The tribological behavior of 316L stainless steel/CoCrMo alloy contacts under aqueous lubrication was investigated in this work. Three types of microgels including poly(N-isopropylacrylamide) (PNIPAM), polyacrylic acid (PAA), and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-PAA) were prepared and used as lubricant additives in aqueous solutions. Tribological tests were conducted using a ball-on-disk reciprocating tribometer, over a range of temperatures, pH, and concentrations of the microgels. The PNIPAM-co-PAA microgels were proven to have excellent anti-friction and anti-wear properties, depending on the temperature and pH values of the solutions. The maximum friction coefficient coincided with the lower critical solution temperature of the PNIPAM-co-PAA microgels at 32 °C. At the same time, the friction coefficient increased with the increase in pH value of the lubricant solution with the PNIPAM-co-PAA microgels. The unique thermal- and pH-sensitive properties of the PNIPAM-co-PAA microgels provided a new strategy for controlling the friction and wear of steel/CoCrMo alloy contacts under aqueous lubrication.

Purpose This paper aims to offeri novel nano-additives polymer microgels to precisely improve the lubrication properties of titanium alloy under different temperatures. Design/methodology/approach The surfactant-free emulsion polymerization method was used to prepare Poly(N-isoprolylacrylamide) (PNIPAM) microgels. A ball-on-disk tribometer was applied to investigated the temperature-sensitive lubrication behavior of PNIPAM microgels. Findings The results show that the as-prepared microgels are ball-like nanoparticles with the size of 50–900 nm. In addition, potassium persulfate as initiator, complete mixing technic and high sodium dodecyl sulfate (SDS) concentration contribute to the formation of microgels with small size. The tribosystem shows a lower friction coefficient with the lubrication of PNIPAM microgels as aqueous solution additives when the temperature exceeding the critical temperature. Originality/value This work reports the temperature-sensitive lubrication of PNIPAM microgels. The critical temperature of PNIPAM microgels could be regulated by the addition of SDS in the solutions. This offers an effective and facile strategy for regulation of the critical temperature of smart microgels, which is helpful for the smart lubrication in the future.

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The tribological behaviour of YG8-cemented carbide/Ti6Al4V (YG8/TC4) contacts under aqueous lubrication was investigated in this work. Three types of nano-additives including poly (N-isopropylacrylamide) (PNIPAM), graphene quantum dots (GQDs), and GQDs@PNIPAM microgels were prepared for use as water lubricant additives. Tribological tests were conducted at different concentrations of nano-additives using a ball-on-disk reciprocating tribometer.The experimental results show that GQDs@PNIPAM has the optimum lubricating performance, the average friction coefficient decreases by 28.7% and the average cutting wear volume of the TC4 disk increases by 29.5% when the concentration is 1.5 wt.%. This provides a new strategy for the cutting of titanium alloy materials, which not only reduces the friction coefficient, but also increases the cutting wear volume of the TC4 disk, thereby improving the machining efficiency.