Fatigue in Materials: Fundamentals, Multiscale Modeling and Prevention : Relationships Among Processing, Microstructure, and Fatigue Properties
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Ashley Spear, University of Utah; Jean-Briac le Graverend, Texas A&M University; Antonios Kontsos, Drexel University; Tongguang Zhai, University of Kentucky

Tuesday 8:30 AM
February 28, 2017
Room: 23C
Location: San Diego Convention Ctr

Session Chair: Ashley Spear, University of Utah

8:30 AM  Keynote
Research Directions in Materials Engineering and Fatigue: An NSF Engineering Perspective: Alexis Lewis1; 1National Science Foundation
    The US National Science Foundation's Directorate for Engineering supports fundamental scientific research, including Materials Engineering and Processing research. This presentation will cover recent trends and opportunities related to research funding from the National Science Foundation, with an emphasis on opportunities in the NSF Directorate for Engineering. In addition to Materials Engineering and Processing programs, programs and solicitations of interest to the Fatigue research community will be presented, including opportunities for collaboration with industry partners, and collaborators outside of the US. Trends in funding and research activities will be outlined, as well as an NSF Engineering perspective on future directions.

9:10 AM  
Low Cycle Fatigue Behavior of Direct Metal Laser Sintered Inconel Alloy 718: Experiments and Crystal Plasticity Modeling: Marko Knezevic1; Saeede Ghorbanpour1; 1University of New Hampshire
    We investigate strength and low cycle fatigue (LCF) of direct metal laser sintered (DMLS) Inconel 718 superalloy as a function of different initial microstructure created by variation in the deposited direction. To further investigate effects of initial microstructure and condition of the material, a set of samples underwent hot isostatic pressing. To have a reference for the LCF behavior of DMLS Inconel 718, a set of wrought Inconel 718 samples in the same condition was also tested, and the results critically compared against the results for the DMLS materials. In order to understand particularities pertaining to LCF behavior of the material at the grain-scale, a dislocation density based hardening law is developed and used within elasto-plastic self-consistent crystal plasticity model to simulate LCF. The results reveal the significant role played by porosity, annealing twins as well as reverse dislocation motion and backstresses on the LCF life of the material.

9:30 AM  
The Effect of Grain Boundaries on Short Crack Growth Behavior in WE43 Magnesium: Jacob Adams1; Wayne Jones1; John Allison1; 1University of Michigan
    Predicting the fatigue response of structural metals is a long standing challenge, particularly in the short crack growth regime where microstructure controls behavior. This paper describes a novel in-situ ultrasonic fatigue technique that utilizes a scanning electron microscope (UFSEM) for characterizing the growth of small fatigue cracks and how they interact with grain scale microstructural features. In this study, the short fatigue crack growth behavior of a hot-rolled rare-earth magnesium alloy WE43 heat treated to produce large grains is investigated using UFSEM. Crystallographic crack propagation paths were selected by initiating and propagating cracks from FIB produced micronotches oriented parallel to basal planes, while the in situ instrumentation was used to provide high resolution details of crack growth behavior near grain boundaries. The degree of grain boundary misorientation significantly influenced the magnitude of crack growth retardation at grain boundaries and could be quantified using this new approach.

9:50 AM  
Enhancing Fatigue Life through Ultrasonic Shot Peening: Garrett Pataky1; Vivic Harrinanan1; 1Clemson University
    Advancements in surface treatments have provided the opportunity to utilize alloys at higher stresses during fatigue loading. Ultrasonic Shot Peening (USP) as developed by Sun-Moon University in South Korea provides shot peening at a frequency of 40 kHz, greatly increasing the shots per square mm. A gearing alloy, 9310 steel, was experimentally studied with four surface treatments: case carburizing, case carburizing and traditional shot peening, case carburizing and USP, and case carburizing and induction heat treating. Endurance limits were found utilizing the up-and-down method to limit the number of samples required. Surface roughness and electron backscatter diffraction (EBSD) analyses were performed to compare the material characteristics after each treatment. The USP raised the endurance limit approximately 15% more than traditional shot peening and showed a more consistent coverage pattern.

10:10 AM Break

10:30 AM  
Development of Advanced Nickel-Titanium-Hafnium Alloys for Tribology Applications: Sean Mills1; Ronald Noebe2; Christopher DellaCorte2; Aaron Stebner1; 1Colorado School of Mines; 2NASA Glenn Research Center
    High hardness, strength, dent resistance, corrosion resistance, and favorable reaction with lubricants make binary Ni-Ti alloys with 53 to 56 at.% Ni desirable for specialized bearing applications. However, following the rapid quenching from solid solution that is required for high hardness, these alloys often exhibit high residual stress that leads to machining distortion, and sometimes even cracking of bearing components over time. Present work on a new bearing alloy development effort is discussed in which small amounts of Hf are added to tribological Ni-Ti compositions. Specifically, a time/temperature/transformation study is reported showing that Hf additions slow transformation kinetics, which allows for high hardness without quenching, thereby solving the residual stress issue of the binary system. Rolling contact fatigue performance of the ternary alloys and initial work into understanding the fatigue mechanisms for these advanced alloys will also be presented.

10:50 AM  
Effects of Alloying and Microstructure on Ultrasonic Fatigue Behavior of Binary Ti-Al Alloys: Qianying Shi1; Sinsar Hsie1; J. Wayne Jones1; John Allison1; 1University of Michigan
    Binary Ti-Al alloys (Ti-4wt.%Al and Ti-7wt.%Al) were investigated in this study to develop a fundamental understanding of very high cycle fatigue behavior of alpha-titanium alloys. Heat treatment on cogged and rolled alloys was carried out to obtain target microstructures with different grain size and recrystallization degree. Ultrasonic fatigue instrumention and a custom combination of ultrasonic fatigue and scanning electron microscopy were used under fully reversed loading to study small crack growth from FIB-produced micro-notches for materials with a range microstrucutures. The role of aluminum content, grain size and recrystallization degree were explored through the ex-situ and in-situ characterization of crack initiation sites, crack propagation paths and crack growth rates. Current results indicated no significant difference in fatigue lifetimes, crack initiation and growth rates between alloys with different aluminum content, in spite of the significantly higher yield and tensile strength in the Ti-7wt.%Al alloy. The explanations for this behavior are discussed.

11:10 AM  
Low Cycle Fatigue Properties of a CoCrFeMnNi Equiatomic High-entropy Alloys: Tsung-Ruei Sui1; E-Wen Huang1; Jien-Wei Yeh2; 1National Chiao Tung University; 2National Tsing Hua University
    High Entropy alloy (HEA) is featured by its fracture toughness. In this study, we choose equiatomic CoCrFeMnNi as our material which is a single phase face centered cubic solid solution. By doing in-situ neutron experiment and analyze it with Whole Powder Pattern Model(WPPM) fitting, dislocation interaction has been investigated. The cyclic effects on high entropy alloy will be reported.