Tribological reliability of amorphous metallic alloys – TriboRAMA

- Elaboration and shaping of bulk metallic glasses (arc-melting, moulding, micro-machining, polishing)
- Mechanical and structural characterisation (XRD, TEM, DSC, NMR, hardness, 3-point bending, ultrasonic waves)
- Surface characterisation (SEM, EDS, PM-IRRAS, XPS, confocal microscopy)
- Synthesis of organic molecules
- Tribometry under various modalities (sliding and rolling) and contact conditions (pressure, speed, environment)

- Obtaining, in a controlled manner, 7 grades of Cu-Zr based bulk metallic glasses in the form of millimeter-sized plates or rollers with very low roughness (Ra < 0.2µm).
- Importance of understanding the structural relaxation steps prior to possible partial crystallization.
- Success in the synthesis of organic molecules with 3 new polar endings.
- Demonstration of (i) the independence of the population of hydroxyl groups and surface oxides (ii) and the strong dependence of the surface roughness on the creation of organic clusters dispersed on metallic glasses.
- Demonstration that the relative humidity of the environment surrounding the tribological contact plays a very important role in friction and wear.
- Demonstration that the tribological behaviour can be very predictive and in a reproducible way if the contact conditions are well controlled.
- Obtaining very low levels of friction and wear for certain material pairs involving bulk metallic glasses.

Project’s perspectives are jointly oriented towards : (1) the realization of metallic glasses in the form of micro-gears, (2) the correlation between hardness/plasticity charts and tribological responses, (3) the links between deformation modes (shear bands, cracking... ) and wear volumes, (4) the influence of the chain length of the synthesized molecules on the morphology of the clusters formed, (5) the characterization of the grafting and of the clusters resulting from new synthesized molecules, (6) the tribological behavior of raw and functionalized bulk metallic glasses in rolling mode, (7) the development of experimental setups to widen the ranges of contact pressures and speeds, (8) the tribological responses of contacts involving bulk metallic glasses pairs, (9) the tribological durability of functionalized-in-surface bulk metallic glasses.

S. Stoens, G. Colas, R. Daudin, P-H. Cornuault, Effects of relative humidity on the tribological behavior of Cu-Zr-based bulk metallic glasses, 17èmes Journées de la Matière Condensée (JMC17), Rennes, France, 25-27 Août 2021
S. Stoens, R. Daudin, A. Lenain, S. Gravier, G. Colas, P-H. Cornuault, Strong dependence of relative humidity on the tribological behavior of Cu-Zr based BMGs in ambient air, 7th World Tribology Congress (WTC), Lyon, France, July 2022

Bulk metallic glasses (BMG), also known as amorphous metallic alloys (AMA), are deprived of atomic long range order. They are obtained by very fast cooling of the metallic melt preventing the atoms from organizing themselves into an ordered crystalline structure. This peculiar microstructure offers them specific properties such as very high mechanical strength, resistance to corrosion as well as very low surface roughness. They are however limited to small sizes which make them unlikely to be used as structural materials but more expected to become materials of choice to be used inside micro-devices. This have naturally let to their potential for tribological applications, especially in the field of micro-systems where miniaturization drastically increases stringent contact conditions. Unfortunately, the tribological behaviour of BMG is still highly debated as well as very unpredictable as it greatly depends on the composition and the contact conditions with no clear correlation with their intrinsic mechanical properties. The goal of TriboRAMA project is to significantly improve the tribological understanding, performance and reliability of a specific class of BMGs (CuZr-based). We propose to tune their composition, their microstructure and their surface properties to control their tribological properties. Ultimately, the project is expected to develop BMGs achieving low-wear and reliable tribological behaviour in the field of microsystems.
Supported by extensive tribological experiments and analyses, the project will (i) study the contact conditions to promote the use of BMG in real conditions for the industry (ii) propose guidelines for the optimization of the tribological response of BMG thanks to the modification of the composition as well as the impact of partial crystallization throughout thermal treatment (volume functionalization) (iii) study and develop efficient procedure for grafting alkylphosphonic acids molecules serving as a protective dry lubricant (surface functionalization).
TriboRAMA is organized around four scientific work package each led by one of the four different partners: two academics and two industrials. Femto-ST laboratory, in lead of the project, will evaluate the tribological behavior and performance of the BMG while SIMaP laboratory will be responsible of the production and characterization of functionalized-in-volume BMG. Concerning the industrial partners, Vulkam will produce BMG samples, develop new compositions and design micro-gears prototypes while Afuludine will be responsible of the development and study of BMG surface grafting for surface functionalization.
The present project is expected to produce cutting-edge scientific results, overcome current technical constraints and propose new BMGs achieving low-wear and reliable tribological behavior for industrial applications.