Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Advanced Materials and Processing
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

Tuesday 2:00 PM
February 28, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Peter Liaw, University of Tennessee; Somayeh Pasebani, Oregon State University

2:00 PM  Keynote
Microstructure, Texture and Mechanical Properties of the 14YWT Nanostructured Ferritic Alloy NFA-1: G. Robert Odette1; Md Ershadul Alam1; Soupitak Pal1; Takuya Yamamoto1; 1University of California Santa Barbara
    It is a privilege to address the topic of the mechanical performance of advanced structural alloys, in this symposium honoring the lifetime achievements of Professor K. L. Murty, on the occasion of his 75th birthday. We first describe the temperature-dependent deformation and fracture properties of a 14YWT nanostructured ferritic alloy (NFA) plate. Deformation and fracture are accompanied by extensive delamination due to the propagation of pre-existing {100}<110> low toughness cleavage oriented microcracks. We then describe the <110> fiber texturing and cleavage system formation mechanisms leading to the microcracking found by detailed dislocation level TEM studies. We next describe how the texturing and microcracking can be modified by both stress-state control during subsequent hydrostatic extrusion and high temperature heat treatments. The microcracked plate provides a laboratory to study the fundamental mechanisms of the micro-cleavage fracture brittle-to-ductile transition. Notably, our observations rationalize the universal shape of the macro toughness-temperature master curve.

2:30 PM  Invited
Dynamic Behavior of a Nanocrystalline Cu-Ta Alloy: Scott Turnage1; Kris Darling2; Mansa Rajagopalan1; Chad Hornbuckle2; Kiran Solanki1; 1ASU; 2ARL
    This investigation analyzes the compressive high strain rate (103 to 104 s-1) mechanical behavior of a nanocrystalline (<100 nm mean grain size) Cu 10 at.% Ta alloy processed through ball milling followed by equal channel angular extrusion. High strain rate behavior is measured with a split Hopkinson pressure bar at temperatures ranging from 25 ˚C to 800 ˚C. For comparison, quasistatic tests (10-3 s-1) are also reported for the same range of temperatures. Aberration corrected transmission electron microscopy (TEM) is performed to analyze the microstructure of the samples before and after testing. Results show the effects of both temperature and strain rate on flow stress. Microstructure and mechanical behavior data reveals that twin and grain growth as a result of increased temperature cause phonon drag to play a more significant role at lower strain rates.

2:50 PM  
The Creep-resistant High Entropy Alloys (HEAs): Haoyan Diao1; Dong Ma2; Wei Guo2; Jonathan Poplawsky2; Chuan Zhang3; Fan Zhang3; Karin Dahmen4; Peter Liaw5; 1The University of Tennessee ; 2Oak Ridge National Laboratory; 3CompuTherm, LLC; 4University of Illinois at Urbana-Champaign; 5The University of Tennessee
    To create and design novel structural materials with the enhanced creep resistance, high-entropy alloys (HEAs) have attracted the interest of many scientists. In contrast to traditional alloys, HEAs have revolutionized alloy-design approaches, by employing the use of multi-principal elements. HEAs have shown to be suitable materials for elevated-temperature applications. Appropriate heat-treatments can successfully induce NiAl precipitates into the FCC matrix in HEAs and increase the yield strength. The fundamental creep and stress relaxation studies on both single-phase and NiAl-strengthened AlxCoCrFeNi have been performed at different stress levels and temperatures, using in-situ neutron diffraction. The microstructural evolution during creep test has been investigated by the atom probe tomography (APT) and transmission electron microscopy (TEM). The thermodynamics and kinetics of NiAl precipitates has been studied, through an integrated approach, i.e. coupling modeling [thermodynamic calculations and crystal-plasticity finite-element modeling (CPFEM)] with advanced experiments, to identify HEAs that outperform conventional alloys for high-temperature applications.

3:10 PM  Invited
Structure-property Correlations in Metallic Components Synthesized Using Selective Laser Melting: Upadrasta Ramamurty1; 1Indian Institute of Science
    Selective laser melting (SLM) is a commonly used method for additive manufacturing of metallic components. It not only imparts a substantially finer microstructure but also a distinct mesoscale structure to them. A complex interplay between these micro- and meso-structural features can lead to property combinations that were hitherto thought as not possible. The possible presence of residual stresses and microporosity will also affect the properties. This will be examined in this presentation through the results of the characterization of several different alloy components made through SLM, with particular emphasis on understanding their quasi-static tensile, fracture, fatigue crack growth, and unnotched fatigue properties. We will demonstrate that while the SLM process offers new avenues for material design that can exploit the micro- and meso-structures generated by the process for simultaneous enhancement in strength and toughness, their fatigue resistance is a big concern due to the porosity.

3:30 PM Break

3:45 PM  Keynote
Design of Creep-resistant Copper Alloys: Steven Zinkle1; Ying Yang2; Lance Snead3; 1University of Tennessee; 2Oak Ridge National Laboratory; 3Massachusetts Institute of Technology
    High strength, high conductivity copper alloys are useful for a variety of applications including welding electrodes, high field magnets and thermal management substrates. Although yield strengths of 300-1000 MPa and conductivities 200-360 W/m-K have been achieved, all current commercially available high strength, high conductivity Cu alloys suffer significant thermal creep deformation at temperatures above 300-400°C and therefore these copper alloys are not suitable for structural applications above ~300°C. Analysis of deformation mechanisms near 300-400°C suggests the creep deformation is controlled by dislocation (power law) creep and grain boundary sliding creep mechanisms. Computational thermodynamics was used to design a series of new Cu-Cr-Nb-Zr alloys with intermediate-size Cr2Nb and Cu5Zr particles to pin grain boundary sliding and fine-scale Cr precipitates to suppress dislocation creep after suitable heat treatment and thermal aging. Room temperature conductivity and elevated tensile and thermal creep properties of the newly designed alloys will be presented.