Role of Alloying on the Fatigue Behavior in Magnesium Alloys
Discipline: Nanoscience or Materials Science
Session: 2
Room: 5 - Embassy A
Arianna Mena - Ohio State University
Co-Author(s): Justin Smith, Ohio State University, Columbus, OH Aeriel Murphy-Leonard, Ohio State University, Columbus, OH
As the structural material with the best strength to density ratio, it is important to understand the mechanical behavior in Magnesium. The cyclic stress strain (CSS) behavior is noted by its distinct twinning deformation mechanism; however, the introduction of rare earth elements has shown evidence of a non-basal slip preference over twinning that ultimately effects the fatigue life of the material. The CSS behavior and mechanisms of crack initiation were explored in two extruded Mg alloys: Mg-2Nd-1Y-0.1Zr-0.1Ca (rare-earth, RE) and Mg-2Zn-0.5Ca (ZX21) (wt. %). Flat, rectangular, dog bone specimens were extracted from the extruded bars and tested under fully-reversed, strain-controlled, low-cycle fatigue conditions at total strain amplitudes between 0.4-1.2%. A methodology employing a combination of scanning electron microscopy (SEM), ex-situ, and in-SEM loading was used to characterize the evolution of deformation and damage throughout the microstructure. The initial crystallographic texture was measured using electron back scatter diffraction (EBSD) and it was determined that the Mg-RE displayed a random texture. Contrarily, ZX21 showed a very weak basal-type texture. In the Mg-RE alloy, the CSS behavior exhibited stable, symmetric hysteresis loops where the maximum tensile and compressive stresses were similar throughout the fatigue lifetime. In ZX21, the presence of deformation twins led to a loop shape that evolved with cycling. These findings have guided in-SEM experiments to identify what the active slip system is in the material. Future work includes an in-depth study of dislocations and twins as they evolve with cycling utilizing transmission electron microscopy (TEM). Understanding the role of specific crystallographic grain orientations and interfaces on the crack initiation sites can allow for a prevention of cracks or extension of the fatigue life of a material.
Funder Acknowledgement(s): Department of Energy, Office of Basic Energy Sciences, Mechanical and Radiation Effects Program, Award # DE-SC0022976.
Faculty Advisor: Aeriel Murphy-Leonard, leonard.649@osu.edu
Role: I have completed the entirety of this research with the guidance of my Principal Investigator Dr. Aeriel Murphy-Leonard. My coauthor Justin Smith has aided in obtain comparative data for other alloys as well as assisted in some of the cyclic strain controlled experiments.