Date: Friday, Apr 8th
Presenter: Jay Kruzic, OSU Materials Science/MIME
Bulk metallic glasses (BMGs) are a relatively new class of engineering materials with unique and unusual properties that make them potential candidates for many structural applications. Favorable properties include near theoretical strengths combined with reasonable fracture toughness, low damping, large elastic strain limits, and the ability to be thermoplastically formed into precision shaped parts with complex geometries, all of which are generally distinct from, or superior to, corresponding crystalline metals and alloys. One property which has been perceived as a limitation for BMGs has been low fatigue resistance relative to crystalline metallic materials; however, not all studies to date have been in agreement on this point. For the most studied BMG, Zr41.25Ti13.75Ni10Cu12.5Be22.5, the reported 10^7 cycle fatigue strengths vary by a factor of seven, and fatigue thresholds vary by a factor of three. While some of the reported scatter may be explained by different testing configurations, this does not account for all the observed variations, for example, those within single studies. Fatigue behavior for several Zr-based BMGs will be discussed. In general, it is concluded that free volume, residual stresses, and test environment all play a role in affecting the fatigue behavior of BMGs and these factors were often uncontrolled in early studies. Furthermore, by understanding these effects it appears viable to tailor the fatigue properties of bulk metallic glasses for given applications.
Prof. Jay Kruzic completed his B.S. degree in Materials Science and Engineering from the University of Illinois, Urbana-Champaign, and his M.S. and Ph.D. degrees in Materials Science and Mineral Engineering from the University of California, Berkeley. After three years of post-doctoral work at Lawrence Berkeley National Laboratory, he moved to the Mechanical Engineering Department at Oregon State University where he currently is an associate professor of mechanical engineering and materials science. His research focuses on the mechanical behavior of a wide range of traditional materials (metals, ceramics, intermetallics, composites), biomaterials, and biological tissues, with emphasis on the mechanisms of fracture and fatigue.