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The aim of this study is to obtain and characterize surface layers on low carbon steel with the pack boronnitro-carburizing process. Different mixtures of commercial powders (Turbonit ® and Ekabor ®) were used to investigate the case properties, microstructure and phases formation on AISI 1020 steel. A series of experiments were conducted in solid medium with powders blend, with weight proportions of 0/100;25/75;50/50;75/25;100/0 at temperatures of 1000 and 1100º C for 2 and 10 hours. Roughness measurement of all treated specimens was assessed to compare with pre-treatment condition. Hardness profile and comparative analysis of phase structure, morphology and composition was carried out to treatment conditions. Optical microscopy shows differences on layers surface, depth and microstructure case-diffusion zone. Results found indicated that for the same treatment time and temperature, hardness was changed, but the diffusion case depth was kept similar. DRX and XPS indicated the formation of boron nitride after certain treatments.

Sliding wear behavior of niobium carbide coated AISI 52100 bearing steel balls against AISI 1045 quenched steel discs was investigated. Thermo-reactive diffusion (TRD) treatment was carried out at 1000 °C for 4 hours by pack cementation method. NbC phase with 11 µm in thickness was identified by SEM microscopy and XRD technique. Ball-on-disc wear tests were carried out without lubrication under 2 and 10N load at sliding speeds of 0.1 and 0.3 m/s. A 300% increase in sliding speed resulted in 24% and 27%, increasing in friction coefficient of niobium carbide coated AISI 52100 steel balls for 2N and 10N. Wear resistance of AISI 52100 steel was improved up to 78 times after TRD treatment depending on applied load and sliding velocity. Wear mechanisms are adhesive-oxidative for hardened balls and abrasive-oxidative for coated balls against hardened AISI 1045 steel discs. Keywords: Sliding wear; Steel; Niobium carbide coating; Friction. INTRODUCTIONThermo-reactive deposition/diffusion (TRD) treatment is a method for surface coating steels with a hard and wear-resistant layer of carbides, nitrides, carbonitrides [1] or borides [2] by the diffusion of carbon, nitrogen or boron in the steel substrate into a deposited layer of the carbide-, nitride-or boride-forming element.The TRD treatment can be performed using salt baths [3,4], fluidized beds [5,6] or pack cementation [7][8][9][10][11][12] at high temperatures (850-1050 °C) with treatment times of 0.5-10 hours, resulting in a layer of depth 5-15 µm.Pack cementation TRD powder usually consists of a metallic element (carbide-, nitride-or boride-forming); one inert filler that does not take part in the formation reactions of the layers, usually Al 2 O 3 or SiC; and an activator, for example NH 4 Cl that, when dissociated, chemically binds with the carbide-, nitride-or boride-forming element to form chlorides that will then react with the substrate to generate, for example, carbide layers [12,13].Niobium carbide can be used in high-temperature environments because it has a high melting point (3873 °C) The aims of this work are to produce a wear resistant coating of niobium carbide on AISI 52100 steel balls using the pack cementation method and evaluate its tribological behavior. AISI 52100 steel can be used in tools for cold work dies, cold extrusion tools, bearings, etc. Increasing the quality of the tools is only about 5% of its cost and its preparation time, making it feasible to consider any surface treatment as an investment [19]. Ball-on-disc wear tests were conducted according to ASTM G99-05 standard at sliding speeds of 0.1 and 0.3m/s and under loads of 2 and 10N. was carried out in an electrical resistance furnace under an argon atmosphere at atmospheric pressure. The hardened AISI 52100 steel balls were also analyzed. AISI 1045 steel discs, 6 mm in thickness, were cut from a bar of diameter 25.4 mm. The steel discs were sanded with silicon carbide abrasive paper up to 600 grit and polished with 1 µm alumina suspension. The AISI 1045 plain carbon steel ...

The purpose of the investigation was to examine the possibility of improving tool life by reducing the wear effect and improving the adhesion of a thin film through a compound configuration that consists in boriding and PVD deposition. Single layer coatings of TiN were deposited by PVD (cathodic arc) on quenched and tempered and on borided powder metallurgy (P/M) AISI M2 steel. Adhesion test was performed according VDI 3198. Microhardness measurements were performed on Vickers scale and the tribological behavior evaluated through dry sliding wear test, using a ball-on-disk apparatus. The wear tracks were analyzed through scanning electron microscopy (SEM) and confocal microscopy. After the wear test the samples were transversally cut, coating and substrate were investigated using scanning electron microscopy (SEM). The results showed a better adhesion of the coating for the borided sample comparing to the quenched and tempered sample. The wear mechanisms of quenched/tempered-TiN (Q/T-TiN) samples against Al 2 O 3 ball were different from the wear mechanisms of borided-TiN (B-TiN) sample against Al 2 O 3 ball.