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Transition metal silicides are of great interest as high-temperature structural materials. Recent investigations aimed at the development of high-temperature Niobium-base structural alloys where silicide phases play a major role. Tantalum, in spite of its high atomic mass, is a potential micro-alloying element in these alloys to provide higher strength at high temperatures. In this work the invariant reactions of the Ta-Si system were reviewed via microstructural characterization of as-cast alloys. Samples were prepared by arc melting and their microstructures were characterized by scanning electron microscopy and x-ray diffractometry. The results confirmed the solid phases and the nature of the invariant reactions in this system. Few corrections in the currently accepted phase diagram are suggested: (1) the composition of the liquid phase that participates in peritectic formation of TaSi should be near 32 at.% Si instead of 28 at.% Si; (2) the inclusion of the βTaSi ↔ αTaSi + L metatectic reaction involving the βTaSi, αTaSi and L phases. [ABSTRACT FROM AUTHOR]

The currently assessed V–B phase diagram indicates a peritectoid formation at 1727 °C (V3B4+VB⇔V5B6) for the V5B6 boride. The observation of this phase in several as-cast V–B alloys has lead us to a systematic evaluation of its stability, specially its possible formation from the liquid. In this work, V–B alloys (52–56 at.% B range) were produced through arc melting and heat-treated under high vacuum at 2000 °C for 2 h. The materials in both as-cast and heat-treated conditions were characterized through scanning electron microscopy (SEM) (backscattered electron (BSE) images) and X-ray diffraction (XRD). The features observed in the as-cast samples allowed us to conclude that this phase should be formed from the liquid through the L+V3B4⇔V5B6 peritectic reaction. In spite of not reaching equilibrium condition during heat-treating, the results from the characterization of heat-treated samples have indicated the stability of the V5B6-phase at 2000 °C, in disagreement with the currently accepted V–B phase diagram. [Copyright &y& Elsevier]

This work discusses on influence of niobium or molybdenum addition on microstructure and tensile properties of NiCr-based dental alloys. In this regard, the Ni-24Cr-8Nb, Ni-22Cr-10Nb and Ni-20Cr-12Nb (wt. %) alloys produced by arc melting process. To compare the typical Ni-22Cr-10Mo dental alloy was also produced. These ternary alloys were analyzed by chemical analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), thermogravimetric analysis (TG), Vickers hardness and tensile tests. Although the mass losses of the samples during arc melting, the optical emission spectrometry showed that the initial compositions were kept. The Ni-22Cr-10Mo alloy produced a matrix of Niss (ss—solid solution), whereas Ni3Nb disperse in a Niss matrix was also identified in Ni-Cr-Nb alloys. Excepting for the Ni-22Cr-10Nb alloy with mass gain of 0.23%, the as-cast Ni-Cr alloys presented mass gains close to 0.4% after heating up to 1000 °C under synthetic airflow. The hardness values, the modulus of elasticity, yield strength and ultimate tensile strength have enhanced, whereas the ductility was reduced with increasing niobium addition of up to 12 wt.-%.The Ni-22Cr-10Mo alloy presented an intergranular fracture mechanism containing deep dimples and quasi-cleavage planes, whereas the shallow dimples were identified on fracture surface of the as-cast Nb-richer Ni-Cr alloys due to the presence of higher Ni3Nb amounts. [ABSTRACT FROM AUTHOR]

Metal–silicon alloys have been extensively studied due to their potential as high temperature structural materials. In this sense, information from accurate phase diagram becomes important. The niobium–silicon–titanium system has been studied experimentally and thermodynamically assessed by different authors, resulting in contradictory isothermal sections and liquidus projections. This work presents results of detailed microstructural characterization of as-cast niobium–silicon–titanium alloys to assess the liquid composition associated to the invariant reactions and of equilibrated samples to determine the 1200 °C isothermal section. Important discrepancies were found between the data obtained in this work and the previous studies of the niobium–silicon–titanium system liquidus projection, especially in the intermediate region. A good agreement between our results and the calculated and experimental isothermal sections proposed in the literature is observed. However, compositional changes are suggested for the location of the observed three-phase equilibria fields. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ta–Ge phase diagram propose for the first time. [•] The phase αTa5Ge3 was not observed in samples investigated in this work. [•] Three eutectics reactions where determined with the liquid compositions at 20.5; 28.0; 97.0at.% Ge. [Copyright &y& Elsevier]

This work aims to evaluate the microstructure and corrosion behavior in SBF medium of spark plasma sintered Ti-xZr-20Si-10B (x = 5, 7, 10, 15 and 20 at.-%) alloys. Metastable Ti-Zr-Si-B (at.-%) powders previously prepared ball milling for 600 min were used as starting materials. Spark plasma sintering (SPS) of mechanically alloyed Ti-Zr-Si-B powders was performed under controlled atmosphere at 1100 °C for 12 min using 20 MPa in order to obtain cylindrical bodies with 10 mm diameter. SPS samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and corrosion tests. The electrochemical corrosion behavior of these alloys was evaluated in electrolytic solution 1.5 SBF (Simulated Body Fluid) at 36.5 °C and pH 7.4 by means of open circuit potential (OCP) measurements and potentiodynamic polarization tests. SPS process produced dense and homogeneous samples. Despite the short sintering time, the Ti-Zr-Si-B alloys presented near-equilibrium and homogeneous microstructures. Ti 6 Si 2 B dissolving between 6.6 and 8.3 at.-% Zr was formed in the quaternary alloys with 5 and 7 at.% Zr, respectively. In detrimental to its formation, the Ti 3 Si phase was preferentially formed in the SPSed alloys with 10, 15 and 20 at.-% Zr, dissolving between 11.2 and 15.4, 16.9–24, and 20.6–25.3 at.-% Zr, respectively. No transpassive domain was noted in the Ti-15Zr-20Si10B alloy at higher potentials after the passive layer break occurred around the 1.44 V, which presented pits on its corroded surface in SBF medium. SPSed Ti-7Zr-20Si-10B alloy exhibited better corrosion resistance in SBF medium than the Ti pure and Ti-6Al-4V alloy. Image 1 • SPS process produced homogeneous and dense Ti-Zr-Si-B samples. • Ti 6 Si 2 B has dissolved up to 8.3 at.-% Zr in Ti-7Zr-20Si-10B alloy. • Ti 3 Si containing significant Zr amounts was found in alloys with 10–20 at.-% Zr. • Higher corrosion resistance in SBF medium of Ti-7Zr-20Si-10B alloy than Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

• Fe-Nb is of great interest for microstructure and manufacturing alloys. • Accurate heat capacity and other thermodynamic properties are key information. • For the first time, the molar heat capacities of Fe2Nb and Fe7Nb6 were measured. • Quasi-Harmonic Approximation (QHA) calculations were also performed. • Results show that Kopp-Neumann is insufficient for CALPHAD databases. [Display omitted] The molar heat capacities of the Fe 2 Nb and Fe 7 Nb 6 intermetallic compounds are reported here for the first time. The results were obtained via Differential Scanning Calorimetry (DSC) measurements, performed in a temperature range between 348 and 1038 K. The alloys were prepared by arc-melting high purity metals under argon flux and later heat-treated at 1200 ∘C for 336 h encapsulated in quartz tubes under argon to ensure thermodynamic equilibrium. The resulting samples were then characterized using X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). The heat-capacity DSC measurements were carried out using an alternating step method with 20 and 50 K steps, with the resulting C p associated with the midpoint of each temperature interval. A fit to a simplified C p (T) curve was employed, due to the scatter in the data. Quasi-Harmonic Approximation (QHA) calculations were also performed, showing a good agreement with the measured values. Experimental results of heat capacity, along with other thermodynamic properties and phase equilibria, are key information for binary and ternary systems, specially for CALPHAD-type assessments. The results were therefore compared with the Kopp-Neumann approximation, used in recent assessments, showing that the parameters of both compounds can be improved in current CALPHAD databases, which motivates future work on the Fe-Nb system. [ABSTRACT FROM AUTHOR]

[Display omitted] Boron and Silicon site occupancies of the T2 phase in the Cr–Si–B system were investigated experimentally and by first-principles electronic-structure calculations. A sample with nominal composition Cr 0.625 B 0.175 Si 0.2 was arc-melted under argon, encapsulated in a quartz-tube and heat-treated at 1400 ∘ C for 96 hours. It was then analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD) with synchrotron radiation. An excellent agreement was obtained between experiments and theoretical calculations, revealing that Si occupies preferably the 4 a sublattice of the structure, as boron atoms in 8 h nearest-neighbors form very stable dumbbell bonds. Site preferences are thus a key factor for the stabilization of the structure. The results of this work provide important information to support a better description of this phase in alloys with Si and B, since T2 phases are known to occur in many important Transition Metal–Si–B ternary systems, such as Nb/Mo/W/Ta/V–Si–B. [ABSTRACT FROM AUTHOR]