Growth morphologies and mechanism of TiC in the laser surface alloyed coating on the substrate of TiAl intermetallics

Abstract

TiC-type MC carbide is an important constituent and strengthening phase for nickel-base superalloys, metal matrix composites (MMCs) and intermetallic matrix composites (IMCs). Its growth morphology, size and distribution have a strong effect on the mechanical properties of materials. In addition, TiC carbide is a typical faceted crystal due to its high Jackson factor. Therefore, the solidification behavior of TiC carbide is an important research subject. In the present study, TiC reinforced composite coatings on the surface of intermetallic alloy γ-TiAl were successfully synthesized by means of laser surface alloying, the growth mechanism and phase morphologies of TiC were investigated as a function of solidification cooling rate. The growth morphology of TiC solidified at a cooling rate of 1.0×10 2 K/s is found to be dendritic, having a platelet/catenulate growth characteristic on dendrite arms. As the solidification cooling rate increases to 2.2×10 2 K/s, the growth morphology of TiC changes to a well-developed dendrite having a three-dimensional network growth characteristic. In spite of the variety of growth morphologies under different solidification conditions, TiC still grows by the lateral growth mechanism. Moreover, the growth kinetics of TiC/Al 3Ti eutectic plays an important role in controlling the carbide growth morphologies.