Abstract Usually, scraps of X22CrMoV12-1 alloy are obtained through machining of steam turbine blades and recycled through casting. However, this process is considered too costly. The viability of recycling X22CrMoV12-1 scraps with addition of vanadium carbide (VC) through powder metallurgy was analyzed in this study. Scraps of X22CrMoV12-1 alloy with VC were milled in a planetary ball mill during 10, 30 and 60 hours. The granulometry of the powder was determined through laser granulometry. The evolution in particles morphology and amorphization was conducted using scanning electron microscope (SEM) and x-ray diffraction (DRX) techniques. Stress-strain curves were obtained through compressive strength test. The results indicated that the best milling condition found was 60 hours. Also, the X22CrMoV12-1 alloy with VC addition produced by powder metallurgy showed good mechanical strength. Thus, this route was considered promising to reshape this material with smaller energy involved in the process.

resumo: A utilização de resíduos de demolição da construção civil em concreto autoadensável (CAA) tem o potencial de reduzir o impacto ambiental e o custo financeiro. Nesse contexto, este artigo tem como objetivo verificar o comportamento da incorporação de agregados reciclados da construção civil nos traços de argamassas autoadensáveis (AAA) em substituição ao cimento, apresentando-se como uma alternativa interessante às matérias-primas naturais. Este estudo usou o software EMMA® para otimizar a escolha das porcentagens de agregados reciclados finos ao substituir o cimento. As proporções escolhidas foram 0%, 5%, 15% e 25%, através da análise da curva de empacotamento de partículas dos respectivos traços. A proporção de 0% tem em sua composição cimento, metacaulim, areia, superplastificante (SP) e água. Os parâmetros obtidos, por meio de testes no estado fresco do mini-slump e mini-funil V, certificaram as amostras como AAA. Os ensaios de resistência à compressão e a tração na flexão no estado endurecido demonstraram redução nas propriedades mecânicas do material com a substituição do cimento. Conclui-se que os resíduos usados de tijolo e cerâmica podem ser adicionados em substituição ao cimento na AAA sem perda significativas de propriedades no estado fresco e endurecido.

abstract: The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in the hardened state demonstrated a reduction in mechanical properties of the material with cement replacement. It is concluded that the waste used brick and ceramic can be added in replacement to the cement in SCM without significant loss of properties in the fresh and hardened state.

Abstract Nodular cast iron is a fundamental material used in engineering. It has unique properties and is one of the most produced materials in the world nowadays. The production of nodular cast iron involves melting of raw materials such as steel scrap, pig iron, machining returns and alloy irons. With the development of increasingly technological steels through the addition of chemical elements to meet a specific application, there is an increasing difficulty in acquiring steel scrap content low alloy for the production of nodular cast iron. The chemical elements present in the steel scrap favor the appearance of unwanted phases and particles. The present study evaluated the effect of the addition of the elements copper, chromium, molybdenum and nickel in levels between 0.50% w and 1.0% w in the formation of nodular cast iron microstructure. While nickel and copper were evenly distributed in the matrix, chromium and molybdenum formed carbides. In addition, chromium strongly favored the formation of perlite in nodular cast iron and molybdenum, the martensite.

Abstract The Al4.5wt%Cu is an aeronautical and automobile alloy with extensive use in industry for structural purposes. The aim of this work was to evaluate two different solidification processes of the Al4.5wt%Cu alloy, conventional and unidirectional, as well as its recrystallization process. Firstly, the Al4.5wt%Cu alloy was deformed by cold rotary forging and then heat treated at temperatures that varied from 250 to 450 °C. The samples for analysis were obtained after 54, 76 and 91% of reductions in area. Tests of optical microscopy, scanning electron microscopy and Vickers microhardness were performed to evaluate the recrystallization process. The results indicated that the recrystallization started at 350 ºC, being that the conventional samples presented full recrystallization after 5 minutes, while the unidirectional samples presented only partial recrystallization. In general, both solidification processes presented similar results for all of the analysis performed.

Brazilian aeronautical industries report that, due to the high mechanical properties presented commercially, AA2024-T351 alloy presents fissures and non-homogeneous deformations during the mechanical processing. This work proposes a manufacturing process capable of increasing the ductility of the material to withstand tensions during processing and a subsequent treatment to recover the mechanical strength of the alloy. The sequence of operations begins with the super-heat treatment at 415ºC 2.5 h, solubilization at 495ºC 2.0 h, mechanical conformation with a degree of area reduction from10% to 90% and artificial aging at 190ºC at times of 2, 4, 6 and 8 hours. The results allowed to obtain an operational sequence where it is possible to form the alloy in the desired component, without loss of mechanical properties and structural defects, in the shortest time possible of heat treatment, reducing the manufacturing costs and increasing productivity.

Abstract 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.

In this study, the high energy mechanical milling was utilized to the production of duplex stainless steel powders from the recycling chips with and without the addition niobium carbide. The effect of milling time and addition carbide on the morphology, particle size and magnetic properties of the powders was investigated. The utilization of the powder metallurgy constitute an important alternative for the reuse of waste in the industrial sector. The milling was realized using a planetary ball mill for 20 hours at a milling speed of 350 rpm and ball-to-powder weight ratio of 15:1were used, and the (0% and 3 wt. %) niobium carbide (NbC) addition. Scanning electron microscopy and particle distribution analysis were used for characterization of morphology and measure of particle size. Also, to analyze the transformations of phases were investigated using the magnetic characterization and x-ray diffraction. The results indicated that the addition of niobium carbide results in the reduction of the particle size of steel of the order of 20%, besides the reduces the transformation of austenite into strain induced martensitic phase.

The aluminum bronze alloy is part of a class of highly reliable materials due to high mechanical strength and corrosion resistence being used in the aerospace and shipbuilding industry. It's machined to produce parts and after its use cycle, it's discarded, but third process is considered expensive and besides not being correct for environment reasons. Thus, reusing this material through the powder metallurgy (PM) route is considered advantageous. The aluminum bronze chips were submitted to high energy ball milling process with 3% of niobium carbide (NbC) addition. The NbC is a metal-ceramic composite with a ductile-brittle behaviour. It was analyzed the morphology of powders by scanning electron microscopy as well as particle size it was determined. X ray diffraction identified the phases and the influence of milling time in the diffractogram patterns. Results indicates that milling time and NbC addition improves the milling efficiency significantly and being possible to obtain nanoparticles.

Os aços inoxidáveis duplex são aqueles que possuem uma microestrutura constituída por duas fases distintas, ferrita (α) ferromagnética e austenita (γ) paramagnética, presentes em quantidades aproximadamente iguais. Neste trabalho, a microestrutura do aço duplex UNS S31803 foi modificada através de tratamento térmico (TT) de solubilização à temperatura de 1050°C por 30 minutos, seguido de resfriamento em água. Em seguida, as amostras foram envelhecidas por 5, 15, 30, 60 e 180 minutos, à temperatura de 850°C. Este tratamento promoveu a formação de uma fase deletéria, a fase sigma, que se forma através da decomposição da ferrita, rica nos elementos Cr e Mo, que são formadores desta fase. A formação desta fase altera as propriedades mecânicas e químicas (resistência à corrosão) dos aços duplex e superduplex. As propriedades magnéticas e mecânicas foram avaliadas em cada uma das condições estudadas e correlacionadas com a microestrutura. As propriedades magnéticas das amostras foram obtidas em um Magnetômetro de Amostra Vibrante (MAV), no qual se fez o levantamento da curva de histerese deste material. As propriedades mecânicas das amostras foram caracterizadas por microdureza Vickers empregando-se uma carga de 0,2 kgf. A caracterização microestrutural foi realizada utilizando um microscópio óptico. Com o aumento do tempo de tratamento térmico de envelhecimento, ocorreu o aumento do percentual de fase sigma formada, e diminuição da fase ferrita. Devido a essa transformação, houve alteração das propriedades magnéticas do aço duplex. A fase ferrítica foi calculada através de dois métodos: ferritoscópia e medição da magnetização de saturação; em ambos os casos foi observada a diminuição da fase ferromagnética.

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.

O presente trabalho caracteriza a microestrutura de uma liga de bronze de alumínio (similar a liga C63020) submetida a diferentes tratamentos térmicos (TT). Os ciclos de temperaturas estabelecidos são responsáveis pela formação de fases que interferem diretamente na resistência mecânica do material. Utilizou-se uma microssonda EDS acoplada a um microscópio eletrônico de varredura para a identificação das fases resultantes após TT. Os resultados obtidos mostraram que a liga em estudo possui dois processos diferentes de endurecimento em virtude da variação da temperatura de homogeneização. A amostra homogeneizada a 900°C e temperada em água sofreu transformação martensítica e teve suas tensões aliviadas após ser revenida a 500°C por duas horas. Para a amostra TT a 770ºC por 2h e revenida a 500ºC/2h, ocorreu o endurecimento por precipitação.

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.

Os espaçamentos interdendríticos primário e secundário são parâmetros microestruturais que exercem significativa influência nas propriedades mecânicas de peças fundidas. Foram testados, através de simulação numérica, diferentes modelos fornecidos pela literatura para a previsão da redistribuição de soluto e dos parâmetros microestruturais em função dos parâmetros térmicos. Os resultados numéricos são confrontados com experimentais obtidos para o aço inoxidável austenítico AISI 304 solidificado direcionalmente, permitindo a determinação dos modelos mais adequados para as condições empregadas. A solidificação direcional foi obtida através de uma coquilha de cobre refrigerada à água colocada na parte inferior de um dispositivo projetado e construído. Foram obtidos os perfis de temperatura, para várias posições a partir da interface metal/coquilha, através do emprego de termopares do tipo S e de um sistema de aquisição de dados computadorizado. Com os perfis térmicos foram determinados os principais parâmetros térmicos do processo de solidificação, isto é, a velocidade de crescimento da ponta da dendrita, o gradiente térmico à frente da isoterma liquidus e a taxa de resfriamento. Para a determinação e quantificação das fases formadas, utilizaram-se microscopia ótica e MEV.

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.