Superlubricity of Titanium Alloy Enabled by MoS2 Flakes and a-C:H Film

Abstract

Titanium alloys are often used in engineering fields including aerospace, cryogenic technologies, and weaponry due to their remarkable qualities. However, several issues including a high coefficient of friction, weak wear resistance, and low hardness hinder their widespread usage. Despite several efforts to enhance their tribology, achieving ultra-low friction on titanium alloy surfaces remains a challenging problem in materials science. Here, we report on the superlubricity of a MoS2 + a-C:H (Mo-a films) composite film, prepared by magnetron sputtering and spraying to lubricate titanium alloy surfaces. Robust superlubricity was achieved by the Mo-a composite films with a coefficient of friction (COF) below 0.007 in a helium environment. Compared to the reference titanium alloy substrates, the introduction of Mo-a composite film reduced the friction coefficient to roughly 1%, and the a-C:H film reduced wear by three orders of magnitude. High-resolution characterizations indicate that this enhanced tribology can be attributed to the formation of transfer film, which is enriched with nanostructured graphene sheets and MoS2 nanoscrolls, and is formed due to shear stress-induced structural transformation of a-C:H films and MoS2 nanosheets. This transfer film transitioned the initial high-resistance steel-to-a-C:H contact to super low-resistance steel-to-transfer film contact, thus achieving superlubricity and a remarkable wear reduction. This work outlines a pathway to solving the poor wear resistance and high friction coefficient problem of titanium alloy surfaces, which can be an important guideline for applications of titanium alloys in mechanical engineering.

Polyethylene Glycol Monolaurate Lubrication Triggers Liquid Superlubricity on Diamond-like Carbon Film

“…Since the liquid film became thinner, the roughness asperities of the friction pair collided violently. In this case, the friction promoted the chemisorption of PEGM molecules on the friction pair and triggered the formation of carbonaceous flakes and transferred film, therefore reducing the friction between the asperities. , Hence the COF could decrease rapidly to below 0.01 in a very short time. Nevertheless, when the lower specimen was changed from the DLC film to other materials, such as steel, Si 3 N 4 , and sapphire, etc., the COFs were higher than that on the DLC film due to the weak interaction between the PEGM molecules and the other surface materials except for the DLC film that cannot trigger the tribochemical reaction.…”

Solid Lubrication System and Its Plasma Surface Engineering: A Review

“…MoS 2 is also a layered hexagonal crystal structure material [215][216][217]. The layers consist of S-Mo-S three-atomic-layer structures held together by weak van der Waals forces between the layers [194,[218][219][220]. In the occurrence of sliding, the crystalline layers of MoS2 will easily slide and orient parallel to the direction of relative movement, which provides the lubricating effect [209,[221][222][223].…”

Tribochemistry of mercaptoimidazoline as an additive in emulsion between self-mated GCr15 ball interfaces and its friction-reduction mechanism

“…Efficient lubrication will improve the service life of the mechanical equipment and increase production efficiency and as a result save resources and energy, therefore reducing carbon emissions [2]. As a result, a wide variety of lubricants have been developed; including solid (e.g., coatings [3][4][5], greases, hexagonal boron nitride, etc), liquid (ionic liquids [6], petroleum oil, etc), and gaseous (air, steam, etc) lubricants.…”