Tribological performance and anti-wear mechanism of cadmium-based phosphate microspheres as lubricant additives

Nanomaterials are widely used as promising additives in tribology. In this study, large cadmium-based phosphate (CdP) microspheres assembled from nanosheets were synthesized, and the tribological performance and anti-wear mechanism of the CdPs as additives in lubricating oils were investigated using a reciprocating ball-on-disc tribometer and surface characterization techniques. Oxygen-free oil with CdP significantly reduced the friction coefficient (COF) and wear rate (WR) of TA5 titanium alloys. Compared with pure polyalphaolefin 8 (PAO8), lubrication with PAO8 containing 25 wt% CdP reduced the average COF and WR by 70.03 % and 99.56 %, respectively. The extraordinary anti-wear property was attributed to the adsorption and deposition of CdP on the titanium alloy surface through P–O–Ti bonds, which resulted in a smooth tribofilm containing CdP. This tribofilm can prevent the adhesion of debris from the titanium alloy on the worn surface of the alloy and reduce adhesive and abrasive wear. However, the adsorption of CdP on the titanium alloy was compromised when an oxygen-containing oil was used as the base oil because the oxygen-containing oil molecules can bind to the titanium alloys and block the positions occupied by CdP. Based on the experimental results, it is concluded that CdP is an excellent anti-wear additive for titanium alloys.