STRESS RELAXATION IN MULTIPHASE SYSTEMS : MICROMECHANICAL STUDY OF THE EFFECTS OF DIFFUSION AND VISCOUS SLIDING AT PHASE INTERFACES

多相系统中的应力松弛：相界面扩散和粘性滑动效应的微机械研究

基本信息

批准号：
10450256
负责人：
WAKASHIMA Kenji
金额：
$ 6.14万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

Theoretical and experimental work has been done in this project with a primary objective to indicate a new route to the understanding of high-temperature deformation behavior (creep) of metal-matrix composites (MMCs) with ceramic reinforcements--a class of light-weight high-stiffness 'advanced materials' currently ranked above conventional metallic materials especially for use in elevated temperature environment. Emphasis is placed on the viscous nature of metal-ceramic phase interfaces which causes 'stress relaxation' and hence plays a substantial role in creep of MMCs. First, as basic preliminaries to our intention, a series of analysis based on 2-D and 3-D continuum models has been made to formulate a micromechanical description of creep in two-phase (or multi-phase) solid systems wherein both diffusional mass flow and viscous sliding occur along phase interfaces. This description is applied to diffusional creep in polycrystals, leading us to make comments on existing theories where … More in the role of boundary sliding is entirely ignored. It is found that such theories can be justified only if boundary viscosity is so small that sliding can occur instantaneously. Further effort is devoted exclusively to our primary objective, giving special attention to particulate SiC-reinforced aluminum-based MMCs produced by powder-metallurgy processing routes. To begin with, 'anelastic relaxation' caused by diffusional creep around ceramic particulates is addressed. A micromechanical model of the relaxation has been presented and its validity confirmed from measurements of dynamic Young's modulus and internal friction, each as a function of temperature, in low-amplitude low-frequency conditions of cyclic uniaxial loading. The model is then extended into the high-stress 'dislocation creep' regime for the matrix, i.e. the case where the matrix itself does not remain elastic but creeps according to the 'power law.' With attention confined to the 'class I creep behavior' characterized by the particular stress exponent n = 3, nonlinear unsteady creep behavior of MMCs has been formulated in an entirely analytical manner. This formulation allows us to gain new insight into a 'puzzle' as to the anomalously high apparent stress exponents in 'minimum creep rate' data for MMCs. The crux of the matter consists in that damage processes (particle cracking and interface debonding) very likely occur in creep at high stresses and hence not all the minimum creep rate data should be interpreted as representatives of the steady state. This has been substantiated by carefully designed experiments on a particulate SIC/6061 A1 MMC. Less

该项目完成了理论和实验工作，主要目标是为理解陶瓷增强金属基复合材料（MMC）的高温变形行为（蠕变）提供新途径——一类轻质材料。高硬度“先进材料”目前排名高于传统金属材料，特别是在高温环境下使用，重点放在金属陶瓷相界面的粘性特性上，这种特性会导致“应力松弛”，从而导致应力松弛。首先，作为我们意图的基本准备，我们基于 2 维和 3 维连续体模型进行了一系列分析，以制定两相（或多相）蠕变的微观力学描述。因此，扩散质量流和粘性滑动都沿着相界面发生，该描述适用于多晶中的扩散蠕变，使我们对现有理论进行评论，其中……更多的作用。人们发现，只有当边界粘度非常小以至于可以立即发生滑动时，这种理论才能成立，我们将进一步努力专门致力于我们的主要目标，特别关注颗粒状碳化硅增强铝基MMC。首先，提出了由陶瓷颗粒周围的扩散蠕变引起的“滞弹性松弛”，并通过动态测量证实了其有效性。然后，在循环单轴载荷的低振幅低频条件下，杨氏模量和内摩擦力均与温度有关，然后将该模型扩展到基体的高应力“位错蠕变”状态，即基体本身并不保持弹性，而是根据“幂律”蠕变。将注意力集中在以特定应力指数 n = 3 为特征的“I 类蠕变行为”上，MMC 的非线性非稳态蠕变行为已被研究该公式使我们能够对 MMC 的“最小蠕变率”数据中异常高的表观应力指数获得新的认识。问题的关键在于损伤过程（粒子）。裂纹和界面脱粘）很可能发生在高应力蠕变中，因此并非所有最小蠕变速率数据都应被解释为稳态的代表，这已通过精心设计的颗粒实验得到证实。 SIC/6061 A1 MMC 更少。