Factors of Susceptibility of Human Myiasis Caused by the New World Screw-Worm, Cochliomyia hominivorax in São Gonçalo, Rio de Janeiro, Brazil

This study was carried out between July 2007 and June 2008 and reports on the occurrence of human myiasis caused by the New World screwworm, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae) in São Gonçalo in the state of Rio de Janeiro, Brazil. Liquid or solid vaseline was used to suffocate the larvae, which were then preserved in 70% ethanol and sent to the Instituto Oswaldo Cruz for identification. C. hominivorax were identified in all 22 cases of myiasis. There were 12 male and 10 female patients with ages ranging from 03 to 71. Ethnically the highest incidence was among black people, with 17 cases. Open wounds were the main cause of the parasitosis, whereas poor personal hygiene, the low educational level, alcoholism, bedridden patients, and physical or mental disability were possibly secondary factors; in addition to all these factors the income of the patients was very low

Residual stresses in Co-based laser claddings investigated by lab X-rays and synchrotron diffraction techniques

It is a well known fact that cracking related problems may occur during the laser cladding deposition process. In particular for the improvement of thick coatings it is of prime interest to know how processing parameters affect the residual stress state. The residual strains developed in Co-based thick clad layers were investigated by laboratory Cu-K alpha and Synchrotron X-rays. On the surface the strain tensor is determined by the Sin(2)psi technique. Strain mapping performed by synchrotron radiation shows that tensile stresses dominate the upper region but may change into compressive towards the inner part of the coating. The effect of laser overlap is discussed and a mechanism for stress concentration is proposed

Analysis of coaxial laser cladding processing conditions

The formation of thick Ni-based coating on a steel substrate by coaxial laser cladding using the Nd:YAG 2 kW continuous laser was studied both from a theoretical and experimental point of view. The theoretical analysis concentrated on the transfer of laser irradiation and powder particles using a simple model of heat transfer to the substrate. This approach provides predictions of the laser power required for melting powder particles and substrate, respectively. For an appropriate experimental analysis of the main process parameters involved, a method based on a gradual change of a single processing parameter was examined. Correlations between the main processing parameters and geometrical characteristics of an individual laser track have been found and are discussed. (c) 2004 Elsevier B.V. All rights reserved

Residual stresses in Co-based laser claddings investigated by lab X-rays and synchrotron diffraction techniques

It is a well known fact that cracking related problems may occur during the laser cladding deposition process. In particular for the improvement of thick coatings it is of prime interest to know how processing parameters affect the residual stress state. The residual strains developed in Co-based thick clad layers were investigated by laboratory Cu-K alpha and Synchrotron X-rays. On the surface the strain tensor is determined by the Sin(2)psi technique. Strain mapping performed by synchrotron radiation shows that tensile stresses dominate the upper region but may change into compressive towards the inner part of the coating. The effect of laser overlap is discussed and a mechanism for stress concentration is proposed.</p

Metallic laser clad coatings: on the pirocessing-microstructure-property relationships

A thick metallic coating that is resistant against high loading impact, severe wear and corrosion at high temperatures can be produced through the laser clad method. This work introduces the Orientation Imagining Microscopy based on electron backscatter diffraction in a scanning electron microscope as a very powerful instrument for studying relationships between processing parameters and the microstructure of individual laser tracks and final coatings formed by overlap. The study has been performed on thick (similar to 1mm) Co-based coatings prepared by a 2 kW CW Nd:YAG laser cladding on 42CrMo4 steel substrate using Substantially different laser beam scanning speeds. OIM provides new insights into the microstructure of laser clad coatings and yields very useful information concerning the directional grow of individual grains, the solidification texture and the shape of solidification front during laser cladding. Strong correlations between these parameters and laser cladding speed as well as the presence of internal interfaces with the sharp microstructural and mechanical properties changes are presented and discussed

Thick tool steel coatings with laser cladding

This paper concentrates on thick and crack-free laser clad coatings (up to 3 mm). The coating material is a chromium-molybdenum-tungsten-vanadium alloyed high-speed steel that shows high wear resistance, high compressive strength, good toughness, very good dimensional stability on heat treatment and very good temper resistance. It will be demonstrated that laser cladding of MicroMelt 23 powder offers a relatively wide processing window resulting in the formation of thick, microstructurally uniform, hard, crack- and defect- free coating on ordinary steel substrates. Microstructural observations using light and field emission gun scanning electron microscopy with EDS and EBSD attachments together with internal strain measurements using diffraction of X-rays revealed the reason for low susceptibility to crack formation. An intensive martensitic transformation inside small austenitic cells surrounded by hard carbides following the rapid solidification process compensates the tensile strain and finally results in cornpressive stresses at the coating surface. Laser cladding on different steels substrate geometries will be demonstrated together with hardness profiles and their dependence on cladding conditions

Laser melt injection of hard ceramic particles into Al and Ti alloys - processing, microstructure and mechanical behaviour

The conditions for a successful Laser Melt Injection (LMI) of SiC and WC particles into the melt pool of Al8Si and Ti6A14V alloys were studied experimentally and theoretically by FEM calculations. The laser employed is a high power Nd:YAG. The formation of a relatively thick aluminium oxide layer on the Al melt surface was confirmed during in-situ melting in an Environmental Scanning Electron Microscope (ESEM) at temperatures above 900 degreesC. This oxide layer acts as a barrier for particle penetration but it can be dissolved in the melt at temperatures above 1250 degreesC and consequently it opens a "window" for particle injection. The finite element analysis of the laser melting process of Al-Si alloy leads to the conclusions that the laser scan velocity has only a small influence on the substrate temperature distribution in the vicinity of the laser beam and that the size of extended part of laser melt pool (which is the best place for injection) is extremely small. Therefore, in contrast to Ti-alloys an extension of a melt pool size behind the laser beam, which serves as an effective instrument for successful LMI of ceramic particles, is not a successful processing route in the case of Al alloys. The relationship between microstructure, tensile and wear properties has been investigated for SiC/Al-Si and WC/Ti-Al-V metal matrix composite layers. Although the presence of hard and brittle phases formed during the laser processing decreases the tensile strength in comparison with substrate materials, a massive improvement of wear resistance of both layers is confirmed. As in-situ (BSEM) tensile tests show the crack-initiation process in the WC/Ti-Al-V layer strongly depends on the type of WC powder used in the laser melt injection process