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

梯度纳米结构金属材料，其晶粒尺寸梯度范围从表面的纳米级到内部的微米级，是一类新型材料，具有优异的机械性能。然而，目前对这些纳米级金属和合金的表面耐磨性和接触疲劳行为的了解非常有限。与具有均匀粒度的材料不同，表面区域仅提供一种表面磨损保护，而在纳米级材料中，表面区域有可能通过增加对损伤起始和随后损伤进入材料内部的阻力来提供两种类型的保护。通过建模和实验，石溪大学和麻省理工学院之间的这个合作项目，旨在获得具有梯度纳米结构表面的金属材料的损伤起始和损伤演化过程的科学理解。通过推进当前对分级纳米结构材料的表面磨损保护和接触疲劳抗性相关机制的理解，该项目促进了在数十亿美元的摩擦学行业（包括飞机、汽车、电子封装、核能和生物医学应用）中可靠引入新材料的路线图的发展。本项目的重点是对梯度纳米结构金属材料的接触疲劳抗裂性有一个基本的认识。特别是，由晶粒尺寸梯度和屈服强度梯度决定的位错活动对裂纹尖端钝化和裂纹尖端屏蔽的影响进行了评估。为预测梯度纳米材料接触疲劳裂纹萌生条件，建立了基于黏附的分析模型框架。在有限元中建立了基于位错堆积的多尺度塑性模型来预测梯度纳米结构金属和合金的接触疲劳损伤演化路径。接触疲劳和磨损实验旨在为分级纳米材料的接触疲劳和磨损行为提供定量评估，并验证所开发的分析和数值模型，而微观结构观察则确定了有助于抵抗接触疲劳和磨损损伤保护的变形机制。本文确定了一种新的工程功能梯度纳米材料的设计范例，该材料提供了接触疲劳损伤抵抗能力的增强，超越了传统上具有（大部分均匀）表面改性层的材料的经典极限。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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 protection 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.