Structural reorientation and compaction of porous MoS2 coatings during wear testing

Industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature. Here, we investigate the wear behavior of physical vapor deposited (PVD) MoS2 coatings: A dense, nanocrystalline MoS2 coating, and a porous, prismatic-textured MoS2 coating. Transmission electron microscopy (TEM) investigations before and after wear testing evidence a crystallographic reorientation towards a basal texture in both samples. A basal texture is usually desirable due to its low-friction properties. This favorable reorientation is associated to a tribological compaction of the porous specimens. Following running-in, sliding under high contact pressure ultimately leads to a wear rate as small as for an ideal chemical vapor deposited (CVD) grown bulk MoS2 single crystal reference. This suggests that the imperfections of industrial grade MoS2 coatings can be remediated by a suitable pretreatment

Surface Properties and Tribological Behavior of Additively Manufactured Components: A Systematic Review

Innovative additive manufacturing processes for resilient and sustainable production will become even more important in the upcoming years. Due to the targeted and flexible use of materials, additive manufacturing allows for conserving resources and lightweight design enabling energy-efficient systems. While additive manufacturing processes were used in the past several decades mainly for high-priced individualized components and prototypes, the focus is now increasingly shifting to near-net-shape series production and the production of spare parts, whereby surface properties and the tribological behavior of the manufactured parts is becoming more and more important. Therefore, the present review provides a comprehensive overview of research in tribology to date in the field of additively manufactured components. Basic research still remains the main focus of the analyzed 165 papers. However, due to the potential of additive manufacturing processes in the area of individualized components, a certain trend toward medical technology applications can be identified for the moment. Regarding materials, the focus of previous studies has been on metals, with stainless steel and titanium alloys being the most frequently investigated materials. On the processing side, powder bed processes are mainly used. Based on the present literature research, the expected future trends in the field of tribology of additively manufactured components can be identified. In addition to further basic research, these include, above all, aspects of process optimization, function integration, coating, and post-treatment of the surfaces

Effects of Nitrogen Modification of Porous PVD–MoS₂ Coatings on the Tribological Behavior under Rolling–Sliding Conditions in Vacuum

In order to improve the tribological performance of PVD–MoS2 coatings, which are frequently used as a solid lubricant for operating in challenging environments, e.g., in a vacuum, they can be modified with nitrogen. This work evaluates the tribological behavior and a possible compaction occurring during the initial tribological load in the rolling contact for pure and nitrogen-modified PVD–MoS2 coatings in a vacuum. Short-running tests (1000 cycles) of coated steel discs paired with uncoated steel discs made from 100Cr6 (1.3505, AISI 52100) were conducted on a two-disc tribometer. The slide-to-roll ratio of 10.5% was kept constant, while the load was varied in two steps from 1.1 GPa to 1.6 GPa. Subsequently, a comparison was made between the worn and the pristine coatings by means of nanoindentation and an optical analysis of the wear track. The formation of a load-bearing solid lubrication was achieved for both MoS2-variants. The main differences affected the material transfer and wear mechanisms. The worn coatings reached a similar wear coefficient of 4 × 10−6 mm3N−1m−1 and a possible compaction of the coatings was found, indicated through an increased indentation hardness (for MoS2 1158% and MoS2:N 96% at a 1.1 GPa load). The assumed tribological mechanism changed with nitrogen modification, but scales with increasing load. The nitrogen-modified MoS2 coating showed less compaction than pure MoS2, while the frictional behavior was improved by a 17% reduction of the coefficient of friction

Structural reorientation and compaction of porous MoS₂ coatings during wear testing

This research was funded by the German Research Foundation (DFG) Priority Program SPP 2074 “Fluid-free lubrication systems with high mechanical loads”, grant number (GEPRIS) 407707942 (ME 4368/7-1, ME 2670/8-1 and TR 1043/7-1)

Ti3C2T solid lubricant coatings in rolling bearings with remarkable performance beyond state-of-the-art materials

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes, are agrowing class of 2D materials, which offer great solid lubrication ability for low friction applications due totheir weakly bonded multi-layer structure and tribo-layer formation with self-lubricating characteristics. Todate, most studies have assessed their tribological response in basic laboratory tests. However, these tests donot adequately reflect the complex geometries, kinematics, and stresses present in machine components.Here, we aim at bridging this gap through assessment of the friction and wear performance of multi-layerTi3C2Tx MXene solid lubricant coatings used in rolling bearings. MXenes’ tribological response is comparedwith state-of-the art solid lubricant coatings, which include molybdenum disulfide (MoS2), tungsten-dopedhydrogenated amorphous carbon (a-C:H:W), and hydrogen-free, more graphite-like amorphous carbon (a-C).Multi-layer Ti3C2Tx MXene coatings reduce wear on the bearing washers by up to 94 %, which can beattributed to the transfer of the lubricious MXene nano-sheets to secondary tribo-contacts of the bearing.While the frictional torque of all solid lubricant coatings is similar during steady-operation, the MXenecoated bearings extend the service life by 30 % and 55 % compared to MoS2 and DLC, respectively. This2 contribution demonstrates the ability of MXene solid lubricant coatings to outperform state- of-the-art solidlubricants in dry-running machine components such as rolling bearings