A Novel Surface Nanocrystallization and \(SNH)\ Process for Improved Fatigue and Wear Resistance

该项目是一种新型的表面纳米化和硬化（SNH）工艺，其中金属部件在受控气氛下用高能球撞击。它将适用于大型和小型工程部件，并提供源自定制微观结构、成分和粒度的平滑梯度以及所需残余应力分布的协同作用的上级疲劳和磨损性能。康涅狄格大学（UConn）和田纳西大学（UT）已经联合起来调查与SNH过程相关的关键问题。康州大学将带来高能球磨和SNH工艺方面的专业知识，而UT将提供疲劳机制和建模领域的专业知识。研究的一个主要目标是开发和构建一个特殊的SNH机与独立控制的各种SNH过程变量，如表面晶粒尺寸，晶粒尺寸梯度，成分梯度，形成新的化合物，残余应力，和表面处理。 该项目的目标是进行系统和全面的实验，以建立Ti-6-4合金表面纳米化的加工图，包括使用高分辨率透射电子显微镜（HREM）进行详细的显微组织和位错密度研究。基于建立的机制，分析和数值模型将被开发来预测表面纳米化的一般趋势。SNH处理的Ti-6-4合金的机械性能将使用纳米压痕、销-盘磨损和高循环疲劳测试进行量化。这些研究建立的疲劳机制将作为基础，发展理论模型，预测具有表面纳米晶粒和晶粒尺寸梯度的材料的疲劳裂纹萌生和扩展行为。本基金项下的工作试图通过开发和测试一种称为表面纳米化和硬化的新工艺，开发具有上级机械性能的块体纳米晶金属部件（SNH）。表面中的超细晶粒尺寸与适当的晶粒尺寸梯度进入本体预期导致结构部件的疲劳寿命提高。该项目计划包括本科生和高中生沿着研究生研究人员的参与。

The project is on a novel surface nanocrystallization and hardening (SNH) process wherein metallic parts are impacted with high-energy balls under a controlled atmosphere. It will be suitable for both large and small engineering components and offer superior fatigue and wear properties derived from the synergy of the tailored microstructure, the smooth gradients of both composition and grain size, and the desired residual stress distribution. The University of Connecticut (UConn) and the University of Tennessee (UT) have joined together to investigate the key issues related to the SNH process. UConn will bring in expertise in the high-energy ball milling and SNH process, while UT will provide expertise in the area of fatigue mechanisms and modeling. A major goal of the study are to develop and construct a special SNH machine with independent control of a variety of the SNH process variables such as the surface grain size, grain-size gradient, composition gradient, formation of new compounds, residual stresses, and surface finishing. The objective of the project is to perform systematic and comprehensive experiments to establish the processing maps for surface nanocrystallization of the Ti-6-4 alloy including detailed microstructure and dislocation density studies using high-resolution transmission electron microscopy (HREM). Based on the mechanisms established, analytical and numerical models will be developed to predict the general trend of surface nanocrystallization. Mechanical properties of the SNH-processed Ti-6-4 alloys will be quantified using nanoindentation, pin-on-disc wear, and high-cycle fatigue tests. The fatigue mechanisms established in these studies will be used as a basis to develop theoretic models for the prediction of fatigue crack initiation and propagation behavior in the material with surface nano-grains and a grain-size gradient.The work under this grant attempts to develop bulk nanocrystalline metallic components with superior mechanical properties through the development and testing of a new process known as surface nanocrystallization and hardening (SNH). The ultra fine grain size in the surface with appropriate grain size gradient into the bulk is expected to result in improved fatigue life of the structural components. The project plans include participation of undergraduate and high school students along with graduate researchers.