Correlation of Microstructure, Hardness, and Fracture Toughness of Fe-Based Surface Composites Fabricated by High-Energy
- PDF / 837,843 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 53 Downloads / 269 Views
.
INTRODUCTION
RECENTLY, structural materials have been increasingly exposed to severe industrial working conditions, and this exposure is largely confined to the surface region. Accordingly, active researches have been conducted on surface composites in which the excellent resistance to heat, corrosion, and wear of carbides, borides, or nitrides is fully utilized by direct irradiation with a high-energy electron beam.[1–3] This high-energy (several-MeV energy range) electron beam irradiation can achieve excellent surface properties while maintaining substrate properties.[4–8] Surface compositing is a process method in which hardness, wear resistance, and thermal resistance can be enhanced by depositing desired elements on a substrate to form a composite layer. This method contributes to the development of new materials having excellent properties and to the decrease in production costs, by compositing only the surface of high-priced materials.[9,10] Conventional electron beam processing has been mainly applied to the welding of relatively small parts because it needs a vacuum chamber. High-energy DUK-HYUN NAM and JEONGHYEON DO, Research Assistants, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea. SUNGHAK LEE, Professor, Center for Advanced Aerospace Materials, is jointly appointed to the Materials Science and Engineering Department, Pohang University of Science and Technology (POSTECH). Contact e-mail: [email protected] Manuscript submitted December 31, 2008. Article published online September 22, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
electron beam irradiation, on the other hand, can be continuously performed in the air and thus can treat a very large area at one time, which makes it advantageous for the fabrication of large structures or parts. Upon irradiating the material surface with a high-energy electron beam, the high kinetic energy of electrons is transformed to thermal energy, which can easily melt ceramics having melting temperatures above 3000 °C.[5] When the material substrate, on which ceramic powders are evenly deposited, is irradiated with an electron beam, the powders and substrate surface region are melted and solidified to form surface composites. This irradiation rarely forms pores or cracks because of high thermal efficiency and homogeneous heating and cooling. Compared with the laser beam method, the electron beam irradiation method has a thermal efficiency twice as high and produces thicker coatings (several millimeters in thickness). It also produces a strong interface between the melted region and substrate, and barely influences substrate properties because of short irradiation time.[11] Transition metal elements such as V, Nb, Cr, and Ti readily form carbides, borides, or nitrides in steels, and these can be used as reinforcing or coating materials because they are very hard and are wear- and thermalresistant.[12–14] The Fe-based surface composites reinforced with carbides, borides, or nitrides
Data Loading...
