Titanium alloys are extensively used in the aerospace, chemical, and biomedical industries. However, it has always been a challenge in the manufacturing and machining of titanium alloys because they exhibit poor friction and wear characteristics, which results in serious problems and significantly restricts their further production and application. Therefore, in the present study, the wear contact between GCr15 steel and Ti6Al4V alloy is specifically studied by considering black phosphorus nanosheets (BP-NS) as water-based lubrication additives, which is expected to have a great potential application in manufacturing and machining titanium alloys. The influence of BP nanosheet size on the coefficient of friction (COF) and wear rate of Ti6Al4V alloy has been comprehensively studied, based on comparisons among adding large BP nanosheets (L-BP) (2–4 μm), medium BP nanosheets (M-BP) (300–500 nm), and black phosphorus quantum dots (BPQDs) (6–10 nm). Compared with ultrapure water, the COF and wear rate of Ti6Al4V alloy are reduced by 42.4% and 82.3%, respectively, when BPQDs are used as water-based lubrication additives. This paper also shows that a lower COF and wear rate is achieved with the addition of BPQDs than the other two BP nanosheet sizes. Derived from the friction tests and worn surface analysis of Ti6Al4V alloy, lubrication mechanisms of different-sized BP lubricants were proposed. The interlaminar shearing between BP-NS and the adsorbed films were the main mechanisms for L-BP and M-BP lubricants, while the adsorption, repair, and ball-bearing effects were mainly presented in the BPQD lubricants. The discoveries in this paper would be beneficial to developing novel lubricants for the manufacturing and machining of titanium alloys.

In this investigation, a self-assembly method was used to fabricate black phosphorus (BP)/MoS 2 composites as water-based lubrication additives. The tribological behaviours of the lubrication additives for GCr15 steel ball/TC4 titanium alloy disk contact under different mass ratios, loads and rotational speeds were also investigated. The experimental results showed that 0.01 wt.% BP and 0.04 wt.% MoS 2 as water-based lubrication additive have the best the synergistic lubrication effect. Compared with pure water, coefficient of friction (COF) and wear rate of the lubrication additive at the test conditions of 8 N and 150 r/min were reduced by 32.6% and 68.8%, respectively. As the loads increased, the COFs and wear rates of all the lubricants including pure water, BP as water-based lubrication additive (BP-WL), MoS 2 as water-based lubrication additive (MS-WL) and BP/MoS 2 composites as water-based lubrication additive (BM-WL) were all reduced. As the rational speeds increased from 100 to 250 r/min, all the lubricants were firstly decreased and then increased.Based on tribological tests and wear surface analysis, the lubrication mechanism of BM-WL is proposed. The interlaminar shear and the adsorption of BP/MoS 2 composites on the wear surface of the friction pairs are the key to reducing COFs sand wear rates. In addition, the tribo-chemical reaction films consists of FeO/Fe 2 O 3 , Al 2 O 3 and TiO 2 were formed during the friction process, which can effectively protect the surface of the titanium alloy/steel contact from wear.

The unique tribological characteristics of black phosphorus quantum dots (BPQDs) have recently attracted much attention. However, the long-term stable lubrication of BPQDs and prevention of degradation in ultrapure water remain huge challenges. Herein, BPQDs@silica (BPQDs@SiO2) core–shell materials were designed and synthesized. The BPQDs are uniformly distributed in the SiO2 shell. The as-prepared BPQDs@SiO2 as the water-based lubrication additive has remarkable lubricity, wettability, and stability. In particular, compared with the average coefficient of friction (COF) and wear rate of ultrapure water, those of BPQDs@SiO2, being a water-based lubrication additive, could be reduced by 45.7 and 83.0% at 10 N and 150 r/min, respectively. The lubrication mechanisms of BPQDs@SiO2 as a water-based lubrication additive were proposed based on the friction test and wear surface analysis. The excellent lubricity performances of BPQDs@SiO2 are owed to the polishing of the SiO2 shell, the extreme pressure property of the BPQD core, and the tribo-chemical reaction film. This investigation established a simple, convenient, and feasible method for using the BPQDs@SiO2 materials as a water-based lubrication additive. It is expected that BPQDs with a core-shell nanostructure will open up new ideas for the development of excellent lubricating nanomaterials.