Reinforcement and damage mechanisms in three- and four-phase aluminum-matrix composites
Materials in Sintering Processes and Generative Manufacturing Processes
Final Report Abstract
The global objective of the project was to understand the reinforcement and damage mechanisms in three- and four-phase aluminium-matrix composites. To this aim, two types of composites based on a near-eutectic AlSi12CuMgNi matrix alloy were studied: first, with a single ceramic reinforcement (Al2O3 fibres) and, second, with a hybrid ceramic reinforcement (fibres and SiC particles). Fibres in both composites were random-planar oriented Saffil ®. The investigation of the unreinforced matrix alloy revealed the major role of the intermetallic (IM) phases (formed from alloying elements) in the mechanical properties and micromechanical response of the material under load. Together with precipitates of the eutectic Si, the IM phases form a 3D interconnected network acting as a stiff skeleton embedded in the Al ductile matrix. During compression tests, both Si and IMs carry a significant part of the load (as shown by in-situ neutron diffraction) transferred from the plastically deformed Al matrix. Consequently, the presence of the IM particles (as a second reinforcement) leads to significant increase of the compressive strength of the AlSi12CuMgNi alloy in comparison, e.g. to the AlSi12 alloy. Based on these results, it was necessary to consider the role of the IMs in both composites, which made them to four- and five-phase respectively. It is well known that during production (e.g. casting) the mismatch in the thermal expansion coefficients between matrix and reinforcement phases causes the formation of micro-residual stress (m-RS), which is closely related to fracture initiation. The residual stress state in the as-cast composites was investigated by neutron diffraction (ND). Contrary to the common understanding, it was found that randomly oriented eutectic Si and SiC particles show possess deviatoric RS. To rationalize such behaviour a novel analytical approach was developed based on the Maxwell scheme, which allows accounting for the interaction between phases. Indeed, the interaction of particles with fibres (having preferred orientation and hence possessing large deviatoric stress) explains the formation of deviatoric RS also in randomly oriented phases. The fundamental study of the mechanical properties and micromechanical behaviour of the composites under applied load was conducted by the combination of mechanical tests, X-ray computed tomography (to reveal the initial microstructure and the damage mechanisms), and in-situ ND compression tests (to cast light on the load sharing mechanisms). To rationalize the experimental results a micromechanical model was developed, also based on the Maxwell homogenization scheme. It was found that the addition of a second ceramic reinforcement (SiC particles) increases the composite’s strength and reduces the anisotropy of the mechanical properties (with respect to composite reinforced with fibres). The hybrid composite with the fibre plane orthogonal to the load axis was found to marginally damage at low plastic deformation but underwent catastrophic failure at high strain. In both composites the IM phase plays an important reinforcing role, especially at high strains, when all phases suffer extensive damage. Interestingly, the cracks observed in all reinforcement phases do not propagate to the Al matrix (even at failure). The developed model allowed understanding this behaviour, predicting that the Al matrix remains under compression in all principal directions. Such behaviour has never been shown nor explained before. It was shown, that the solution heat treatment (ST) leads to the spheroidization of Si particles and hence to partial disintegration of the 3D network. This, according to the project’s hypothesis, must lead to a strength reduction and a global modification of the load sharing mechanisms. However, the in-situ ND compression tests revealed only a slight decrease in the load bearing capabilities of the Si phase for both composites in the ST condition, with respect to the as-cast condition. The same trend held for the SiC phase in the hybrid composite. The obtained results indicate that the disintegration of the eutectic Si network only marginally influences the uniaxial behaviour of composites with high amount of ceramic reinforcements and proves the effectiveness of the Si network for applications at elevated temperatures.
Publications
- The role of intermetallics in stress partitioning and damage evolution of AlSi12CuMgNi alloy, Materials Science and Engineering: A 736 (2018) 453-464
S. Evsevleev, T. Mishurova, S. Cabeza, R. Koos, I. Sevostianov, G. Garcés, G. Requena, R. Fernández, G. Bruno
(See online at https://doi.org/10.1016/j.msea.2018.08.070) - Maxwell scheme for internal stresses in multiphase composites, Mechanics of Materials 129 (2019) 320-331
I. Sevostianov, G. Bruno
(See online at https://doi.org/10.1016/j.mechmat.2018.12.005) - Micromechanical modeling of non-linear stressstrain behavior of polycrystalline microcracked materials under tension, Acta Materialia 164 (2019) 50-59
G. Bruno, M. Kachanov, I. Sevostianov, A. Shyam
(See online at https://doi.org/10.1016/j.actamat.2018.10.024) - Advanced Deep Learning-Based 3D Microstructural Characterization of Multiphase Metal Matrix Composites, Advanced Engineering Materials 22(4) (2020) 1901197
S. Evsevleev, S. Paciornik, G. Bruno
(See online at https://doi.org/10.1002/adem.201901197) - Explaining Deviatoric Residual Stresses in Aluminum Matrix Composites with Complex Microstructure, Metallurgical and Materials Transactions A 51(6) (2020) 3104-3113
S. Evsevleev, I. Sevostianov, T. Mishurova, M. Hofmann, G. Garcés, G. Bruno
(See online at https://doi.org/10.1007/s11661-020-05697-1) - Stress-induced damage evolution in cast AlSi12CuMgNi alloy with one- and two-ceramic reinforcements. Part II: effect of reinforcement orientation, Journal of Materials Science 55(3) (2020) 1049-1068
S. Evsevleev, S. Cabeza, T. Mishurova, G. Garcés, I. Sevostianov, G. Requena, M. Boin, M. Hofmann, G. Bruno
(See online at https://doi.org/10.1007/s10853-019-04069-4)
