# Copper Alloys Performance in High-Pressure and Low-Velocity Conditions Using a Custom Tribometer
## 4 Conclusions  
This work used a custom tribometer to study copper alloys suitable for use in plain bearings, specifically for heavy machines operating at high pressures and low speeds (PV factor). The main concluding remarks are:  
The uncertainty estimate value for the friction coefficient of custom equipment is 0.4%, and the equipment built within the proposed premises has a negligible effect on the computed friction coefficient.  
The comparison of custom to reference equipment indicates that the variability is attributed to the samples rather than equipment differences. There is the possibility of conducting future proficiency studies under a broader range of tribological conditions.  
Significative microstructural differences between NAB and HLB interfere with the observed mechanical and tribological performance, including the lower friction coefficient of HLB due to the insoluble Pb precipitates and the lower specific wear rate of NAB due to the kappa precipitates.  
Increasing the PV factor in HLB material reduces the friction coefficient due to frictional heating smearing the Pb, which acts as a lubricant. In contrast, NAB shows a considerable increase in the friction coefficient with higher PV factors, especially at PV 5.0 tests, due to additional abrasive wear.  
Measured and calculated temperatures are within the same order of magnitude. NAB measured and calculated temperature values show a strong correlation. Although HLB correlation coefficient is slightly lower, it follows a similar trend and is consistent with the theoretical model. There are opportunities to improve temperature measurement and the thermal model for specific conditions, which could be done through methods like numerical simulation.  
The results show that the NAB alloy experiences more significant subsurface strains than the HLB alloy due to the smearing of self-lubricating lead particles with low shear strength. The NAB alloy also dissipates more energy due to friction, causing more significant plastic strain. The lower wear rate in the NAB alloy results in slower debris detachment, leading to a buildup of subsurface plastic strain.  
Copper alloys and composites that combine the low friction coefficients of HLB with the high wear resistance of NAB offer an opportunity to develop solid lubricant potential, and an in-depth study of this potential can be carried out.  
M.R.d.S. designed, built, and validated the equipment; [PERSON], V.T.d.S., F.G.L. and D.A.S. performed the experiments; [PERSON], V.T.d.S., F.G.L., D.A.S. and I.F.M. contributed results analysis; and [PERSON] and I.F.M. wrote the paper. All authors have read and agreed to the published version of the manuscript.  
FAPESP, CAPES, and CNPq agencies financially support the Surface Phenomena Laboratory at the University of Sao Paulo.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Centro de Pesquisa, Desenvolvimento e Ensaios, da Termomecanica Sao Paulo S.A. donated materials for analysis and assigned laboratories for analysis.  
The authors declare no conflicts of interest.