Screen Shot 2015-02-04 at 12.22.05 PMOptimization in Advanced Materials Processing: A Case Study on Residual Stresses in Nanocrystalline Thin Films

Hang Yu, Department of Materials Science and Engineering, Massachusetts Institute of Technology

Tuesday, February 17, 2015
1:30 p.m.
Engineering Research Center (ERC) 490, Tempe campus [map]

Abstract
Parameter optimization in advanced materials processing requires an in-depth understanding of the underlying processing science, such as nucleation, growth, and complex kinetic processes that occur far from equilibrium. Based on such understanding, the processing parameters can be designed and programmed for the optimal material performance. In
this talk, Yu will demonstrate this research strategy through a case study on the optimization of residual stresses in nanocrystalline thin films. From in situ stress measurements and structural characterization, it can be shown that the level of residual stress in a
nanocrystalline film is determined by two competing mechanisms: grain growth during film thickening and adatom attachment to the surface sites at grain boundaries. The competition of these two mechanisms results in three types of stress evolution behaviors, featuring a tensile stress, a compressive stress, and a compressive-tensile stress transition, respectively. This finding leads to the development of processing maps for residual stress optimization, e.g. through the control of atomic mobility, rate of condensation, angle of theincident flux, and vacuum conditions. As examples, different ways of depositing nanocrystalline films with zero residual stress and with highly tensile residual stress will be demonstrated. Application of this methodology can be applied towards future work in similar directions, including processing of smart materials and additive manufacturing.

Biosketch
Dr. Hang Yu earned his B.S. in Physics from Peking University in 2007, and his Ph.D. in Materials Science and Engineering from Massachusetts Institute of Technology in 2013. He is currently a postdoctoral associate in Professor Christopher Schuh’s group at Massachusetts Institute of Technology. Dr. Hang Yu’s research interests and expertise lie in the area of advanced materials processing, including processing of thin films and shape memory materials. His most recent work has been focusing on materials processing and meso-scale optimization in additive manufacturing. Dr. Hang Yu has served in several research communities, such as the Materials Research Society (MRS) and the Gordon Research Conferences/Seminars; he is currently a member of the Member Engagement committee in MRS

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