Materials Science Forum Vol. 802

Abstract: In this work, the microstructural features of the particles based on 66% Co-28% Cr-6% Mo alloy, were investigated by X-ray diffraction and Scanning electron microscopy (SEM). Powders obtained by high-energy ball milling in an inert atmosphere, and held in SPEX mill with times between 15min and 120min, about ball/powder ratio of 6:1, were characterized by X-ray diffraction indicating in all conditions, Co phase as the crystalline phase of the system. The powders have a morphology that indicate a continuous reduction in average particle size as a function of increasing time, however, the shape of the particles initially flat for times up to 30 minutes, becomes spherodized after 30 minutes of grinding.

Abstract: In this study, the effect of ball/powder ratios for grinding particles of a dental alloy consisting of 66%Co-28%Cr-6%Mo was investigated. Metal powders were obtained from SPEX mill, with tungsten carbide balls, setting the milling time to 60 minutes, 50% of volume of grinding vessel filled with powder and argon inert atmosphere. The ball/powder ratio was varied between 4:1, 6:1, 8:1, 10:1.The powders were characterized by XRD indicating Co as only crystalline phase present, which indicates that Cr and Mo enter into solid solution with the matrix Co. Measurement of crystallite size conducted using the Scherrer equation indicate the crystallite size about 10 to 6nm, due to the increase of the ball/powder ratio of 4:1 to 10:1. The morphology of the milled powders were analyzed by scanning electron microscopy (SEM) and indicate that the agglomerates created by the grinding process must have average sizes varying between 100μm and 200μm with the modification of the ball/powder.

Abstract: TiFe compound was produced by high-energy ball milling of TiH₂ and Fe powders, followed by heating under vacuum. TiH₂ was used instead of Ti in order to avoid the strong particles adhesion to grinding balls and vial walls. Mixtures of TiH₂ and Fe powders were dry-milled in a planetary mill for times ranging from 5 to 40 hours. The amount of sample, number and diameter of the balls were kept constant in all experiments. After milling, samples were heated under dynamic high-vacuum for the synthesis reaction. As-milled and heat-treated materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The mean crystallite sizes and microstrains were determined by XRD line profile analysis using the Warren-Averbach method. As-milled materials presented only Fe and TiH₂ phases. Nanostructured TiFe compound was formed after heat treatment. TiH₂ was effective for providing low adherence of the powders during milling.

Abstract: In this works, aluminum scraps powders were mixed with commercial graphite and mechanically alloyed in a high-energy ball mill and subsequently powders sintering. The initial grinding of aluminum scraps for 2 hours and then mixed with commercial graphite powder at a proportion of (y)Al-(x)C (wt%) (x = 1, 5 e 10, 25). The mixture of aluminum and graphite powders was processed for a time at 5 hours of milling. The samples were sintered at a temperature of 750°C and 1000°C. Samples were analyzed by scanning electron microscopy and X-ray diffraction. The results of this study were to find important parameters of composition and sintering, because the increase in concentration of carbon in the aluminum indicates that the material may have different applications.

Abstract: The synthesis, microstructural, electrical and mechanical properties characterization of composites based on Cu-Ni–Ag-Al₂O₃ is a work that exposes the investigation of the correlation of the microstructures formed in the material with its physical properties and its manufacturing method. Cermets based on copper, nickel and silver have been doped with alumina varying the proportions of these components to create, by powder metallurgy, a material that has good electrical conductivity and good mechanical strength compared with that of pure copper, together with a manufacturing process which is both cost and energy efficient. The conductivity values vary between 30 to 55% IACS showing that the thermal treatments were effective for electrical connector uses.

Abstract: It has been studied the correlation of the obtained microstructures in cermets of Cu-Cr-Ag-Al₂O₃ with the physical properties and the fabrication method varying the components proportions to obtain by powder metallurgy a material with good electrical conductivity and also good mechanical strength compared with pure copper allied to efficient fabrication and economical energetically process. The electrical conductivity data correspond to 40% IACS indicating that the utilized thermal treatments were relatively good for electrical contact applications and also mechanically.

Abstract: This work aims the processing of metal matrix AA2124 aluminium alloy composites reinforced by alumina (Al₂O₃) and silicon carbide (SiC). The composites were manufactured by powder metallurgy techniques, in a grinding using a ball mill spex type (high energy) at a ratio of balls/ powders of 10:1 and grinding time of 30 and 60 minutes using stearic acid (C₁₈H₃₆O₂) as lubricant to each one of the samples. The fractions used in both reinforcements were 5, 10 and 15% in mass. The microstructural characterizations of AA2124 alloy powders with the reinforcements of alumina (Al₂O₃) and silicon carbide (SiC) powders were obtained by scanning electron microscopy (SEM) and the particles sizes and distribuition of the particle sizes in powders produced were obtained by laser diffraction, whereas the sintered characterizations were obtained by scanning electron microscopy (SEM) and mechanical characterization of the sintered tests was achieved by Vickers hardness (HV). The composites were uniaxially cold compacted (room temperature), at a pressure of 7.0 t / cm2, thus forming small pellets that were sintered (at a temperature of 500 °C) in a vacuum furnace at IPEN (SP). There was observed the influence of the respective bulk fractions of reinforcement particles used in mechanical characteristics presented in the resulting composites.

Abstract: Multi-wall carbon nanotubes (MWCNT), up to 2% in weight, were dispersed into AA6061 aluminium alloy by high-energy ball milling (HEBM) process, for further consolidation into extruded metal-matrix composites (MMC) bars. Three distinct routes were employed: the simple one step loading of materials inside the milling vials, an ultrasonically assisted dispersion of MWCNT and alloy powder into acetone prior to the milling, and the gradual introduction of MWCNT into the vials, during the milling process. Mixed powders obtained were evaluated in terms of the MWCNT integrity after HEBM, and the dispersion level obtained for several milling times. It was found that MWCNT remain relatively undamaged even for milling times up to 10 h, being embedded into the ductile alloy particles through the breaking/welding process during HEBM. However, shorter milling times result in poor dispersion of MWCNT in the milled powders. This tendency can be improved by using pre-milling mixture procedures, as the ultrasonically assisted wet dispersion of nanotubes and alloy powder.

Abstract: In this work the processing of composites containing graphite or hexagonal boron nitride dispersed in a ferrous matrix alloyed with phosphorous was addressed, with the goal of developing self-lubricating sintered materials with high mechanical resistance. Phosphorous is an alloy element characteristic in powder metallurgy for promoting the formation of liquid phase and alpha phase at high temperature, wherein both phenomena are densification inducers. It is expected therefore with that to rearrange volumetrically the solid lubricant reservoirs, so permitting the composites to present better mechanical properties. In order to understand what really occurs at high temperature, sintering was studied in situ in a dilatometer. Furthermore, microstructural and mechanical properties were carried out to characterize the sintered parts. The main remark was that graphite reacts with the matrix going into solid solution and therefore not being disposed as solid lubricant after sintering. On the other hand, h-BN remains insoluble in the Fe-P matrix and without reducing drastically the strength of the composite.

Abstract: High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.