Quasicrystals are a distinctive class of metallic materials combining long-range atomic order with the absence of conventional translational symmetry. Their unusual structure can provide a valuable combination of properties, including high hardness, corrosion resistance, thermal stability, low surface energy, and relatively low adhesion to contacting surfaces.
These characteristics make quasicrystalline materials promising functional components for coatings, metal-matrix composites, polymers, and advanced lubricants.
A laboratory study investigated the effect of an Al-Cu-Cr ternary quasicrystalline powder on the anti-wear performance of two widely used lubricating greases:
The results demonstrated that a relatively small amount of quasicrystalline powder can significantly alter lubricant performance within a friction contact. The concentration dependence was clearly nonlinear: the greatest improvement was obtained not at the highest tested concentration, but at the lowest one — 1 wt.%.
The purpose of the investigation was to determine how the concentration of Al-Cu-Cr powder affects the anti-wear properties of lubricating greases.
Four formulations were evaluated for each base grease:
The primary measured parameter was the average wear-scar diameter produced on steel balls during a standardized tribological test.
A smaller wear scar indicates better anti-wear protection under the specified testing conditions.
The tests were carried out using a ChMT-1 four-ball friction machine according to GOST 9490-75.
The contact assembly consisted of four steel balls. Three stationary balls were fixed in a cup containing the test grease, while a fourth upper ball rotated against them under a specified axial load.
The principal testing parameters were as follows:
| Parameter | Test condition |
|---|---|
| Testing equipment | ChMT-1 four-ball friction machine |
| Ball material | ShKh-15 bearing steel |
| Ball diameter | 12.7 mm |
| Axial load | 196 N |
| Test duration | 60 minutes |
| Rotational speed | 1,460 ± 70 rpm |
| Temperature | 20 ± 5 °C |
| Number of replicates | 3 per formulation |
After each test, the grease was removed from the contact area. Wear scars on the three stationary balls were measured in two perpendicular directions with a resolution of at least 0.01 mm.
Measurements were performed using a SIAMS 700 solid-material microstructure analyzer equipped with an Olympus GX51 optical microscope.
Each test used a new grease sample and a new set of four steel balls. The repeatability of the results was evaluated at a 95% confidence level.
The unmodified Litol-24 Sintek grease produced an average wear-scar diameter of 0.90 mm.
Adding 1 wt.% Al-Cu-Cr reduced the average value to 0.58 mm.
| Formulation | Average wear-scar diameter | Change versus base grease |
|---|---|---|
| Litol-24 Sintek | 0.90 mm | — |
| Litol-24 + 1% Al-Cu-Cr | 0.58 mm | −35.6% |
| Litol-24 + 5% Al-Cu-Cr | 0.71 mm | −21.1% |
| Litol-24 + 10% Al-Cu-Cr | 0.73 mm | −18.9% |
The 1 wt.% formulation delivered the best result.
The reduction from 0.90 to 0.58 mm corresponds to an approximately 36% decrease in average wear-scar diameter. This indicates a substantial improvement in the anti-wear performance of the lubricant under the four-ball test conditions.
When the concentration was increased to 5 wt.%, the wear-scar diameter increased to 0.71 mm. This was still better than the result of the unmodified grease, but the improvement was smaller than that achieved with 1 wt.%.
At a concentration of 10 wt.%, the average wear-scar diameter was 0.73 mm. Increasing the quantity of quasicrystalline powder therefore did not provide an additional performance benefit.
The unmodified CIATIM-201 grease produced an average wear-scar diameter of 0.80 mm.
After the addition of 1 wt.% Al-Cu-Cr, the average diameter decreased to 0.40 mm — exactly half of the original value.
| Formulation | Average wear-scar diameter | Change versus base grease |
|---|---|---|
| CIATIM-201 | 0.80 mm | — |
| CIATIM-201 + 1% Al-Cu-Cr | 0.40 mm | −50.0% |
| CIATIM-201 + 5% Al-Cu-Cr | 0.56 mm | −30.0% |
| CIATIM-201 + 10% Al-Cu-Cr | 0.64 mm | −20.0% |
Once again, the 1 wt.% concentration produced the strongest result.
A 50% reduction in wear-scar diameter indicates the formation of a substantially more stable tribological contact and a pronounced increase in the protective capability of the base grease.
At 5 wt.%, the wear-scar diameter was 0.56 mm, representing a 30% reduction compared with the unmodified grease. At 10 wt.%, the diameter increased to 0.64 mm, although the result remained better than the baseline value.
Both test series demonstrated the same general trend:
The strongest improvement was observed in CIATIM-201.
| Base grease | Original value | Value with 1% Al-Cu-Cr | Reduction |
|---|---|---|---|
| Litol-24 Sintek | 0.90 mm | 0.58 mm | 35.6% |
| CIATIM-201 | 0.80 mm | 0.40 mm | 50.0% |
The same additive concentration therefore produced different levels of improvement in the two base greases.
This suggests that the effectiveness of a quasicrystalline additive is determined not only by the properties of the particles themselves, but also by their interaction with the base oil, thickener, and overall microstructure of the grease.
The results demonstrate a strong concentration dependence of the modified lubricant performance.
When properly dispersed, a small quantity of Al-Cu-Cr particles may act within the friction contact through several possible mechanisms.
Hard quasicrystalline particles may carry part of the mechanical contact load, reducing the intensity of direct metal-to-metal interaction.
Quasicrystalline phases are associated with relatively low surface energy and low adhesion. These characteristics may reduce the tendency of contacting steel surfaces to adhere or seize under boundary-lubrication conditions.
Well-dispersed particles may contribute to the formation of a mechanically stable intermediate layer between the steel surfaces.
A finely dispersed solid phase may redistribute local contact stresses and limit the development of localized surface damage.
Additional surface and tribofilm analysis is required to verify these mechanisms directly. Nevertheless, they are consistent with the observed reduction in wear-scar diameter.
A larger quantity of a functional additive does not necessarily produce better tribological performance.
At concentrations of 5 and 10 wt.%, several unfavorable effects may have occurred:
When particles form agglomerates, they no longer function as a uniformly distributed protective phase. Under some conditions, large clusters may instead intensify mechanical surface damage.
Industrial formulation development must therefore consider more than the chemical and phase composition of the powder. Particle size, particle-size distribution, dispersion technology, storage stability, and compatibility with the base grease are equally important.
The experimental results indicate that Al-Cu-Cr can function as an effective anti-wear additive for conventional lubricating greases.
The result obtained with CIATIM-201 is particularly notable. This grease is valued primarily for low-temperature operation, but its load-carrying and anti-wear performance is limited. Adding 1 wt.% Al-Cu-Cr reduced its wear-scar diameter by half under the reported test conditions while retaining the use of an accessible conventional base material.
Litol-24 also demonstrated a substantial improvement. The reduction from 0.90 to 0.58 mm suggests that an enhanced formulation could provide additional protection in applications where a standard multipurpose grease is exposed to elevated wear conditions.
Potential application areas for optimized formulations may include:
Transition from a laboratory formulation to an industrial lubricant would, however, require additional endurance, temperature, corrosion, storage, and field testing.
The experiments directly demonstrate a reduction in average wear-scar diameter after the addition of Al-Cu-Cr powder to both greases.
The study did not include direct measurements of:
The findings should therefore be interpreted primarily as evidence of an anti-wear effect under the specified four-ball testing conditions.
A broader test program is required to characterize the complete friction-reducing and operational performance of the formulations.
Future work could include:
The concentration range around 1 wt.% is especially important. The reported results indicate that the actual optimum may lie close to this value or possibly below it.
The laboratory tests confirmed that Al-Cu-Cr quasicrystalline powder can substantially improve the anti-wear performance of lubricating greases.
The best results were obtained at a concentration of 1 wt.%:
Increasing the concentration to 5 or 10 wt.% did not provide further improvement. Instead, the effectiveness of the additive progressively decreased, potentially due to particle agglomeration, changes in grease structure, and localized abrasive effects.
The central finding is that a pronounced anti-wear benefit does not require a large amount of quasicrystalline material. With effective dispersion, a concentration of approximately 1 wt.% may be sufficient to significantly improve the performance of a conventional lubricating grease.
These findings support the development of cost-efficient, next-generation grease formulations in which the distinctive surface and mechanical properties of quasicrystals are used to improve equipment reliability, durability, and service life.
Keywords: quasicrystals, Al-Cu-Cr, lubricating grease, Litol-24, CIATIM-201, tribology, anti-wear additive, wear-scar diameter, four-ball test, composite lubricants.