In situ formation of TiC particulate composite layer on cast iron by laser alloying of thermal sprayed titanium coating
HEUNG-IL PARK, KAZUHIRO NAKATA, SHOGO TOMIDA
JOURNAL OF MATERIALS SCIENCE
abstract:Commercial ake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a CO2 laser to produce the wear resistant composite layer. The macro and microstructural changes of an alloyed layer with the traveling speeds of laser beam, the precipitate morphology of TiC particulate and the hardness prole of the alloyed layer was examined. From the results, it was possible to composite TiC particulate on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of the laser remelted cast iron substrate without a titanium coating was about 1 104 K/s to 1 105 K/s in the order under the condition of this study. The microstructure of the alloyed layer consisted of three zones; the TiC particulate precipitate zone (MHV 400 500), the mixed zone of TiC particulate + ledeburite (MHV 650 900) and the ledeburite zone (MHV 500 700). TiC particulates were precipitated as a typical dendritic morphology. The secondary TiC dendrite arms were grown to a polygonized shape and were necking. Then the separated arms became cubic crystal of TiC at the slowly solidied zone. In the rapidly solidied zone near the fusion boundary, however the ne granular TiC particulates were grouped like grapes.
keywords:traveling; cooling rate; speeds; titanium powder; plasma spraying; CO laser; remelting; particulate composite
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