Micro Welding of Ni-based Alloy Monel 400 Thin Foil by Pulsed Nd:YAG laser

In this study a pulsed Nd:YAG laser was used to join Monel 400 thin foil with 100 mu m thickness. Pulse energy was varied from 1.0 to 2.25J at small increments of 0.25J. The macro and microstructures were analyzed by optical microscopy, tensile shear test and microhardness. Sound laser welds without discontinuities were obtained with 1.5 J pulse energy. Results indicate that using a precise control of the pulse energy, and so a control of the bottom foil dilution rate, it is possible to weld Monel 400 thin foil. The process appeared to be very sensitive to the gap between couples.

Metallurgical evaluation of a copper-based alloy for dental castings.

The present study was designed to evaluate the metallurgical properties of an experimental, low-cost copper-zinc-aluminum-nickel alloy for dental castings. Some specimens were subjected to heat treatment after induction casting. The extent of corrosion was determined by measuring weight loss of specimens stored in a sodium sulfite solution. In the as-cast specimens, tests demonstrated the presence of three phases: the first consisted of copper-zinc-aluminum, the second was similar but lower in copper and aluminum, and the third consisted of an intermetallic compound of manganese-nickel-phosphorus. After heat treatment, the first phase remained relatively constant, the second was converted to Cu3Al, and the third increased in volume. The weight loss from the as-cast specimens was eight times that of the heat-treated specimens. It was concluded that the heat treatment substantially changed the microstructure and improved the corrosion resistance of the experimental alloy.

Cutting performance of diamond coated Si3N4 tool during turning

Silicon nitride cutting tools have been used successfully for machining hard materials, like: cast irons, nickel based alloys, etc. However these cutting tools with diamond coating present little information on dry turning operations of gray cast iron. In the present work, Si3N4 square inserts was developed, characterized and subsequently coated with diamond for dry machining operations on gray cast iron. All experiments were conducted with replica. It was used a 1500, 3000, 4500 m cutting length, feed rate of 0.33 mm/rev and keeping the depth of cut constant and equal to 1 mm. The results show that wear in the tool tips of the Si3N4 inserts, in all cutting conditions, was caused by both mechanical and chemical processes. To understand the tool wear mechanisms, a morphological analysis of the inserts, after experiments, has been performed by SEM and optical microscopy. Diamond coated PVD inserts showed to be capable to reach large cutting lengths when machining gray cast iron. © (2010) Trans Tech Publications.

O meteorito condrítico Saulo Gomes

This paper aims to present the results of petrographic and lithochemical studies obtained in one of the three artifacts, which fell on the farm Buritis in Buritizal County in August 1967, which were collected and stored until the present by reporter Saulo Gomes. The petrographic analysis showed that the artifact is composed by spherical and irregular chondrules with serial granulometry and size averaging around 1 mm and the largest reaching about 6 mm in diameter. The chondrules are made of olivine, ortho and clinopyroxene, crystallite glass, nickel iron alloy and troillite (kamacite and/or taenite/tetrataenite) and inter chondrules glassy material occurs in association with troillite, nickel and other alloy iron-based compounds. The lithochemical data show excellent correlation with the C chondrite, noting only small differences above or between them. The study made it possible to classify the artifact as type L3 and L4 ordinary chondrite.

Ferromagnetism and superconductivity in CeFeAs 1-xP xO (0≤x≤40)

We report on superconductivity in CeFeAs 1-xP xO and the possible coexistence with Ce ferromagnetism (FM) in a small homogeneity range around x=30% with ordering temperatures of T SC≅T C≅4 K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to TNFe≈40 K and does not shift to lower temperatures with a further increase of the P concentration. Therefore, a quantum-critical-point scenario with TNFe→0 K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and x-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short-range AFM Fe ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering. © 2012 American Physical Society.

Influence of Heat Treatment and Oxygen Doping on the Mechanical Properties and Biocompatibility of Titanium-Niobium Binary Alloys

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A study of the microstructural characteristics of dental amalgams

Metallographic studies by scanning electron microscopy and energy dispersive spectroscopy carried out for two types of dental amalgam showing a porous multiphase material. Surface analysis shows that the structure of the Dispersalloy amalgam consists of gamma-Ag3Sn, gamma(1)-Ag2Hg3, eta'-Cu6Sn5, epsilon-Cu3Sn and eutectic Ag-Cu phases. while Velvalloy amalgam consists mainly of gamma, gamma(1) and gamma(2)-Sn7-8Hg phases. The latter phase presents an uniform distribution often associated with voids.

Laüe back-reflection method for crystallographic orientation of a martensitic Cu-Zn-Al single crystal of the monoclinic system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudio de los procesos de corrosion de una aleacion metalica de cobre usada en odontologia

Corrosion phenomena in a dental copper-based alloy are experimentally studied using electrochemical techniques. Two heating sources, torch and induction, were used in the casting experiments. In the corrosion essays, the optimum casting cycle and the polarization curves were obtained. It was found that the heating sources have little influence on the corrosion processes of the metallic alloys studied.

Automatic microstructural characterization and classification using artificial intelligence techniques on ultrasound signals

Secondary phases such as Laves and carbides are formed during the final solidification stages of nickel based superalloy coatings deposited during the gas tungsten arc welding cold wire process. However, when aged at high temperatures, other phases can precipitate in the microstructure, like the γ″ and δ phases. This work presents a new application and evaluation of artificial intelligent techniques to classify (the background echo and backscattered) ultrasound signals in order to characterize the microstructure of a Ni-based alloy thermally aged at 650 and 950 °C for 10, 100 and 200 h. The background echo and backscattered ultrasound signals were acquired using transducers with frequencies of 4 and 5 MHz. Thus with the use of features extraction techniques, i.e.; detrended fluctuation analysis and the Hurst method, the accuracy and speed in the classification of the secondary phases from ultrasound signals could be studied. The classifiers under study were the recent optimum-path forest (OPF) and the more traditional support vector machines and Bayesian. The experimental results revealed that the OPF classifier was the fastest and most reliable. In addition, the OPF classifier revealed to be a valid and adequate tool for microstructure characterization through ultrasound signals classification due to its speed, sensitivity, accuracy and reliability. © 2013 Elsevier B.V. All rights reserved.

Influência da dopagem com oxigênio nas propriedades anelásticas e biocompatibilidade de ligas Ti-5%pNb e Ti-10%pNb

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Utilização de técnicas do planejamento de experimentos na otimização de um processo de torneamento da superliga NIMONIC 80A

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da usinagem em torneamento da superliga a base de niquel NIMONIC 80

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito de elementos substitucionais e intersticiais na microestrutura, dureza e módulo de elasticidade de ligas Ti-Nb

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeito da aplicação do fluido de corte na usinagem da superliga Nimonic 80A

The nickel alloys have a chemical composition with high tenor of alloy elements which are responsible for the material's mechanical and thermal properties, but also are the main causative of problems during the machining, making the process difficult. The objective of this work is the study of the machining by external cylindrical turning of the nickel based alloy Nimonic 80A, seeking the machining optimization of this alloy, seeking the best condition of lubricant fluid use, providing real increases of productivity without the need of investments in new production means. Besides, the results of this work should offer more detailed information regarding the behavior of this alloy in relation to machining by turning. The machining experiences were accomplished in a specimen of the nickel alloy, considering the machining parameters: cutting speed (75 and 90 m/min), cutting depth (0,8 mm) and feed rate (0,15 and 0,18 mm/v). The valuations were accomplished in a CNC lathe and tools with of hard metal inserts. After each stage of the turning the measures of the cutting length were accomplished, of the waste of the tools through a magnifying glass (8x) and the roughness of the specimen evaluated in each phase of the process, with the aid of a portable roughness meter. Through light optical microscopy it was possible to observe the wear of the cutting tools for each appraised condition. The roughness values, Ra and Ry, for the appraised conditions were always superiors to the theoretical values. After analysis of the results it was possible to end that, the best acting for this work strip tested it was obtained for ap=0,8mm: f=0,15mm/rev and VC=75m/min, what resulted in a larger cutting length (1811 m)