Elementary processes which govern the formation of nano grained and ultra fine grained (N&UFG) zones during oscillating sliding high temperature wear (HTW)

HTW限制了许多技术上重要的金属系统的可开发使用寿命，例如柴油发动机中的气门/气门座摩擦系统。当金属摩擦系统暴露在HTW下时，摩擦副的表面区域会形成摩擦层。这些层对于了解耐磨性的微观结构是至关重要的。本项目的目的是研究高温焊接过程中摩擦层的特定深层，在那里形成纳米晶和超细晶结构(N&UFG)。需要了解导致N和UFG区形成的基本微结构过程，以了解在高于K熔点一半的温度下控制HTW的机制。在HTW暴露(不同程度)后，将使用聚焦离子束提取(FIB)从表面区域获取样品。然后用扫描电子显微镜(STEM)结合高角年度暗场探测器(HAADF)对N&UFG区域进行分析，这种方法非常适合研究足够大的微结构区域中的位错和平面缺陷所引起的集体现象。研究将使用两种经典的模型铝合金，Al11Zn和Al5 Mg，据报道，这两种合金在蠕变和严重塑性变形过程中形成位错诱发亚结构的倾向不同。它们将作为圆盘材料在300至500°C的温度范围内(在Ar气氛和空气中)暴露在磨损载荷下。柜体将使用由工具钢(德国等级：100Cr6)制成的耐磨销。拟议项目的科学目标是促进更好地了解在高温气冷条件下金属材料中形成的摩擦层的N区和UFG区的形成和演化的基本过程。

HTW limits the exploitable service life of many technologically important metallic systems, like for example valve/valve seat tribo systems in Diesel engines. When a metallic tribo system is exposed to HTW, tribo layers form in the surface regions of the wear partners. These layers are of central importance for the microstructural understanding of wear resistance. The present projects aims at studying a specific deeper zone of the tribo layer, where a nano crystalline and ultrafine grained structure (N&UFG) develops during HTW. The elementary microstructural processes which lead to the formation of this N&UFG zone need to be understood to appreciate the mechanisms which govern HTW at temperatures above half of the melting point in K. After HTW exposure (of different degrees), specimens from the surface regions will be taken using focused ion beam extraction (FIB). Then the N&UFG regions will be analyzed using scanning transmission electron microscopy (STEM) in combination with a high angular annual dark field (HAADF) detector, a TEM method which is well suited to investigated collective phenomena depending on dislocations and planar defects in sufficiently large microstructural regions. The investigations will be performed using two classical model Al alloys, Al11Zn and Al5Mg, which have been reported to differ in their tendencies to form dislocation induced substructures during creep and during severe plastic deformation. They will be exposed to wear loading as disk materials in the temperature range between 300 and 500°C (under Ar atmosphere and air). A wear resistant pin made out of tool steel (German grade: 100Cr6) will be used as counter body. The scientific objective of the proposed project is to contribute to a better understanding of the elementary processes which govern the formation and evolution of the N&UFG zones of tribolayers which form in metallic materials under conditions of HTW.