Multilayer Mo2N-Ag/SiNx films for demanding applications: Morphology, structure and temperature-cycling tribological properties

Nowadays there is the need to avoid the excessive consumption of liquid lubricant oils, as they are harmful to the environment and hard to disposal. Self-lubricant films have been seen as the sustainable solution to achieve a long-term lubrication under high temperature-cycling conditions. In this manuscript, multilayer Mo2N-Ag/SiNx films with a fixed modulation ratio (thickness of Mo2N-Ag to SiNx) of 3:1, with changing modulation period (Λ, thickness of Mo2N-Ag and SiNx) from 8 to 200 nm were produced to achieve an effective balance between the lubricious phase diffusion control and the adequate formation of the low friction tribo-layers. Results showed that a dual-phase of fcc-Mo2N and fcc-Ag co-existed in Mo2N-Ag layers, while the SiNx layer exhibited an amorphous character. Both room temperature (RT) lubricant and wear-resistance properties of the films were improved by increasing Λ from 8 to 64 nm, while a further increase of Λ degraded the wear-resistance properties. The multilayer film at Λ = 64 nm exhibited an excellent RT-500 °C temperature-cycling tribological properties. Mechanical properties and the synergistic effect of both modulation layers were the cause for the improvement of the tribological properties.Supported by the National Natural Science Foundation of China, China (51801081, 52071159, 52171071, 52172090); Portugal National Funds through FCT project, Portugal (2021.04115); Outstanding University Young Teachers of ‘‘Qing Lan Project” of Jiangsu Province, China; Excellent Talents of ‘‘Shenlan Project” of Jiangsu University of Science and Technology, China; China Merchants Marine Scientific Research and Innovation Fund, China. Filipe Fernandes acknowledges the funding received in the aim of the projects: MCTool21 - ref. ‘‘POCI-01-0247- FEDER-045940”, CEMMPRE – ref. ‘‘UIDB/00285/2020” and SMARTLUB – ref. ‘‘POCI- 01-0145-FEDER-031807”.info:eu-repo/semantics/publishedVersio

Tribological Properties of Mo2N Films at Elevated Temperature

Mo2N films were synthesized using the reactive magnetron sputtering system in a mixture of argon and nitrogen, and the tribological properties were investigated at different testing temperatures against an Al2O3 counterpart. The relative intensity ratio (RIR) method was used to calculate the weight fraction of the tribo-film (MoO3) on the wear tracks of the films. The results showed that the average friction coefficient first increased from 0.30 at 25 °C to 0.53 at 200 °C, and then decreased to 0.29 at 550 °C, while the wear rate decreased from 2.1 × 10−6 mm3/Nmm at 25 °C to 5.3 × 10−7 mm3/Nmm at 200 °C and then increased to 3.1 × 10−5 mm3/Nmm at 550 °C. The weight fraction of tribo-film was mainly attributed to changes in the average friction coefficient and the wear rate. Besides this, the relative humidity also influenced the tribological properties at 25–200 °C

Nano-voids formation at the interaction sites of shear bands in a Zr-based metallic glass

Understanding the formation mechanism of voids is a significant issue in controlling the catastrophic fracture in the form of shear bands in metallic glasses. Here, using an amplitude-modulation atomic force microscope, we investigated the nano-voids formation at the mutual interaction of shear bands in a Cu50Zr50 metallic glass. The results of phase shift revealed higher energy dissipation and more soft zones for the nano-voids. The formation of these nano-voids results from tensile stress concentration caused by the interaction of shear bands, based on the results of finite element simulation. The appearance of nano-voids and stress distribution at the site of shear band interaction is essential in understanding the plastic deformation and fracture of metallic glasses