티타늄 용사피막을 이용한 주철의 레이저 표면합금화

Laser Assisted Surface Alloying of Cast Iron with Thermal Sprayed Titanium Coatings

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a $CO_2$ laser to produce the wear resistant composite layer. From the experimental results of this study, it was possible to composite TiC particles 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 laser remelted cast iron substrate without titanium coating was about $1{\times}10^4$ K/s to $1{\times}10^5$ K/s in the order under the condition used in this study. The microstructure of alloyed layer consisted of three zones, that is, TiC particule crystallized zone (MHV $400{\sim}500$), the mixed zone of TiC particule+ledebulite (MHV $650{\sim}900$) and the ledebulite zone (MHV $500{\sim}700$). TiC particules were crystallized as a typical dendritic morphology. The secondary TiC dendrite arms were grown to the polygonized shape and were necking. And then the separated arms became cubic crystal of TiC at the slowly solidified zone. But in the rapidly solidified zone of fusion boundry, the fine granular TiC particules were grouped like grape.