Improvement in microstructure uniformity and mechanical properties of surface modified graphene reinforced Ni-based composites by laser deposition

Abstract

Graphene (Gr) is regarded as one of the promising nano reinforcement of metal matrix composites (MMCs) to improve the comprehensive performance owing to its superior physical and mechanical properties recently. However, the agglomeration and survivability at high-temperature of Gr as well as the compatibility between Gr and metal, have severely restricted the application of Gr in MMCs. Herein, the surface modification coupled with a mixing method without ball-milling was employed to protect Gr from the structural damage. Then, the modified Gr (CoFe@Gr) reinforced Ni-based alloy composites were fabricated via laser deposition technique in an argon protective atmosphere. The results showed that the pristine Gr nanosheets were successfully incorporated into composites, but some of them were transformed into the nanospheres while others formed “core-shell” structure with carbides under the high-energy laser irradiation. Compared with alloys adding Gr directly, the addition of CoFe@Gr composite powders not only promoted the uniform distribution of the second phases in matrix phase but also inhibited the generation of the pores defects resulted from the burning of Gr without surface modification. The changes in microstructure contributed to the lower coercivity of composites. Moreover, the micro-hardness and compressive strength values of composites were increased by 12.55% and 45.50% as compared with that of as-deposited alloys, respectively. This was mainly attributed to the improved interface compatibility between Gr and Ni matrix, the thermal mismatch effect and the second phase strengthening effect. This work is expected to provide a technique guidance for Gr reinforced MMCs that the fabrication conditions requiring high temperature.