Abstract: TiC reinforced composite coating was fabricated by laser surface alloying on the substrate of TiAl intermetallics. The growth morphology and mechanism of the TiC carbide under rapid solidification conditions were investigated as a function of laser beam scanning speed. TiC carbide under a laser scanning speed of approximate 6.0mm/s is found to be dendritic having the necklace-like faceted growth characteristic on the dendritic arms. TiC carbide under a laser scanning speed of approximate 16.4mm/s is in well-developed dendrite having three-dimensional network growth characteristic. The intrinsic lateral growth of MC carbide and the growth kinetics of TiC and Al3Ti eutectic play an important role in controlling the growth morphology of MC carbide.
Growth morphology and mechanism of TiC carbide in laser surface alloyed composite coating on substrate of TiAl intermetallics
Abstract:
TiC reinforced composite coating was fabricated by laser surface alloying on the substrate of TiAl intermetallics. The growth morphology and mechanism of the TiC carbide under rapid solidification conditions were investigated as a function of laser beam scanning speed. TiC carbide under a laser scanning speed of approximate 6.0 mm/s is found to be dendritic having the necklace-like faceted growth characteristic on the dendritic arms. TiC carbide under a laser scanning speed of approximate 16.4 mm/s is in well-developed dendrite having three-dimensional network growth characteristic. The intrinsic lateral growth of MC carbide and the growth kinetics of TiC and Al 3Ti eutectic play an important role in controlling the growth morphology of MC carbide.
Fig.2 SEM micrograph showing well-developed dendritic MC carbide solidified at 2.2×102 K/s having three-dimensional interconnecting network-like growth morphology
图3 具有“小片链状”生长特征的树枝状TiC的生长示意图
Fig.3 Sketch showing growth process of dendritic TiChaving necklace-like faceted platelet growth morphology
(a) — Nucleation of TiC; (b) — Transition of octahedral TiC to platelet-like TiC; (c) — Growth of thin rods along 〈110〉 direction on surface of {111}planes; (d ) — Bridging by rod-branching; (e ) — Formation of necklace-like faceted dendrite arm
Fig.4 Sketch of well-developed dendritic TiC having three-dimension alloy inter-connecting network growth morphology
(a) —Nucleation of TiC carbide; (b) —Thin-rods bifurcating repeatedly along 〈110〉directions on surface of {111}planes; (c) —formation of a dendritic arm of TiC carbide; (d ) —Bridging by rod-branching; (e ) —Formation of three-dimensionally inter-connecting TiC dendrite