Nickel alloys and composites are interesting engineering materials as a result of a combination of mechanical, corrosion and wear resistance at service temperatures that exceed those of steels and steel-based materials. The present study aimed at sintering Ni-graphite composites from NiO-SiC mixtures and investigate the in-situ formation of graphite. NiO powders were mixed with SiC (0, 3, 5 and 10 wt.%) and attrition-milled during 1 h. The mixtures were then granulated using 1.5 wt.% paraffin in hexane solution and uniaxially pressed under 400 MPa. The cylindrical pellets were then sintered at 1200 ºC. The sintered materials were characterized by density measurements, dilatometric and microstructural analyses, as well as Vickers microhardness. The results showed that Ni-graphite composites were successfully produced from NiO-SiC mixtures with full reduction of NiO and dissociation of SiC to form a Ni-Si matrix and graphite nodules. mechanical steelbased steel based Nigraphite Ni NiOSiC insitu situ 0, 0 (0 3 wt attritionmilled attrition milled h 15 1. wt. 40 MPa 120 ºC measurements analyses microhardness NiSi Si nodules ( 4 12

Abstract This work presents a study on effect of cutting parameters in force, texture and chips morphology obtained during the turning of a self-lubricating sintered composite. The tests were performed varying the cutting speed (vc = 100 and 200 m/min), feed (f = 0.1 and 0.2 mm), depth of cut (ap = 0.5 and 1 mm), as well as the materials manufacturing route in single pressing (SP) and double pressing (DP). The variation in the cutting parameters influenced the components of the machining force. The cutting, feed and passive force were approximately 10%, 10% e 25% higher, respectively, for DP materials. The turning process generated surfaces with values of maximum height (Sz) between 28.3 to 10.8 μm, Kurtosis (Sku) > 3 and Skewness (Ssk) < 0.3. The chip type obtained was segmented and the chip thickness ratio was influenced by the variation of the cutting parameters and the materials manufacturing route.

In powder metallurgy the addition of alloying elements is a widely used alternative to increase the service life of mechanical components. However, they have an associated cost. One less exploited process is surface enrichment (or surface alloying), whose same result is obtained on the surface, but at a much lower cost. Self-lubricating composites are especially complex to be enriched, precisely because they have to avoid the deposition of alloying elements over the lubricant stocks. This paper reports the characterization and tribological properties of self-lubricating composites enriched with molybdenum or nickel. Sintered samples were produced for comparative purposes. Wear resistance, friction coefficient and wear rate were analyzed for the evaluation of tribological properties. The results showed that the enrichment process did not cover the lubricant stocks. In addition, the Mo-enriched samples presented the best tribological results, with a 250 % increase in scuffing resistance in relation the sintered sample, and lower wear rate.

Powder metallurgy is a growing sector in industrial production, as it offers outstanding energy, cost and material savings in comparison with established processing routes such as casting. Hot work toll steels are usually produced by ingot metallurgy, but also by powder metallurgy, namely hot isostatic pressing and powder forging routes. In this paper we investigate the possibility of production of a hot work tool steel (AISI H13) by conventional (die compaction and pressureless sintering) and metal injection molding routes, aiming to reduce cost and production time. The sintering behavior was studied from 1250 °C until 1430 °C and the resulting parts were compared in terms of microstructure, hardness and tensile strength. The results showed that both shaping routes together with pressureless sintering are suitable to produce this alloy. By combining the best shaping approach and a tailored sintering cycle, it was possible to produce samples with 400 HV10 as well as tensile strength of 1 GPa, which are comparable to the ones obtained by powder forging.

Flat sintered copper and copper-zirconia substrates, with zirconia nanoparticles contents of 1 and 3 vol%, were produced by aqueous tape casting and controlled sintering. Aqueous suspensions were prepared to a solid content of 58 vol% using 3 wt% commercial binder emulsion. The green tapes were treated at 350 ºC in air to remove organics and sintered at temperatures ranging from 800 to 1000 ºC in atmosphere of Ar/5%H2. Copper tapes reached almost full densification at 900 ºC. Composite with 1 vol% zirconia, sintered at 800 ºC, maintained high density and provided a noticeable increase of the mechanical strength, whereas further additions up to 3 vol% reduced the densification and the resulting mechanical performance became poorer.

RESUMO O processamento coloidal é uma técnica amplamente usada para a produção de componentes cerâmicos. Diversos artigos científicos foram publicados na última década apresentando a possibilidade de se obter suspensões aquosas concentradas estáveis de partículas metálicas a partir do seu controle de pH e uso de dispersantes. Este artigo tem o objetivo de estudar a produção de um aço com microestrutura austenítica usando pós elementares de ferro (Fe) e níquel (Ni) via rota coloidal. Para tanto, foram realizadas medições de potencial zeta entre os pHs 2 e 12 para a composição Fe30Ni em massa. As suspensões aquosas atingiram concentrações de sólidos de até 45% v/v e processadas por colagem de barbotina. Os compactados colados foram caracterizados por densidade (Arquimedes), análise térmica diferencial (ATD) e dilatometria. Após a sinterização aos 900°C e 1100°C/1h, os compactados apresentaram microestrutura com formação de maclas de recozimento, porosidade inferior a 10% em volume e microdureza Vickers aproximada de 160 HV.

ABSTRACT Colloidal processing is a widely used technique to produce ceramic components. Several papers have been published in the last decade presenting the possibility to obtain aqueous concentrate stable suspension of metallic particles from their pH control and using dispersants. This paper aims to study the production of a steel with austenitic microstructure using elemental iron (Fe) and nickel (Ni) powders via colloidal route. For this, Zeta potential measurements were performed between pH 2 and 12 to Fe30Ni wt% composition. Aqueous suspensions reached solids concentrations of up to 45% v/v and processed by slip casting. The compacts were characterized by density (Archimedes), differential thermal analysis (DTA) and dilatometry. After sintering at 900°C to 1100°C/1h, the sintered bodies presented a microstructure with of annealing twins, porosity less than 10 %v/v approximate Vickers microhardness of 160 HV.

Abstract To modify the surface structure of AISI 1005 steel and its properties without any dimensional loss, different plasma surface treatments were performed at low temperatures (500 ºC) in this study. The samples were subjected to single plasma treatments including: nitriding (N5% and N3%), carburizing (CE) and ferritic nitrocarburizing (NC) and to duplex treatments of nitriding followed by carburizing (N5%+CE and N3%+CE) and ferritic nitrocarburizing followed by carburizing (NC+CE). The gas mixture used for these treatments was varied as follows: nitriding (5%N2+95%H2 and 3%N2+97%H2), carburizing (5%CH4+95%H2) and ferritic nitrocarburizing (5%N2+1.5%CH4+93.5%H2). A microstructural characterization of the samples was carried out using optical and scanning electron microscopy in addition to XRD analysis. Microhardness testing was also performed. The XRD analysis showed a stabilization of the outermost cementite layer for all of the carburizing treatments. The results show that a greater hardness increase was achieved for the nitriding treatment as well as a more regular compound layer. However, a greater depth of hardening was obtained in samples with NC+CE and N5%+CE, which extended to the hardened depth to 800 µm.

When multifunctional surface engineering processes that combine purpose-oriented phases are applied to soft substrates, a combination of high wear resistance, high load support and low coefficients of friction can be achieved. In this study, the effects of different nitrided layers on the tribological behaviour of a diamond-like carbon (DLC) film deposited on a SAE 1040 steel were investigated. The nitriding was carried out under different temperatures and gas mixtures to create three distinct nitrided layers: two compound layers with predominant ε and γ' phases and a diffusion layer. All of the surfaces were then coated with DLC deposited via plasma-enhanced chemical vapour deposition (PECVD). The tribological tests indicated that the best performance was achieved for a specific combination of hardness, surface roughness and nitride type. The best load-bearing capacity between the DLC coating and the soft substrate was achieved when the nitrided layer was primarily a diffusion layer.

In this work carbon steel plates were dip-coated with a composite film obtained from a colloidal suspension of Ni-TiO2. Suspensions with different solids contents were used to evaluate the adherence of the film and the microstructural features. The samples were characterized using both optical and scanning electron microscopy, energy dispersive spectroscopy and microhardness. The microstructural analysis revealed that the films have high porosity at the surface. However, an interfacial region was observed demonstrating that there was good adhesion between both materials. This region shows an increased hardness that can be attributed to diffusion mechanism of nickel from the composite film to the steel matrix. Besides the interface, there was an abnormal grain growth, followed by a region of smaller grains of austenite and at longer distances near the center of the plate some colonies of pearlite appear.

Processing of high manganese austenitic sintered steels present several challenges concerning thermodynamic reactions that occur during the sintering of these materials such as Mn oxidation, sublimation and even the formation of liquid phases or undesired compounds, e.g. grain boundary carbides. Therefore it is extremely important to adjust the sintering parameters to obtain the adequate microstructure and properties. In this work, the effect of some sintering parameters, i.e. temperature, gas atmosphere and cooling rate are studied by dilatometry. The experiments revealed that the sintering temperature has small impact on the microstructure formation. On the other hand, the decrease on oxygen chemical potential in the furnace atmosphere resulted in less oxidation of the powder particles. Moreover, the increasing on the cooling rate to 50 °C/min avoided the formation of grain boundary carbides. As a main conclusion, a special sintering cycle for Hadfield steel samples was suggested.

Copper is a well know material for use as heat sink or heat exchanger. However, copper has a considerable low tensile strength and temperature limit. A material that has a good thermal conductivity, low cost, but also resistance is the desired. Effects of copper on the sintering and thermal properties of iron-copper composites produced by powder metallurgy and Fe on copper-iron composites have been investigated. Copper and iron were varied from 20 to 80 vol.% in the samples, alternating the continuous phase. Sintering studies were performed by in-situ dilatometry aiming to define the proper conditions for sintering, without swelling normally associated with copper. Results indicate that the type of sintering, final microstructure, specially the phases relation and distribution and not only the amount of copper, have a great effect into the thermal properties. By controlling the sintering parameters, it is possible to obtain dimensionally stable samples with higher thermal conductivity and lower copper amount.

In this work, plasma carburizing of sintered pure iron at low temperature was investigated. Samples were carburized under a dc abnormal glow discharge in two mixed atmospheres (5%CH4 + 95%H2 and 20%CH4 + 80%H2) at 500 °C and 700 °C for 3 and 6 hours. The influence of these parameters was investigated by Scan Electron Microscopy (SEM), X-ray Diffraction (DRX), Raman spectroscopy and microhardness measurements. There is a correlation between temperature and layer morphology, and a layer of polycrystalline cementite was obtained at 500 °C and 700 °C on a ferrite substrate. Furthermore, the carburized layer thickness increased with an increase in the treatment time and the methane percentage. The topography is very dependent on the treatment temperature.

A moldagem de pós por injeção é um processo de fabricação de elevada produtividade que possibilita obter componentes de geometria complexa, estreita precisão dimensional e boas propriedades mecânicas. Neste processo, uma mistura de uma determinada quantidade de pós e ligantes orgânicos (polímeros, ceras e óleos) é obtida por meio de uma massa de injeção (feedstock) o qual tem características reológicas adequadas para promover a injeção desta massa em uma cavidade de um molde. A produção de ligas de níquel por meio deste processo é uma alternativa para produção de produtos que requerem aplicações avançadas onde se exige resistência a corrosão e oxidação, resistência mecânica a altas temperaturas e baixo coeficiente de atrito. Neste trabalho apresentamos um estudo das propriedades microestruturais e mecânicas de uma liga de níquel (Ni-Fe-Cr-P) processada via moldagem de pós por injeção, utilizando pós de níquel carbonila com e sem a presença de fase líquida durante a sinterização. Os resultados foram comparados com a mesma liga processada por compactação de pós. Os resultados demonstraram a necessidade de maior quantidade de matéria orgânica para o desenvolvimento da massa de injeção (feedstock: 15% m/m de polímero) para os tipos de pós metálicos utilizados (níquel carbonila do tipo INCO 123) se comparado ao feedstock de ligas comerciais que normalmente utilizam uma quantidade menor de matéria orgânica (feedstock: 9% m/m de polímero). A maior quantidade de matéria orgânica necessária para a preparação do feedstock deve-se a morfologia dos pós empregados (superficie rugosa - tipo spiky) que promove retenção de carbono durante o processo de extração, ocasionando a necessidade de otimização do ciclo de extração térmica e sinterização. Ciclos mais lentos e a baixa temperatura promoveram a total retirada dos ligantes. A liga de Ni-Fe-Cr-P injetada apresentou contração de aproximadamente 50%, além de elevado teor de poros quando comparado ao material compactado, o que influenciou as propriedades mecânicas e dureza aparente do material.

The powder injection molding is a manufacturing process that allows high productivity to obtain complex geometry components, dimensional accuracy and good mechanical properties. In this process, a mixture of a quantity of powders and organic binders (polymers, waxes, oils) is obtained through injection of a mass (feedstock) which has rheological properties suitable for promoting the injection of this mass in a cavity of a mold. The production of nickel alloy by this process is an alternative to production of products that require advanced applications, which require resistance to corrosion and oxidation, mechanical strength at high temperatures and low coefficient of friction. This paper we present the study of the microstructural and mechanical properties of a nickel alloy (Ni-Fe-Cr-P) processed by powder injection molding, using carbonyl nickel powders with and without the presence of liquid phase during sintering. The results are compared with the alloy processed by powder compaction. The results demonstrate the need for increased amount of organic matter for developing the injection mass (feedstock: 15 wt.% polymer) for the types of metallic powders used (nickel INCO type 123 carbonyl) compared to commercial alloy feedstock typically use a smaller amount of organic matter (feedstock: 9 wt.% polymer). The largest quantity of organic matter needed for the preparation of the feedstock due to the morphology of the powders used (spiky) which promoted carbon retention during the extraction process, resulting in the need to optimize the extraction cycle and thermal sintering. Slower cycles and low temperature promoted the complete extraction of the ligands. The Ni-Fe-Cr-P alloy injected showed shrinkage of approximately 50%, and high levels of pores as compared to the compacted material, which influenced the mechanical properties and apparent hardness of the material.

The purpose of this work was to develop nickel self-lubricating composites using solid lubricant as second phase and obtained by powder metallurgy. The work involved the study of chemical stability and chemical interaction between the nickel alloy matrix and solid lubricating additives (molybdenum disulfide, graphite and hexagonal boron nitride). The results showed a thermodynamic stability during sintering for the composites containing the phases of graphite and hexagonal boron nitride. The presence of molybdenum disulfide phase permits a reaction with the matrix, the formation of a liquid phase of nickel sulfide and the solubilization of molybdenum in the matrix.

This work reports experimental results on sintered PIM 316L stainless steel low-temperature plasma nitriding. The effect of treatment temperature and time on process kinetics, microstructure and surface characteristics of the nitrided samples were investigated. Nitriding was carried out at temperatures of 350, 380, 410 and 440 ºC , and times of 4, 8 and 16 h, using a gas mixture composed by 60% N2 + 20% H2 + 20% Ar, at a gas flow rate of 5.00 × 10-6 Nm³s-1, and a pressure of 800 Pa. The treated samples were characterized by scanning electron microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma nitriding is a diffusion controlled process. The calculated activation energy for nitrided layer growth was 111.4 kJmol-1. Apparently precipitation-free layers were produced in this study. It was also observed that the higher the treatment temperature and time the higher is the obtained surface hardness. Hardness up to 1343 HV0.025 was verified for samples nitrided at 440 ºC. Finally, the characterization of the treated surface indicates the formation of cracks, which were observed in regions adjacent to the original pores after the treatment.