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The exposure of mechanical components to bad weather and conditions, such as corrosive environments, is recurrent, making the use of nickel alloys in various market segments favorable due to their high corrosion resistance as compared to other types of materials. However, the need to increase the shelf-life and performance of these materials turns surface treatments into an important alternative to optimize surface properties, which makes it possible to use alloys in new applications. In this scenario, the boriding process is a valuable treatment option, since it allows for the improvement of surface properties in ferrous and non-ferrous materials. In the present study, the boriding thermochemical treatment was performed on the Inconel 718 alloy, under different temperature and time conditions. The roughness, microstructure and mechanical properties of the alloy were evaluated by confocal microscopy, scanning electron microscopy, X-ray diffraction and instrumented indentation, respectively. The results showed that, as the temperature or time parameters increase, there is increased layer thickness and hardness, as well as evidence of formation of CrB, FeB and Ni3B + Ni2B + Ni4B3 in the layer. The assessment of the behavior of the treated samples subjected to corrosion testing was performed by using the potentiodynamic polarization technique, revealing less corrosion potential and no passivation in the boride layers.

Boriding treatment was applied to AISI 1020 steel to improve its wear resistance. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, Vickers microhardness testing, fracture toughness, and confocal microscopy. The microscale abrasive wear behavior was also investigated. SiO2 abrasive particles were used as abradant with slurry concentrations of 0.5 and 1.0 g/cm3. Normal loads of 0.49 and 0.98 N were used. Fe2B phase was identified in the boride layer via XRD analysis. The Fe2B layer was 169 μm thick with a mean hardness of 1608 ± 101 HV0.05 and fracture toughness of 5.35 ± 1.43 MPa m1/2. A reduction in the hardness of the outermost surface of the boride layer was observed owing to the formation of a porous region. Boriding treatment improved the wear resistance of the steel substrate. Sliding abrasive wear was the main mechanism under all tested conditions. The presence of micro-rolling abrasion and fracture-based mechanisms was observed for untreated and borided samples, respectively. Keywords: Microscale abrasion, Boriding, AISI 1020 steel, SiO2

The aim of this study is to obtain and characterize surface layers on low carbon steel with the pack boron-nitro-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.

The replacement of electrolytic hard chrome (EHC) by high velocity oxy-fuel (HVOF) sprayed coatings is investigated due to the toxicity of EHC process. The wear behavior of AISI 4140 steel coated by HVOF-, EHC-process was compared to quenched and tempered (Q&T) steel using a pin-on-disc apparatus. The wear tests were conducted at room temperature, 10 N applied load and 0.1 m/s sliding speed in dry condition. The results were interpreted on the basis of the microstructure and hardness. Wear micromechanisms were investigated by SEM. The predominant presence of the WC phase and the formation of W2C and W3C phases, associated with decarburization of superheated regions of the CoCr binding phase of HVOF-coated samples were observed by X-ray diffraction analysis. Wear tests results show that the WC-10Co-4Cr coating exhibits better wear resistance than the EHC coating and Q&T steel. The formation of a wear resistant tribolayer was determinant to the excellent wear behavior of the thermally sprayed coating.