Micromechanics and indentation creep of magnesium carbon nanotube nanocomposites: 298 K–573 K

In the present study, the time-dependent plastic deformation (creep) response of magnesium/carbon nanotube (CNT) nanocomposites containing 0.25, 0.5, and 0.75 vol% of CNTs is investigated through instrumented indentation tests against monolithic pure magnesium. The Mg-CNT nanocomposites were synthesized via powder metallurgy coupled with microwave sintering followed by hot extrusion. Indentation creep tests were performed at 298, 373, 473, and 573 K with a cubic boron nitride Berkovich indenter. Creep tests are dual-stage, i.e., all tests involve loading to a prescribed peak load (50 mN), holding this peak load constant for a set dwell period (120 s), and finally unloading. Three load rates of 0.5, 5, and 50 mN/s were tested. Results are explained through hardness, microstructure, and CNT volume fraction in each sample. Mg reinforced with 0.25–0.5 vol% CNTs exhibit the best creep resistance. At the ambient temperature of 298 K, dislocation creep is the dominant creep mechanism. At elevated temperatures, multiple creep mechanisms are identified. However, diffusion creep mechanisms are expected to prevail when temperatures exceed 573 K. These materials are promising candidates for aerospace, automotive, military, and many other industrial applications. To this end, the findings of this study can be used for material selection in these industries. This work may also be used as a baseline for future high-temperature nanoindentation creep studies on other nanocomposites.