Date of Award

Summer 2006

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Roumiana S. Petrova

Second Advisor

Roland A. Levy

Third Advisor

Reginald Farrow

Abstract

Boronization is a thermal diffusion process in which needle like boride layers are formed at the surface of the metallic substrate. The boride coatings formed by the diffusion process have high hardness and strong ware and corrosion resistance. In order for coatings of this nature to be industrially successful, their service life should be long and characterization should be extensive. Measuring the residual stresses of the coatings caters to each of these aspects.

In this study, AISI 1018 steel samples were boronized by a powder-pack process for four hours at 850°C in an argon atmosphere. Characterization techniques included coating thickness, microhardness, residual stresses and elemental distributions. The average thickness of the coating was determined to be 45μm while the average boride needle penetration was found to be 57μm Line-scan energy dispersive x-ray analysis helped verify the presence of the boride layers. It also showed an accumulation of carbon at the boride layer/substrate interface. Microhardness distributions revealed a maximum Knoop and Vickers hardness of 2,050 and 2,150, respectively. Residual stress measurements were obtained from x-ray diffraction data and evaluated using the multiple tilt sin2ψ technique for the iron monoboride layer and the substrate. The residual stresses were found to be compressive for both the iron monoboride layer and the substrate. Their respective values were found to be -237MPa and -l50MPa.

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