Title: On the microstructure of a thin wall formed under thermal and stress fields induced in laser solid freeform fabrication process

Authors: Masoud Alimardani, Christ P. Paul, Ehsan Toyserkani

Addresses: Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue W., Waterloo, Ontario, N2L 3G1, Canada. ' Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue W., Waterloo, Ontario, N2L 3G1, Canada. ' Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue W., Waterloo, Ontario, N2L 3G1, Canada

Abstract: In laser solid freeform fabrication (LSFF), the final microstructures and consequently the physical properties of the successive deposited layers of additive materials are determined through melting, solidification and solid state transformations caused by a moving laser beam. In this paper, temperature distribution and stress field induced during the multilayer LSFF process and their correlation with the local microstructure formation are studied throughout the fabrication of a four-layer thin wall of SS304L. For this purpose, parallel to the experimental investigation, a coupled 3D time-dependent numerical model is employed to simulate the process. The numerical and experimental results show that stress concentrations formed at the end points of the wall are the locations prone to potential delaminations and crack formations. Different types of microstructures, such as dendritic with and without secondary arm spacings, are observed at various locations within the same layer due to different cooling rates.

Keywords: laser solid freeform fabrication; LSFF; microcracks; numerical modelling; coupled temperature; stress; strain; microstructure; temperature distribution; cooling rates; rapid manufacturing; laser SFF; microcracking; simulation; delaminations; crack formation.

DOI: 10.1504/IJMMP.2010.035945

International Journal of Microstructure and Materials Properties, 2010 Vol.5 No.2/3, pp.276 - 297

Available online: 10 Oct 2010 *

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