In this work a re-investigation of the solubility limits of the (Nb), Nb3Al, Nb2Al and the Nb-rich side of the NbAl3 phases on the Nb-Al system is presented. Alloys in the binary fields ((Nb)+Nb3Al, Nb3Al+Nb2Al and Nb2Al+NbAl3) were arc-melted, and then equilibrated at 1000, 1200 and 1400 ºC. The phases were confirmed via X-ray powder diffractometry, and their compositions were determined via EPMA measurements. The results showed agreement with the literature concerning the solubility limits of (Nb), Nb3Al and NbAl3 phases, while important differences in the values were found for the Nb2Al phase. In addition, the lattice parameters of the Nb2Al phase were determined via Rietveld refinement. This new set of more accurate experimental information indicates that a thermodynamic reassessment is necessary to precisely describe this system.

Alloys containing Me-Si-B (Me - Refractory Metal) are of great interest for high temperature structural applications and accurate knowledge of its low order systems (binaries and ternaries) is important to predict the phase relations in the multicomponent alloys. Recent reevaluations of binaries containing Me-Si found out that the accuracy of the description of this type of systems could be improved. Knowing this, a reevaluation of the invariant reactions in the V-Si system via microstructural characterization of as-cast alloys is presented. Alloys of key compositions were prepared by arc melting pure V (min. 99.75%) and Si (min. 99.998%) and characterized via scanning electron microscopy (SEM) using back-scattered electron (BSE) mode, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results of this study confirmed the solid phases, the nature of the invariant reactions and determined new compositions for the liquid participating in certain invariant reactions.

The focus of this work was to determine microstructural features in commercial Ni-Cr alloys which could be used to identify indirectly the presence of beryllium. Thus, eight commercial alloys were characterized by chemical analysis, thermal analysis, X-ray diffraction (XRD), scanning electron microscopy - back-scattered electron images (SEM/BSE), energy-dispersive spectroscopy (EDS). The results indicate that the presence of beryllium can be inferred from microstructural analysis via XRD and SEM/BSE. The X-ray diffractograms of the beryllium-containing alloys showed clearly the existence of the NiBe intermetallic phase. SEM/BSE images of these alloys show a very characteristic eutectic microstructure which also indicates the presence of this element. These characteristics are not observed in the beryllium-free alloys.

A partial isothermal section (Ti-TiSi2-TiB2 region) of the ternary Ti-Si-B system at 1250 ° C was determined from heat-treated alloys prepared via arc melting. Microstructural characterization has been carried out through scanning electron microscopy (SEM), x-ray diffraction (xRD) and wavelength dispersive spectrometry (WDS). The results have shown the stability of the near stoichiometric Ti6Si2B phase and a negligible solubility of boron in the Ti-silicides as well as of Si in the Ti-borides. The following three-phase equilibria have been observed in the Ti- TiSi2-TiB2 region: Ti ss+TiB+Ti6Si2B, Ti ss+Ti6Si2B+Ti5Si3, Ti5Si3+Ti6Si2B+TiB, Ti5Si3+TiB+Ti3B4, Ti5Si3+Ti3B4+TiB2, Ti5Si3+TiB2+Ti5Si4, Ti5Si4+TiB2+TiSi and TiSi+TiB2+TiSi2.

Recently, a new ternary phase was discovered in the Ti-Si-B system, located near the Ti6Si2B composition. The present study concerns the preparation of titanium alloys that contain such phase mixed with α-titanium and other intermetallic phases. High-purity powders were initially processed in a planetary ball-mill under argon atmosphere with Ti-18Si-6B and Ti-7.5Si-22.5B at. (%) initial compositions. Variation of parameters such as rotary speed, time, and ball diameters were adopted. The as-milled powders were pressureless sintered and hot pressed. Both the as-milled and sintered materials were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Sintered samples have presented equilibrium structures formed mainly by the α-Ti+Ti6Si2B+Ti5Si3+TiB phases. Silicon and boron peaks disappear throughout the milling processes, as observed in the powder diffraction data. Furthermore, an iron contamination of up to 10 at. (%) is measured by X-ray spectroscopy analysis on some regions of the sintered samples. Density, hardness and tribological results for these two compositions are also presented here.

An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8%) and boron (minimum 99.5%) slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.