Materials Science Forum Vol. 1012

Abstract: In this work, the consolidation of blended elemental powders of iron, manganese and aluminum (Fe-25Mn-15Al wt.%) was performed by Equal Channel Angular Pressing (ECAP). Samples were consolidated at room temperature in a Φ = 120° die by a single pass and a second pass in route A. Both samples were heat treated at 650 °C and water cooled. Prior to heat treatment, samples presented a dense but chemically inhomogeneous structure. Fe and Al particles were highly deformed, whereas, Mn was almost undeformed. Mn particles were partially shattered by friction with Fe and Al particles. After heat treatment, the samples were characterized by SEM-EDX and presented substantial interdiffusion along the particles interfaces. It is believed that higher deformations by ECAP may improve the sinterability of consolidated samples in order to densify and chemically homogenize it.

Abstract: Superduplex stainless steel alloy exhibit high mechanical and corrosion resistance, which main industrial application is in the petrochemical industry. The manufacture and maintenance of such equipment usually involve welding processes, followed by post-welded heat treatment and it often becomes impossible to apply heat treatments. Thereby, the purpose of this work is to verify the effect of a post-welded heat treatment on shielded metal arc welding in steel grade ASTM A890/A890M - grade 6A. The microstructure in the as-welded condition consisted of austenite, secondary austenite, and ferrite phases and, the post-welded heat treatment condition exhibited only austenite and ferrite. The hardness in the melt zone reached values of 300 HV after welding and, the value was reduced to 260 HV in the post-welded heat treatment condition.

Abstract: The Cu-8.5wt % Sn alloy presents an extensive microsegregation during its solidification. That microsegregation results in the formation of a eutectoid mixture, which is detrimental to subsequent forming processes. This study deals with the influence of solidification time and cooling rate on the microstructure of that alloy. The unidirectional solidification technique allowed the acquisition of thermal data. The optical microscopy enabled the microstructural characterization of the material, the measurement of dendrite arm spacings and the quantification of the volume fraction of the eutectoid mixture. A semi-analytical mathematical model was proposed to estimate the volume fraction of the eutectoid mixture. The model expresses the volume fraction as an implicit function of the Fourier number. The results showed that the microstructure is dendritic and that the characteristic spacings increase with the solidification time between the liquidus and the peritectic temperatures. The data also showed that for higher cooling rates the dendrite arm spacings are smaller and that there is a tendency for the volume fraction of eutectoid mixture in the columnar zone to increase with the Fourier number and to decrease with the cooling rate. The proposed model allowed obtaining values of volume fraction with the same order of magnitude of the experimental data, but with behavior tendency opposite to that observed.

Abstract: This study aims to correlate thermal parameters in the directional solidification of Al-10wt% Si-5wt% Cu alloy with the resulting microstructure and, in addition, with hardness and corrosion resistance. The results include primary dendritic arm spacing (PDAS), tip growth rate (V_L), cooling rate (T_R), scanning electron micrographs (SEM), hardness values and corrosion resistance parameters obtained by electrochemical impedance spectroscopy (EIS) and by the Tafel extrapolation method, conducted in 3% (m/v) NaCl solution at room temperature. The results show that coarser PDAS exhibit a tendency to increase in corrosion resistance, except in the positions with higher concentrations of the intermetallic compound Al₂Cu, that surrounded by an aluminum rich phase tends to have a higher resistance to corrosion. The hardness values remained constant.

Abstract: Rare earth permanent magnets are essential components in many fields of technology due to their excellent magnetic properties. There are some techniques used in the manufacture of permanent rare earth magnets: the powder metallurgy to obtain anisotropic HD sintered permanent magnets and the melt spinning and HDDR processes to obtain isotropic and anisotropic bonded permanent magnets. In this work, the influence of the melt spinning parameters on the microstructural and magnetic properties of the Pr₁₄Fe_balCo₁₆B₆ alloy was studied. The alloy was melted and rapidly cooled at 9.9 x 10⁵°C/s. The parameters used in the process were: wheel speed of 15 m/s and 20 m/s and ejection pressure of 25.3 kPa and 50.7 kPa. Ribbons and/or flakes of 30 μm thickness and width until 5 mm were obtained. Results show that the melt spinning alloys are nanocrystalline and that the parameters of the process influence the microstructure and their magnetic properties. Mean crystallite size up to 38.5 nm and intrinsic coercivity (iHc) up to 254 kA/m were obtained.

Abstract: In the Metal Market, it has been important to understand the structure of steels, so that it is possible to develop new cutting materials at lower costs and more resistant to high temperatures and wear. This is possible by raising the mechanical strength for solid solution in fast steels, ie, addition of alloying elements to the steel in its solid state, the alloys fundamental to this process were: cobalt, manganese, silicon, tungsten and vanadium. Among the thermal treatments, tempering and quenching were used to raise the degree of hardness and strength of the steel. The samples studied were high speed steels HS6-5-3, HS6-5-3-5, K190 e K390. Hardness and metallographic tests were carried out on the samples and with the results generated, it was possible to draw a comparison and understand which alloying elements provide the least oxidation, corrosion and greater impact strength of fast steel.

Abstract: This work evaluates the microstructure and the yield strength under compression at room temperature and at 800°C of specimens prepared with AISI 310 stainless steel powder (D50 = 10 μm), manufactured by gelcasting. Parts were vacuum sintered in a single batch at 1280°C. At room temperature, specimens presented average yield strength of 270 MPa, and at 800°C, 105 MPa. Microstructure analysis involved the measurement of grain size along the vertical axis of cylindrical specimens, with special attention to the effect of particles settling, and was conducted using scanning electron and optical microscopy, and X-ray diffraction. Settling effect was assessed considering the position where the specimen was taken and was negligible: both density and yield strength did not vary significantly along the vertical axis.

Abstract: Deep cryogenic treatment (DCT) is industrially applied to improve the wear resistance characteristics of tool steels. However, on non-ferrous metals, the knowledge about the obtained characteristics after DCT is limited. The purpose of this work was to investigate how DCT affects the properties and the behavior of the Cu-14Al-4Ni alloy treated at different times and after thermomechanical cycling was performed. In the present investigation, there was performed a comparative experimental analysis of the transformation temperatures, microhardness and shape recovery capacity of the alloy obtained by smelting, treated by DCT and thermomechanically cycled. The DCT provided the stabilization of the martensitic phase β'₁ and, consequently, the stabilization of the phase transformation temperatures and the shape recovery capacity of the shape memory effect of the alloy, increasing the alloy life.

Abstract: In nickel laterite agglomerates from rotary kiln of RKEF process the phases lizardite and/or chrysotile, clinochlore, quartz and hematite were identified. The product contain SiO₂ (32.67%), Fe₂O₃ (24.68%), MgO (21.81%) and NiO (3.30%) as principal components. When thermal treatment were carried out weight differences can be observed where the adsorbed water removed during drying, without phase changes in temperatures ranging from 60°C to 100°C, indicated influence of mineral assemblage. Phase changes and weight loss was observed in calcination with clear crystalline restructuring of the serpentines and clinochlore at 500°C. Above this temperature new phases are crystallized until 820°C, when is formed forsterite and enstatite, provably trevorite and remaining unchanged quartz. There were identified nickel minerals. The nickel occurs in bearing phases as Mg-Ni ion substitution in the crystal structure. On the analyzed conditions might infer that these new phases formed can affect the pyrometallurgical process of reduction.

Abstract: In this work, the hydride-dehydride process (HDH) parameters to obtain Nb47Ti and Ti13Nb13Zr alloys powders were investigated, aiming the production of orthopedic implants by additive manufacturing (AM). Nb47Ti and Ti13Nb13Zr alloys were previously obtained by electron beam melting furnace (EBMF). During the hydriding step, the alloys were heated at two activation temperatures, 800 and 1000 °C, under constant hydrogen pressure (1.8 bar), for 40 min followed by a controlled cooling rate step (2 °C/min). The hydride alloys were milled in a ring-type mill, for milling times ranging from 2 to 6 min, until to achieve the required particle size range (between 15 and 45 μm). The dehydriding step of the alloys was carried out under high vacuum at 700 °C for times up to 5 h. The alloys treated under distinct HDH steps were characterized by X-ray diffraction, scanning electron microscopy, dynamic image analysis, inert gas fusion and gravimetry. The alloys hydrides (δTiH_x phase) were detected in both investigated activation temperatures, with hydrogen (H) contents up to 3.04 and 3.62 wt.% for the Nb47Ti and Ti13Nb13Zr alloys, respectively. During the hydriding step it was also observed a significant increase of nitrogen (N) and oxygen (O) contents regarding he as-cast alloys. The Nb47Ti alloy showed a lower embrittlement degree than the Ti13Nb13Zr alloy, resulting in higher milling times to reach the required particle size distribution. The higher oxygen pick up was observed during the milling step. After the dehydriding step, the HDH powders showed H contents lower than 0.01 wt.%, beside a significant N decreasing. Particles with irregular (or angular) shapes were obtained. However, the particle size was in the required range.