A Tribaloy family of alloys (CoMoCrSi) are characterized by a substantial resistance to wear and corrosion within a wide range of temperatures. These properties are a direct result of their microstructure including the presence of Laves phase in varying proportions. Tribaloy T-800 exhibits the highest content of Laves phase of all other commercial Tribaloy alloys, which provides high hardness and wear resistance. On the other hand, a large content of the Laves phase brings about a high sensitivity to brittle fracture of this alloy. The main objective of this work was a development of the Tribaloy T-800 coatings on the Ni-based superalloy substrate (RENE 77), which employs a Laser Engineered Net Shaping (LENS^TM) technique. Technological limitations in this process are susceptibility of T-800 to brittle fracture as well as significant thermal stresses due to rapid cooling, which is an inherent attribute of laser techniques. Therefore, in this work, a number of steps that optimized the LENS^TM process and improved the metallurgical soundness of coatings are presented. Employing volume and local substrate pre-heating resulted in the formation of high quality coatings devoid of cracks and flaws.

Complex hydride systems for hydrogen (H₂) generation for supplying fuel cells are being reviewed. In the first group, the hydride systems that are capable of generating H₂ through a mechanical dehydrogenation phenomenon at the ambient temperature are discussed. There are few quite diverse systems in this group such as lithium alanate (LiAlH₄) with the following additives: nanoiron (n-Fe), lithium amide (LiNH₂) (a hydride/hydride system) and manganese chloride MnCl₂ (a hydride/halide system). Another hydride/hydride system consists of lithium amide (LiNH₂) and magnesium hydride (MgH₂), and finally, there is a LiBH₄-FeCl₂ (hydride/halide) system. These hydride systems are capable of releasing from ~4 to 7 wt.% H₂ at the ambient temperature during a reasonably short duration of ball milling. The second group encompasses systems that generate H₂ at slightly elevated temperature (up to 100 °C). In this group lithium alanate (LiAlH₄) ball milled with the nano-Fe and nano-TiN/TiC/ZrC additives is a prominent system that can relatively quickly generate up to 7 wt.% H₂ at 100 °C. The other hydride is manganese borohydride (Mn(BH₄)₂) obtained by mechano-chemical activation synthesis (MCAS). In a ball milled (2LiBH₄ + MnCl₂) nanocomposite, Mn(BH₄)₂ co-existing with LiCl can desorb ~4.5 wt.% H₂ at 100 °C within a reasonable duration of dehydrogenation. Practical application aspects of hydride systems for H₂ generation/storage are also briefly discussed.

The water-atomized ATOMET 28, 1001, 4701, and 4801 powders, manufactured by Rio Tinto Metal Powders, were used for additive manufacturing by a laser engineered net shaping (LENS) technique. Their overall morphology was globular and rounded with a size distribution from about 20 to 200 µm. Only the ATOMET 28 powder was characterized by a strong inhomogeneity of particle size and irregular polyhedral shape of powder particles with sharp edges. The powders were pre-sieved to a size distribution from 40 to 150 µm before LENS processing. One particular sample—LENS-fabricated from the ATOMET 28 powder—was characterized by the largest cross-sectional (2D) porosity of 4.2% and bulk porosity of 3.9%, the latter determined by microtomography measurements. In contrast, the cross-sectional porosities of bulk, solid, nearly cubic LENS-fabricated samples from the other ATOMET powders exhibited very low porosities within the range 0.03–0.1%. Unexpectedly, the solid sample—LENS-fabricated from the reference, a purely spherical Fe 99.8 powder—exhibited a porosity of 1.1%, the second largest after that of the pre-sieved, nonspherical ATOMET 28 powder. Vibrations incorporated mechanically into the LENS powder feeding system substantially improved the flow rate vs. feeding rate dependence, making it completely linear with an excellent coefficient of fit, R² = 0.99. In comparison, the reference powder Fe 99.8 always exhibited a linear dependence of the powder flow rate vs. feeding rate, regardless of vibrations.

Ball milling (BM) for 5 h reduced the thermal release of B₂H₆ to nearly zero.

LiAlH₄ and CaCl₂ were employed for mechano-chemical activation synthesis (MCAS) of Ca(AlH₄)₂ and LiCl hydride composite. After short ball milling time, their X-ray diffraction (XRD) peaks are clearly observed. After ball milling for a longer duration than 0.5 h, the CaAlH₅ diffraction peaks are observed which indicates that Ca(AlH₄)₂ starts decomposing during ball milling into CaAlH₅+Al+1.5H₂. It is estimated that less than 1 wt % H₂ was mechanically dehydrogenated in association with decomposition reaction. After 2.5 h of ball milling, no Ca(AlH₄)₂ diffraction peaks were observed on XRD patterns which suggests that Ca(AlH₄)₂ was decomposed. Thermal behavior of ball milled powders, which was investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), indicates that a certain fraction of Ca(AlH₄)₂ could have been disordered/amorphized during ball milling being undetectable by XRD. The apparent activation energy for the decomposition of Ca(AlH₄)₂ and CaAlH₅ equals 135 kJ/mol and 183 kJ/mol, respectively.

A non-stoichiometric, amorphous a-Mn(BH₄)_(2x) hydride, accompanied by a NaCl-type salt, was mechanochemically synthesized from the additive-free mixture of (2NaBH₄ + MnCl₂), as well as from the mixtures containing the additives of ultrafine filamentary carbonyl nickel (Ni), graphene, and LiNH₂. It is shown that both graphene and LiNH₂ suppressed the release of B₂H₆ during thermal gas desorption, with the LiNH₂ additive being the most effective suppressor of B₂H₆. During solvent filtration and extraction of additive-free, as well as additive-bearing, (Ni and graphene) samples from diethyl ether (Et₂O), the amorphous a-Mn(BH₄)_(2x) hydride transformed into a crystalline c-Mn(BH₄)₂ hydride, exhibiting a microstructure containing nanosized crystallites (grains). In contrast, the LiNH₂ additive most likely suppressed the formation of a crystalline c-Mn(BH₄)₂ hydride during solvent filtration/extraction. In a differential scanning calorimeter (DSC), the thermal decomposition peaks of both amorphous a-Mn(BH₄)_(2x) and crystalline c-Mn(BH₄)₂ were endothermic for the additive-free samples, as well as the samples with added graphene and Ni. The samples with LiNH₂ exhibited an exothermic DSC decomposition peak.