Tribological performance of AISI 4140 steel quenching hardened with NaOH solution and coated with AlTiCrN by PVD method

• Significant Hardness Increase: Quench hardening with 10 wt% NaOH dramatically increased AISI 4140 steel hardness from 480 HV to 696 HV. • Enhanced Surface Properties: The study confirms that NaOH heat treatment significantly improves the physical, mechanical, and tribological properties of both the steel and the AlTiCrN coating. • Comprehensive Characterization: Microstructure, phase, hardness, and wear analyses, including SEM, EDS, and XRD, were used to fully assess the combined treatment’s impact. • Improved Wear Performance: Tribological tests at varying distances (500, 1000, 1500 m) under 30 N load demonstrated the positive effect of the combined process on wear resistance. In this detailed study, the physical, mechanical, and tribological properties of AISI 4140 steel samples subjected to quench hardening with 10 wt% sodium hydroxide (NaOH) solution and then coated with Aluminium Titanium Chromium Nitride (AlTiCrN) using Physical Vapour Deposition (PVD) technique were investigated. The study included microstructure characterization, phase analysis, coating thickness linear measurements, microhardness, tribological analysis, and evaluation of worn surface examinations, aiming to distinguish the combined effect of AlTiCrN coating and hardening process. The surface properties, elemental distribution, and post-wear tribological properties of the coating layer were investigated in detail using X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) techniques assisted by Scanning Electron Microscopy (SEM). Tribological tests were carried out with a liner wear tribometer at three different wear distances of 500, 1000, and 1500 m under 30 N load. When the results were examined, the hardness obtained from the sample without any heat treatment was 480 HV, while the hardness of the sample hardened by heat treatment with NaOH solution was measured as 696 HV. The hardness of the sample hardened with NaOH solution and coated with AlTiCrN was measured as 1732 HV. It was observed that NaOH solution heat treatment caused a significant increase in the hardness values of the samples. As a result, NaOH solution heat treatment was observed to be a highly effective correlation in improving the physical, mechanical, and tribological properties of AlTiCrN coating and 4140 steel.