Waldemar Alfredo Monteiro

Application of Magnesium Alloys in Transport

New light materials are currently inserted in world strategies of transport vehicle industry since the environment necessities for pollution and reduction of fuel consumption. There‐ fore the industry takes part of the risk of development of such alloys but, in fact, some of this has been made at academic level. Some aspects of the necessities and characteristics con‐ cerning those alloys are: low costs, insulation (sound and thermal), impact safety, deforma‐ tion strength, recyclability and guarantee (to aging as example). All those aspects are linked with the increasing of new vehicle models and reflect in production programs that are more and more complexes (Raynor, 1959; Roberts, 1960; Eliezer et al, 1998).

Nitriding Process Characterization of Cold Worked AISI 304 and 316 Austenitic Stainless Steels

The nitriding behavior of austenitic stainless steels (AISI 304 and 316) was studied by different cold work degree (0% (after heat treated), 10%, 20%, 30%, and 40%) before nitride processing. The microstructure, layer thickness, hardness, and chemical microcomposition were evaluated employing optical microscopy, Vickers hardness, and scanning electron microscopy techniques (WDS microanalysis). The initial cold work (previous plastic deformations) in both AISI 304 and 306 austenitic stainless steels does not show special influence in all applied nitriding kinetics (in layer thicknesses). The nitriding processes have formed two layers, one external layer formed by expanded austenite with high nitrogen content, followed by another thinner layer just below formed by expanded austenite with a high presence of carbon (back diffusion). An enhanced diffusion can be observed on AISI 304 steel comparing with AISI 316 steel (a nitrided layer thicker can be noticed in the AISI 304 steel). The mechanical strength of both steels after nitriding processes reveals significant hardness values, almost 1100 HV, on the nitrided layers.

Low Temperature Effect in Electrical Properties of Sintered Copper-Nickel-Aluminum Alloys

The major effort of sintered metallic alloys (compression, homogenization and sintering of metallic powder) is the observation of the evolution of electrical conductivity, mechanical properties (microhardness tests) and microstructures changes after appropriate thermomechanical treatments with the use of copper-nickel-aluminum alloys as electric material. In this case, the purpose was to verify the possible changes in these materials when subjected at low temperatures. Samples of Cux%Niy%Alz% initially compressed, sintered and homogenized were characterized by optical metallography (microstructure) and mechanical strength (hardness Vickers) at room temperature. Data of x-ray diffraction of polycrystalline samples were collected with a conventional Difractometer. After this was made measurements of electrical properties (electrical conductivity) at low temperatures of samples obtained from precursors of high purity in powder form, for the study of the influence of powder metallurgy processes in physical properties of metallic alloys in this condition.

Sintering of Ternary Copper Alloys (Powder Metalurgy) – Electrical and Mechanical Properties Effects

The foreword of Paul Beiss (RWTH Aachen) in the book “Modeling of Powder Die Compac‐ tion”, edited by Peter R. Brewin, Olivier Coube, Pierre Doremus and James H. Tweed (2008, Springer-Verlag London Limited) shows us that the “Die compaction of powders that develop green strength on compaction is the absolutely dominating forming technology for powdered materi‐ als. Areas of application are structural parts, hardmetal and ceramic indexable inserts, pharmaceuti‐ cal tablets, electrical contacts, filters, hard magnets, soft magnetic composites, friction materials and many others. In particular, multi cross-sectional net-shape geometries have been gaining importance continuously, because the ability to deliver complex shapes with higher and higher productivity has contributed to competitive advantages over alternative forming techniques. Since the raw material us‐ age is better than 90% in die compaction, even in areas that could be served by competing manufac‐ turing technologies, die compaction of powders is often the most economical solution. The industries applying this technique have seen tremendous innovation especially in shape capability, reproducibili‐ ty and productivity over the last 15 years that has resulted in high added value, astonishing growth rates and increased employment also in high labor cost countries”.

Mechanical and Structural Characterization of Cu-Ni-Ag/Y2O3 Composites Obtained by Powder Metallurgy

Metal-ceramic composites are recently being used as electrode materials in solid oxide fuel cell (SOFC), which have received much attention as alternative energy sources. In this work cermets of Cu-Ni-Ag/Y2O3 were synthesized with different quantities of Ni and Ag. Various samples were prepared from pure precursors by conventional powder metallurgy processing and sintered at 800°C. The characterization by differential scanning calorimetry (DSC) and thermal gravimetric analyze (TGA) indicate that the presence of Y2O3 could increase the corrosion resistance of the metallic copper alloys. The copper crystalline structure presents internal strengths and possibly crystallites with different cell parameters due to the effect of thermal and mechanical treatments in presence of Y2O3. The highest electrical conductivity and highest hardness were obtained for the composition with 5% Y2O3 and 5% nickel, which increases the hardness and could contribute to the higher conductivity through a precipitation mechanism.

Structural and electrical properties of copper-nickel-aluminum alloys obtained by conventional powder metallurgy method

This work looked for to search out systematically, in scale of laboratory, copper-nickel-aluminum alloys (Cu-Ni-Al) with conventional powder metallurgy processing, in view of the maintenance of the electric and mechanical properties with the intention of getting electric connectors of high performance or high mechanical damping. After cold uniaxial pressing (1000 kPa), sintering (780oC) and suitable homogenization treatments (500oC for different times) under vacuum (powder metallurgy), the obtained Cu-Ni-Al alloys were characterized by optical microscopy, electrical conductivity, Vickers hardness. X rays powder diffraction data were collected for the sintered samples in order to a structural and microstructural analysis. The comparative analysis is based on the sintered density, hardness, macrostructures and microstructures of the samples.

Microstructure and microanalysis studies of copper-nickel-tin alloys obtained by conventional powder metallurgy processing

The aim of this article was to analyze the microstructural development in samples of Cu-Ni-Sn alloys (weight %) obtained by powder metallurgy (P/M). The powders were mixed for 1/2 hour. After this, they were pressed, in a cold uniaxial pressing (1000 kPa). In the next step the specimens were sintered at temperatures varying from 650 up to 780°C under vacuum. Secondly, the samples were homogenized at 500oC for several special times. The alloys were characterized by optical microscopy, electrical conductivity and Vickers hardness. X rays powder diffraction data were collected for the sintered samples in order to a structural and microstructural analysis. The comparative analysis is based on the sintered density, densification parameter, hardness, macrostructures and microstructures of the samples.

Microstructural and Mechanical Characterization of Gray Cast Iron and AlSi Alloy after Laser Beam Hardening

A localized source of heat, such as that of laser beam, can provide a convenient means of producing a surface layer of altered microstructure. By using surface hardening treatment, wear resistance can be increased. Experiments were performed using a Nd:YAG pulsed laser under different processing conditions. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray mapping (SEM) were employed to observe the effect of laser melting treatment on the microstructural properties of the samples. Depending on the selected laser treatment working conditions, different microstructures characteristics of surface melting can be achieved in the treated zone. Higher microhardness values were found at the treated area showing a superficial hardening of the sample and, consequently, an improvement of the wear resistance of these automotive alloys. The aim of this work is to find the optimal process parameters and to evaluate the characteristics of the laser superficial hardening (LSH) in a pearlitic gray iron and Al-Si alloy used in an automobile industry (bearing and piston materials in automotive industry).

Comparison of Microstructural Aspects by Electron Microscopy Observed in Al-Mg Based Alloys Obtained by Conventional and P/M Processes After Thermomechanical Treatments

Al-Mg based alloys have special attention due to the lightness of the material and certain mechanical properties and reciclability. Normally classified as non-heat-treatable these alloys obtain higher strength either by strain-hardening or by solid solution. The P/M process in the Al-Mg-Zr alloys in study leading to fine grain structure after the thermal treatment. The understanding of the observed phenomena depends of the fact that materials produced by powder metallurgy present complex interface reactions in a great amount of nucleation sites and a subtle change in the structure of the material causes an important variation in your properties. Alloys in study presented interesting values of properties, with evident technological potential.

Study of Electrical, Mechanical and Microstructural Properties of Composites Based on Cu-Ni-Ag-Al2O3 Obtained by Powder Metallurgy

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.