Materials Science Forum Vol. 802

Abstract: In this work, different commercial Co-Cr-Mo powders were used in selective laser sintering. Commercial powders with particle size distribution between 5 and 50μm were sintered by laser sintering, and characterized. The samples were characterized by X-ray diffraction, indicating Co as the only crystalline phase. Relative density was measured by Archimedes method showing values between 90 and 96% of TD, depending on the powder used. Scanning electron microscopy performed on the cross section of the sintered samples, indicates that the microstructural features are similar, but the surface finish of the samples differ significantly due to the morphology and size distribution of the starting powders used.

Abstract: Shape memory alloys (SMAs) are a class of material that undergoes a reversible shape change after a plastic deformation. The recovery of the original shape is possible due to a structural transformation upon heating to a critical temperature. The shape memory effect is related to a martensitic-austenitic transformation from a phase with a low symmetry (martensite) to a high-temperature phase (parent phase) [1]. Cu-based shape memory alloys have the advantage of large thermal and electrical conductivities and the system Cu-Al-Ni alloys are quite attractive due to better stabilisation against aging phenomena [2].

Abstract: In this study it was evaluated the performance of coatings based on Cr₃C₂-25 (80Ni-20Cr) and CrC-30NiCr. The coatings were deposited by high velocity oxygen fuel (HVOF), with an average thickness of layer equal to 7.8μm. Samples were subjected to adhesive wear test (according ASTM G99) with a pin Ø 6 mm (SAE 52100). In the test was applied normal force equal to 50 N and tangential speed equal to 0.5 m/s. The test time was 30 minutes at room temperature, without lubrification. The wear surfaces were characterized by optical microscopy, scanning electron microscopy and X-ray diffraction. The microhardness of the coatings was also evaluated. The results showed that the coating based on Cr₃C₂-25(80Ni-20Cr) presented a performance ten times higher in wear resistance when compared to coating CrC-30NiCr.

Abstract: First results of a possible alternative route for plasma assisted processing of 410 LHC steel powder compacts are shown in present work. Carburizing treatment was performed simultaneously with the sintering of samples. The main motivation of this study was verifying the possibility to eliminate the manufacturing step of the carburizing thermochemical treatment, which is normally applied in the production of sintered steel parts subjected for extreme wear conditions. Treatment was carried out in pulsed DC abnormal glow discharge, using gas mixture (atmosphere) of 99%(80% Ar + 20% H₂) + 1.0% CH₄, at 1100 °C, during 60 min, and 9 Torr, for two different conditions, termed: a) Sintering-Carburizing at high flow (for 480 sccm); and b) Sintering-Carburizing at low flow (for 120 sccm). Characterization of the treated samples was performed by Optical Microscopy, SEM, XRD, and microhardness measurements. The presence of CH₄ in the plasma atmosphere proved to be viable to carburize the sample surface while the sintering stage was carried out. Despite of this, further studies are required to optimize both the carburizing + sintering effects, aiming to produce non-brittle structures and parts, opening a new R&D field to the plasma sintering of metallic materials.

Abstract: Plasma immersion ion implantation (PIII) method is often used to cleaning and enhancing mechanical properties of the surface of materials. In this work, the AISI 304 was treated in a PIII system to improve tribological and wear resistance properties. The new HV pulser was prepared to reach high average power (10 kW) using solid-state technology and a pulse transformer rather than using a conventional one based on hard-tube tetrodes with HV storage capacitors. For preliminary tests, low-density nitrogen plasma and pulses of 10 kV, 30μs width, and 1 kHz were used. A larger vacuum chamber used (600 liters) is very important for treating large area components and for batch processing. This is necessary in industrial applications and in cases that require high quality processing as in spatial or medical components. Stainless steel support was used to hold the samples in our case. XRD, SEM, and pin-on-disk surface diagnostics were used for investigation and characterization of the treated surfaces.

Abstract: The phosphorus content has significant effect on the steels quality and their applications. The iron ore resources around the world has continuously increased the amount of phosphorous due to the increase of the mining volume with less sterile generation aiming at the efficient utilization of the mining resources, as consequence larger amount of materials with high iron content but with higher phosphorous has been incorporated in the mining body. An alternative to enhance the mining efficiency is to perform a pre treatment of part of the mining body and subsequent blending to attain the acceptable phosphorous in the steelmaking. A viable alternative for reducing the phosphorus content of these residue is to use the acid leaching process which is considered an economical process for the dephosphorization of the iron ore, however, depending on the way the element phosphorus is contained in the ore it will demand additional energy. The objective of the present paper is to study the effective heating and cooling rates of iron ore using microwave energy and its subsequent cooling effect in a short period (thermal shock). Through the X-ray diffraction analysis and applying the Rietveld method it has been possible to demonstrate the mineralogical composition of the iron ore samples and the effect of rapid heating and cooling suitable to promote the fissure formation, thus enhancing the leaching efficiency. The scanning electron microscopy (SEM) was used to analyze the structure of ore due to the effect of its heating and cooling rates.

Abstract: The present study aimed to explore possible thermal processing conditions of a steel AISI 43100, seeking the best combination of properties, especially strength and ductility. Different routes of heat treatments for continuous cooling were applied to the material, and the mechanical properties were evaluated by tensile and hardness tests. The microstructure and fracture micromechanisms were characterized by scanning electron microscopy (SEM). It was observed a strong influence of cooling rate on the formation of microstructure, reflecting directly in mechanical properties.

Abstract: This work presents the results of treatments by CO₂ laser of automotive rings covered with carbon black slurry, aiming to improve the friction rate and the ring lifetime. The results of this treatment were characterized by scanning electron microscopy, Vickers hardness, ball on disk test and X-ray energy dispersive spectroscopy. The scanning electron microscopy showed that the laser treated area extent reaches near to 120 μm depth. The measured hardness was about 950 HV_0,05 and the friction coefficient lower than 0.2. The energy dispersive spectroscopy along the treated cross section showing carbon diffusion into the metallic substrate.

Abstract: The article to be presented will cover the whole process done in a fracture test for impact, taking into account the thermal treatment of the sample to be studied. The main objective of this article is to observe, verify, analyze and understand how the temperature difference of several samples influences the type and appearance of the fracture. The impact test have a great importance in industry, is through this that you can verify that the material is ideal for application in the production of equipment and vehicles that operate in high or low temperatures. The evaluation criteria of this trial are the energy absorbed by the sample, and the percentage of its characteristic lateral extension, and the percentage of fracture, ductile or fragile, and corresponding to a ductile fracture mode, in which the test at higher temperatures, the impact energy is relatively large, and fragile fracture mode, being one that as the temperature decreased, the impact energy will suffer decline. The most important result of the impact test is the measure of the energy absorbed by the test body to deform and break, measured by the variance of the gravitational potential energy of the hammer (machine component of the impact test) before and after impact. Therefore, providing the conclusion that the smaller the energy absorbed by the sample, more fragile it is depending on the temperature applied.

Abstract: Diamond-like carbon (DLC) films are widely known for their attractive properties. High adhesion between coating and substrate is necessary to ensure these properties. The bombardment by energetic species during growth tends to generate high intrinsic compressive stresses levels, which have several consequences in coating performance. However, this problem can be solved with the deposition of a thin interlayer with intermediary properties. In this work, films were grown on M2 steel using a modified plasma enhanced chemical vapor deposition PECVD pulsed-DC discharge. In order to improve the coating adherence on the substrate, a silicon interlayer was deposited varying the growth time, which generated different interlayer thickness. Tribological tests were performed to study adhesion and friction gradient. Raman spectroscopy was used to verify the structural arrangement of carbon atoms. The results showed that thickness variation in silicon interlayer leads to significative changes in adhesion between coating and substrate.