The aluminum bronze alloy is part of a class of highly reliable materials due to high mechanical strength and corrosion resistence being used in the aerospace and shipbuilding industry. It's machined to produce parts and after its use cycle, it's discarded, but third process is considered expensive and besides not being correct for environment reasons. Thus, reusing this material through the powder metallurgy (PM) route is considered advantageous. The aluminum bronze chips were submitted to high energy ball milling process with 3% of niobium carbide (NbC) addition. The NbC is a metal-ceramic composite with a ductile-brittle behaviour. It was analyzed the morphology of powders by scanning electron microscopy as well as particle size it was determined. X ray diffraction identified the phases and the influence of milling time in the diffractogram patterns. Results indicates that milling time and NbC addition improves the milling efficiency significantly and being possible to obtain nanoparticles.

This study aims to analyze the efficiency of niobium and vanadium carbides in the high energy mechanical milling of aluminum bronze alloy. Two series of experiments were made following the same steps for both niobium carbide (NbC) and vanadium carbide (VC) additions: 30 g of chips were weighed and placed in a stainless steel jar with 3 % of carbide and 1 % of stearic acid for a mass/sphere relationship of 1:10. The milling was realized using a planetary ball mill for 10, 30 and 50 hours in an inert argon atmosphere at 300 rpm. Results shown in laser diffraction indicate a great reduction in the particle sizes of powders when VC is used. For 30 hours milling, D50 values ranged from 1580 μm with NbC to 182.3 μm with VC addition. The D50 values ranged from 251.5 μm with NbC to 52.26 μm with VC addition, for 50 hours milling. The scanning electron microscopy showed that in 10 hours of milling, the energy was not sufficient to achieve the shear of chips in both cases. For 30 hours, it's possible to observe particles with sizes between 100 μm and 800 μm with NbC addition while for the same milling time, with VC it's possible to see particles with different sizes, but with many shapes of fine particulates. For 50 hours milling, particles achieved the smaller sizes between 50 and 200 μm with NbC and ranging from 5 until 50 μm with VC addition.Keywords: aluminum bronze; niobium carbide; vanadium carbide; high energy ball milling; powder metallurgy. Alexandre Nogueira Ottoboni Dias

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The most efficient method to reduce material loss and frictional energy losses is by using lubrication. An alternative is the use of solid lubrication, specifically by using solid lubricants evenly distributed in a metallic matrix, thus forming self-lubricating composites, which are capable to induce low coefficients of friction in mechanical systems. Molybdenum disulfide (MoS2) is a very versatile solid lubricant, suitable for lubrication in critical circumstances such as vacuum, high temperatures and pressures. Therefore, the aim of this research is to produce samples of sintered composites consisting of homogeneously distributed MoS2 in a bronze matrix obtained by cold uniaxial pressing and to compare the wear rates and friction coefficient between the MoS2-free bronze and the self-lubricating composites. Different MoS2 percentages were used in order to characterize the tribological properties of the composites as a function of the MoS2 content. At the end of the experiments, it was found that samples with 20% MoS2 did not sinter properly, due to the large amount of lubricant between the bronze particles. It was also found that the mixture with 5.0% MoS2 had proper sintering, satisfactory hardness, achieved lower friction coefficient and better material wear performance due to the optimal amount and good distribution of MoS2 when compared with the rest of conditions studied.

Aluminum bronze alloy is applied in environments that require materials of high mechanical resistance and wear, such as marine, oil & gas and aerospace ones. This study analyzes the densification of composites based on aluminum bronze with additions of the vanadium (VC) and niobium (NbC) carbides, and the influence of these carbides in the milling efficiency and improvement of the diffusion process between particles to obtain better results for density and porosity. The composites were produced by powder metallurgy from aluminum bronze powders obtained from the mechanical milling process of discarded scraps. The efficiency of the sintering process depends on parameters, such as the time and temperature of sintering, together with the size of the particles obtained from the milling process. This study aimed to obtain and characterize the composites produced by the powder metallurgy route, with NbC and VC addition and to analyze physical properties, such as density and porosity. The powder morphologies, particle sizes and samples sintered were performed by scanning electron microscopy (SEM), X ray diffraction (XRD), laser diffraction analysis and optical microscopy (OM). The results indicate that addition of VC improves the milling efficiency, when compared to NbC addition, since it promotes a greater reduction of the particle size, directly favoring the sintering process. In this case, to achieve similar particle size, twice the milling time was required when NbC was used. The density values achieve ~ 73% of reference material for VC addition and ~ 68% for NbC and porosities varying between 27% and 38%.

The 316L stainless steel (316L SS) is one of the most used metallic materials for implants, due to its high mechanical properties and low cost. However, it is bioinert. One possibility to improve its biocompatibility is the production of a composite with β-tricalcium phosphate (β-TCP) addition. This study investigated the mechanical behavior of 316L SS/β-TCP composites through powder metallurgy. For this, used were 3 compositions, with 0 %, 5 % and 20 % of β-TCP. The compositions with 5% and 20% were milled during 10 hours with a mass/sphere ratio of 1:10 and 350 rpm. All compositions were uniaxially pressed with 619 MPa and sintered during 1 hour at 1100°C. The microstructural and mechanical evaluations were performed through scanning electron microscopy, density and compressive strength. The results indicated that, by increasing the percentage of β-TCP in the compositions, the mechanical resistance decreases, as a consequence of its low load support.

In this work it was analyzed the evolution of mechanical properties of Dual-Phase steel as a function of volume fractions of ferrite and martensite, obtained from steel type LNE 380. The intercritical region and the existing phases in function of temperature were determined using the THERMOCALC software. The samples of steel were quenched at different temperatures to obtain differents microstructures consisting of ferrite, pearlite and martensite. The microstructural characterization of the samples was performed by qualitative and quantitative metallography. The mechanical properties were determined by hardness and impact tests. It was concluded that the volume fraction of ferrite and martensite calculated experimentally agrees with the simulation and the variation of these fractions affects significantly the hardness of the steel, but does not significantly affect the results of fracture toughness.

This article analyzes the influence of mechanical ball milling parameters on processed aluminum bronze chips in order to increase the efficiency of this process in terms of particles' size reduction. Also evaluated is the addition of vanadium carbide (VC) in this response, along with its microstructure and magnetic properties. The experiments have been carried out in accordance with DOE design methodology. After machined, its residues can still be reused to produce composites through powder metallurgy routes, preserving good mechanical properties without onus to the environment. The study aims to produce and characterize powders resulting from ball milling processes, identifying the influential parameters, in addition to verify its soft magnetization behavior. The powder morphologies and particle sizes underwent scanning electron microscopy (SEM), coupled with energy-dispersive spectroscopy (EDS) and laser diffraction particle analyses, respectively, in addition to phase identification via X-ray diffraction (XRD). Moreover, saturation magnetization (M s ), remanent magnetization (M r ), coercivity (H c ), and remanence-to-saturation ratio (M r /M s ) were determined through magnetic hysteresis curves obtained from a vibrating sample magnetometer (VSM). Results indicate that % VC and milling time are the main parameters to improve the milling efficiency and obtain submicrometric particles with sizes almost 800 times smaller than the initial chips. After the milling process, aluminum bronze powders presented certain amorphization, a decrease of about 24% in M s and an elevation about 81% in H c , both compared with the as cast material. The M r /M s ratio indicates a slight conservation of magnetization.