Identification of self-lubricative mode for the ultrasonic treated AA6061-B₄C-CNT hybrid composites

Abstract

This research investigates the self-lubricative behavior of boron carbide (B4C) and carbon nanotube (CNT) reinforced 6061 aluminium alloy hybrid composites. Hybrid composites were prepared by varying the volume percentages (5–15%) of B4C and CNT. Novel ultrasonic vibration (frequency of 20 kHz and power of 2.5 kW) assisted stir casting process was used for fabricating hybrid composites. A pin-on-disc type tribometer mounted with EN-8 as the counterface material was used to evaluate the friction and wear behavior of hybrid composites under dry sliding conditions. Normal loads ranging from 15–45 N and sliding speeds ranging from 1–2 m/s were applied during the experiments. The self-lubricative properties of different hybrid composites were assessed through the examination of the worn surface of pins using surface characterization techniques such as Scanning electron microscopy, Electron dispersive spectroscopy and Raman spectroscopy. The experimental results indicated that the addition of CNT particles increased the hardness of hybrid composites. The matrix strengthening efficiency of CNT was found to be greater at 10 vol.% of B4C, indicating a maximum hardness ranging from 102 to 109 VHN. In comparison, 10 vol.% of CNT hybrid composites showed superior tribological performance at all wear testing conditions. The mode of wear of hybrid composites suggested by the analysis on the worn pin surface was as follows: Scarce (5 vol.% CNT), Tribolayer (10 vol.% CNT) and Fracture (15 vol.% CNT).