Mechanical and Creep Behavior of Advanced Materials: A SMD Symposium Honoring Prof. K. Linga Murty: Mechanical Behavior of Titanium and Zirconium Containing Alloys
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 2:00 PM
March 2, 2017
Room: 24A
Location: San Diego Convention Ctr

Session Chair: Raj Vaidyanathan, University of Central Florida; Indrajit Charit, University of Idaho

2:00 PM  Keynote
Microstructure-property Interrelationships in Metastable Beta Titanium Alloys with Refined Distributions of the Alpha Phase: Yufeng Zheng1; Gopal Viswanathan1; Rajarshi Banerjee2; Hamish Fraser1; 1The Ohio State University; 2University of North Texas
    In the recent past, there has been much interest in the development of super-refined distributions of the alpha phase in a beta matrix in metastable beta titanium alloys. This paper will describe the metallurgical factors that influence the heterogeneous nucleation of the alpha phase, in these alloys, which results in these refined distributions. These factors involve instabilities (soft phonon modes) in the beta phase, and these have been directly observed using high resolution electron microscopy. The interest in these super-refined distributions of the alpha phase involves the anticipated new balances of properties that may result. The second part of this presentation will describe the interrelationships between microstructure and mechanical properties (tensile deformation), with an emphasis on the development of an understanding of the mechanisms of deformation, in these metastable beta titanium alloys. This research involves deformation of the hcp alpha phase, in line with the work of Prof. K.L. Murty!

2:30 PM  Invited
Increasing the Elevated-temperature Strength of a Beta Titanium Alloy through Thermomechanically-induced Phase Transformation: Vahid Khademi1; Carl Boehlert1; Masahiko Ikeda2; 1Michigan State University; 2Kansai University
    The effects of temperature and thermomechanical loading on the elevated-temperature tensile strength, deformation behavior, and phase transformation were studied for a low-cost metastable beta titanium alloy: Ti-13Cr-1Fe-3Al (wt.%). In-situ and ex-situ tensile tests were performed at temperatures between 25 C to 500 C. TEM was performed to investigate the phase transformation behavior, and the strength and Vickers hardness were compared at different loading conditions. The beta phase transformed to the omega phase under a combination of load and time at temperature. The temperature range of the phase transformation was investigated by dynamic mechanical analysis and compared with data from differential scanning calorimetry and electrical resistivity techniques. Slip trace analysis indicated that dislocation slip is the primary deformation mechanism. Both temperature and thermomechanical loading have a significant influence on deformation mode, phase transformation, and tensile strength, which can be increased by over fifty percent at elevated temperatures.

2:50 PM  Invited
In Situ Neutron Diffraction Studies of Crystallographic Texture at Stress and Temperature with Implications for Training Shape Memory Alloys: Raj Vaidyanathan1; 1University of Central Florida
    The overall objective of this work is to provide connections between crystallographic texture and thermomechanical deformation in shape memory alloys (SMAs). Specifically, three deformation modes are assessed: (i) isothermal (deformation at constant temperature), (ii) isobaric (thermal cycling to temperatures above and below the phase transformation temperatures under constant stress), and (ii) isostrain (thermal cycling to temperatures above and below the phase transformation temperatures under constant strain). This is accomplished by subjecting a polycrystalline NiTi (nominal composition 49.9 at.% Ni) SMA to in situ neutron diffraction at Los Alamos National Laboratory and Oak Ridge National Laboratory under stress and temperature wherein the evolving texture is determined in carefully selected experiments involving combined uniaxial and/or multiaxial loading sequences. The results are analyzed and presented in the context of their implications for training these alloys for engineering applications.

3:10 PM  
Correlating Variability in Fatigue Life with Fracture Mechanisms in a Near-α Titanium Alloy: Vikas Sinha1; Sushant Jha2; Adam Pilchak3; Reji John3; James Larsen3; 1Air Force Research Laboratory/UES, Inc.; 2Air Force Research Laboratory/Universal Technology Corporation; 3Air Force Research Laboratory
    Unlike the quasi-static mechanical properties, such as strength and ductility, fatigue life can vary significantly for nominally identical material and test conditions in many materials, including Ti-alloys. This makes life prediction and management more challenging for components that are subjected to cyclic loading in service. The differences in fracture mechanisms can cause the variations in fatigue life. In this study, the fatigue fracture mechanisms are investigated in a near-a titanium alloy, Ti-6Al-2Sn-4Zr-2Mo, which had been tested under condition that resulted in life variations by more than an order of magnitude. Both short and long life specimens are examined for this alloy in two different microstructural conditions. The crack-initiation and small crack growth processes, including their contributions to fatigue life variability, are elucidated via quantitative characterization of fatigue fracture surfaces. The spatial and crystallographic orientations of fracture features were determined in an SEM with quantitative tilt fractography and EBSD, respectively.

3:30 PM Break

3:40 PM  Invited
Creep of Zirconium and Zirconium Alloys: Troy Hayes1; Michael Kassner2; 1Exponent; 2University of Southern California
    Controlling mechanisms for creep of zirconium and zirconium alloys continue to be debated. In previous studies, the authors analyzed cumulative zirconium and zirconium alloy creep data over a broad range of stresses (0.1 to 115MPa) and temperatures (300 to 850°C) based on a literature review and experiments. Zirconium obeys traditional power-law creep with a stress exponent of approximately 6.4 over stain-rates and temperatures usually associated with the conventional “five-power-law” regime. The measured activation energies for creep correlated with the activation energies for zirconium self-diffusion. Thus, dislocation climb, rather than the often assumed glide mechanism, appears to be rate controlling. The stress exponents of the creep data in the five-power-law regime for Zircaloy-2 and Zircaloy-4 were determined to be 4.8 and 5.0, respectively. Further advances in the understanding of the controlling mechanisms for zirconium and zirconium alloys will be presented based on a review of the literature over the past decade.

4:00 PM  
Study of Accelerated Creep Behaviour of Zr-2.5Nb Pressure Tubes: Avinash Gopalan1; Harshit Khandelwal1; Sandeep Chandanshive1; Ram Singh1; 1Bhabha Atomic Research Center
    The pressure tubes in Indian Pressurized Heavy Water Reactors are made from Double Melted (DM) ingot or Quadruple Melted (QM) Zr-2.5Nb ingots. For safety assessment of the reactors, the creep deformation occurring normal to the tube axis is one of the important properties to be characterised. In present work, creep behaviour of Zr-2.5Nb pressure tube manufactured from both DM and QM ingots is studied. Tests have been performed at three different temperatures each corresponding to three different stress levels. The activation energy of creep deformation and stress exponent were evaluated and it was found that the results were in close range for DM and QM specimens.

4:20 PM Concluding Comments