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Ti–6Al–4V parts obtained by selective laser melting typically have an acicular α′ martensitic microstructure whose ductility is low. Thus, post-heat treatments are useful for increasing ductility. In this work, the effects of sub-β- transus heat treatments on the mechanical properties of Ti–6Al–4V parts with porous structures are correlated with martensite α′ phase decomposition. The precipitation of β phase and the gradual transformation of α′ into α phase by the diffusion of excess vanadium from α′ to β phase are proposed to be the main events of martensite α′ phase decomposition in parts fabricated by selective laser melting. The heat treatment performed at 650 °C for 1 h produced no microstructural changes, but the samples treated for at the same temperature 2 h showed a fine precipitation of β phase along the α′ needle boundaries. The heat treatment performed at 800 °C for 1 or 2 h produced a fine α+β microstructure, in which β phase are present as particles fewer in number and larger in size, when compared with the ones present in the sample heat-treated at 650 °C for 2 h. Heat-treatment of the parts at 800 °C for 2 h proved to be the best condition, which improved the ductility of the samples while only slightly reducing their strength. [ABSTRACT FROM AUTHOR]

In the development of new materials for orthopedic implants, special attention has been given to Ti alloys that show biocompatible alloy elements and that are capable of reducing the elastic modulus. Accordingly, Ti–Nb–Si alloys show great potential for application. Thus, this is a study on the microstructures and properties of Ti–35Nb– x Si alloys ( x =0, 0.15, 0.35 and 0.55) (wt%) which were thermally treated and cooled under the following conditions: furnace cooling (FC), air cooling (AC), and water quenching (WQ). The results showed that Si addition is effective to reduce the density of omega precipitates making beta more stable, and to produce grain refinement. Silicides, referred as (Ti,Nb) 3 Si, were formed for alloys containing 0.55% Si, and its formation presumably occurred during the heating at 1000 °C. In all cooling conditions, the hardness values increased with the increasing of Si content, as a result from the strong Si solid solution strengthening effect, while the elastic modulus underwent a continuous reduction due to the reduction of omega precipitates in beta matrix. Lower elastic moduli were observed in water-quenched alloys, which concentration of 0.15% Si was more effective in their reduction, with value around 65 GPa. Regarding Ti–35Nb– x Si alloys ( x =0, 0.15 and 0.35), the “double yield point” phenomenon, which is typical of alloys with shape memory effect, was observed. The increase in Si concentration also produced an increase from 382 MPa to 540 MPa in the alloys׳ mechanical strength. Ti–35Nb–0.55Si alloy, however, showed brittle mechanical behavior which was related to the presence of silicides at the grain boundary. [ABSTRACT FROM AUTHOR]

In the present work the fluxing technique was applied to the Sn–51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 °C) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 °C) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample. [Copyright &y& Elsevier]

Abstract: Ordered intermetallic phases of Pt with several transition metals have been prepared and their electrocatalytic properties studied. In light of these tests it is proposed that these catalysts could be used as electrodes in fuel cells, as they combine an excellent capacity to adsorb organic fuels at the Pt sites with low susceptibility to being poisoned by intermediates and reaction products at the transition-metal sites. An experimental procedure used to obtain the four intermetallic phases Pt–M (M=Mn, Pb, Sb and Sn) is described. The phases thus produced were characterized by X-ray diffraction, scanning electron microscopy with surface analysis by energy-dispersive X-ray spectrometry, scanning tunneling microscopy and X-ray photoelectron spectroscopy. The data thus obtained support the conclusion that the method described here is highly effective for the preparation of Pt–M phases featuring a range of structural and electronic modifications that will allow a useful relation to be established between their physicochemical properties and predicted electrocatalytic activity. [Copyright &y& Elsevier]

Abstract: Composite materials allow one to associate fragile and ductile phases in order to obtain a good combination of properties. In situ composites obtained through eutectic transformation may present a combination of phases under a condition of equilibrium. Samples of the eutectic Ni–Ni3Si alloy were arc-melted and characterized in the as cast and directionally solidified (DS) conditions. The as cast microstructure was refined and uniform, while the DS microstructure was aligned in the direction of heat extraction and presented a plane solid/liquid interface. The alloy displayed an interesting combination of relatively high strength and tensile ductility at room temperature (3.7% total strain; UTS=810MPa), and a modulus of elasticity E =264MPa. High temperature tests showed that the yield strength decreased almost linearly as the temperature rose. No brittle to ductile transition temperature was found. [Copyright &y& Elsevier]

Presenting high fracture toughness is a decisive condition to any structural material, and when considering brittle alloys, the Vickers indentation method to determine fracture toughness is an interesting alternative. Like many other intermetallics, the Al3Nb–Nb2Al eutectic alloy shows high strength at high temperatures and low fracture toughness at room temperature. Al3Nb–Nb2Al samples, both in the as-solidified condition and in the directionally solidified condition, had their hardness and fracture toughness determined by the Vickers indentation method. Lower values of hardness were found when higher loads were used, and fracture toughness was found to be about 2.0 MPa m1/2. The as-solidified condition is harder and less tough, and when fracture occurs, cracks always develop by cleavage. [Copyright &y& Elsevier]

This work aimed to provide new insights into the manufacturing of a composite material composed of alternating micrometric layers of CP-Ti and Ti–6Al–4V, which was achieved using a modified laser powder bed fusion platform. Dense materials were obtained, and interface analysis revealed the formation of a solid solution intermixed region. Both CP-Ti and Ti–6Al–4V layers exhibited a hexagonal martensitic microstructure. Texture preservation between layers was observed, and it was attributed to epitaxy during the solidification process. The multi-layered material exhibited increased strength with higher volume fractions of Ti–6Al–4V. The composite materials exhibited a compressive yield strength ranging from 670 to 930 MPa, values that did not follow the simple rule of mixtures. • Successful fabrication of fine multi-layered CP-TI/Ti–6Al–4V composites. • Utilization of a modified laser powder bed fusion machine. • Control of mechanical properties through volume fraction adjustment of Ti–6Al–4V. [ABSTRACT FROM AUTHOR]