Cesar Edil da Costa

Mechanical behaviour of the interphase between matrix and reinforcement of Al 2014 matrix composites reinforced with (Ni3Al)p

The 2XXX series aluminium alloys reinforced with intermetallics present a special behaviour due to the reaction between matrix and reinforcement. This reaction forms an interphase that influences the mechanical and chemical behaviour of the composite, reducing the capability of the material to improve its properties after heat treatment. In this work, an approach is made to the study of this interphase, using particulate intermetallics with the same chemical and stoichiometric composition but obtained in different ways: mechanical alloying and gas atomising. A microstructural study was carried out by SEM, including qualitative analysis, showing the chemical gradient formed at the interphase both as-extruded and after T6 treatment. The mechanical behaviour of the interphase is studied through nanoindentation that allows the determination of hardness and Young modulus. Finally, all these properties are correlated with a fractrographic study of the fracture mechanisms. A harder interphase is formed for the mechanically alloyed system promoting a transgranular cleavage fracture micromechanisms, while intergranular cleavage fracture is found in atomised intermetallic containing composites.

Characterization of casting iron powder from recycled swarf

Abstract In this work a study of recycling about gray cast iron chips from machining process and its use as a starting material in the powder metallurgy process is presented. This investigation is focused in the complete characterization of the obtained powders from a detailed study of mechanical grinding efficiency of this swarf. Both, recrystallizing annealing heat treatment and decarburization process of the powders were realized. Also, a study of dilution with pure iron was done, with the purpose to improve the final powder physical characteristics, such as compressibility and sintering. The powder properties were evaluated by optical and scanning electron microscopies, X-ray difratometry and dilatometry techniques. The results achieved are promising associated to viability of gray cast iron swarf recycling and their posterior utilization, in the powder form, as a starting material for the fabrication of many sintered components.

Acquired Properties Comparison of Solid Nitriding, Gas Nitriding and Plasma Nitriding in Tool Steels

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.

Nanocomposite of photocurable epoxy-acrylate resin and carbon nanotubes: dynamic-mechanical, thermal and tribological properties

In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT) are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (%) MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM) and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

PROPERTIES OF AA6061 ALUMINUM ALLOY REINFORCED WITH DIFFERENT INTERMETALLICS AND CERAMICS PARTICLES

Aluminum alloys have been increasingly applied as a structural material in composite materials using metal matrix due to their excellent mechanical properties and low weight. The reinforcement are of fundamental importance in composite materials, owing to the their responsibility to support stresses acting on the metal matrix. Therefore, ceramic reinforcements can be replaced by intermetallic components with high mechanical properties and good thermal stability. The intermetallic components react chemically with the matrix, characterized by strong interactions, which makes possible the development of the new families of materials. The composite materials using aluminum reinforced with nickel aluminides and ceramic were developed using techniques based on a combination of powder metallurgy and extrusion processes, which makes possible to obtain more dense materials under lower processing temperatures. The powders of AA6061 and Ni3Al were manually mixed for 30 minutes, with different percentages of intermetallics and ceramics particles, 5 and 10% in weight. The composite powders were submitted to a hot extrusion process for 40 minutes at 540oC, and 385 MPa, with a reduction ratio of 25:1. This process insures extruded composites with a refined structure and a good distribution of the reinforcement particles. The material characterization were performed through structural analysis via scanning electron microscopy; mechanical behavior via tensile and hardening tests; and analysis of the fracture. The results show that the method used is effective to obtain composite materials with improved characteristics.

Intergranular Corrosion Resistance of 2014 Aluminium Alloys Reinforced with Ni3Al

Intergranular corrosion is typical from 2xxx series aluminium alloys. In this work, this property has been evaluated in 2014 aluminium matrix composites. The base alloy was manufactured through mechanical alloying, and reinforced with Ni 3 Al particles of two types (manufactured through mechanical alloying and through rapid solidification). Corrosion tests were carried following ASTM G110 standard. Corrosion was evaluated by scanning electron microscopy and energy dispersive X-ray analysis. It has been studied the influence that the different kinds of intermetallic and T6 heat treatment have on the corrosion resistance of 2014 aluminium alloy. Results show that, in all cases, intermetallics highly improve the corrosion resistance of base aluminium alloy, and that T6 heat treatment is also favourable.

Study of the nitrided layer obtained by different nitriding methods

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 - e 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.

Study of the recycling grey cast iron swarf by powder metallurgy : an alternative for the development of new materials

This work is concerned with issues related to using grey cast iron swarf from dry machining in powder metallurgy. In a first stage, a complete study on the characteristics of the raw powder is performed, in which aspects related to the dilution in different proportion of pure iron were studied. Low compacting pressure produces workpieces more resistant and that the ideal sintering temperature is 1160 °C. In a second stage, aiming at reduction of the powder, a heat treatment is performed. New dilutions using the decarburized powder were made and results showed better structural homogeneity and an improvement in the mechanical properties. The steel alloy 50/50% of swarf powder provided the best results. In a third stage, a cylindrical bearing was produced. New dilutions were made. Based on the control of the interconnected porosity, radial and wear resistance, the sample prepared with 100% swarf powder provided the best results.

Development of Ni/h-BN Self-Lubricating Composite Powder by High-Energy Ball Milling

Solid lubricants have had good acceptance when used in problem areas where the conventional lubricants cannot be applied: under extreme temperatures, high charges and in chemically reactive environments. In case of materials manufactured by powder metallurgy, particles of solid lubricants powders can be easily incorporated to the matrix volume at the mixing stage. In operation, this kind of material provides a thin layer of lubricant that prevents direct contact between the surfaces. The present study aimed at incorporating particles of second phase lubricant (h-BN) into a matrix of nickel by high-energy ball milling in order to obtain a self-lubricating composite with homogeneous phase distribution of lubricant in the matrix. Mixtures with 10 vol.% of h-BN varying the milling time of 5, 10, 15 and 20 hours and their relationship ball/powder of 20:1 were performed. The effect of milling time on the morphology and microstructure of the powders was studied by X-ray diffraction, SEM and EDS. The composite powders showed reduction in average particle size with increasing milling time and the milling higher than 5 hours resulted in equiaxial particles and the formation of nickel boride.

Mechanical Properties of Composite AA2024 Matrix with Aluminium Carbide Dispersed by High Energy Milling

Dispersion strengthened aluminium composites have been prepared by mechanical alloying. At this work were studied the turning conditions to get in situ formation and dispersion of Al4C3 on 2024 alloy by graphite addition. The alloy matrix was obtained by attrition milling a mixture of starting powders; further additions of carbon (2,5; 5 and 10% wt) were performed by means of a planetary mill. Through an adequate sintering the reinforcement formation was showed by X-Ray diffraction analysis of powders with milling times next to 20 hours. The microhardness values appointed that mechanical properties were held even soft material addition (graphite) and improved by age hardening. Pin-on-disc test revealed the composite have low friction coefficient, due to lubricant carbon action and enough low volumetric wear due to high hardness of bulk Al4C3 reinforcement.