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.

4:15 PM  Invited
Compatibility of a Complex Concentrated Alloy with Non-aqueous Coolants: Justin Lee1; Timothy White1; Rajiv Mishra2; James Earthman1; 1University of California, Irvine; 2University of North Texas
    A number of nonaqueous coolants such as various molten salts, sodium and lead-bismuth have been targeted for advanced nuclear reactor facilities. Stainless steels and Ni-based superalloys have often been considered for these applications, at least to some extent because they were already approved for conventional nuclear applications. However, the structural and environmental requirements of advanced next-generation reactor systems are likely to be best met by alloys that are designed for the non-aqueous coolants that will be employed. The present research investigates a recently developed complex concentrated (high entropy) alloy under biaxial stresses in non-aqueous liquids that are possible coolants in next generation power generation facilities. This single-phase face-centered cubic alloy, Al0.1CoCrFeNi, has potential for producing passive surface layers in a number of different environments at elevated temperatures.

4:35 PM  Invited
Radiation Response of Nanotwinned Metals: Xinghang Zhang1; Jin Li2; Cuncai Fan1; Kaiyuan Yu3; Youxing Chen4; Haiyan Wang1; 1Purdue University; 2Texas A&M University; 3China University of Petroleum; 4Los Alamos National Laboratory
    Design of radiation tolerant materials for application in extreme radiation environment is a significant scientific challenge. Numerous types of defect sinks, such as grain boundaries and phase boundaries, have been applied to mitigate radiation damage. Twin boundaries have been long considered as ineffective defect sinks. In this presentation, we will review some of our recent studies on radiation tolerance of nanotwinned metals. In situ Kr ion irradiation in a transmission electron microscope, reveal drastic different response of nanotwinned metal to Kr ion irradiation damage compared to their bulk counterparts. Defect migration kinetics (diffusivity of defect clusters) was determined in coarse grained and nanotwinned metals. These studies provide a different perspective towards understanding of twin boundary enabled significant enhancement of radiation tolerance in nanostructured metallic materials.

4:55 PM  Invited
Influence of Fine Scale Alpha Precipitation on the Mechanical Properties of the Beta Titanium Alloy Beta-21S: Srinivas Mantri1; Deep Choudhuri1; Rajarshi Banerjee1; 1University of North Texas
    Microstructures containing a high volume fraction of very fine-scale alpha precipitates were produced in the β-21S alloy by introducing a low temperature (~400C) annealing step during the heat-treatment. Specimens with fine-scale alpha exhibited substantially higher strengths (~1200MPa) compared to those containing coarser alpha precipitates (~950 MPa). Furthermore, reasonable tensile elongation values ~8% to failure could be achieved for these high strengths provided grain boundary fracture can be limited. Failure mechanisms responsible for the mechanical response of the fine-scale alpha microstructures will be discussed in the presentation.

5:15 PM  Invited
Emulating Neutron Damage in Nanocrystalline Copper via In-situ Ion Irradiation: Walid Mohamed1; Sumit Bhattacharya2; Laura Jamison1; Marquis A. Kirk1; Korukonda Murty3; Abdellatif Yacout1; 1Argonne National Laboratory; 2Northwestern University; 3NC State University
    The hypothesis that nanocrystalline (nc) materials should possess enhanced radiation tolerance characteristics remains questionable to date considering the remarkable deviation in experimental observations reported in this regard. Emulating neutron damage in materials through controlled ion irradiation experiments has accelerated nuclear materials development by avoiding typical shortcomings of neutron irradiation. In this work, the IVEM Tandem facility is used to irradiate samples of nc-copper up to temperatures and doses similar to that of neutron irradiation experiments conducted on the same material. While irradiation induced grain growth controlled the response of nc-copper to neutron irradiation starting at relatively low damage level (dpa < 0.01), irradiation hardening became dominant at dpa > 1 dpa. Interestingly, minimal grain growth was observed in nc-copper irradiated with 1 MeV Kr+ ions up to 2 dpa. Further ion irradiation experiments are in progress to investigate any potential effect of dose rate and TEM foil thickness.