Collaborative Research: Improving contact fatigue and wear properties using graded nanostructured surfaces in metallic materials

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Non-technical summaryGraded nanostructured metallic materials, with grain-size gradients ranging from the nanometer-level in the surface regions to the micrometer-level in the interior regions, are a novel class of materials that have exhibited promise for exceptional mechanical properties. However, at present, there is very limited understanding of the surface wear resistance and contact fatigue behavior of these nano-graded metals and alloys. Unlike in the case of materials with a uniform grain-size, where the surface region provides only one type of surface wear protection, in the nano-graded materials, the surface region has the potential to provide two types of protections by increasing the resistance to both damage initiation and subsequent damage progression into the interior of the material. Through modeling and experiments, this collaborative project between Stony Brook and MIT, seeks to obtain a scientific understanding of damage initiation and damage evolution processes in metallic materials with graded nanostructured surfaces. By advancing the current understanding of the mechanisms associated with surface wear protection and contact fatigue resistance of graded nanostructured materials, this project facilitates the development of a road-map for the reliable introduction of novel materials in the multi-billion dollar tribology industry that includes aircraft, automotive, electronic packaging, nuclear energy, and biomedical applications. Technical SummaryThis project is focused on obtaining a fundamental understanding of the contact fatigue crack resistance in graded nanostructured metallic materials. In particular, the influence of dislocation activities that are dictated by grain-size gradients and yield strength gradients, on crack tip blunting and crack tip shielding, is assessed. An adhesion-based analytical modeling framework is developed to predict the conditions for contact fatigue crack initiation in graded nanomaterials. A dislocation pile-up based multi-scale plasticity model is implemented in finite elements to predict contact fatigue damage evolution pathways in graded nanostructured metals and alloys. Contact fatigue and wear experiments are designed to provide a quantitative assessment of contact fatigue and wear behavior of graded nanomaterials and validation for the analytical and numerical models developed, while microstructural observations identify deformation mechanisms that contribute to contact fatigue resistance and wear damage protection. A new design paradigm for engineering functionally-graded nanomaterials that provides enhancements in contact fatigue damage resistance, beyond the classical limit that has been traditionally obtained in materials with (mostly uniform) surface modified layers, is identified.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.