Electron Beam Glazing of Hardfacing Alloys
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ELECTRON BEAM GLAZING OF HARDFACING ALLOYS M. KURUP,
A. TAUQIR AND P. R. STRUTT
University of Connecticut, Storrs, CT 06268 B. H. KEAR Exxon Research and Engineering Company, Annandale, NJ 08801 ABSTRACT
Electron beam glazing has been used to reprocess hardfacing deposits of conventional Stellite 6 alloy, and TiC, TiB 2 particle strengthened Stellite 6. By varying the scanning mode and power density, a wide variety of microstructures have been developed, with significant increases in hardness. Single-pass line source scanning produces a distribution of moderately sized carbides (2-5 pm) in a dendritic matrix, whereas multi-pass processing gives a more homogeneous refined microstructure with submicron carbides. Point source scanning, in contrast, produces the most refined microstructures. Effective control of the carbide distribution, including both fine and coarse carbides, may be the key to tailoring the microstructure for specific wear applications. INTRODUCTION
The essential characteristics of a hardfacing surface layer include (i) good bonding to the underlying substrate, (ii) minimal porosity, and (iii) metallurgical homogeneity. Although currently used coatings considerably improve wear and corrosion resistance there is a vital need to improve characteristics (i)-(ii) cited above. A unique approach for achieving these desirable attributes is to re-process deposited hardfacing
layers by electron beam glazing. Another decided advantage of this rapid solidification technique is the formation of highly refined and homogeneous microstructures. An example of this is the fine-scale dendritic titanium carbide distribution in a steel matrix produced by electron beam glazing of the commercial Ferro-TiC alloy SK [1]. This treatment has been shown to produce a definite improvement in metal-tometal wear resistance [2]. A class of hardfacing materials in widespread use is the series of cobalt alloys based on the "Stellite" alloy developed early in the century
by Haynes. The development and properties of these materials has been described by Anthony [3]. Recently, Liu [4] demonstrated that perfectly bonded layers of Stellite 6, Table I, can be formed on stainless steel by laser-cladding. This work and the electron beam glazing studies on an iron-base material encourage the view that improved wear and corrosion resistance of Stellite alloys may be achieved by electron beam glazing. MATERIALS AND EXPERIMENTAL TECHNIQUE
Prior to electron beam processing, layers of the cobalt-base alloy Stellite 6 were formed on a steel substrate by laser-cladding. The specimens used were from a previous study [4] and involved the fusion of Stellite 6 powder onto a 304 stainless steel substrate with a high power CO A 1.25 cm x 1.25 cm heating area produced by optically 2 laser. scanning the beam was used for the process. Values of the beam power and speciTen velocity were in the range 5.1 to 7.0 kW and 0.42 to 0.68 cm.s . Processed layers with a 7:1 dilution ratio of Stellite to base Mat.
Res. Soc. Symp. Proc. Vol.
28 (1984)
Published
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