Mirian de Lourdes Noronha Motta Melo

Comparative analysis of niobium and vanadium carbide efficiency in the high energy mechanical milling of aluminum bronze alloy

This study aims to analyze the efficiency of niobium and vanadium carbides in the high energy mechanical milling of aluminum bronze alloy. Two series of experiments were made following the same steps for both niobium carbide (NbC) and vanadium carbide (VC) additions: 30 g of chips were weighed and placed in a stainless steel jar with 3 % of carbide and 1 % of stearic acid for a mass/sphere relationship of 1:10. The milling was realized using a planetary ball mill for 10, 30 and 50 hours in an inert argon atmosphere at 300 rpm. Results shown in laser diffraction indicate a great reduction in the particle sizes of powders when VC is used. For 30 hours milling, D50 values ranged from 1580 μm with NbC to 182.3 μm with VC addition. The D50 values ranged from 251.5 μm with NbC to 52.26 μm with VC addition, for 50 hours milling. The scanning electron microscopy showed that in 10 hours of milling, the energy was not sufficient to achieve the shear of chips in both cases. For 30 hours, it’s possible to observe particles with sizes between 100 μm and 800 μm with NbC addition while for the same milling time, with VC it’s possible to see particles with different sizes, but with many shapes of fine particulates. For 50 hours milling, particles achieved the smaller sizes between 50 and 200 μm with NbC and ranging from 5 until 50 μm with VC addition.

Caracterização de uma liga de bronze de alumínio submetida a diferentes tratamentos térmicos

This study characterizes the microstructure of an aluminum bronze alloy (similar to the C63020) subjected to different heat treatments. The established temperature cycles are responsible for the formation of phases that directly interfere with the mechanical strength of the material. We used an EDS microprobe coupled with a scanning electron microscope to identify the phases resultant after the heat treatment. The results showed that the alloy under study has two different processes of hardening due to the variation of temperature of homogenization. The homogenized sample at 900°C and quenched in water had its martensitic transformation and stress relieved after being tempered at 500°C for two hours. For the sample heat treated at 770°C for 2 h and tempered at 500°C/2h, precipitation hardening occurred.

Study of the Tempering Effect in Phase Transformations of 13Cr1Ni0.15C and 13Cr2Ni0.1C Steels

The martensitic stainless steels are applied in specific conditions due to theirs corrosion and mechanical resistance. The study of these steels after heat treatment is relevant because it may involve the production and development of new steels with better properties for several applications. This study investigates the effect of heat treatment of quenching and tempering in two martensitic steels - 13Cr2Ni0.1C and 13Cr1Ni0.15C (% weight). Dilatometric tests were performed in the samples after melting process in order to obtain the initial and final temperatures of formation of austenite and martensite. The results showed that the quenched samples have the highest hardness and a martensitic microstructure with delta ferrite presence. On the other hand, the samples after tempering showed different matrix suggesting that the martensite decomposition with no change of the delta ferrite.

Determination of Surface Roughness in Turning of Aluminum Bronze Alloy (UNS С 63020) Using Cutting Tools with Carbide Geometry Positive and Negative

In todays industry, production processes evolve every day, together with the development of new materials and geometries for tools and machines more accurate and efficient. These new technologies allow more flexible processes, such as replacement of the grinding process by turning of hardened materials. This change brings significant reductions in costs of tooling, setup time and machining.This work is a study of the conditions for turning aerospace alloy - Bronze Aluminum (UNS 63020)-hardened and tempered with a hardness of 35 HRC with carbide tools with positive and negative geometry.We analyzed the surface roughness of the specimen and as a criterion for end of life of the cutting tool was used to flank wear, crater wear, chip on the tool and/or the breach thereof.All the cutting parameters, when in their highest levels, do not contribute significantly to the reduction in tool life, while the surface roughness for the increase in the feed (f) and the cutting speed (vc) showed a greater influence on surface finish of the piece.

Análise dos modelos utilizados para a previsão dos parâmetros microestruturais obtidos durante a solidificação direcional do aço inoxidável austenítico AISI 304

In the case of dendritic structure, the mechanical properties of foundry products depend on the parameters: primary and secondary arm spacings. Therefore, it is very important that the computational programs use reliable equations for correlating the calculated thermal parameters with the obtained interdendritic spacings. This study presents a numerical and experimental analysis of some models for predicting the secondary arm spacings as a function of thermal parameters. The comparison between the numeric and experimental results for stainless steel permits the determination of the adequate equation for unidirectional solidification.

Influence of Aging Time on the Tensile Strenght of a Duplex Stainless Steel

This article was aimed at studying the influence of different aging times during the precipitation phase of the UNS S31803 (SAF 2205) duplex steel. To do so, all the test specimens were solution heat treated at 1050oC for 1 hour and quenched in water. After this step, the samples were aged at 850°C for periods of 10, 60 and 600 minutes and cooled in water. The aging heat treatments (TT) were performed in order to precipitate the sigma phase. Samples were subjected to microhardness and tensile tests so that the influence of the microstructural changes over the mechanical properties of the steel was assessed. Based on the microhardness and tensile test data, it was possible to verify a significant change over the mechanical properties of the UNS S31803 steel.

Morphological Analysis of Chip Generated by the Process of Turning on Bronze Aluminium Industry Used in Aeronautics via Electronic Scanning Microscopy

In machining processes the chip is considered the disposal of no interest and so little analysis of the morphology observed as the types and forms submitted. The machining does not equal the composition of the physical properties of metal forming, it involves forces or active and inactive stocks. The combination of parameters, conditions and variables of the machining is a means of speculating and trying to explain the phenomena. Such actions reflect directly on the wear of tooling, and structural integrity. The experimental study of machining is of essential importance for the theory of plasticity can not explain satisfactorily the observed phenomena. The speed and the deformations are very large in the machining process, compared with those treated in this theory. This material may reveal why this chip segmented nature which are characterized by continuous large deformation in narrow bands between segments with little or no strain in their interiors. This is a very different from the continuous chip. With the aid of a tool in the expanding area of technology and scientific processing and analysis of images could provide a better analysis of the chips. The goal of this study was to relate the microstructure of the chips of superalloy Aluminum Bronze (C 63020) with milling parameters used in the process of turning on a CNC lathe Nardini - LOGIC 175, in order to analyze the behavior of even through a mechanical process.

Influência do tratamento térmico de envelhecimento a 850ºC na microestrutura e nas propriedades mecânicas e magnéticas do aço Duplex UNS S31803

Duplex stainless steels are those that have a microstructure constituted by two phases, ferromagnetic ferrite (α) and paramagnetic austenite (γ), which are present in approximately equal volumetric fraction. In this work, the microstructure of duplex steel UNS S31803 was modified by a thermal solubility treatment at temperature of 1050 °C for 30 minutes, followed by water cooling. Next, specimens were aged for 5, 15, 30, 60 and 180 minutes at temperature of 850°C. This treatment promoted the formation of a deleterious phase, the sigma phase, which is formed by the decomposition of ferrite, rich in the elements Cr and Mo. The formation of this phase changes the mechanical and chemical properties of the duplex and super duplex steels. The magnetic and mechanical properties were evaluated in each of the conditions mentioned and a correlation with the microstructure was made. The magnetic properties of the specimens were obtained in a Vibrating Sample Magnetometer (VSM), where the material hysteresis curves were obtained. The mechanical properties of the samples were characterized by Vickers micro-hardness measurements performed with a load of 0.2 kgf. Microstructural characterization was carried out by using an optical microscope. VSM tests results showed that as the aging time increased, the volume fraction of sigma phase also increased, causing a diminution of the steel duplex magnetic properties. The diminution of the magnetic properties of the duplex steel with the aging time is attributed to the lower fraction of ferrite as more sigma phase is formed by the decomposition of ferrite. The hardness results showed an increasing of the hardness of the material as the aging temperature increased, which confirms the higher brittleness of the steel due to the higher amount of sigma phase.