Search

The microstructure, texture, and mechanical properties of the Al/Ni/Cu composite during various accumulative roll bonding (ARB) cycles were studied using optical microscopy, scanning electron microscopy, x-ray diffraction, shear punch test, and hardness test. In addition, ImageJ software and Rietveld software were used in order to study microstructure and dislocation density variations, respectively. It was found that Ni and Cu layers were fractured and distributed in the Al matrix due to differences in their mechanical properties. Fracture and distribution of Cu and Ni particles after cycle five led to the alteration of the composite structure from a layered to a particle-reinforced structure. ARB process leads to the formation of strong orientation along the β-fiber and also to pronounced copper and dillamore components in both Al and Cu phases. Furthermore, the shear yield stress and ultimate shear strength of the composite increased as the ARB process advanced; however, shear elongation presented a non-uniform variation. Investigation of the fracture surfaces revealed that the mechanical properties of the composite are affected not only by the strain hardening of the Cu layer, but also by the structural change in the composite during the initial ARB cycles. During the last stages of the process, however, changes in mechanical properties were mostly governed by reinforcement particles serving as strain concentration zones and the strain hardening of the Al matrix. [ABSTRACT FROM AUTHOR]

The influence of elemental cerium addition on the cooling curve parameters and microstructure of hypereutectic Al-23Si alloy was investigated in this work. The cooling rate of the treated and untreated alloy samples was varied by solidifying the melt against chills of different materials in a stainless-steel tube. The cooling curve was recorded and nucleation temperatures of various phases in the alloy were measured. The results show that the chilling improves the effectiveness of the modifier. The two main phases of the alloy, primary silicon and eutectic silicon, were nucleated at temperatures of about 661.2 and 571.6 °C, respectively. The addition of Ce to slowly cooled alloys resulted in an increase in undercooling temperature of both the phases, with a decrease in its nucleation temperature, whereas the same additions increased the nucleation temperatures in chilled alloys. Based on the thermal analysis results, a relation between thermal analysis parameter (ΔTG) and silicon particle size of the alloy was proposed. [ABSTRACT FROM AUTHOR]

Highly reactive integrated material systems have recently gained attention, as they promise a feasible tool for heterogeneous integration of micro electromechanical systems. As integrated energy sources they can be used to join heterogeneous materials without applying too much thermal stress to the whole device. An alternative approach is proposed, comprising a single layer of a reactive nanocomposite made of intermixed metal nanoparticles, instead of multilayer systems. In this study the development of the reactive nanocomposite from choice of materials through processing steps, handling and application methods are described. Eventually the results of the experiments upon the reactivity of the nanocomposites and the feasibility for bonding applications are presented. Analysis of the composites was performed by phase-analysis using x-ray diffraction and reaction propagation analysis by high-speed imaging. Composition of products was found to vary with initial particle sizes. Beside of other phases, the dominant phase was intermetallic NiAl. [ABSTRACT FROM AUTHOR]