[show abstract][hide abstract] ABSTRACT: The corrosion behavior of TiC particles reinforced Mg-Al alloy in 3.5% NaCl solution has been evaluated using electrochemical techniques. Tested alloys included an Mg-9Al (Mg AZ91E) alloy with and without 56 wt. % TiC particles. Electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance, electrochemical noise, and electrochemical impedance spectroscopy measurements. All techniques showed that the composite exhibited a lower corrosion rate than the base alloy. Evidence of galvanic effects that increased the composite corrosion rate was found between the matrix and the TiC particles. Additionally, the tendency to suffer from pitting corrosion was higher for the base alloy than that for the composite. Electrochemical impedance results showed the importance of adsorption/diffusion phenomena in both materials.
International Journal of Corrosion. 01/2011; 2011:1-7.
[show abstract][hide abstract] ABSTRACT: A novel modification of the metal inert gas (MIG) welding method, which was developed to weld metal matrix composites, was
applied to join plates of aluminium 12.5mm thick. The plates were prepared with square edges and with a small single-V preparation
with an angle of 45° in the upper part. The electric arc was indirectly applied on the single-V butt weld over strips of Al-2024
placed on top of the joint. Thermal analysis showed that the efficiency of the MIG process with indirect electric arc (IEA)
is increased due to the reduction of heat losses and fully penetrated welds with a high depth-to-width ratio can be produced
as compared to plain MIG welding in which partial penetration and lack of lateral fusion were observed. Microstructural examination
of the welds revealed distinct characteristics such as partially melted grains trapped within the weld next to the fusion
line for IEA welds and the typical epitaxial and columnar growth from the base metal partially melted grains for plain welds,
i.e. direct application of the electric arc (DEA).
Journal of Materials Science 08/2007; 42(18):7956-7963. · 2.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: The present work describes the interactions that occur between molten Al–Mg alloys and solid TiC substrates. The sessile drop technique was used to study the wetting behavior of Al–Mg alloys on TiC sintered ceramic substrates under argon in the temperature range of 750–900 °C. The effect on the wetting behavior of the interfacial reaction layer was studied. All the Al–Mg alloys react with TiC at the interface. The interface thickness varied with the samples, and depends on the temperature and the time of the test. The spreading kinetics and the work of adhesion were evaluated. The high activation energies values obtained suggested that chemical reaction is the driving force for drop spreading.
[show abstract][hide abstract] ABSTRACT: Molten Mg was pressurelessly infiltrated into TiC preforms (56 vol.%) under flowing Ar at temperatures of 850, 900 and 950 °C. The rate of infiltration exhibited a strong temperature dependency. The mechanical strength of the composites increased from 172 to 233 MPa for processing temperatures of 850 and 950 °C, respectively.
[show abstract][hide abstract] ABSTRACT: Metal inert gas welding of Al-1010/TiC/50p composites was carried out on 9 mm thick square bars by applying the electric arc directly and indirectly. Three pre-heating temperatures were used, 50, 100 and 150C but only direct electric arc (DEA) was applied at room temperature. Welds were microstructurally examined and tested under tensile load. Complete penetration was achieved using both DEA and IEA methods. Uniform welds were obtained using indirect electric arc (IEA), meanwhile broadening was observed in the upper part in DEA welds facilitated by mixture of the base material with the filler. Microstructural observations showed good lateral fusion of the parent composites, little or no dissolution of TiC by IEA and only slight dissolution by DEA, which led to TiAl
formation during solidification. The presence of Al4C3 was not detected. Microhardness weld profiles revealed that the use of IEA reduces the heat affected zone (HAZ). Mechanical failure of the samples was consistently in the weld zone. Mechanical strength in IEA welds (182–186 MPa) was consistent irrespective of the pre-heating conditions and dependant only of the consumable (Al-2024). The mechanical strength of DEA welds was affected to some extent by the incorporation of the reinforcing particles into the weld region and wettability aspects inherent to the welding conditions. The use of IEA seems to be a suitable route for joining Al-based composites even when the reinforcement content is high.
Journal of Materials Science 05/2003; 38(12):2771-2779. · 2.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: Structural characterizations based on transmission electron microscopy observations were carried out on as-fabricated and heat-treated Al-2024/TiC composites. These composites types reinforced with TiC particles were produced with a pressureless melt infiltration route at 1200°C for 2h under argon atmosphere. The composites were heat-treated at 530°C during 150min, cold-water quenched and subsequently artificial and natural aged at 190°C for 12h in an argon environment and at room temperature for 96h, respectively. Different precipitate types were obtained and they were identified as CuAl2, Al3Ti, Ti3AlC and Ti3Al. Most of the precipitates were found to be uniformly distributed in the matrix and some regions show precipitates which have a cubic morphology (Ti3Cu). High-resolution electron microscopy images were partially used for the characterization of the precipitates in these composites.
Composites Part A-applied Science and Manufacturing - COMPOS PART A-APPL SCI MANUF. 01/2003; 34(1):17-24.
[show abstract][hide abstract] ABSTRACT: Microstructural and mechanical properties characterizations of nanocrystalline Ni–Al+M alloys were carried out. M represents the addition of transition elements such as Fe, Ga and Mo. Mechanical alloying (MA) and densification by hot-pressing techniques were used to produce and consolidate the alloys. The mechanical alloyed powders have a microstructure consisting of nanometer size particles. The main effect of these elements on the microstructure of the NiAl alloy is the refinement of the grain size since this process gives rise to crystallite sizes in the nanometric range. Also, the three minor additional elements form a solid solution with the intermetallic structure of the NiAl. Additions of Mo in the range of 2–6 at.% cause second phase formation of Mo2C. Mechanical properties (hardness, yield stress and strain) were obtained as a function of composition and sintering temperature. The highest hardness value is obtained for the NiAl+2Ga+6Mo (at.%) alloy and always corresponded to the highest densifications (98%) for the sintered samples at 1200 °C during 30 min. The Ni–Al alloys with different additions of elements lead to higher deformations than those reported previously.
[show abstract][hide abstract] ABSTRACT: The wetting of TiC by liquid aluminum and magnesium under static argon between 800 and 1000 °C is studied using the sessile drop technique. Extensive interfacial reaction occurs between Al and TiC, leading to the formation of aluminum carbide; conversely no reaction occurs for Mg/TiC.
Scripta Materialia 01/2003; 48(12):1625-1630. · 2.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: The microstructure and chemical characteristics of nanocrystalline NiAl intermetallic phase with a B2 crystalline structure are studied. Nanophase NiAl powder with the addition of minor elements (Fe, Ga and Mo) was prepared by mechanical alloying under argon atmosphere. Structural characterization based on X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) observations were carried out on the NiAl compounds. The effects of the different microalloyed elements on the microstructure are explored.
[show abstract][hide abstract] ABSTRACT: The effect of alloying elements on the wetting behavior of TiC substrates by commercial aluminum alloys (1010, 2024, 6061, 7075) and its relation to phase formation at the metal–ceramic interface was investigated at 900 °C using a sessile drop technique. It was found that wetting behavior in Al-alloys/TiC is typical of reactive systems, furthermore, wettability of TiC by pure Al-1010 was better than the alloys. Interface examination revealed the formation of Al4C3 in all the cases; the thickness of the reaction layer varied within the samples and was discontinuous in nature, particularly for the 7075/TiC and 6061/TiC systems, which exhibited poor wetting. The formation of alloyed phases in the ceramic surface decreased the amount of the undesirable Al4C3 at the metal/ceramic interface.
Composites Part A Applied Science and Manufacturing 01/2002; 33(10):1425-1428. · 2.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Composites of a commercial Al-2024 alloy reinforced with particulate TiC have been produced by the pressureless melt infiltration route. Infiltration was carried out at 1200°C for 2 h and composite materials containing 52 and 55 vol.% TiC were obtained. The phases other than the matrix and the reinforcement were identified as CuAl2, AlTi3, Ti3AlC, and TiAl3. It was found that the composites were age hardenable after solutionizing at 530°C for 150 min and subsequent natural or artificial ageing at 190°C. Mechanical properties of the composites, as-fabricated and heat-treated, showed a strong dependency on the ceramic content. After heat treatment, the 55% TiC composites showed an increase of hardness from 28.5 to 38.5 HRC; meanwhile ultimate tensile strength increased from 379 to 480 MPa. A similar behavior, as a function of heat treatment, was observed for the composites containing 52% TiC, but the estimated values were lower than those obtained for the 55% TiC composites. Scanning electron microscope (SEM) examination revealed transgranular fracture throughout the CuAl2 agglomerated precipitates in the as-fabricated composites. In the heat-treated conditions, brittle and intergranular fractures were observed.
Materials Science and Engineering A 09/2000; 289(1-2):109-115. · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: A study of the infiltration process of several alloys (Al-2024, Al-6061, and Al-7075) into preforms of TiC was carried out. The preforms were sintered for one hour under argon at 1250,1350, and 1450°C with the aim of achieving different levels of densification. Using a thermogravimetric analyzer (TGA), infiltration profiles were obtained by continuously monitoring the weight change of preforms partially immersed in molten aluminum. Infiltration was carried out at different temperatures (ranging from 900 to 1200°C) under argon to evaluate infiltration kinetics. The infiltration rate of the aluminum into the preforms followed parabolic behavior and the activation energy changed according to the extent of preform densification. Average activation energies of 74, 99, and 138 k J mol were obtained for the Al-7075, Al-6061, and Al-2024 alloys, respectively. Prior to infiltration, an incubation period was observed and its length depended on the temperature; lower the infiltration temperature, longer was the incubation period.
Materials and Manufacturing Processes 03/2000; 15(2):163-182. · 1.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: The mechanism of reduction of iron ore agglomerates by both isothermal and nonisothermal TG studies was investigated, and the work was complemented with the structural characterization of the total and partially reacted samples. Three different commercial hematite pellets were studied. The mechanisms of reduction were obtained under isothermal conditions, resulting in a fitting to chemical reaction models. Nonisothermal reduction was carried out using a TGA system (CAHN TG-171) from 600 to 1,000 °C maintaining a lineal heating rate of 4, 7 and 10 °C/min, and the reducing atmospheres used were H2 (100 %) and H2-CO (95:5). The kinetic parameters were evaluated by Coats & Redfern, Dixit & Ray and Prakash & Ray techniques. It was found that the lower the heating rate, the higher the reduction degree and the higher activation energy. The activation energy for reduction with the mixture H2-CO was always higher than that obtained with pure H2.
Se estudió el mecanismo de reducción en aglomerados de mineral de hierro mediante análisis termogravimétricos tanto isotérmicos como no isotérmicos, complementando el estudio por caracterización estructural de muestras parcial y completamente reducidas. Se estudiaron tres tipos de pelets hematíticos grado comercial. Los mecanismos de reducción se determinaron isotérmicamente y resultaron ser modelos de control por reacción química. La reducción no isotérmica se realizó en un TGA CAHN-171 de 600 a 1.000 °C a velocidad de calentamiento lineal de 4, 7 y 10 °C/min, en atmósferas reductoras de H2 (100 %) y H2-CO (95:5). Los parámetros cinéticos se evaluaron por las técnicas propuestas por Coats & Redfern, Dixit & Ray y Prakash & Ray. Se encontró que a menor velocidad de calentamiento, mayor es el grado de reducción no isotérmico y mayor la energía de activación del proceso. La energía de activación con la mezcla H2-CO, siempre fue mayor que con H2 puro.
Revista de Metalurgia 08/1997; 33(4):239-249. · 0.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the present work, the effect of the firing conditions such as temperature, basicity, firing cycle and oxygen potential, on the formation of mineral phases in magnetitic iron ore briquettes was studied. It was found that a high oxygen potential (air) favors the oxidation reaction of magnetite to hematite and as a consequence calcium ferrite formation. The calcium ferrite increased with the increase of the basicity and decreased with the increase of the temperature. At a medium partial pressure of oxygen (ρO2 = 5 x 10-3 atm.), the agglomerate was composed in the majority of magnetite with small amounts of reoxidized hematite and negligible amounts of calcium ferrite. It could be noticed that magnetite increased and hematite decreased with increase of basicity. The mineral phases present in the briquettes fired at the gas mixture composed by 1 % CO, 24 % CO2 and 75 % N2 and then cooled in air, include magnetite and highly oxidized phases such as hematite and calcium ferrite.
Se estudió el efecto de las condiciones de sinterización tales como temperatura, basicidad, ciclo térmico y potencial oxidante en la formación de fases minerales en briquetas de mineral de hierro magnetítico. Se encontró que un alto potencial de oxígeno (aire) favorece la reacción de oxidación de magnetita a hematites y como consecuencia la formación de calcioferrita. La calcioferrita se incrementó con el aumento de la basicidad y disminuyó con el incremento de la temperatura. Para un potencial de oxígeno medio (ρO2 = 5 x 10-3 atm.), el aglomerado estuvo compuesto en su mayor parte por magnetita con pequeñas cantidades de hematites reoxidada y cantidades insignificantes de calcioferrita. Se observó que la magnetita se incrementa y la hematites disminuye con el aumento de la basicidad. Las fases minerales presentes en briquetas sinterizadas en la mezcla gaseosa de 1 % CO, 24 % CO2 y 75 % N2, incluyen la magnetita y fases altamente oxidadas como hematites y calcioferrita.
Revista de Metalurgia 06/1997; 33(3):161-171. · 0.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: The influence of microstructures formed by serpentine addition on mechanical strength is investigated. It was found that the microstructure formed depends mainly on firing temperature, basicity and serpentine percent. The mineralogical phases present were quantified by the point-count method. The addition of serpentine on acid briquettes (CaO/Si O2 = 0.3), mainly on those fired at 1,275, 1,300 and 1,325 °C, leads to the formation of magnesio-ferrite that diminishes the mechanical strength of fired briquettes, and at the temperature of 1,250 °C the mechanical strength decreases because of the presence of glassy slags. On the other hand, the addition of serpentine on basic briquettes (CaO/Si O2 = 1.2) leads to the formation of olivines and ferrites that improve the mechanical strength of fired briquettes.
Se estudia la influencia de las microestructuras formadas sobre la resistencia mecánica de mineral de hierro aglomerado con serpentina. Se deduce que la microestructura formada depende de la temperatura de sinterización, de la basicidad y del valor porcentual de serpentina, principalmente. Las fases mineralógicas presentes se cuantificaron utilizando la técnica de conteo por puntos. En briquetas acidas (CaO/SiO2 = 0,3) sinterizadas a 1.275, 1.300 y 1.325 °C, se encontró que la serpentina induce la formación de magnesio-ferritas que traen, como consecuencia, una disminución de la resistencia mecánica, mientras que, a la temperatura de sinterización de 1.250 °C, la aparición de escorias vítreas es la causa principal de la disminución de resistencia. En el caso de briquetas básicas (CaO/SiO2 = 1,2), la adición de serpentina produce la formación de olivinas y calcio-ferritas que originan un aumento de la resistencia mecánica de los sinterizados.
Revista de Metalurgia 12/1995; 31(6):368-378. · 0.24 Impact Factor