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Microstructure of Ni2B Laser-Induced Surface-Alloyed α-Fe

Published online by Cambridge University Press:  10 February 2011

G. Dehm ,
C. Scheu  and
M. Bamberger
G. Dehm
Affiliation:
Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel, [email protected]
C. Scheu
Affiliation:
Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel, [email protected]
M. Bamberger
Affiliation:
Department of Materials Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel, [email protected]
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Abstract

Substrate surfaces of α-Fe were laser alloyed with a CW-CO2 laser using Ni2B powder. Single laser scans and laser scans with a 50% overlap between successive passes were carried out to obtain hard surface coatings on the α-Fe substrate. High hardness values in the range of 520 - 600 Hv1 were achieved by laser boriding of α-Fe, compared to a substrate hardness of ∼ 110 Hv1. The improvement in hardness is caused by an off-eutectic microstructure, which consists of Fe dendrites and Fe3B and Fe lamellae. Both phases, Fe3B and Fe, contain Ni in solid solution. For samples treated with a single laser scan the Fe phase solidifies in the bcc structure. In contrast, a 50 % overlap between successive laser passes causes the iron to crystallize in the fcc γ-phase. The difference in crystallographic structure is caused by the amount of Ni dissolved in Fe during laser alloying: only ∼ 9 at.% Ni is contained in the α-Fe phase after a single laser scan, while up to ∼ 40 at.% of Ni is dissolved in the γ-Fe phase after a 50 % overlap between each laser scan due to the nearly complete melting of all injected Ni2B particles. However, the Fe3B phase solidifies during laser alloying independent of the amount of Ni in the orthorhombic Fe3C structure, which is metastable for Fe contents exceeding 45 at.%.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 481: Symposium P – Science and Technology of Semiconductor Surface Preparation , 1997 , 45
Copyright
Copyright © Materials Research Society 1998

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