Abstract This article evaluates the effect of recrystallization annealing soaking time on the tribological behavior of cold upsetted low carbon steel. The 40% cold formed steel was subjected to annealing at 900 °C, for 10, 20, 30, 40, 50 and 60 minutes. The mechanical properties of hardness, tensile strength, yield strength and ductility, measured through specific deformation, as well as the precipitation of carbides through microstructural analysis were examined. In order to analyze the volume of removed material, the wear test was performed using a pin-on-disk tribometer according to ASTM G99. The results showed that the combination of lamellar perlite precipitation and pearlitic interlayer spacing reduction increases the mechanical strength of 1020 steel, reduces ductility, increases friction coefficient and increases wear observed by the volume of removed material increase.

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.

Herein, it was conducted a study in order to examine the main fracture characteristics in the transverse rupture strength test (TRS) of a high speed steel (HSS) AISI M2 produced by powder metallurgy (PM) and with boriding treatment. Four conditions have been studied: as-sintered, borided, normalized and borided + TiN. The TRS tests were conducted in accordance with ASTM B528-12 standard. Density, Vickers hardness and transverse rupture strength properties were evaluated. Fractography was observed by scanning electron microscope (SEM). TRS test in the as-sintered condition had the best performance. The fractography of samples showed very irregular appearance, with interconnected porosity for the matrix of the samples and the boride layer had a smooth surface with low porosity. It was observed on the boride layer, the growth of boride layers inside the pores, filling them, which is a positive factor on the TRS. However, cracks were observed in the FeB/Fe2B interface of boride layer, which embrittle the material and reduce the TRS. In fractography of borided samples, it is observed that two fracture modes occur, mode I and mode II. This should be explained owing to the difference between the elasticity modulus of FeB and Fe2B interface.

ABSTRACT 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 Al2O3 ball were different from the wear mechanisms of borided-TiN (B-TiN) sample against Al2O3 ball.

In this study, plasma nitriding, gas nitriding and solid nitriding were performed in AISI H13, AISI P20 and N-8550 tool steels. The aim of the study was compare the acquired properties after the thermochemical treatments and evaluate the efficiency of the solid nitriding treatment. The samples were analyzed using a microhardness tester and a scanning electron microscope. The typical nitriding layers were observed - white layer and diffusion layer. The phases Fe4N - γ´ and Fe2,3N - ε were identified using an X- Ray diffractometer. The microhardness values of the nitrided layers obtained by the solid nitriding treatment were compatible with the other values of microhardness obtained by plasma and gas nitriding. The thickness of the nitrided layer obtained by the solid nitriding treatment was irregular.

Plasma nitriding, gas nitriding and solid nitriding were applied in tool steels (AISI H13, AISI P20 and N-8550). The acquired properties were compared and evaluated on these three processes with the aim to verify the solid nitriding performance. In order to promote the solid nitriding, the samples were surrounded by a solid compound with the Fe4KCN stoichiometric formula, inside an aluminum recipient. All thermochemical nitriding processes were performed at 560 °C. The wear behavior has been assessed by dry sliding wear test, using a pin-on-disk apparatus, the amount of wear was obtained by the use of a profilometer. The wear tracks were analyzed using SEM (Scanning Electron Microscopy). After the wear test the samples were transversally cut, to obtain the Vickers microhardness. Solid nitriding presented good performance, formation of a nitriding layer, values of microhardness compatible with the other processes and the best results of wear.

Neste trabalho são estudados os efeitos da adição de nanotubos de carbono de parede múltipla (NCPM) em uma matriz de Poli(L-ácido láctico) (PLLA). Foras avaliadas duas rotas distintas de dispersão dos NCPM, uma utilizando agitação mecânica em solvente e a outra utilizando sonificação de alta energia em solvente. As propriedades mecânicas destes nanocompósitos foram avaliadas utilizando nanoindentação e microdureza vickers. Através da calorimetria exploratória diferencial foram determinadas as propriedades térmicas dos nanocompósitos (Tg, Tc, Tm e cristalinidade) obtidas. Por último, as propriedades tribológicas foram determinadas através de ensaios de deslizamento do tipo pino sobre disco, onde foram utilizadas diferentes cargas normais. As propriedades mecânicas e térmicas não foram significativamente afetadas pela adição do nanotubos, o que não se repetiu nas propriedades tribológicas, onde tanto o método de dispersão quanto a concentração de NCPM afetaram as propriedades. A micrografia das trilhas de desgaste sugere ainda que o mecanismo atuante foi modificado com a incorporação dos nanotubos, o mesmo pode ter acontecido nas amostras sonificadas.

This work studied the effects of the addition of Multiwalled Carbon Nanotubes (MWCNT) to a PLLA matrix. Two distinct methods of preparation were employed: a combination of a solvent/ mechanical stirring and a combination of a solvent/high energy sonication. The mechanical properties of the nanocomposites were determined by nanoindentation and by the Vickers hardness test. Thermal properties of the nanocomposites (Tg, Tc, Tm and crystallinity degree) were determined by DSC. The tribological properties of the nanocomposites were determined by using a pin-on-disc apparatus. Mechanical and thermal properties did not present significant alterations, although tribological properties presented significant changes caused by the method of preparation and different loads. SEM images indicated that the wear mechanism was changed by the addition of MWCNT.