-Royce Plc; John Marcin, Collins Aerospace; Akane Suzuki, GE Aerospace Research

Monday 8:30 AM
September 13, 2021
Room: On-Demand Session Room
Location: Virtual Event

Stress-induced Variant Selection of γ″ Phase in Inconel 718 during Service: Mechanism and Effects on Mechanical Behavior: Hailong Qin¹; Zhongnan Bi¹; Ruiyao Zhang²; Tung-Lik Lee³; Hongyao Yu¹; Hongbiao Dong²; Jinhui Du¹; Ji Zhang¹; ¹Central Iron and Steel Research Institute; ²University of Leicester; ³ISIS Neutron Source
    The stress-induced variant selection (SIVS) of ă″ phase caused by thermo-mechanical coupling condition is studied systematically. The SIVS index f is devised and utilized to quantify the degree of SIVS via SEM image post-processing within <001> oriented grains. Applied stress condition does not affect the volume fraction, average size and crystallographic orientation of the ă″, but changes the proportion of the three variants. The SIVS behavior of ă″ phase is dependent upon the applied stress direction and grain orientation. By considering the variation of the SIVS index with thermal aging and creep parameters, a causal relationship between degree of SIVS with temperature, stress, and time is elucidated. The yield strength and tensile strength at 650°C decreases with the increase of SIVS degree. Contour map for the degree of SIVS is presented to evaluate the service temperature and stress of an Inconel 718 component. The formation mechanism of SIVS of ă" is proposed: the orienting effect of stress conditon is appreciable only during Ostwald ripening, due to the change of the ă″/ă lattice mismatch.

Hot Corrosion and Creep Properties of Ni-base Single Crystal Superalloys: Yutaka Koizumi¹; Kyoko Kawagishi¹; Tadaharu Yokokawa²; Michinari Yuyama¹; Yuji Takata¹; Hiroshi Harada¹; ¹National Institute for Materials Science; ²National Institute for Materials Sciencei
    Hot corrosion behavior at 700 °C (Type II) and 900 °C (Type I) and creep property from 800 °C to 1100 °C were investigated for representative alloys from the 1st generation to the 6th generation of Ni base single crystal superalloys. From the metal loss in the corrosion test and creep rupture life, it is found that corrosion resistance and creep strength are improved with generation advances. Regression analysis was performed to the results of the corrosion test at both 700 °C and 900 °C. Equations for predicting corrosion characteristics were constructed, and alloying elements contributing to corrosion resistance were estimated.

Effect of Re on Long-term Creep Behavior of Nickel-based Single Crystal Superalloys for Industrial Gas Turbine Applications: Fan Lu¹; Longfei Li¹; Stoichko Antonov¹; Yufeng Zheng²; Hamish Fraser²; Dong Wang³; Jian Zhang³; Qiang Feng¹; ¹University of Science and Technology Beijing; ²The Ohio State University; ³Institute of Metal Research, Chinese Academy of Sciences
    Understanding the long-term creep behavior (creep lives longer than 5000 h) of nickel-based single crystal (SX) superalloys is of great interest for the service safety of industrial gas turbine (IGT) blades. However, understanding the influence of various factors on long-term creep behavior of nickel-based SX superalloys has always been a challenge. In this study, the creep behavior of nickel-based SX superalloys with or without 2 wt.% Re addition were investigated at 900 °C and 200 MPa. Microstructural characterization was systematically conducted to elucidate the microstructural evolution of the experimental alloys after creep rupture tests. The results indicated that the creep lifetime was increased significantly by 2 wt.% Re addition, which dramatically reduced the creep strain rate and caused the lattice misfit of ă/ă′ phases to inverse from positive to negative, leading to N-type rafting exhibiting a stronger barrier to dislocations during creep. The evolution of lattice misfit of the ă/ă′ phases was closely associated with the elemental partitioning behavior between the ă/ă′ phases, which was determined as a consequence of "time accumulation effect" and corresponding elemental diffusion special for prolonged time. This study provides a new insight in the effect of Re on the long-term creep life and microstructure evolution of nickel-based SX superalloys. Such knowledge will be helpful to provide the guideline of superalloys design for large-scale IGT blades.

Effects of Al, Cr and Ti on the Oxidation Behaviors of Multi-component γ/γʹ CoNi-based Superalloys: Xiaoli Zhuang¹; Longfei Li¹; Qiang Feng¹; ¹University of Science & Technology Beijing (USTB)
    The effects of Al, Cr and Ti on the oxidation behaviors of multi-component ă/ăʹ CoNi-based superalloys, Co-30Ni-(6-8)Al-3W-1Ta-(3-6)Ti-(12-14)Cr, were investigated at 800 °C, 900 °C and 1000 °C for 100 h. The results show that Al has a superior effect for improving the oxidation resistance of the alloys in comparison with Cr, particularly at 900 °C and 1000 °C, while Ti was detrimental to the oxidation performance of the alloys. Oxidation resistance of alloys containing 6 at.% Al were primarily provided by Cr2O3 layer, which was not sufficiently protective at 900 °C and 1000 °C. Continuous Al2O3 layers could form in alloys containing 8 at.% Al at 800 °C and 1000 °C, but failed at 900 °C. Higher content of Cr can assist the formation of continuous Al2O3 layer. For the target service temperature of 800 °C or below, alloys with lower Al and higher Ti content may be suitable since higher solvus temperature and volume fraction of the ă' phase could be achieved with sufficient oxidation resistance provided by dense Cr2O3 layer. While for a higher target service temperature above 900 °C, higher content of Al (≥ 8 at.%) is required to form continuous Al2O3 layer. The current study is helpful to understand the oxidation behavior of multi-component CoNi-based superalloys and provide guidance for alloy composition design and optimization.