Cr2C3–NiCr VPS thermal spray coatings as candidate for chromium replacement

The present investigation has been carried out with the aim of determining the tribological behavior of a VPS chromium carbide coating both in the as-deposited and heat-treated conditions. A commercial powder of Cr2C3–25% NiCr was sprayed employing a VPS system (Medicoat AG, Switzerland) onto plain low carbon steel coupons. The samples were subsequently annealed for 2 h at 600 °C, 800 °C and 900 °C in Ar. The microstructural characterization was carried out by using SEM and XRD before and after the heat treatment of the samples. SEM observations were employed for determining the degradation mechanisms that took place during the wear tests. When the coated systems rubbed against alumina under a 5 N normal load in air, a progressive change in the mechanism, from a mixed adhesive and abrasive, to a predominant abrasive was observed, as the heat treatment temperature increased. The wear constants were found to be of the order of approximately 10− 6 mm3/N.m, which indicates a wear resistance of nearly 4 times higher in comparison with the wear results reported in the literature for similar coating systems obtained by employing HVOF deposition. However, the heat treatment carried out at 900 °C brought about only 20% increase in the sliding wear resistance of the coated system

Analysis of indentation size effect in copper and its alloys

For describing the indentation size effect (ISE), numerous models, which relate the load or hardness to the indent dimensions, have been proposed. Unfortunately, it is still difficult to associate the different parameters involved in such relationships with physical or mechanical properties of the material. This is an unsolved problem since the ISE can be associated with various causes such as workhardening, roughness, piling-up, sinking-in, indenter tip geometry, surface energy, varying composition and crystal anisotropy. For interpreting the change in hardness with indent size, an original approach is proposed on the basis of composite hardness modelling together with the use of a simple model, which allows the determination of the hardness–depth profile. Applied to copper and copper alloys, it is shown that it is possible to determine the maximum hardness value reached at the outer surface of the material and the distance over which both the ISE and the workhardening take place

Microstructure modelling of hot deformation of Al–1%Mg alloy

This study presents the application of the finite elementmethod and intelligent systems techniques to the prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element is defined using a hybrid model. The hybrid model is based on neuro-fuzzy and physically based components and it has been combined with the finite element technique. The model simulates the evolution of the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation) and their effect on the recrystallisation behaviour of the stock. This paper presents the theory behind the model development, the integration between the numerical techniques, and the application of the technique to a hot rolling operation using aluminium, 1 wt% magnesium alloy. Furthermore, experimental data from plane strain compression (PSC) tests and rolling are used to validate the modelling outcome. The results show that the recrystallisation kinetics agree well with the experimental results for different annealing times. This hybrid approach has proved to be more accurate than conventional methods using empirical equations

Caracterizaci\uf3n morfol\uf3gica de los Sesiidae (Insecta: Lepidoptera) perforadores del fruto del cacao ( Theobroma cacao L.), presentes en la regi\uf3n costera del estado Aragua, Venezuela.

Description of adult and immature stages of Carmenta theobromae (Busck), 1910 and C. foraseminis Eichlin 1995; the cacao fruit borers in the coastal region of Aragua State, Venezuela was made. Specimens were obtained from bored cacao pods collected at the Cacao germplasm bank (INIA-Ocumare de la Costa) and La Sabaneta (a locality near Choron\ued) between the years 2000 and 2003. Breeding under laboratory conditions provided enough material for the description of eggs, larvae, pupae and adult stages of each species. Differentiating adult characters were: color of the scales of the vertex and frons of the head, wings and abdomen; number and color of longitudinal bands on mesonotum; color of maxillary palpi and forecoxae. The eggs differ in color, shape, size, and texture of the corion. Last instar larvae presented differences in: body color, cephalic width, thoracic shield shape, color of abdominal setae and anal shield, and the photofobic grade. Pupae presented the greater number of diagnostic characters: Color, galea shape, texture of pronotum, mesonotum, and first abdominal segment, the shape of alar furrow, second abdominal spiracle, and the apical abdominal region (anal and genital). Hence we propose the use of pupal characters to diagnose the presence of both species in the field, using the pupal exuviae found in the bored pods.Se realiz\uf3 la descripci\uf3n de las fases adulta e inmaduras de Carmenta theobromae (Busck, 1910) y C. foraseminis Eichlin 1995 (Lepidoptera: Sesiidae) perforadores del fruto del cacao (Theobroma cacao L.) en la regi\uf3n costera del estado Aragua. Los ejemplares fueron obtenidos a partir de frutos de cacao perforado, colectados del Banco de Germoplasma del INIA-Ocumare de la Costa y de la Hacienda La Sabaneta (Choron\ued) entre 2000-2003. La cr\ueda en condiciones de laboratorio, permiti\uf3 describir las fases de huevo, larva, pupa y adulto de cada especie. Los caracteres que diferencian a los adultos son: Color de las escamas del v\ue9rtice, frente, alas y abdomen, n\ufamero de bandas longitudinales en el mesonoto, color de los palpos maxilares y de las coxas anteriores. Los huevos se diferencian por el color, forma, tama\uf1o, y la textura del cori\uf3n. Las larvas del \ufaltimo instar, presentaron diferencias en los siguientes caracteres: color del cuerpo, el ancho cef\ue1lico, forma del escudo tor\ue1cico, color de las setas abdominales, del escudo anal y el grado de fotofobia. La fase de pupa present\uf3 el mayor n\ufamero de caracteres diagn\uf3stico para diferenciar ambas especies. Estos son: Color, forma de las galeas, textura del pronoto, mesonoto y del tergo A1, la forma del surco alar, forma del espir\ue1culo del A2 y caracteres de la regi\uf3n apical (anal y genital) del abdomen. Se propone la utilizaci\uf3n de los caracteres de pupas para diagnosticar la presencia de ambas especies, a partir de las exuvias encontradas en los frutos perforados en el campo

A contact area function for Berkovich nanoindentation : Application to hardness determination of a TiHfCN thin film

In nanoindentation, especially at very low indenter displacements, the indenter/material contact area must be defined in the best possible way in order to accurately determine the mechanical properties of the material. One of the best methodologies for the computation of the contact area has been proposed by Oliver and Pharr [W.C.Oliver, G.M.Pharr, J.Mater. Res. 7 (1992) 1564], which involves a complex phenomenological area function. Unfortunately, this formulation is only valid when the continuous stiffness measurement mode is employed. For other conditions of indentation, different contact area functions, which take into account the effective truncation length or the radius of the rounded indentertip, as well as some fitting parameters, have been proposed. However, most of these functions require a calibration procedure due to the presence of such parameters. To avoid such a calibration, in the present communication a contact area function only related to the truncation length representative of the indenter tip defect, which can be previously estimated with high resolution microscopy, has been proposed. This model allows the determination of consistent indentation data from indenter displacements of only few nanometers indepth. When this proposed contact area function is applied to the mechanical characterization of a TiHfCN film of 2.6 μm in thickness deposited onto a tool steel substrate, the direct determination of the hardness and elastic modulus of the film leads to values of 35.5±2 GPa and 490±50 GPa, respectively

An analysis of the elastic properties of a porous aluminium oxide film by means of indentation techniques

The elastic modulus of thin films can be directly determined by instrumented indentation when the indenter penetration does not exceed a fraction of the film thickness, depending on the mechanical properties of both film and substrate. When it is not possible, application of models for separating the contribution of the substrate is necessary. In this work, the robustness of several models is analyzed in the case of the elastic modulus determination of a porous aluminium oxide film produced by anodization of an aluminium alloy. Instrumented indentation tests employing a Berkovich indenter were performe data nanometric scale, which allowed a direct determination of the film elastic modulus, whose value was found to be approximately 11 GPa. However, at a micrometric scale the elastic modulus tends toward the value corresponding to the substrate, of approximately 73 GPa. The objective of the present work is to apply different models for testing their consistency over the complete set of indentation data obtained from both classical tests in microindentation and the continuous stiffness measurement mode in nanoindentation. This approach shows the continuity between the two scales of measurement thus allowing a better representation of the elastic modulus variation between two limits corresponding to the substrate and film elastic moduli. Gao's function proved to be the best to represen the elastic modulus variation

Factors affecting the efficency and persistance of Bacillus thuringiensis var. israelensis on Anopheles aquasalis Curry (Diptera: Culicidae), a malaria vector in Venezuela

The efficacy and persistence of four commercial formulations of against early fourth instar larvae of Anopheles aquasalis, were evaluated in laboratory conditions. The formulations were: Vectobac-G (0,2%, Abbott), Vectobac-AS (0.6%, Abbott), Teknar (1,6%,Z\ue9neca) and an experimental microencapsulated formulation M-Bti (0,1%, J. Margalit, Harvard Univ.). The microencapsulated formulation required the smallest LC50 and LC95 (0.006 and 0.05 ppm, respectively); Vectobac-G required the largest LC50 and LC95 for fourth instar larvae of An. aquasalis (0.48 ppm and 4.8 ppm, respectively). However, LT50 was shortest for Vectobac-G (3.7 h) and the longest for M-Bti (6.7 h). Increment of larval density and larval age reduced the M-Bti efficacy. Teknar was the formulation least affected by larval density, larval age, water type, and sunlight radiation. These results suggest the need to evaluate the effect of extrinsic and intrinsic factors on Bti formulations, in order to use those formulations most effective, according to breeding sites characteristics and species to be controlled.Se evaluaron en condiciones de laboratorio, la eficacia y persistencia de cuatro formulaciones comerciales de contra Anopheles aquasalis. Las formulaciones fueron: Vectobac-G (0,2%, Abbott), Vectobac-AS (0,6%, Abbott), Teknar (1,6%, Z\ue9neca) y una formulaci\uf3n experimental microencapsulada M-Bti(0,1%, J. Margalit, Harvard Univ.). La formulaci\uf3n Microencapsulada requiri\uf3 de las menores CL50 y CL95 (0,006 y 0,05 ppm, respectivamente), y Vectobac-G requiri\uf3 la mayor CL50 (0,48 ppm) y CL95 (4,8 ppm) para larvas de cuarto instar temprano de An. aquasalis. Sin embargo el TL50 fue menor para Vectobac-G (3,7 h) y la formulaci\uf3n Microencapsulada requiri\uf3 del mayor TL50 (6,7 h). El incremento en la densidad larval y la edad de las larvas redujo la eficacia del M-Bti, mientras que Teknar fue la formulaci\uf3n menos afectada por la densidad larval, la edad de las larvas, el tipo de agua y la radiaci\uf3n solar. Estos resultados sugieren la necesidad de evaluar el efecto de factores extr\uednsecos e intr\uednsecos a las formulaciones de Bti, con la finalidad de utilizar aquellas que sean las m\ue1s eficaces, en funci\uf3n de las caracter\uedsticas del criadero y de la especie a controlar

Sliding wear of a-C:H coatings against alumina in corrosive media

This paper reports the results obtained from the study of friction and sliding wear in two corrosive solutions of an a-C:H coating deposited on 316L stainless against an alumina ball, employed as static counter part. Calculations of the values of the von Mises stresses developed at the coating–substrate interface, as soon as the ball touches the coated sample, and how this state of stress influences the response of the coated system under the corrosion environment, are presented and discussed. The results obtained from these calculations, as well as from the experiments conducted in the present research, are compared with other experiments published in the literature, where a-C:H coatings deposited on different substrates and with different coating architectures were tested in similar corrosive media. It has been determined that in those systems, where the von Mises stress in the coating, found in the vicinity of the interface, exceeds the threshold value of approximately 370MPa, coating failure with spallation will take place, regardless of the substrate nature on which this coating has been deposited. From this analysis it has been concluded that the coating yield strength is of utmost importance in conferring the a-C:H coated system there quired stability in a corrosive solution