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The aim of this work is to correlate the homogeneity of the microstructure of two certified hardn... more The aim of this work is to correlate the homogeneity of the microstructure of two certified hardness standard blocks, both with the same hardness value range, with its uniformity hardness values. In order to identify the morphological characteristics of the blocks studied, as grain size distribution, an automatic image analysis system with software based on ASTM E112 and ASTM E1382
Journal of Iron and Steel Research, International, 2009
The presence of nonmetallic inclusion particles which appear during steelmaking process is harmfu... more The presence of nonmetallic inclusion particles which appear during steelmaking process is harmful to the properties of steels, which is mainly as a function of some aspects such as size, volume fraction, shape, and distribution of these particles. The automatic image analysis technique is one of the most important tools for the quantitative determination of these parameters. The classical Student approach and the Extreme Values Method (EVM) were used for the inclusion size and shape determination and the evaluation of distance between the inclusion particles. The results thus obtained indicated that there were significant differences in the characteristics of the inclusion particles in the analyzed products. Both methods achieved results with some differences, indicating that EVM could be used as a faster and more reliable statistical methodology.
Journal of Failure Analysis and Prevention, 2010
Metallic materials designed for applications in orthopedic or dental surgical implants must show ... more Metallic materials designed for applications in orthopedic or dental surgical implants must show a group of properties, including biocompatibility, mechanical strength and resistance to degradation (by wear or corrosion) outstand. In order to assure that the properties are achieved, the implant materials must fulfill certain requirements, usually specified in standards. The standards also include chemical composition, microstructure and even macrographic aspects. The main aim of this work was to perform a failure analysis on a titanium-based dental implant and connect the possible causes of failure with the associated material requirements which were previously mentioned. Evaluation techniques included metallographic analysis by optical microscopy and fractographic analysis by scanning electron microscopy (SEM). The results of the examinations suggested that, in spite of their adequate microstructures, the implants fractured due to the overload generated by stress raisers which were found in the implants.
Journal of Failure Analysis and Prevention, 2009
The increasing lifetime of the population on a world-wide scale over the last decades has led to ... more The increasing lifetime of the population on a world-wide scale over the last decades has led to a significant growth in the use of surgical implants for replacement of bones and teeth in affected patients. Other factors, such as scientific-technological development and more frequent exposure of individuals to trauma risk, have also contributed to this general trend. Metallic materials designed for applications in surgical implants, no matter whether orthopedic or dental, must show a group of properties in which biocompatibility, mechanical strength, and resistance to degradation (by wear or corrosion) are of primary importance. In order to reach these aims, orthopedic materials must fulfill certain requirements, usually specified in standards. These requirements include chemical composition, microstructure, and even macrographic appearances. In the present work, three cases of implant failure are presented. These cases demonstrate the most frequent causes of premature failure in orthopedic implants: inadequate surgical procedures and processing/ design errors. Evaluation techniques, including optical and scanning electron microscopy (SEM), were used to evaluate macroscopic and microstructural aspects of the failed implants, and the chemical composition of each material was analyzed. These evaluations showed that design errors and improper surgical procedures of outright violation of standards were the cause of the failures.
Journal of Failure Analysis and Prevention, 2011
As in the case of implants, the increase of the life expectancy and of the risk of accidents, thu... more As in the case of implants, the increase of the life expectancy and of the risk of accidents, thus causing a higher incidence of surgeries, has led to an increased use of surgical instruments. The reliability of these instruments, used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. Using some techniques such as optical microscopy, scanning electron microscopy, and hardness tests, this work has as purpose the identification of the possible causes of failure of surgical torch meters used for dental implants fixation, trying to correlate with the microstructural characteristics of the austenitic and martensitic stainless steels used in their manufacture. The results thus obtained allowed the identification of the main causes of the failure, primarily related to microstructural heterogeneities which resulted from inadequate heat treatment and with the presence of non-metallic inclusions, which favored brittle fracture and corrosion.
Engineering Failure Analysis, 2005
The main reason for the existence of superalloys is their outstanding strength at high temperatur... more The main reason for the existence of superalloys is their outstanding strength at high temperatures, which make them suitable for the fabrication of gas turbine components. Contributing factors are the high modulus of their close packed FCC lattice and the presence of elements, like aluminum and titanium, which enable the formation of c 0 phase, Ni 3 (Al,Ti), that dispersed in the c matrix has a hardening effect. The presence of chromium is essential to guarantee oxidation resistance and other alloying elements are important to impart high-temperature strength. Carbon content is usually sufficient to allow the formation of carbides which improve creep resistance. In this work, two failure cases of nickel base superalloy components were analyzed by scanning electron microscopy (SEM). The microstructural aspects provided sufficient evidences to conclude that, in the first case overheating led to failure and in the second case the significant microstructural degradation of the surface can lead to failure.
Journal of Failure Analysis and Prevention, 2008
The petroleum industry has changed significantly over the past decades. For example, in Brazil, o... more The petroleum industry has changed significantly over the past decades. For example, in Brazil, oil extraction under very deep sea water is growing very quickly. As a consequence, materials and components used for such applications must have properties required to withstand adverse conditions and ensure satisfactory performance and reliability in service. Nonetheless, components that normally fulfill these standard requirements can fail under severe service conditions such as high pressure and temperatures and high concentrations of H2S and CO2, Among the factors that can cause the premature failure in metallic components are the use of inadequate materials, the presence of defects that appeared during the production, and errors of project, assembly, or maintenance. Failure analysis allows the identification of causes and thus contributes to improvements in the operation and performance of similar equipment. In this work, light optical microscopy and scanning electron microscopy (SEM) were used to analyze the microstructure and fracture surface of two centrifugal pump shafts that failed during use in a Brazilian petroleum refinery. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.
The aim of this work is to correlate the homogeneity of the microstructure of two certified hardn... more The aim of this work is to correlate the homogeneity of the microstructure of two certified hardness standard blocks, both with the same hardness value range, with its uniformity hardness values. In order to identify the morphological characteristics of the blocks studied, as grain size distribution, an automatic image analysis system with software based on ASTM E112 and ASTM E1382
Journal of Iron and Steel Research, International, 2009
The presence of nonmetallic inclusion particles which appear during steelmaking process is harmfu... more The presence of nonmetallic inclusion particles which appear during steelmaking process is harmful to the properties of steels, which is mainly as a function of some aspects such as size, volume fraction, shape, and distribution of these particles. The automatic image analysis technique is one of the most important tools for the quantitative determination of these parameters. The classical Student approach and the Extreme Values Method (EVM) were used for the inclusion size and shape determination and the evaluation of distance between the inclusion particles. The results thus obtained indicated that there were significant differences in the characteristics of the inclusion particles in the analyzed products. Both methods achieved results with some differences, indicating that EVM could be used as a faster and more reliable statistical methodology.
Journal of Failure Analysis and Prevention, 2010
Metallic materials designed for applications in orthopedic or dental surgical implants must show ... more Metallic materials designed for applications in orthopedic or dental surgical implants must show a group of properties, including biocompatibility, mechanical strength and resistance to degradation (by wear or corrosion) outstand. In order to assure that the properties are achieved, the implant materials must fulfill certain requirements, usually specified in standards. The standards also include chemical composition, microstructure and even macrographic aspects. The main aim of this work was to perform a failure analysis on a titanium-based dental implant and connect the possible causes of failure with the associated material requirements which were previously mentioned. Evaluation techniques included metallographic analysis by optical microscopy and fractographic analysis by scanning electron microscopy (SEM). The results of the examinations suggested that, in spite of their adequate microstructures, the implants fractured due to the overload generated by stress raisers which were found in the implants.
Journal of Failure Analysis and Prevention, 2009
The increasing lifetime of the population on a world-wide scale over the last decades has led to ... more The increasing lifetime of the population on a world-wide scale over the last decades has led to a significant growth in the use of surgical implants for replacement of bones and teeth in affected patients. Other factors, such as scientific-technological development and more frequent exposure of individuals to trauma risk, have also contributed to this general trend. Metallic materials designed for applications in surgical implants, no matter whether orthopedic or dental, must show a group of properties in which biocompatibility, mechanical strength, and resistance to degradation (by wear or corrosion) are of primary importance. In order to reach these aims, orthopedic materials must fulfill certain requirements, usually specified in standards. These requirements include chemical composition, microstructure, and even macrographic appearances. In the present work, three cases of implant failure are presented. These cases demonstrate the most frequent causes of premature failure in orthopedic implants: inadequate surgical procedures and processing/ design errors. Evaluation techniques, including optical and scanning electron microscopy (SEM), were used to evaluate macroscopic and microstructural aspects of the failed implants, and the chemical composition of each material was analyzed. These evaluations showed that design errors and improper surgical procedures of outright violation of standards were the cause of the failures.
Journal of Failure Analysis and Prevention, 2011
As in the case of implants, the increase of the life expectancy and of the risk of accidents, thu... more As in the case of implants, the increase of the life expectancy and of the risk of accidents, thus causing a higher incidence of surgeries, has led to an increased use of surgical instruments. The reliability of these instruments, used in applications of considerable responsibility, depends on the characteristics of the materials, as well as on the conditions of manufacture. Using some techniques such as optical microscopy, scanning electron microscopy, and hardness tests, this work has as purpose the identification of the possible causes of failure of surgical torch meters used for dental implants fixation, trying to correlate with the microstructural characteristics of the austenitic and martensitic stainless steels used in their manufacture. The results thus obtained allowed the identification of the main causes of the failure, primarily related to microstructural heterogeneities which resulted from inadequate heat treatment and with the presence of non-metallic inclusions, which favored brittle fracture and corrosion.
Engineering Failure Analysis, 2005
The main reason for the existence of superalloys is their outstanding strength at high temperatur... more The main reason for the existence of superalloys is their outstanding strength at high temperatures, which make them suitable for the fabrication of gas turbine components. Contributing factors are the high modulus of their close packed FCC lattice and the presence of elements, like aluminum and titanium, which enable the formation of c 0 phase, Ni 3 (Al,Ti), that dispersed in the c matrix has a hardening effect. The presence of chromium is essential to guarantee oxidation resistance and other alloying elements are important to impart high-temperature strength. Carbon content is usually sufficient to allow the formation of carbides which improve creep resistance. In this work, two failure cases of nickel base superalloy components were analyzed by scanning electron microscopy (SEM). The microstructural aspects provided sufficient evidences to conclude that, in the first case overheating led to failure and in the second case the significant microstructural degradation of the surface can lead to failure.
Journal of Failure Analysis and Prevention, 2008
The petroleum industry has changed significantly over the past decades. For example, in Brazil, o... more The petroleum industry has changed significantly over the past decades. For example, in Brazil, oil extraction under very deep sea water is growing very quickly. As a consequence, materials and components used for such applications must have properties required to withstand adverse conditions and ensure satisfactory performance and reliability in service. Nonetheless, components that normally fulfill these standard requirements can fail under severe service conditions such as high pressure and temperatures and high concentrations of H2S and CO2, Among the factors that can cause the premature failure in metallic components are the use of inadequate materials, the presence of defects that appeared during the production, and errors of project, assembly, or maintenance. Failure analysis allows the identification of causes and thus contributes to improvements in the operation and performance of similar equipment. In this work, light optical microscopy and scanning electron microscopy (SEM) were used to analyze the microstructure and fracture surface of two centrifugal pump shafts that failed during use in a Brazilian petroleum refinery. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.