Aluminum-based metal matrix composites (MMCs) reinforced with quasicrystalline (QC) Al–Cu–Fe particles are a promising class of materials for aerospace, automotive, and other industries. The unique combination of the lightness of the aluminum matrix and the high hardness and low friction coefficient of the QC particles provides excellent mechanical and tribological properties. However, to achieve optimal QC characteristics, it is necessary to control the interphase interaction between the matrix and the reinforcing particles.
One of the promising approaches to strengthening aluminum-based CMMs reinforced with Al–Cu–Fe CC particles is the use of an interphase reaction. During this reaction, intermetallic compounds are formed at the interface between the aluminum matrix and CC particles, which improve adhesion, reduce the coefficient of thermal expansion, and increase the strength of the material.
Composite materials are complex engineering systems where the constituent elements are often in a state of thermodynamic nonequilibrium both during production and in service. Diffusion processes and phase transformations at the interphase boundaries may occur at any of these stages. These temperature-dependent reactions between the matrix and the reinforcing component play a determining role in the properties of metal matrix composites. Thermodynamic and kinetic principles make it possible to predict and control the evolution of the interface morphology in composite systems. Powder metallurgy, using lower temperatures compared to liquid-phase processing, provides more precise control over the kinetics of interphase reactions. The key factors determining interphase reactions, composition, phases, and structure are: (1) the effect of surface energy at the boundaries, including nucleation, and (2) the effect of stresses accompanying diffusion at the interphase boundaries.
Reactions between the matrix and the reinforcement usually have a negative effect on the performance of composites. For example, in Mg/Al2O3 composites, the interfacial reaction between magnesium and alumina forms a brittle layer, which leads to an unacceptable decrease in strength. Therefore, such reactions should be avoided. However, interfacial reactions are not always detrimental. In the Al/Al–Cu–Fe composite containing a quasi-crystalline phase (QC), the reaction between the aluminum matrix and the QC reinforcement is used to increase the strength of the material at room temperature due to the formation of a new microstructure consisting of an aluminum matrix strengthened by particles of the ω-phase Al7Cu2Fe. The ω-phase (space group P4/mnc) has a tetragonal structure with the lattice parameters a = 0.6336 nm and c = 1.4870 nm and contains 40 atoms per unit cell, which classifies it as a complex metallic alloy family. Al/ω composites not only exhibit increased strength at room temperature, but also outperform Al/QC composites in tensile strength at temperatures below 570 K.
According to the Al–Cu–Fe phase diagram, the tetragonal ω-phase Al7Cu2Fe is stable between the icosahedral phase and aluminum at room and elevated temperatures. Therefore, during processing (e.g., powder compaction) at temperatures above 723 K, atomic diffusion occurs at the Al/Al–Cu–Fe QC boundary, causing a transition from the quasi-crystalline phase to the ω-phase with an increased Al content.
In this paper, the reaction between the aluminum matrix and Al62.5Cu25Fe12.5 reinforcement to form the ω-phase Al7Cu2Fe and its effect on the mechanical properties of composites are investigated. The QC to ω phase transition upon heating is studied by in situ high-energy X-ray diffraction to establish the relationship between the structural changes induced by heating and the observed changes in the mechanical properties of composites cured at different temperatures.
The mechanism of the interphase reaction involves the diffusion of aluminum, copper, and iron atoms across the interface, which leads to the formation of new phases. The rate and composition of the resulting intermetallic compounds depend on the temperature, time, and composition of the initial components. Careful control of the process parameters allows optimizing the structure of the interphase boundary and, consequently, the mechanical properties of the CMM.
Studies have shown that the formation of a thin layer of intermetallic compounds, such as Al7Cu2Fe, at the interface between the aluminum matrix and the Al–Cu–Fe CC particles leads to a significant increase in the tensile strength and hardness of the composite. This is due to the fact that intermetallic compounds effectively block the movement of dislocations in the matrix and prevent premature failure of the material.
In conclusion, the use of interfacial reaction for strengthening of aluminum-based CMMs reinforced with Al–Cu–Fe QC particles is a promising approach to create materials with improved mechanical properties for a wide range of applications. Further research aimed at optimizing the process parameters and controlling the interfacial structure will allow the full potential of these composite materials to be realized.
Author: F.Aliab, S. Scudino, MS Anwar, R.N. Shahid, V.C. Srivastava, V. Uhlenwinkel, M. Stoica, G. Vaughan, J. Eckert
Institute: IFW Dresden, Institute for Complex Materials, PO Box 27 01 16, D-01171 Dresden, Germany, Materials Processing Group, DMME, Pakistan Institute of Engineering and Applied Sciences, Nilore, Islamabad, Pakistan, Metal Extraction and Processing Department, National Metallurgical Laboratory, Jamshedpur 831007, India, Institute of Materials Science, University of Bremen, D-28359 Bremen, Germany, European Synchrotron Radiation Facility ESRF, BP 220, 38043 Grenoble, France, Dresden University of Technology, Institute of Materials Science, D-01062 Dresden, Germany