Superalloys 2024: General Session 5: Blade Alloy Mechanical Behavior
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Tuesday 8:30 AM
September 10, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort
Session Chair: Catherine Rae, University of Cambridge; Jeremy Rame, Naarea
8:30 AM
Tensile Testing of Ni-based Single Crystal Superalloys: What is the Correct “Point of View”?: Satoshi Utada1; Qinan Han2; Ang Li2; Melvin Miquel1; Celal Polatoğlu1; Magnus Hasselqvist3; Yuanbo Tang1; Roger Reed1; 1University of Oxford; 2Nanjing University of Aeronautics and Astronautics; 3Siemens Energy AB
The anisotropy of deformation of a single crystal superalloy is studied using a newly designed furnace arrangement which allows for videography from multiple apertures and subsequent digital image correlation (DIC). Thus, for initially cylindrical specimens, the full field of surface strain is measured at a 25 μm spatial resolution. Our approach is tested for STAL15 along each of the <001>, <011>, and <111> crystallographic orientations at 800 °C. The time-dependent anisotropic deformation along each of these crystallographic directions is quantified. Crystal plasticity finite element (CPFE) calculations are used to rationalise the observations; it is demonstrated that the predictions are particularly sensitive – on account of the plastic anisotropies – to the boundary conditions used for the loading. Implications for the testing of single crystal superalloys are discussed in detail, with a particular view towards improving testing protocols.
8:55 AM
Mechanisms of Dwell Fatigue in Single Crystal Ni-base Superalloys at Intermediate Temperatures: Jane Woolrich1; Simon Gray2; Ian Edmonds1; Edward Saunders1; Catherine Rae3; 1Rolls-Royce plc; 2Cranfield University; 3University of Cambridge
Single crystal (SX) nickel-base superalloys have been developed specifically to withstand the high temperatures that would engender severe creep degradation in a lesser alloy. Use in gas turbine blades has long been a driver for the development of ever more capable alloys that can survive higher temperatures without significant material damage[1]. The drive for increased financial efficiency has included a desire for increased duration, and longer time between overhauls, as well as reduced specific fuel consumption. The long-term behaviour of SX alloys at lower temperatures, such as that experienced at the blade root fixings, has not historically influenced alloy design, but has become increasingly important as the target time between overhauls increases.This study looks at the behaviour of an example of a 2nd, 3rd and 4th generation SX alloy at a temperature commensurate with that outside the gas path, in keeping with that around the blade root. The influence of dwell on both the predicted life and consequent fractography is examined. In addition, the dependence of crack growth rate with secondary orientation is assessed. Finally, the crack trajectory close to the crack tip is considered and the possible influence of different regions of the loading cycle discussed.
9:20 AM
Anisotropic Tensile Properties of Ni-based Single-crystal Superalloys: A Phase-Field-Informed Crystal-plasticity Finite-element Investigation: Jean-Briac le Graverend1; Rajendran Harikrishnan1; 1Texas A&M University
Ni-based single-crystal superalloys, mostly used in turbine blade applications, are inherently anisotropic and usually cast in the direction. Any slight misorientations result in anomalies in the microstructural evolution, thereby, causing variation in the mechanical response. As the stability of the microstructure dictates the structural integrity of the blade, it is essential to understand the microstructural state as a function of the crystallographic orientation. Therefore, to predict the microstructural evolution of single-crystal superalloys at any given orientation on the standard stereographic triangle, a crystallographic-sensitive phase-field model was developed. The phase-field simulations for the perfect , , and orientations agreed well with the experimental characterizations. For the first time, a model also predicts the microstructures for misorientations (10°) away from the main crystallographic directions. Finally, for a quantitative assessment of the macroscale performance of various orientations, the 3D phase-field microstructures were employed to carry out crystal-plasticity finite-element (CPFE) micromechanical simulations for strain-controlled monotonic tensile tests at 1050°C.
9:45 AM
Retardation and Acceleration of Dwell-fatigue Crack Propagation in Ni-base Superalloys: Experimental and Numerical Investigations on CMSX-4 and IN718: Shiyu Suzuki1; Hayato Matsuoka2; Qihe Zhang2; Zhiqi Chen2; Itsuki Sasakura2; Motoki Sakaguchi2; 1Japan Aerospace Exploration Agency; 2Tokyo Institute of Technology
Effect of tensile dwell on crack propagation under subsequent fatigue loading during dwell-fatigue crack propagation in Ni-base superalloys was investigated using a single crystal superalloy, CMSX-4, and a wrought superalloy, IN718. Crack propagation tests with single tensile dwell introduced during pure fatigue loading under various conditions of stress intensity and dwell time were conducted at 900 °C and 650 °C for CMSX-4 and IN718, respectively. In CMSX-4, fatigue crack retardation occurred after the tensile dwell, which was attributed to stress relaxation induced by creep deformation during the dwell and the resultant residual compressive stress during the subsequent fatigue loading. Fatigue crack propagation rate after the tensile dwell was quantified by evaluating effective stress intensity factors based on the residual compressive stress field obtained by finite element analysis. In IN718, acceleration of the fatigue crack propagation occurred after the tensile dwell at high Kmax values whereas the retardation occurred following temporary acceleration after the dwell at low Kmax values. The acceleration was attributed to grain boundary (GB) damage caused by oxygen diffusion along the GBs induced by high stress near the crack tip during the tensile dwell. The transition from the crack retardation to the acceleration in IN718 was rationally explained based on a size relationship between the stress relaxation area and the GB damage zone around the crack tip caused by the tensile dwell.