Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Miscellaneous Structure-property Correlations
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

Thursday 8:30 AM
March 2, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Koteswararao Rajulapati, University of Hyderabad; Walid Mohamed, Argonne National Laboratory

8:30 AM  Keynote
Structure-property Relationships in Steel Fibers: Krishan Chawla1; 1University of Alabama at Birmingham
    Metallic filaments can show very high strength levels, which stems from the work hardening that metals undergo during mechanical working. This is particularly true of steel filaments which are commonly used in making cables. The elastic modulus, however, does not change significantly with deformation. Metallic filaments show very consistent strength values vis vis other high strength fibers such as carbon or ceramic fibers. The Weibull modulus of metallic fibers is an order of magnitude higher than that of ceramic fibers. The strength of steel fibers is mainly controlled by its carbon content and its microstructure (ferritic grain size and the interlamellar spacing in the pearlitic regions.) The microstructure is determined by composition and final working conditions. I will focus mostly on eutectoid steel filaments used in making cables for suspension bridges.

9:00 AM  Invited
Indentation Probes for Measurements of Localized Materials Properties: David Bahr1; Michael Maughan2; Raheleh Mohammad Rahimi1; 1Purdue University; 2University of Idaho
    Instrumented indentation using spherical or sphero-conical probes allows for spatially resolved probes of elastic and plastic properties of materials, including the onset of plasticity. Spherical indentations have the ability to probe strain hardening behavior, but similarly have the added complication of deconvoluting size effects from spatial variations. In this presentation the issue of the appropriate length scale to be used for measuring properties of a wide range of engineering materials is addressed, and applied to several structure material systems, including the effects of residual stresses and deformation gradients in shot peened and severely plastically deformed materials. Parameters for predicting the minimum size needed to create statistically valid test volumes with indentation will be discussed.

9:20 AM  Invited
Spherical Nanoindentation Stress-strain Curves: Surya Kalidindi1; 1Georgia Institute of Technology
    This paper reviews the recent progress made in extracting meaningful indentation stress-strain curves from the raw datasets measured in instrumented spherical nanoindentation experiments. Much of this recent progress was made possible through the introduction of a new measure of indentation strain and the development of new protocols to locate the effective zero-point of initial contact between the indenter and the sample in the measured datasets. This has led to an important key advance in this field where it is now possible to reliably identify and analyze the initial loading segment in the indentation experiments. Major advances have also been made in correlating the local mechanical response measured in nanoindentation with the local measurements of structure at the indentation site using complementary techniques.

9:40 AM  Invited
Surface Finish Effects on Fracture Behavior of Sn-4Ag-0.5Cu Solder Joints: Jamie Kruzic1; Dick Casali2; 1UNSW Australia; 2Intel Corporation
    Lead free solders have only been widely used by industry in consumer microelectronics since 2006. One area of research not fully explored is the effects of copper surface finishes on the mechanical properties of a microelectronics solder joint experiencing shock conditions. The addition of a surface finish should influence the solder and interface metallurgy, which in turn will affect the deformation behavior and high strain rate interfacial fracture toughness. The present paper examines the effect of using bare copper, immersion silver, nickel-gold, and organic solderability preservative surface finishes on the interfacial fracture toughness of simulated solder joint samples. Additionally, the effects of surface the finishes on the solder microhardness and solder joint microstructure are examined using optical and electron microscopy. The overall aim is to determine the ‘surface finish-microstructure-mechanical property’ relationship for Sn-4Ag-0.5Cu solder joints used in ball grid arrays experiencing shock loading conditions.

10:00 AM Break

10:15 AM  Invited
The Wigner Energy Spectral Fingerprints of Radiation Damage: Penghui Cao1; Sean Lowder1; Ki-Jana Carter1; Michael Short1; 1Massachusetts Institute of Technology
    The current unit of radiation damage, the displacements per atom (DPA), is a calculated exposure parameter that does not directly yield the defect populations responsible for irradiation-induced material properties. Were an 'a posteriori' measure of radiation damage to exist, it would help to answer numerous, lingering questions about the nature and effects of irradiation. We propose the use of Wigner energy spectral fingerprints as this new unit of radiation damage. They can be measured after irradiation, and they yield information about the resulting defect populations. We present a combination of time-accelerated molecular dynamics (MD) simulations and differential scanning calorimetry (DSC) measurements, which together paint a more measurable picture of the multiscale nature of radiation damage. Potential applications range from settling the neutron/ion equivalency question, to quantitatively understanding dose rate effects, to using nanocalorimetry to verify historical uranium enrichment.

10:35 AM  Invited
Mechanical and Microstructural Effects of Thermal Aging on Cast Duplex Stainless Steels by Experiment and Finite Element Method: Samuel Schwarm1; Sarah Mburu1; R. Prakash Kolli1; Daniel Perea2; Jia Liu2; Sreeramamurthy Ankem1; 1University of Maryland, College Park; 2Pacific Northwest National Laboratory
    Cast duplex stainless steel piping in light water reactors experience thermal aging embrittlement during operational service. Interest in extending the operational life to 80 years requires an increased understanding of the microstructural evolution and corresponding changes in mechanical behavior. We analyze the evolution of the microstructure during thermal aging of cast CF–3 and CF–8 stainless steels using electron microscopies and atom probe tomography. The evolution of the mechanical properties is measured concurrently by mechanical methods such as tensile tests, Charpy V-notch tests, and instrumented nanoindentation. A microstructure-based finite element method model is constructed and utilized in conjunction with the characterization results in order to correlate the local stress-strain effects in the microstructure with the bulk analysis. This work is supported by the Nuclear Energy University Programs (NEUP), contract number DE-NE0000724.

10:55 AM  Invited
Digital Stress Imaging in Mesoscale Microstructure Dependent Deformation Visualized Using Nano-mechanical Raman Spectroscopy: Role of Initial Manufacturing Originated Residual Stresses: Vikas Tomar1; 1Purdue University
    This talk will focus on work done in my group with emphasis on direct measurements of stresses during mesoscale microstructural deformation of Ni based and Zr based alloys during 3-point bending tests for fracture toughness at elevated temperatures. A novel nano-mechanical Raman spectroscopy measurement platform was designed for temperature, stress, and chemistry mapping at micro to nanoscale for different temperature and load conditions. During the 3-point bending test to measure fracture toughness , notch tip plastic stresses as a function of microstructure, load, and temperature, with micron scale resolution were measured. The temperature field distribution was correlated to stress distribution and residual microstructure stresses around the area of the notch tip. A new finite element method formulation that incorporated different elastic and plastic material properties from indentation experiments at different locations was validated. We find that residual stress is an important indicator of scatter in material failure data.

11:15 AM  
Fracture Behavior and Grain Boundary Sliding during High-temperature Low-stress Deformation of AZ31 Magnesium Alloy: Peiman Shahbeigi Roodposhti1; Korukonda Murty2; 1University of Connecticut; 2North Carolina State University
    Low-stress, high-temperature creep tests were conducted on AZ31 Magnesium alloy to clarify the creep mechanisms and fracture behaviors. A stress exponent of ~2 and activation energy close to that for grain boundary diffusion indicate grain boundary sliding as the dominant creep mechanism in this regime. Many stress concentrated sites were developed by precipitates, and grain boundary sliding mechanism lead to diffusional cavity formation and premature failures. Both ductile and brittle types of fracture were observed on the rupture surfaces. X-ray diffraction line profile analysis, based on Williamson-Hall and Williamson-Smallman techniques employed to evaluate the dislocation density in the steady state region. Analyses revealed a reduction in dislocation density of crept samples due to dynamic recovery (DRV). A reasonable correlation is noted between experimental data and Langdon’s model for grain boundary sliding.

11:35 AM  Cancelled
On the Strain Rate Sensitive Characteristics of Nanocrystalline Aluminum Alloys: Koteswararao Rajulapati1; 1University of Hyderabad
    Traditional engineering applications demand adoption of multiphase materials or composites. Therefore in the current study, nanocrystalline aluminium was reinforced with Pb, W, Al12W, Pb-W phases with nano sized features. These materials were processed using ball milling and were subsequently compacted into bulk forms using spark plasma sintering. The structural characterization was done using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and scanning probe microscopy. Their mechanical behavior was studied using Vickers microindentation and nanoindentation. Nanoindentation was done at different peak loads and loading rates to understand the rate-sensitive deformation characteristics. Strain rate sensitivity and activation volume were measured to have insights on the associated deformation mechanisms. The observed flow behavior has been correlated with the microstructural features of these novel multi-phase nanocrystalline alloys.