Laser surface melting (LSM) is an effective method for modifying the surface properties of metallic materials, allowing to obtain structures with unique characteristics. In this paper, the formation of the icosahedral phase (i-phase) in the Al-Cu-Fe-Cr alloy obtained by mechanical alloying and subsequent consolidation using LSM was investigated.
The initial alloy had a decagonal structure (d-phase) with inclusions of other intermetallics. After LPP, the formation of the i-phase was observed in the heat-affected zone. The mechanism of i-phase formation includes melting of the d-phase and subsequent crystallization from the supercooled melt. The rapid cooling rate during LPP promotes the formation of metastable phases, such as the i-phase.
The Al-Cu-Fe-Cr alloy is one of the most thoroughly studied systems for the creation of quasicrystalline (QC) coatings, in particular in terms of phase formation and use as wear-resistant coatings. Laser remelting of the surface causes changes in the local microstructure, which allows improving the mechanical and tribological characteristics of structural materials without changing the chemical composition of the base.
In this work, the effect of laser surface treatment on the microstructure and mechanical properties of Al85Cu6Fe3Cr6 (in atomic percent) alloy produced by gas sputtering and initially containing decagonal quasicrystals distributed in an aluminum matrix with a face-centered cubic lattice (Al-FCC) was investigated. Different laser parameters (power, table speed and beam diameter) were used to obtain six different laser tracks, which were subsequently classified according to their morphology and suitability for surface treatment.
A detailed analysis of the microstructure of the selected laser track was performed using scanning and transmission electron microscopy. The mechanical properties were assessed using the dynamic ultramicrohardness method. The microstructure of the surface-remelted layer contained crushed icosahedral quasicrystals in the Al-FCC matrix, as well as Al2Cu particles at the quasicrystal/Al-FCC phase boundaries. Large decagonal quasicrystals were present in the Al-FCC matrix of the substrate. The microhardness of the laser-treated material increased from 207 to 250 kgf/mm² compared to the substrate.
Microstructural analysis showed that the grain size of the i-phase varies depending on the laser processing parameters. Optimization of the LPP parameters allows controlling the size and distribution of the i-phase, which affects the mechanical properties of the surface layer. An increase in the microhardness and wear resistance of the surface is associated with the formation of the i-phase, which has high hardness and amorphizing ability.
The presented results demonstrate the potential of using LPP for the formation of icosahedral phases in Al-Cu-Fe-Cr-based alloys, which opens up new possibilities for creating materials with improved functional properties.
Author: J. Saelzera, G. Polus a, A. L. Meijer, T. Wolf, J. F. Gerken a, J. Baumann, A. Zabel, D. Biermann, M. Sipura, N. Piljic
Institute: Master’s Degree Program in Metallurgical, Materials and Mining Engineering, Federal University of Minas Gerais, Belo Horizonte, MG 31270-901, Brazil, Federal Institute of Education, Science and Technology of São Paulo (IFSP), Bragança Paulista, São Paulo, 12903-000, Brazil, School of Mechanical Engineering, University of Campinas, Campinas, São Paulo 13083–860, Brazil, Department of Materials Science, Federal University of São Carlos, São Carlos, São Paulo 13565-905, Brazil, Department of Materials Science, São Carlos School of Engineering, University of São Paulo (EESC–USP), São Carlos, SP 13563-120, Brazil