Laser Surface Alloying Low Carbon Steel Using Chromium and Nickel Powder Feed: Mechanisms, Microstructures, Properties and Models (Corrosion, Conduction, Mass Transfer)
Chande, Tushar Shashikant
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https://hdl.handle.net/2142/71813
Description
Title
Laser Surface Alloying Low Carbon Steel Using Chromium and Nickel Powder Feed: Mechanisms, Microstructures, Properties and Models (Corrosion, Conduction, Mass Transfer)
Author(s)
Chande, Tushar Shashikant
Issue Date
1984
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Abstract
The process of laser surface alloying was studied. The principal objectives were to use elemental powders or their mechanical mixtures to make surface alloys, evaluate alloy microstructure and properties, and develop mathematical models to interpret the observed results. A new powder feeding system was used to alloy AISI 1016 steel surfaces with chromium and chromium plus nickel. Samples were examined microstructurally, and their corrosion resistance and surface roughness were measured. A variable-property heat conduction model was developed to study process responses to changing processing conditions and material properties. A two-dimensional, transient, numerical model for mass transfer was used to simulate the process of alloy generation.
Alloys were made with up to 80 pct chromium and 58 pct chromium with 28 pct nickel, and alloying was generally uniform. Corrosion resistance of samples was comparable to that of AISI 304 stainless steel. Surface roughness decreased when beam diameter or traverse speed increased. A variety of refined microstructures were seen, including grain-boundary precipitates, high dislocation-density laths and amorphous iron-phosphorus alloys. Conduction model calculations showed that with onset of melting sensitivity to changes in surface reflectivity was reduced, that an increase in molten metal thermal conductivity increased melt pool aspect ratio, and that cooling rates increased as energy density in the pool decreased. An increase in the Beer Lambert absorption coefficient (beta) decreased depths of penetration. Changes in pool energy density were used to find an upperbound for (beta). Mass transfer calculations with uniform surface mass flux showed that the good mixing was determined by the pattern of fluid flow and that average solute contents increased linearly with increasing interaction time. Fine powders melted practically instantaneously when added to the melt pool.
Thus, elemental powders or their mechanical mixtures could be used to reproducibly make highly alloyed surface layers with refined microstructures and useful properties. Mathematical models could be used to better interpret the results of laser surface alloying.
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