Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Creep, Creep-Fatigue and Related High Temperature Mechanical Behavior
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Indrajit Charit, University of Idaho; Yuntian Zhu, North Carolina State University; Stuart Maloy, Los Alamos National Laboratory; Peter Liaw, University of Tennessee - Knoxville

Wednesday 2:00 PM
March 1, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Peiman Shahbeigi Roodposhti, University of Connecticut; Mageshwari Komarasamy, University of North Texas

2:00 PM  Keynote
Applying Conventional Creep Mechanisms to Ultrafine-grained Materials: Megumi Kawasaki1; Terence Langdon2; 1Hanyang University; 2University of Southern California
    The creep behaviour of polycrystalline materials is now well described through a series of equations that delineate various mechanisms describing intragranular and intergranular flow processes. The recent ability to fabricate metals with exceptionally small grain sizes, within the submicrometer and nanometer ranges, has raised questions concerning the applicability of these flow processes in these new and advanced materials. This paper examines this problem with special emphasis on the increasing importance of grain boundary effects in materials having very small grain sizes.

2:30 PM  Invited
Multiaxial Creep and Creep-fatigue: James Stubbins1; Kuan-Che Lan1; John Sanders1; Mohsen Dadfarnia1; Petros Sofronis1; Hsiao-Ming Tung1; Xiang Liu1; Calogero Sollima1; Kun Mo1; Guiseppe Brunetti1; 1University of Illinois
    Creep and creep-fatigue have been a limiting feature of elevated temperature design for advanced nuclear systems. The evaluation of the effects of steady and cyclic loading on materials performance at high temperatures is further complicated by multiaxial stress states. This paper will examine the effects of multiaxial stress states on the performance of high temperature alloys, particularly Alloy 617 and Alloy 230. The work will identify microstructural features that seem to control creep including the role of precipitate stability and evolution and the role of grain boundary cavitation in controlling creep life. The additional issue of creep-fatigue interaction will also be examined. This is a major issue for materials design since the design codes put a high degree of conservatism on the possible interacting influences of creep damage and fatigue damage. Nevertheless, the much of this conservatism stems from the results of fatigue with hold-time tests.

2:50 PM  Invited
Creep and Creep Fatigue of Alloy 709 Using In situ Heating during SEM and EBSD Observation: Afsaneh Rabiei1; Hangyue Li2; Paul Bowen2; 1North Carolina State University; 2Birmingham University
    In this study we utilize an in-situ heating - loading and Scanning Electron Microscope (SEM) imaging along with insitu EBSD to study the “real-time” crack growth of alloy 709 under plane stress conditions. Crack propagation modes are studied and compared, primarily at elevated test temperatures between 500 and 800C. Some of the important features of defect nucleation and growth within the specimen (under more constrained conditions) are also addressed by the subsequent fractographic assessments to combine the advantages of in-situ SEM observation to reveal the “real-time” fracture behavior and fractography to assess the failure mechanisms of Alloy 709 under various service conditions.

3:10 PM  Invited
Cyclic Deformation Behavior of Modified 9Cr–1Mo Steel at Elevated Temperatures: Vakil Singh1; Preeti Verma1; 1Indian Institute of Technology (Banaras Hindu University)
    Modified 9Cr–1Mo steel exhibited dynamic strain ageing (DSA) in the temperature range from 250 to 400 C and it was established on the basis of plateau/peak in yield and tensile strength, minima in ductility, serrations in stress–strain curve and negative strain rate sensitivity. High density of dislocations and typical features like dislocation debris, kinks and bowing of dislocations were observed in the regime of DSA. This steel showed cyclic softening irrespective of strain amplitude, strain rate, and temperature. The observed cyclic softening was associated with cell formation at RT and annihilation of array of dislocations at 300 C. In addition to coarsening of carbides at 600 C there was dynamic recovery/recrystallization and also grain rotation. There was transition from equiaxed cell structure to elongated cell structure at strain amplitude of 0.375% and corresponding change from non–Masing to Masing behavior at RT and 300 C.

3:30 PM Break

3:45 PM  Keynote
Environmentally-benign Pb-free Solder Alloys: Complex Load Bearing Materials in Electronic Packaging: Nikhilesh Chawla1; 1Arizona State University
    Metallic alloys are an integral part of electronic packaging. Over the last decade or so, there has been a significant drive to replace Pb-Sn solders with Pb-free, environmentally-benign solders. A fundamental understanding of microstructure evolution and deformation behavior of Pb-free solders is crucial for the successful substitution of these materials in the electronics industry. Prof. Murthy’s contributions in this area have been seminal. In this talk, an overview of the microstructure and creep behavior of Pb-free solders, in bulk form and at small length scales, will be presented. The importance of the solder microstructure and the role of intermetallic phases formed between solder and copper metallization will be addressed. Recent experiments probing the creep behavior of individual constituents in the microstructure, by high temperature micropillar compression, will be described.

4:15 PM  Invited
Effect of Thermo-mechanical History on the Creep Behavior of Sn-Ag-Cu Solders: Babak Talebanpour1; Indranath Dutta1; 1Washington State University
    Solder joints experience cyclic strains and high homologous temperatures during service. This alters the microstructure, and influences the creep response, affecting the reliability of microelectronic packages. Here, the microstructure and the resultant impression creep behavior of Sn-3.0Ag-0.5Cu and Sn-1.0Ag-0.5Cu solders, subjected to various thermo-mechanical cycling and isothermal aging processes, are correlated. The creep rate was found to be proportional to the Ag3Sn particle size in the eutectic for Sn-3.0Ag-0.5Cu, the microstructure of which contains a continuous network of eutectic surrounding proeutectic β grains. In Sn-1.0Ag-0.5Cu, where the eutectic is not continuous, the proeutectic contributes significantly to the creep response. The results are utilized to develop a generalized composite creep model, which shows that the creep rate increases linearly with precipitate size for solders with high eutectic volume fraction, but at a less-than-linear rate for solders with low eutectic volume fraction (i.e., discontinuous eutectic). Supported by SERDP (W912HQ-10-C-0041) and SRC (2008-KJ-1855).

4:35 PM  
Modelling of the Fracture of Precipitate and Austenitic Matrix Interfaces During Creep: Liang Huang1; Maxime Sauzay1; 1French Alternative Energies and Atomic Energy Commission
     316L(N) is a suitable candidate for structural components of the next generation of nuclear power plants. They will be subjected to high temperature and low stress. Microscopic observations carried out by SEM-FEG-EBSD and TEM show that cavities nucleate preferentially along the interfaces of precipitates and austenitic matrix.Crystal elastoviscoplastic laws are used in FE computations to predict the stresses around precipitates in function of creep deformation and temperature. Parameters are given by literature and adjusted using our experimental creep curves (primary and secondary stages only). The calculations take into account the effect of the precipitate geometry and the crystallographic orientations of the neighboring grains. Considering these many microstructure details, the maximum normal stresses along interfaces could reach about 10GPa which is forty times higher than the applied stress. Based on microstructure statistical features and on numerous respective simulations, we can evaluate the cavity nucleation rate depending on stress and temperature.

4:55 PM  Cancelled
Characterisation of Mechanical Properties Using Ball Indentation, Small Punch Creep and Impression Creep Methods: MD Mathew1; 1Saintgits College of Engineering (formerly at Indira Gandhi Center for Atomic Research)
    Tensile and creep properties of materials are usually evaluated using standard test methods. These methods are material intensive. Small specimen testing methods such as, Impression Creep, Small Punch Creep and Ball Indentation allows us to determine the mechanical properties of materials. Creep deformation behavior can be studied using Impression Creep. Small Punch Creep test method is used to evaluate creep deformation and fracture properties of materials. Tensile properties and fracture toughness can be evaluated using Ball Indentation method. Compared to the standard test methods, these methods have several advantages in materials development, structural integrity assessment and characterization of mechanical properties of different but narrow microstructural zones in weld joints. This paper presents a review of the recent advances in these three small specimen testing methods and discusses their relative advantages and limitations using ferrous and non-ferrous alloys.