Twin Formation, Propogation, and Intersection at the Mesoscale

Professor
Mechanical Engineering Department, Materials Dept.
University of California, Santa Barbara

Hexagonal close packed (HCP) crystalline materials, such as Mg and Ti, can provide a potential solution to the ever-increasing portfolio of structural applications that require advanced materials with unprecedented combinations of mechanical properties. Successful incorporation of HCP materials into engineering designs is, however, hindered by their limited plasticity. Perhaps one of the most important and puzzling underlying mechanisms governing their plastic behavior is deformation twinning, a crystalline defect that forms in these materials under straining and most often from the boundaries between
the crystals. The nucleation of twins both inside the crystal and at crystalline boundaries has mostly been addressed computationally at the atomistic scale level. In our research, we employ crystal plasticity based micromechanics modeling to establish and understand the first formation of twin embryos, propagation inside crystals and across their boundaries, and twin expansion. We apply it to Mg and Ti and many of their alloys of great technical interest in order to elucidate the role of solutes. The insight gained from these series of calculations aims to benefit the design of low-density, high strength, and high toughness HCP crystalline alloys, for reducing weight and fuel consumption.