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Environmental-assisted degradation in hydrogen environment, also known as hydrogen embrittlement (HE), has a very important role on physical and mechanical properties of structural materials in the presence of hydrogen. In this research the interactions of high and low fugacity hydrogen with electron beam melted (EBM) Ti–6Al–4V alloy were studied and compared to conventionally manufactured alloy. Parts produced by additive manufacturing (AM) experience relatively high cooling rates and possess unique microstructure features, which might alter the intrinsic properties of the material. Our research describes in details the impact of hydrogen on EBM Ti–6Al–4V alloy by means of hydrogen trapping. The interactions of hydrogen with the material were studied by thermal desorption spectroscopy (TDS), X-ray diffraction, and microstructural observations. Our results suggest that EBM Ti–6Al–4V alloy with relatively fine microstructure has a better resistance for hydrogen induced damage in comparison to a wrought alloy.

Abstract

In the recent years, there has been high interest in renewable energy and highly efficient devices, promoted by the need to stop changing weather patterns. One of the most interesting methods for this is using thermoelectric materials, which are low cost and highly durable. However, the need for higher efficiency values and a higher resistance to oxidation leads to a technological problem in the field of coating. Due to its diverse properties, glass coating has been proposed as a solution to both sublimation of the thermoelectric materials and oxidation. Lead silicate glasses with 30% PbO were doped with 0–5% of Na2O and B2O3to produce glasses with different properties. Differential scanning calorimetry and dilatometry measurements showed that the glass temperature can vary between 428 and 505 °C. The softening temperature is varied between 493 and 560 °C. Below Tg, the coefficient of thermal expansion is varied between 5.9 and 9 ppm/K and above Tgit varied between 17 and 58 ppm/K. This allows the tuning of the glass composition for each thermoelectric material, such as 0.5% B and 1% Na doped PbO -SiO2glass for skutterudites and 1% doped B and 1% Na doped for Mg2Si, PbTe, and GeTe.

Abstract

The pseudoternary (Ge,Pb,Sn)Te system is characterized by demixing to both Pb- and Ge- rich telluride submicrometer and nanosized domains. The present study is concerned with the thermoelectric (TE) properties of the quasi-ternary (Ge0.6Pb0.3Sn0.1)Te compound at 390 °C, during the demixing process over lengthy periods of time up to 695 h. The dimensionality of the various physical metallurgy patterns evolved was correlated to the lattice thermal conductivity, κL, values. Excluding an initial period (<90 h) of increasing κL, associated with a coarse lamellar structure formation, an opposite decreasing trend (down to ∼0.8W/mK after 695 h), associated with nucleation of submicrometer (∼200 nm) circular phases, twinning and dislocation networks, all considered as effective phonon scattering centers, was observed. Expansion of these submicrometer sites, all over the samples, during the heat treatments, without any subsequent coarsening, clearly demonstrates the potential of retaining, or even improvement of the TE properties of (Ge,Pb,Sn)Te alloys following a spinodal decomposition reaction, during long-term operation in practical TE devices, at 390 °C. The presented approach, paves a route for design of stable bulk TE materials, consisting of physical metallurgy driven nano and submicrometer domains, without undesirable coarsening effects, upon elevated temperature operation, which are usually unavoidable while starting with nanopowders.