Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Introductory Session: Unique Mechanical Behavior and Technologies
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

Monday 8:30 AM
February 27, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Indrajit Charit, University of Idaho; Yuntian Zhu, North Carolina State University

8:30 AM Introductory Comments: A short commentary on Prof. K. Linga Murty's short biography and seminal contributions to the field of mechanical and creep behavior of materials

8:35 AM  Keynote
Creep, Deformation and Fracture Studies of Materials for Various Technologies in the Nuclear Materials Research Group at NC State: Korukonda Murty1; 1North Carolina State University
    A brief outline of the research activities during the past 3 decades in the Nuclear Materials Research group at NC State University will be summarized that comprise of creep mechanisms in materials, reliability of solders in electronic packaging, DSA and radiation embrittlement of ferritic steels, anisotropic biaxial creep of hcp metals with emphasis on Zircaloy cladding, condition monitoring of structural materials using ABI, non-interactive NMR studies of dynamical behavior of point and line defects during deformation, and radiation effects in nanocrystalline materials. All the described aspects are the outcomes of research experiences of the author starting from his MS thesis at Cornell University on creep of alpha iron and doctoral thesis research on NMR studies followed by post-doctoral research at the University of California in Berkeley on creep and superplasticity, and University of Newcastle, Australia on radiation effects on yield point phenomena in steels.

9:05 AM  Keynote
Fundamental Discovery of Q-phases and Direct Conversion of Carbon into Diamond and h-BN into c-BN: Jagdish (Jay) Narayan1; Anagh Bhaumik1; 1North Carolina State University
    This lecture addresses fundamental underpinnings of Q-phases and direct Conversion of carbon into diamond and h-BN into c-BN in the form of nanocrystals, microcrystals, nanoneedles and microneedles, and large-area single crystal films for a variety of applications, ranging from abrasives and cutting tools to biosensors and biomedical applications. Mechanical properties are controlled by defects such as twins. According to the phase diagram it can be done only at very high pressures and temperatures (over 120,000Atm and 5000K). Our recent discovery showed that carbon can be converted directly into diamond at atmospheric pressure and ambient temperature in air by laser melting and quenching the super undercooled state. The undercooled state can be quenched into a new state of carbon (Q-carbon) or diamond or the mixture of the two. Similarly, h-BN can be converted into Q-BN or c-BN or the mixture of the two by controlling the undercooling and quenching rate.

9:35 AM  Invited
Anisotropy and Creep Mechanisms during the Hot Forming of Light Alloy Sheet Materials: Eric Taleff1; 1The University of Texas at Austin
    Prof. K. L. Murty laid much of the foundation for our understanding of plastic anisotropy during creep deformation through his enduring investigations of zirconium alloys. Recent investigations into the hot forming of light alloy sheet materials remind us of that fundamental work. Wrought magnesium alloys are of interest for vehicle mass reduction. One route to application that was commercially demonstrated is hot gas-pressure forming of sheet into a complex vehicle closure component. The HCP crystal structure of magnesium, however, can lead to significant plastic anisotropy during forming, which fundamentally depends on the active creep mechanisms. Even in cubic metals, creep mechanisms can produce interesting and unexpected asymmetric effects. The aluminum alloys most commonly used for superplastic forming evidence an asymmetric response to hydrostatic stress, for example. This presentation reviews these effects of creep deformation mechanisms to demonstrate the continued importance of creep anisotropy and asymmetry to technological applications.

9:55 AM Break

10:10 AM  Keynote
In-situ TEM Observation of the Peculiar Movement of <c+a> Dislocations in Mg: Dalong Zhang1; Lin Jiang1; Irene Beyerlein2; Julie Schoenung1; Subhash Mahajan3; Enrique Lavernia1; 1University of California-Irvine; 2Theoretical Division, Los Alamos National Laboratory; 3Chemical Engineering and Materials Science, University of California, Davis
    The mechanism of pyramidal slip, namely the movement of <c+a> dislocations in HCP materials has long been debated. By means of transmission electron microscopy (TEM) observation or molecular dynamics (MD) simulation, different authors have proposed contradicting mechanisms. In particular, based on long-time MD simulations utilizing a recently developed density-functional-theory-validated interatomic potential, one recent report claims to have revealed the linkage between the high hardening/low ductility in Mg and the dissociation of mobile <c+a> dislocations onto basal plane, resulting in sessile configurations which impede further <c+a> dislocation movement. In this talk, we present our most recent in-situ TEM results that would confirm the above-mentioned predictions: (1) New <c+a> dislocations are scarcely nucleated; (2). They quickly move then align with the trace of basal plane; (3) Some <c+a> dislocation with the two ends aligned with basal plane further move by slowly bowing out.

10:40 AM  Invited
The Representation of Grain Boundary Texture Using Hyperspherical Harmonics: Srikanth Patala1; Jeremy Mason2; 1North Carolina State University; 2Boğazii University
    At high temperatures, microstructural evolution in polycrystalline materials is profoundly influenced by the grain boundary properties (energies, and mobilites) and their anisotropies. However, even for simple microstructures, the capability of representing the distributions of GB character, as a function of the five macroscopic degrees of freedom, has not been established. As the statistical distributions directly influence the interfacial network connectivity, developing a framework for quantifying GB distributions is a crucial missing step in the inverse-design of interface-dominated phenomena in polycrystalline systems. In this talk, I will present symmetrized functions, using the familiar hyperspherical harmonics, for representing grain boundary texture in the five-parameter space. The basis functions will also allow for the interpolation of structure-property relationships of grain boundaries, quantification of interfacial statistics in experimental microstructures.

11:00 AM  Invited
Irradiation Creep of Zr-Alloys: Malcolm Griffiths1; Grant Bickel1; Robert DeAbreu1; Wenjing Li1; 1Canadian Nuclear Laboratories
    Irradiation creep of Zr-alloy nuclear reactor core components affects the reactor performance and also limits the reactor life in cases where those components cannot easily be replaced. For Zr-2.5Nb pressure tubing irradiation creep has been extensively studied for a range of temperatures, between 250 C and 350 C, and dose rates, between 1 x 1016 nm-2s-1 and 2 x 1018 nm-2s-1 (E> 1MeV), using data from various materials test reactors and power reactors. These studies have shown that irradiation creep is controlled by a complex combination of slip and diffusional mass transport (referred to as irradiation growth in the absence of stress). Irradiation creep is dependent on the crystallographic texture, the dislocation structure, and the grain structure; the importance of each being a function of irradiation temperature and displacement damage rate. Data will be presented, together with mechanistic modelling, to show what factors affect creep under different irradiation conditions.

11:20 AM  
The Microstructural Evolution of Hot Deformed Ti-IF Steel: Philip Noell1; Ryann Rupp1; Eric Taleff1; 1The University of Texas at Austin
    Deformation at elevated temperatures can accelerate grain growth, leading to the general observation that dynamic grain growth is faster than static grain growth. This effect is particularly important to material processing and service at high temperature. For this study, dynamic grain growth was observed in a Ti-added interstitial-free (Ti-IF) steel during uniaxial tensile deformation to true strains of 0.1 and 0.2 at temperatures in the vicinity of 800°C and a true-strain rate of 10-4 s -1 . This dynamic grain growth strengthens the {111}<110> and {112}<110> texture components. X-ray diffraction, backscattered electron channeling microscopy, and electron backscatter diffraction were used to characterize microstructure in the deformed gauge and undeformed grip regions of tensile-test specimens. Texture is found to sharpen with increasing grain size. It is hypothesized that the observed texture evolution is the result of dynamic normal grain growth preferentially accelerating the growth of grains with specific crystallographic orientations.

11:40 AM  Invited
Effect of Mo and Bi Additions on the Microstructure of Zr-Cr-Fe Alloy after β-quenching: Jianmin Wang1; Baifeng Luan1; Korukonda Murty2; Qing Liu1; 1Chongqing University; 2North Carolina State University
    This work investigates the solid-states phase transformation behavior of Zr-Cr-Fe alloys during rapid cooling from β-phase region. SEM was used to characterize the microstructure evolution of Zr-Cr-Fe alloys containing different Mo and Bi contents. The results show that two different phase transformation modes involved during β to transformation for different domains within prior grains: (i) Martensitic transformation resulting in lath-shaped grains occurs within prior grain interiors. (ii) Massive transformation generating massive-shaped grains initiated along two adjacent prior β parent grain boundaries. a lath width reduced with increasing Mo concentration while Mo strongly retards massive phase transformation. Interestingly microstructures exhibited no significant variation the case of specimens containing different Bi contents irrespective of the phase transformation modes.