Date

March 1982

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

The effects of rapid melting and subsequent quenching on the solidification behavior and solid state transformation structures of laser surface alloyed Fe-Cr, Fe-Ni, Fe-Cr-Ni and Fe-C-Cr systems were investigated as functions of composition (0-50%Cr, 0-20%Ni, 0-20%Cr/Ni, 0-1% C) and cooling rate (10[superscript 3]-10[superscript 6]°C/s). The microstructures were characterized by optical, scanning and thin foil transmission electron microscopy. The effects of laser parameters (laser power, beam size and scan rate) and coating variables (composition, thickness and morphology) on the penetration depth and melt width were also evaluated. The microstructures of Fe-Cr alloys were ferritic in nature, irrespective of the composition (0-50%Cr) and cooling rate (10[superscript 3]-10[superscript 6]°C/s). The transformation structures of Fe-5%Ni and Fe-6%Cr-2%Ni alloys exhibited a mixture of martensite and ferrite. The transformation structures of Fe-C-Cr alloys were studied as functions of the carbon (0.2-1.0%C) and chromium contents (0-40%Cr). The alloys containing up to 10%Cr exhibited a martensitic structure with fine precipitates of M [subscript 3] C carbide and small amounts of retained austenite. The 20%Cr alloys consisted of duplex austenite/ferrite structures. The morphology and substructure of austenite were a function of the carbon content. Carbide precipitation was identified only in a 1.0%C alloy. The 40%Cr alloys were ferritic and the morphology changed from equiaxed grains to regular cells with increasing carbon content. Significant amounts of M[subscript 23]C[subscript 6] carbide were also observed in these alloys. The rapid solidification effects including the retention of supersaturated austenite, lack of carbide precipitation and the morphology of phases are discussed as functions of alloy content and cooling rate.

Identifier

doi:10.6083/M4FT8HZX

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