Advanced Characterization of High-temperature Alloys: Phase Evolution during Manufacturing and Service-induced Deformation: Advanced Characterisation of Deformation Mechanisms: Microscopy
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Katerina Christofidou, University of Sheffield; Benjamin Adam, Oregon State University; Stoichko Antonov, Max-Planck Institut für Eisenforschung GmbH; James Coakley, Chromalloy; Martin Detrois, National Energy Technology Laboratory; Paraskevas Kontis, Norwegian University of Science and Technology; Stella Pedrazzini, Imperial College London; Sophie Primig, University of New South Wales
Monday 2:00 PM
March 20, 2023
Room: 29D
Location: SDCC
Session Chair: Stoichko Antonov, National Energy Technology Laboratory; Cynthia Rodenkirchen, Imperial College London
2:00 PM Invited
High-resolution Characterization of Grain Boundary Precipitates and Their Interfaces in Ni-based Superalloys with B and C Additions: Felix Theska1; Richard Buerstmayr1; Michael Lison-Pick2; Steven Street2; Sophie Primig1; 1UNSW Sydney; 2Western Australian Specialty Alloys (WASA)
Cast & wrought Ni-based superalloys are high-temperature materials for aerospace and power generation applications. René 41 provides the high-temperature strength required for next generation aircraft engines, but wider applications are limited by grain boundary cracking and insufficient grain size control. Alloy design utilizing B & C additions can mitigate grain boundary cohesion and grain boundary pinning. However, complex precipitation reactions may have opposing effects. Thus, more detailed studies are required to understand the impact of B & C additions on grain boundary microstructure and properties.In the present work, René 41 variants with C & B additions are designed to study their hot workability during industrial-scale hot rolling. Electron microscopy reveals the grain boundary microstructure. Site-specific atom probe microscopy reveals the composition of precipitates and their interfaces. Thermodynamic modeling underpins experimental findings. These insights establish pathways to alloy design of future superalloys with improved hot workability and grain size control.
2:30 PM Invited
STEM/SEM Study on the Microstructural Evolution and Deformation Mechanisms of Fe-25Cr-20Ni-1.4Nb-0.2C Steel Fabricated by Laser Powder-bed Fusion: Kinga Unocic1; Rangasayee Kannan1; Lisa Debeer-Schmitt1; Ken Littrell1; Peeyush Nandwana1; Sebastien Dryepondt1; 1Oak Ridge National Laboratory
A high temperature austenitic stainless steel (Fe-25Cr-20Ni-1.4Nb-0.2C), fabricated by laser powder-bed fusion (LPBF), contains a refined microstructure with a high-density cellular structure, nano-sized carbides (e.g., NbC, Cr23C6), and < 5 nm clusters of Cr-Ni-Fe that are localized at the cell walls. Larger carbides are usually found along the main grain boundaries. Some local chemical heterogeneities due alloy processing could affect its local mechanical properties and oxidation behavior. Therefore, it is important to establish a link between the as fabricated microstructure and mechanical behavior. Selected samples after high temperature creep testing were examined and various advanced characterization techniques were performed to understand the effect of temperature and stress on microstructural evolution and deformation mechanisms. The deformation mechanism and microstructure stability will be discussed.
3:00 PM
Advanced Characterization of Centrifugally Cast HP40 Reformer Tubes: Thibaut Dessolier1; Thomas McAuliffe1; Chrétien Hermse2; Wouter Hamer3; Thomas Britton4; 1Imperial College London; 2Shell Nederland Chemie B.V.; 3Shell Global Solutions International; 4University of British Columbia
HP40 is an iron-nickel based alloy with good resistance against high temperature creep and carburization, and this makes the alloy well suited for reformer tubes used in hydrogen production. Our tubes were formed using centrifugal casting, where liquid metal is poured into a spinning ceramic mould and a metal tube is cast. In this study, we apply true nm-to-mm characterization using optical, scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDX) & electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and atom probe tomography (APT) to characterise precipitates in ex-service reformer tubes. In this presentation, we will share state-of-the-art correlative approaches to identify and understand the spatial distributions of different phases and carbides in these alloys and discuss how these structures evolve during service, specifically with decomposition of NbC carbides into G-phase and M6C phase carbides.
3:20 PM
Microstructure Evolution and Mechanical Properties of α′/α″-Strengthened Ferritic Superalloys: Christopher Zenk1; Andreas Bezold1; Andreas Förner1; Steffen Neumeier1; Carolin Körner1; 1Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
High-temperature structural materials based on Fe and Al are highly desirable due to the abundance of these elements and the associated benefits regarding costs and sustainability. By the addition of Ni and Ti to these base elements, ferritic superalloys consisting of an A2 (α-Fe solid solution) matrix and coherently embedded B2-ordered (α′) as well as L21-ordered (α″) strengthening phases can be generated. Our alloy development efforts have led to an LMD-processed eight-component hierarchical precipitate-strengthened alloy with ~50 vol.% precipitate fraction and promising properties. Mechanical properties extracted from high-temperature indentation plastometry and in-situ SEM tensile tests will be presented. A microstructure evolution from a spinodal basket-weave structure to equiaxed precipitates and the formation of Cu-nanoclusters will be discussed on the basis of TEM and APT characterization.
3:40 PM Break
4:00 PM Invited
Characterization of Deformed Structures in γ′ Containing Superalloys: Akshat Godha1; Karthick Sundar1; Shashidhar Gangavarapu1; Nithin Baler1; Surendra Kumar Makineni1; 1Indian Institute of Science Bangalore
This talk will focus on the atomic-scale structural and compositional characterization of cold and high temperature deformed microstructures in γ′ containing multi-component alloys such as Ni-based, Co-based, and NiCoCr-based alloys. The results showcase evolution of defect structures as a function of deformation and heat treatment. The role of solutes in the deformation behavior will be highlighted with a direct correlation to their mechanical properties.
4:30 PM
An In-Situ Elevated Temperature Investigation of Plasticity and Damage Evolution in a Ni-based Superalloy: Prafull Pandey1; Shaolou Wei1; Cemal Tasan1; 1MIT
The present work reveals, via integrated in-situ scanning electron microscopy and post-mortem analyses, the strain rate effect on deformation and damage evolution in a Ni-based superalloy at 700 °C. The alloy tested at strain rates of 4 × 10-4 and 4× 10-3 s-1 show similar yield strength, whereas better ultimate tensile strength and ductility at higher strain rate. The deformation mechanism study using electron channeling contrast imaging reveals planar slip at the lower strain rate, resulting in local stress development and crack nucleation at grain boundaries. Thus, the intergranular cracking is observed as the major softening and damage mechanism at lower strain rate. In contrast, at higher strain rate, the deformation process involves cross slip events which result in high-density dislocation wall formation. We also discuss the origins of the observed slip planarity at lower strain rate by carrying out various microstructural analyses down to the atomic scale.
4:50 PM
TEM Characterization of Tensile Behavior of Advanced Ni-based Single-crystal Superalloys: Benoit Mansoz1; Jonathan Cormier2; Pierre Caron3; Florence Pettinari-Sturmel1; 1CEMES-CNRS; 2Institut Pprime; 3ONERA
TMS-238 is a promising 6th generation superalloy with impressive high temperature creep performance but it exhibits a particular tensile behavior at 650°C with low yield strength, low ductility and non-classical hardening. To study this behavior, TMS-238 specimens with different misorientations away from the perfect [001] orientation were tensile tested at 650°C. TEM investigations were conducted with post mortem observations and in situ TEM tensile tests at 650°C. Similar TEM experiments were also performed using other alloys for reference. Mechanical tests revealed that highly misoriented specimens do not exhibit this atypical hardening behavior but keep a similar low yield strength. TEM investigations revealed a high density of dislocations and stacking faults in the γ phase. EDX analysis confirmed significant amounts of Re and Ru in γ, two elements known to decrease misfit and fault energy, resulting in a lower mobility of dislocations in the matrix and a strong hardening.