Although water/oil-graphite emulsions are widely used in warm forging processes, they carry environmental concerns. In an attempt to replace graphite-based lubricants in warm forging of aluminum alloys, two variants of boron-nitride-silicone lubricants were formulated. The two variants were made by dispersing boron nitride powder in polydimethyl siloxane oil at concentrations of 1% and 8%. The formulated lubricants were initially tested for their thermal degradation characteristics using a thermogravimetric analyzer and compared to the thermal degradation behavior of graphite and silicone oil lubricants. Ring compression tests were then carried out at and . Boron-nitride-silicone lubricant variants did not show significant difference in performance as die temperature was increased from . This is in contrast to graphite, which performed much better at than at , due to thermal oxidation. On the other hand, silicone oil exhibited the worst performance at and the best performance at . In both boron nitride lubricant variants, the polydimethyl siloxane facilitated hydrostatic/hydrodynamic lubrication at , with boron nitride acting as a barrier film that reduced friction. However, the lubrication mechanisms changed at , where the depolymerization of polydimethyl siloxane led to formation of silica due to thermal oxidation. Silica, together with boron nitride, acted as a film barrier with low shear strength. The dual lubrication mechanisms make boron-nitride-silicone lubricants suitable for a wide range of aluminum forging temperatures.
Performance of Graphite and Boron-Nitride-Silicone Based Lubricants and Associated Lubrication Mechanisms in Warm Forging of Aluminum
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Ngaile, G., and Botz, F. (April 7, 2008). "Performance of Graphite and Boron-Nitride-Silicone Based Lubricants and Associated Lubrication Mechanisms in Warm Forging of Aluminum." ASME. J. Tribol. April 2008; 130(2): 021801. https://doi.org/10.1115/1.2805432
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