Strengthening Effects and Deformation Mechanisms in Nanocrystalline Composites

Nanocrystalline transition-metal carbide composites have been well established and areintensively studied materials due to their remarkable properties, such as high hardness,excellent fracture toughness, low friction coefficient, enhanced resistances to oxidation, wear,and cracking compared with their conventional micrometer scale (coarse-grained) counterparts.These exceptional properties are attributed in part to their unique deformation mechanisms,which are believed to be fundamentally different from those present in their coarse-grainedcounterparts and are determined by the stability of their nanostructure, grain boundary, andinterface. Recently, mechanical strengthening and deformation-induced stacking fault havebeen reported in nanostructured titanium-carbide/carbon (TiC-C) composites. However, directexperimental validations at the nanoscale level are not available. Moreover, the atomisticmechanisms and nanostructure-deformation relationships behind the exceptional mechanicalproperties remain largely unexplored, which in turn severely hinders the design andoptimization of nanostructured TiC-C composites with superior mechanical properties.With an integrated experimental and simulation effort via international collaboration,this project aims to apply in situ tensile straining and in situ nanoindentation techniques withhigh-resolution transmission electron microscopy and atomic-scale molecular dynamicssimulations to reveal the strengthening effect of nanostructured TiC-C composite, to uncoverthe deformation mechanism responsible for excellent mechanical properties, and to determinethe nanostructures that trigger the deformation. The results obtained from this research will bevery important for understanding the deformation behaviors of nanocomposites and guiding thestructural design of TiC-C with strengthening and high toughness/ductility, which will motivatefurther experimental and modeling investigations on the mechanical behavior of small-volumematerials.