Abstract
Rapidly solidified microstructures of Fe-Cr-W-C quaternary alloy deposited on low-carbon steel by laser cladding were investigated. The clad-coating alloy, a powder mixture of Fe, Cr, W, and C with a weight ratio of 10:5:1:1, was processed with a high-power continuous wave CO[sub 2] laser. The laser processed microstructure comprised fine primary dendrites of a face-centered cubic (fcc) austenitic [gamma] phase and interdendritic eutectic consisting of a network of pseudohexagonal M[sub 7]C[sub 3] carbides rich in Cr in an fcc austenitic [gamma] phase. The interlamellar spacing in the eutectic matrix was about 20 nm. The relatively high microhardness, about 900 kg[sub f]/mm[sup 2], of such fine microstructures is attributed to the formation of complex ternary carbides uniformly distributed in the eutectic matrix. In situ transmission electron microscopy (TEM) of thermally treated clad coatings revealed that transformation of the primary [gamma] phase to body-centered cubic (bcc) ferrite ([alpha] phase) commenced after heating at 843 K for about 7 minutes. Phase change of the interdendritic [gamma] austenite to a bcc [alpha] ferrite occurred after about 30 minutes of hold period at 843 K. Transformation of the M[sub 7]C[sub 3] carbides did not occur even after heating at 843 K for about 3.2 hours.more » The growth of a thin M[sub 2]O[sub 3] (M = Fe, Cr) oxide scale was detected after heating at 843 K for approximately 24 minutes. After cooling gradually to room temperature, the softened (723 kg[sub f]/mm[sup 2]) microstructure consisted of primary dendrites with a bcc [alpha] ferrite crystal structure and interdendritic ternary eutectic of untransformed M[sub 7]C[sub 3] carbides in [alpha] ferrite.« less
Published Version
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