Effects of laser remelting on CNT's behavior, microstructure and hardness of CNT-doped Fe-base composite

Laser remelting was performed to modify a Fe-base composite doped with multiwall carbon nanotubes (MWCNTs) using a Nd:YAG laser. Columnar and “granular” dendrites of (γFe,Ni) were yielded in remelted layer and partially melted zone (PMZ) of the composite, respectively, among which interdendritic phase (αFe,Cr) precipitated. Higher laser power generated not only thicker remelted layer and PMZ, coarser dendrites and a harder remelted microstructure, but also a transition of CNT-matrix joining from mechanical doping to metallurgical bonding characteristic of CNTs' enwrapping with matrix constituents. Such bonded CNTs with better dispersion effected for the harder remelted layer, as well as for the interdendritic structure harder than the dendrite. The coarsening and disintegration of the CNTs were ascribed to the conjoint effect of laser irradiation and thermal annealing during remelting. The hardness of PMZ and sintered composite substrate were also discussed in view of respective microstructures.