Al Based Nanocomposites Prepared By Mechanical Alloying And Selective Laser Melting Fabrication

In this work, the Ti C/Al Si10 Mg nanocomposite powder was prepared by high-energy ball milling of micrometer-scaled Al Si10 Mg and Ti C powder. The bulk-form Ti C/Al Si10 Mg nanocomposite parts were fabricated by selective laser melting(SLM). On the one hand, the evolution of constitutional phases, microstructural features, particle size distribution and interior nanostructure of the milled powders at various milling times were studied and reasonable mechanisms for the microstructural formation during the high-energy ball milling process were elucidated. On the other hand, the influences of nanopowder characteristics and laser processing parameters on the surface morphology, densification behavior, microstructural features, and mechanical properties(microhardness, tribological properties and tensile properties) of the SLM-processed Ti C/Al Si10 Mg nanocomposite parts were studied. The main conclusions obtained in the paper were presented as follows:The cold-welding mechanism predominates the initial stage of milling, and the milled powder particles experienced a continuous coarsening at the early 5 h milling. With ball milling continued(5-10 h), the fracturing mechanism was activated, the milled powder particles were broken into small pieces at this stage. With ball milling prolonged to 15 h, a dynamic balance was eventually achieved between the cold-welding and fracturing. In this situation, the stable powder characteristics including particle morphology, particle size and its distribution, and interior nanostructure were achieved. The ball milled products were generally nanocomposite powder featured by nanocrystalline(21.9 nm) matrix reinforced with the well-dispersed Ti C nanoparticles with the mean size of 30 nm.Two categories of nanopowder, i.e., ball-milled Ti C/Al Si10 Mg nanocomposite powder and directly mechanical mixed nano-Ti C/Al Si10 Mg powder, were used for SLM. The results showed that the ball-milled Ti C/Al Si10 Mg nanocomposite powder was more suitable for SLM process than that of directly mechanical mixed nano-Ti C/Al Si10 Mg powder. At the same laser processing parameters, the surface morphology, densification level, microstructural features, and mechanical properties(microhardness and tribological properties) of the SLM-processed parts with ball-milled Ti C/Al Si10 Mg nanocomposite powder were better than that of directly mechanical mixed nano-Ti C/Al Si10 Mg powder.The densification level and microstructural features of SLM-processed parts were determined by laser processing parameters, which in turn play a decisive role on mechanical properties of SLM-processed parts. The SLM-processed nanocomposite part had the best densification when the laser power and scan speed were settled at 120 W and 200 mm/s, meanwhile, a novel ring-structured nanoscale Ti C reinforcement with a regular distribution was tailored along the grain boundaries of the matrix. In this instance, the Ti C/Al Si10 Mg nanocomposite part exhibited elevated microhardness(188.3 HV0.1) and tensile strength(486 MPa) without a reduction in elongation(10.9%), reduced coefficient of friction of 0.28 and wear rate of 2.13×10-5 mm3N-1 m-1.