Mechanisms of mass transfer on porosity during solidification

3^rd International Conference on Smart Materials & Structures

March 20-22, 2017 Orlando, USA

Peng-Sheng Wei

National Sun Yat-Sen University, Taiwan

Scientific Tracks Abstracts: J Material Sci Eng

Abstract :

Pore formation and its shape in solid influence not only microstructure of materials, but also contemporary issues of various sciences of biology, engineering, foods, geophysics and climate change, etc. In order to remove and control porosity, understanding its formation is important. A pore formed in solid is a consequence of a bubble nucleated by super-saturation and entrapped by a solidification front. This work accounts for realistic mass and momentum transport across a self-consistently and analytically determined shape of the bubble cap, whose surface is in physico-chemical equilibrium beyond the solidification front. Accurate determination of contact angle from a realistic shape of the cap is required to predict the relevant shape of the pore in solid. It was systematically found that there are two different solute transport models subject to thin and thick thicknesses of concentration boundary layers on the solidification front. Case 1 accounts for species transport from the pore across an emerged cap through a thin concentration boundary layer on the solidification front into surrounding liquid in the early stage, whereas Case 2 is subject to species transport from the surrounding liquid across a submerged cap within a thick concentration boundary layer into the pore. The analytical results find that the variation of solute gas pressure in the pore with time determines development of the pore shape in solid. Increases in mass transfer coefficient and solidification rate decrease the pore radius. The predicted pore shape agrees with experimental data. A realistic prediction and control of the growth of the pore shape has therefore been obtained.

Biography :

Dr. Peng-Sheng Wei received Ph.D. in Mechanical Engineering Department at University of California, Davis, in 1984. He has been a professor in the Department of Mechanical and Electro-Mechanical Engineering of National Sun Yat-Sen University, Kaohsiung, Taiwan, since 1989. Dr. Wei has contributed to advancing the understanding of and to the applications of electron and laser beam, plasma, and resistance welding through theoretical analyses coupled with verification experiments. Investigations also include studies of their thermal and fluid flow processes, and formations of the defects such as humping, rippling, spiking and porosity. Dr. Wei has published more than 80 journal papers, given keynote or invited speeches in international conferences more than 90 times. He is a Fellow of AWS (2007), and a Fellow of ASME (2000). He also received the Outstanding Research Achievement Awards from both the National Science Council (2004), and NSYSU (1991, 2001, 2004), the Outstanding Scholar Research Project Winner Award from National Science Council (2008), the Adams Memorial Membership Award from AWS (2008), the Warren F. Savage Memorial Award from AWS (2012), and the William Irrgang Memorial Award from AWS (2014). He has been the Xi- Wan Chair Professor of NSYSU since 2009, and Invited Distinguished Professor in the Beijing University of Technology, China, during 2015-2017.

Email: pswei@mail.nsysu.edu.tw