Nano-mechanical Properties and Dislocation Interactions of Nanoscale Cu Particles in High Strength Fe-based Alloys

Description

High-strength structural materials are highly desirable for a wide range oflightweighting applications. Nanoparticle strengthening is one of the most effectiveapproaches to improve material strength without significant reduction of ductility.Basically, the stregnthening efficiency depends highly upon the intrinsic mechanicalproperties of the nanoparticles. However, due to their extreme small size which is toosmall for most conventional mechanical techniques, the nano-mechanical properties ofthe nanoparticles are poorly understood, and many interesting and important areasremain to be clarified. With Cu nanoparticles in the high-strength Fe-based alloys as amodel, this proposed research aims at three aspects for a fundamental understanding ofnanoscale mechanics: (1) the intrinsic mechanical properties of the Cu nanoparticleswith different crystalline structures and structural features; (2) the interaction ofdislocations with the Cu nanoparticles; and (3) the correlation between bulk mechanicalproperties and the Cu nanoparticles.First, we intend to determine the intrinsic mechanical properties of the Cu nanoparticleswith different crystalline structures and structural features, such as nano-twins. We willfirst attempt to experimentally determine the mechanical properties of the Cunanoparticles using peak-force tapping atomic force microscope (PFT-AFM). In parallel,first-principles (FP) calculations will be employed to calculate the elastic properties ofthe Cu nanoparticles with different crystalline structures, aiming to correlate thenanoscale mechanical properties with their nanostructures.Second, we plan to understand the dislocation interaction with the Cu nanoparticles.Transmission electron microscope (TEM) characterization will be conducted to determinethe critical size of the Cu nanoparticles for the interaction transition from cutting tolooping models. In addition, molecular dynamics (MD) simulations will be performed toelucidate the effect of the Ni interface on the deformation-induced sheartransformation of the Cu nanoparticles.Finally, we aim at correlating the bulk mechanical properties with the Cu nanoscaleparticles. The strengthening mechanism will be critically evaluated by considering allstrengthening contributions, including modulus strengthening, transformationstrengthening and coherency strengthening, while the work hardening behavior will becorrelated with the dislocation interaction of the Cu nanoparticles, with the aim atpredicting the macroscale stress-strain behavior from the nanoparticles.The successful implementation of this proposed research will lead to an unprecedentedunderstanding of the nano-mechanics of the Cu nanoparticles and their correlation withthe bulk mechanical properties. This comprehension of the nano-macro propertycorrelation can lead to novel developments in advanced high-strength materialsstrengthened by nanoparticles.