Antônio Augusto Couto

Characterization of PVDF/HAP composites for medical applications

Biomaterials (composites and blends) play a major role in the health of modern society. This paper reports on the preparation and characterization of polyvinylidene fluoride (PVDF) and hydroxyapatite (HAP) composites, analyzing the incorporation of HAP in PVDF and investigating their mechanical properties and cytotoxicity (biocompatibility) for use in bone restoration and filling. The material was prepared in film form by the casting method. PVDF pellets were dissolved in dimethylacetamide (DMA), a HAP/DMA emulsion was prepared. The materials were mixed in proportions of 100/00, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70 in weight and left to dry in an oven, resulting in homogeneous, flexible films which were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X ray diffractometry (XRD), contact angle measurement, and by mechanical and cytotoxicity tests.

Creep Behavior of the Inconel 718 Superalloy

A superalloy is an alloy developed for elevated temperature service, where relatively severe mechanical stressing is encountered, and where high surface stability is frequently required. High temperature deformation of Ni-base superalloys is very important since the blades and discs of aero engine turbine, because need to work at elevated temperature for an expected long period. The nickel-base alloy Inconel 718 has being investigated because it is one of the most widely used superalloys. The objective of this work was to evaluate the creep behavior of the Inconel 718 focusing on the determination of the experimental parameters related to the primary and secondary creep states. Constant load creep tests were conducted with at 650, 675 and 700°C and the range of stress was from 625 to 814 MPa to according to ASTM E139 standard. The relation between primary creep time and steady-state creep rate, obeyed the equation for both atmospherics conditions at 650, 675 and 700°C. The microstructural characterization employing the technique of scanning electron microscopy has been a valuable tool for understanding the mechanisms of creep.

Effect of Artificial Aging on the Mechanical Properties of an Aerospace Aluminum Alloy 2024

Aluminum alloys have low specific weight, relatively high strength and high corrosion resistance and are used in many applications. Aluminum Alloy 2024 is widely used for aircraft fuselage structures, owing to its mechanical properties. In this investigation, Aluminum Alloy 2024 was given solid solution treatments at 495, 505, and 515°C followed by quenching in water. It was then artificially aged at 190 and 208°C. Subsequently, hardness measurements, tensile tests as well as impact and fatigue tests were carried out on the heat treated alloys to determine the mechanical properties. The tensile and hardness tests revealed similar mechanical properties for specimens of this alloy that were given the three solid solution treatments. Aluminum Alloy 2024 specimens that were solid solution treated at 515°C and artificially aged at 208°C for 2h exhibited the highest yield and tensile strength. In general, the increase in strength was accompanied by a decrease in ductility. Cyclic fatigue studies were conducted with symmetric tension-compression stresses at room temperature, using a bending-rotation test machine. The alloy solution heat treated at 515°C and aged at 208°C/2h was fatigue tested at constant frequency. The relation between stress amplitude and cycles to failure was established, enabling the fatigue strength to be predicted at more than 7.8x106 cycles, with maximum stress of 110.23 MPa. The fracture surfaces of specimens that failed after fewer cycles showed mainly precipitates and micro voids, whereas specimens that fractured after a higher number of cycles indicated that cracks initiated at the surface. The high cycle fatigue fracture surfaces revealed pores that could be due to precipitates from the matrix.

Microstructure and mechanical behavior of Al9Si0.8Fe alloy with different Mn contents

ABSTRACT It has been reported that the detrimental effect of Fe on the mechanical properties of Al alloys can be eliminated through the addition of Mn. In this study, we examine the effects of the addition of different Mn contents (0.1, 0.2, 0.4 and 0.7 wt-% of Mn) on the microstructure and mechanical behaviour of Al9Si0.8Fe alloy. It is shown that the presence of up to 0.4 wt-% of Mn changed the platelike morphology of β-Al5FeSi into α-Al15(Fe,Mn)3Si2 with a Chinese script-like morphology. Mn contents higher than 0.4 wt-% promoted the formation of α-Al15(Fe,Mn)3Si2 phase with a polygonal morphology. The effect of the addition of up to 0.7 wt-% of Mn on the mechanical properties of Al9Si0.8Fe alloys is in fact quite negligible.

Evaluation of Fatigue Behavior of SAE 9254 Steel Suspension Springs Manufactured by Two Different Processes: Hot and Cold Winding

The fatigue resistance is a property that exerts a strong influence on the suspension spring performance in vehicles. The choice of SAE 9254 steel was due to its wide use in the manufacture of these springs and their fatigue properties and toughness. The manufacture of SAE 9254 steel springs has been made by the hot winding process and the heat treatment by conventional quenching and tempering or by cold winding process and induction hardening and tempering. The shot peening induced a compressive residual stress which increased the fatigue life of the SAE 9254 steel. The residual stress profile from the surface of springs showed a peak in the values of the compressive stress for both manufacturing processes. The maximum residual stress in the cold processed spring was higher than the hot processed spring and maintained much higher values along the thickness of the spring from the surface, resulting from manufacturing processes. The fatigue cracking of the springs, without shot peening, started by torsional fatigue process, with typical macroscopic propagation. The fracture surface showed stretch marks with high plastic deformation.

Determination of Creep Parameters of Ti-6Al-4V with Bimodal and Equiaxed Microstructure

Ti-6Al-4V is the most used of titanium alloy and presents some important properties as metallurgical stability, high specific strength, corrosion and creep resistance [. The aim of this study is to evaluate the creep behavior of Ti-6Al-4V alloy with equiaxed and bimodal microstructures and determine the creep parameters of Ti-6Al-4V in these conditions. It was used a Ti-6Al-4V alloy forged and annealed at 190°C for 6 hours and cooled in air. The material in this condition shows an equiaxed microstructure. For bimodal microstructure, the material was heat-treated at 950°C for 60 minutes and cooled in water until room temperature. After this the material was heat-treated at 600°C for 24 hours and cooled in air until room temperature. Creep tests were performed at 600°C in stress conditions of 125, 250 and 319 MPa at constant load. The alloy with Bimodal microstructure shows higher creep resistance with a longer life time in creep.

Study of the deep drawing behavior and crystallographic texture of AA 3104-H19 aluminum alloy sheets

The aluminum alloy 3104, H19 temper, is commonly used in the production of two-piece beverage cans. The objective of the present study is to compare three different rolled sheets of this alloy. All three of them are routinely used in production lines dedicated to can manufacturing. The yield strength for all three was found around 265 MPa, the ultimate tensile strength 281 MPa, and the average elongation 4.19%. The strain hardening exponent (n) was similar for all three sheets, averaging 0.078. The plastic strain ratios for planar anisotropy (ΔR) and for normal anisotropy ( R ¯ ) were found to be near zero and 0.4, respectively. Values of ΔR near zero indicate there is no earing tendency. The crystallographic texture analysis yielded four dominating components: Brass ({110}<112>) and Copper ({112}<111>), which are typical of strain hardened aluminum, Cube ({001}<100>), usually associated with recrystallization, and Goss ({110}<001>). Such a texture would be conducive to balanced earing. The metallographic images for all three sheets were alike, with constituents not homogeneously distributed and with similar size and chemical compositions in addition to dispersoids finely spread throughout the aluminum matrix. The Erichsen tests also showed alike results with an average of 4.6 mm before failure.

Computational Simulation in Centrifugal Casted Aluminum–Silicon Engine Cylinder Liner

Automotive cylinder liners are mechanical components with the function of internal coating of the cylinder automotive engines. The replacement of parts made of steel/cast iron by aluminum alloys has been made with advantages not only in reducing weight as well as fuel consumption and emission of pollutants. This study was aided by the finite element software Hyperworks, where the mesh was generated and the simulation was performed in Abaqus. The mesh for the engine block was defined with elements of four nodes of tetrahedrons. The liners were designed with hexahedron elements of six nodes. Due to the manufacturing process of the cylinder liners (centrifugal casting), the finite elements model was created in layers to meet the variation in the amount of silicon along the wall thickness. The variation in the amount of silicon affects the physical properties of the liners along the wall thickness. With this model, it was possible to show the viability of application of aluminum liners in engine blocks made of cast iron. The modal analysis showed that the model does not contain its first natural frequency within the range of work of the engine, approving its application with this concept.

Failure Analysis of an Automotive Component (Cardan Yoke) by Scanning Electron Microscopy

Two SAE 1541 (0.39%C; 1.44%Mn; 0.23%Si; 0.16%Ni; 0.16%Cr) carbon steel cardan yokes that were forged, machined, quenched and tempered, as part of the manufacturing process to ensure long term operation under specific loading conditions, failed during its manufacture. The cardan yokes ruptured in the bearing seat region while these were being straightened by bending. This study deals with fracture analysis that was carried out by visual inspection and scanning electron microscopic examination. The focus of this study was to investigate the fracture mechanism associated with the failures. Fractographs of the broken components indicated that the rupture initiated at the edges of the component, from preexisting cracks, due to the bending stresses during the straightening process. The initial stage of rupture was predominantly intergranular in the tempered martensite surface layer, revealing the brittle nature of the component. Cracks were observed at regions prone to stress concentration. Eventual rupture of the component probably initiated at these cracks. This behavior is probably related to metallurgical processing steps like quenching, that causes the formation of a banded structure and promotes circumferential and radial cracking before the tempering. The fracture surface revealed regions with micro dimples and a large smooth area with some elongated inclusions. The morphology of these inclusions was cellular and originated at the grain boundaries of the primary austenite. These inclusions are probably MnS with a dendrite structure, capable of causing brittle intergranular rupture.

EVALUATION OF HEAT TREATMENT AND CERAMIC COATING IN CREEP OF TI-6AL-4V

This study aimed to evaluate the resistance of a Ti-6Al-4V alloy in creep after heat treatments. It was used a Ti-6Al-4V alloy in cylindrical bars forms, forged condition and annealing at 190oC for 6 hours and cooled in air. The microstructure of Ti-6Al-4V alloy was evaluated after heat treatment and was submitted to creep tests at 600oC and stress conditions from 125 to 319 MPa at constant load. The Widmanstätten structure was obtained by heat treatment. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The alloy with Widmanstätten structure and ceramic coating shows greater resistance to creep and oxidation with a longer life time in creep. At higher stress condition, 600°C and 319 MPa, the Ti-6Al-4V alloy with ceramic coating didn’t show higher creep resistance. This condition presented higher tp value and the value. It occurred because at high stress condition the coating is very fragile, decreasing your creep resistance.