Research and /or Engineering Questions/Objective: Aluminum-based metal matrix composites (AMCs) are a promising class of materials for applications as brake disc rotors in the automotive industry, combining low density and suitable tribological properties. Although studies have been conducted with ceramic particles or fibers as reinforcements, the description of the behavior of Interpenetrating Phase Composites (IPCs) still depends on further research in order to clarify their capabilities as friction materials. Methodology: In this study, investment casting was used to produce disc-shaped AlSi11-SiC IPCs with varying concentrations of Fe in the molten alloy, which were tested in a pin-on-disc tribometer against 100Cr6 and commercial brake pad material pins. The measurement of the Fe content in the alloys was done by OES. Tribological tests were conducted in oscillatory (60°) and full rotation modes, with speeds of 0.05 m/s and 2000 rpm, respectively. The resulting wear tracks and 100Cr6 friction pins were characterized by SEM-EDS, GIXRD, optical topography and stereomicroscopy, being compared to similarly-tested non-reinforced alloys. Results: The SiC foam reinforcement reduced the wear of both disc and brake pad material, avoiding adhesion and constituting a tribolayer by the retention of the latter at the composite interface. The Fe content increased general wear and increased adhesion. Moreover, it also induced the nucleation of a-Al15(Fe,Mn)3Si2 and ß-Al5FeSi intermetallics in the composite interface and matrix, respectively, which did not contribute to the aforementioned tribolayer. Limitations of this study: The oscillatory nature of some pin-on-disc tests indicates a deviation from the actual tribological contact verifiable in automotive braking applications. Future studies should consider single-direction rotation tribometry or brake dynamometry as to avoid such discrepancy. What does the paper offer that is new in the field in comparison to other works of the author: Whereas Fe is a well-described contamination of Al alloys, its tribological behavior in AlSi11-SiC IPCs has been poorly described in literature. Moreover, the characterization of tribolayer formation between aluminum based IPCs and commercial brake pad materials is deficient. Conclusion: The undesirable tribological behavior of Fe-rich AlSi11-SiC IPCs were associated to local embrittlement of the matrix due to the brittle intermetallics nucleation. The results suggest that the reduced wear of the brake pad material when tested against the SiCreinforced alloy is due to the retention of the same brake pad material in the ceramic foam after friction. This phenomenon seems to produce tribolayer areas distributed along the wear track prone to lubricate the friction process, which, in turn, avoid adhesion and wear in the tribosystem.
Guilherme Volpato, Ceramic & Composite Materials Research Laboratories, Universidade Federal de Santa Catarina, Brazil; Márcio Fredel; Ulrich Tetzlaff, Laboratory for Materials Analysis, Technische Hochschule Ingolstadt, Germany