Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Poster Session
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 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr

L-114: Effects of Blade Curvature on Fatigue Life of Nickel-based Single Crystal Structures with Film-cooling Holes: Zhixun Wen1; Yamin Zhang1; Youliang Li1; Zhufeng Yue1; 1Northwestern Polytechnical University
    The curved thin-walled structures of multi film cooling holes with different curvatures were adopted to simulate film cooling turbine blades. The low cycle fatigue (LCF) characteristic was studied based on the theory of crystallographic slip damage. The resolved shear stress of slip systems, distribution of fatigue damage and LCF life were analyzed. Results show that there are obvious stress interferences among cooling holes, and the stress distribution is diamond-shape. Two slip bands around the holes were found to be lied on the line at approximately 45 to 135 with respect to the loading axis. The maximum resolved shear stress reduces with the increase of curvature radius. Meanwhile, the LCF life increases positively related with the curvature radius. When curvature radius is less than 13mm, the curvature radius has a remarkable effect on the resolved shear stress and LCF life, however, when the curvature radius exceed 13mm, the curved structure can be replaced with the plate structure. Furthermore, an exponential curve is found to be fit for the relation between the curvature radius and the logarithmic fatigue life.

L-115: Understanding of Microstructure and Mechanical Properties of Friction Stir Processed Aluminum-bearing High-Chromium Ferritic Stainless Steel: Anumat Sittiho1; Vedavyas Tungala2; Indrajit Charit1; Rajiv Mishra2; 1University of Idaho; 2University of North Texas
    There are many issues that affect performance of fusion welds in high-Cr ferritic steels. Friction stir welding (FSW) can be developed as a promising solid state welding technique. Here FSW is applied to a Kanthal APMT steel (Fe-22Cr-5Al-3Mo) plate in a bead-on-plate configuration using a tool rotation rate of 600 rpm and traverse speed of 25.4 mm/min. Vickers microhardness testing across the weld zone did not reveal any significant change. Optical microscopy and transmission electron microscopy are conducted to characterize the microstructure in different regions of the weld (base material, HAZ, TMAZ). The stir zone contains an equiaxed grain structure with a mean grain size of 21 μm. Dispersed particles in the stir zone are found to have coarsened compared to the base material. Furthermore, tensile testing across the weld is performed. Correlations between the microstructure and mechanical properties are established by elucidating the underlying strengthening mechanisms.

L-116: In Situ Investigation on the Micromechanical Behavior of the CuZr-based BMGC by Neutron Diffraction: Dongmei Wang1; Ke An2; Juan Mu3; Yan Chen2; Yandong Wang3; Haijian Xu3; 11.Northeastern University 2.Oak Ridge National Laboratory; 2Oak Ridge National Laboratory; 3Northeastern University
    The micromechanical behavior of CuZr-based Bulk Metallic Glass Composite (BMGC) was investigated by in-situ neutron diffraction technique through three loading-unloading stages with different stress maxima. An inconspicuous martensite peak is observed throughout the 2nd cycle but the remarkable martensitic transformation takes place at a strain of ~-2.2% in the 3rd cycle. The critical stress for the martensitic transformation cannot be determined considering the effect of the residual stress. The pseudoelastic behavior is associated with the martensitic transformation and the work hardening rate is attributed to the different deformation modes of the B2 and amorphous phase. The higher fracture strength and limited total strain are determined by the volume fraction of the amorphous and B2 phase. The interphase and intergranular stress redistribution contribute to the macro-mechanical properties.

L-117: Mechanical and Creep Behavior of EPDM: Saeed Babamohammadi1; Jahan Rasty1; 1Texas Tech University
    EPDM , a type of synthetic rubber, is an elastomer used in roofing systems. Roof assembly consists of structural base element, like fibrous deck as the substrate layer that is fully adhered to top layer EPDM membrane that covers the system and prevents damage and water intrusion. The focus of research was to study the nature and threshold of damage caused by hailstone impact on fully adhered EPDM used in roofing systems. Hail impact experiments were conducted on EPDM of various thicknesses using a hailgun, projecting ice balls at hailstone terminal velocities. Irrecoverable damage to the roofing structure was defined by loss of adhesion between EPDM and the underlying substructure, which makes EPDM susceptible to tearing failure as a result of cyclic wind load. In addition, dynamic Finite Element Analysis (FEA) of hail impact on EPDM were performed using LSDYNA finite element for comparison with the experimental results.

L-118: High Temperature Tensile Properties and Related Microstructural Evolution of Grade 92 Steel: Sultan Alsagabi1; Somayeh Pasebani2; Indrajit Charit3; 1King Abdulaziz City for Science and Technology - KACST; 2Oregon State University; 3University of Idaho
    Ferritic-martensitic steels with good high temperature mechanical properties have many promising applications in fossil and nuclear power plants. In this work, a F92 steel was tensile tested from room to elevated temperatures (up to 700oC). This material exhibited higher strength than traditional P92 steels. The reasons for the observed changes in mechanical properties were investigated by studying microstructural characteristics in deformed specimens using transmission electron microscopy. The microstructural evolution accelerated significantly under loading as temperature increased. For instance, the deformed microstructure at 600C showed early stages of M23C6 precipitate formation under loading. These M23C6 precipitates showed more coarsening tendency whereas the MX-type precipitates retained their size. As coarsening of M23C6 precipitates progressed at elevated temperatures, the strength gradually decreased as the solid solution strengthening deteriorated by removing W and Mo from the solid solution matrix. High temperature creep properties of this steel is also discussed.

L-119: Mechanical Properties and Serrated Flow in Al-bearing, High-Cr Accident-tolerant Ferritic Steel: Ankan Guria1; Indrajit Charit1; 1University of Idaho
    Following the Fukushima-Daiichi incident, there has been considerable interest in developing accident-tolerant fuel cladding materials to make light water reactors (LWRs) safer. Zircaloys are used as the fuel cladding materials in the current LWRs. Under off-normal conditions such as loss-of-coolant accidents (LOCA), exothermic reactions of Zr with steam can lead to severe consequences. In this study, an aluminum-bearing ferritic steel (e.g. Kanthal APMT steel) is investigated to evaluate its feasibility for accident-tolerant fuel cladding applications for an advanced LWR (I2S-LWR) concept under development. Tensile properties of the steel are compared with those of Zircaloys and other steels. Presence of serrations in stress-strain curves of APMT steel under certain test conditions revealed the occurrence of dynamic strain aging. Microstructural characteristics of the deformed specimens are examined by scanning and transmission electron microscopy. The work is supported by the DOE Office of Nuclear Energy’s Nuclear Energy University Programs (NEUP).

L-120: Spherical Nanoindentation Creep Behavior of Indium at Room Temperature: Woo-Jin Kim1; Jung-A Lee1; Yakai Zhao1; Jae-il Jang1; 1Hanyang University
    For investigating time-dependent plastic deformation (i.e., creep) that is known to become more pronounced at small scale, nanoindentation creep test has been widely performed. Recently, some efforts have been made in applying spherical indenter to the research on creep properties, which can overcome some issues related to the use of a sharp indenter. However, in spherical indentation creep, systematic investigation on the effect of various experimental factors is limited by far. Therefore, in this study, the creep deformation of indium, a suitable material for studying room temperature creep due to its low melting temperature, was systematically explored through a series of spherical nanoindentation creep experiments with various indenter radii. From the relation between creep strain rate and maximum stress, the creep stress exponent and the activation volumes were estimated. The obtained results were analyzed in terms of the influences of experimental conditions such as tip radius and creep stress.