Ultrahigh- Amorphous highly conductive coatings Ti-Al-C, (Ti,Mo)-Al-C and (Ti,Cr)-Al-C were deposited on titanium alloy substrates by hybrid magnetron using T₂AlC and Ti₃AlC₂ MAX-phases-based targets and in parallel cathode-arc evaporation of Mo or Cr targets. The (Ti,Cr)-Al-C coating demonstrated the highest long-term oxidation resistance, and after heating in air at 600 °C for 1000 h, its surface electrical conductivity became even slightly higher after long-term heating: increased from s= 9.84×10⁶ S/m to s= 4.35×10⁵ S/m, which is explained by the crystallization of the amorphous coating during heating process. The nanohardness and Young's modulus of the coating after deposition were within 15 GPa and 240 GPa, respectively. The (Ti,Cr)-Al-C coating showed the highest electrochemical corrosion resistance among all deposited coatings in 3.5 wt.% NaCl aqueous solution at 25 °C: corrosion potential E_corr = 0.044 V vs. saturated calomel electrode, corrosion current density i_corr = 2.48×10^-9 A/cm². The hybrid magnetron deposited (Ti,Cr)-Al-C coatings can be used to protect interconnects in lightweight molten carbonate fuel cells elements.

The sintering processes of TaB₂ and TaB₂ mixtures with 20 and 30 wt. % SiC, ZrSi₂, Si₃N₄, and MoSi₂ were investigated under hot pressing (HotP) conditions at 30 MPa, 1750-1970 °C, 0.33 - 1.0 h, and high pressure–high temperature (HP-HT) conditions at 4.1 GPa, 1800 °C, 0.33 h,, as well as TaB₂ and its mixtures with 20 and 30 wt.% SiC under spark plasma sintering (SPS) at 45 MPa, 1500-1950 °C, 0.05 h. The highest values of mechanical characteristics of single-phase TaB₂ samples were achieved after sintering by the HotP (1900 °C, 1 h) – Vickers hardness Н_V(9.8 N) = 32.4 ± 0.1 GPa (density r =11.8 g/cm³) and SPS (1950 °C, 0.05 h) - Н_V(49 N) = 20.8 ± 2.0 GPa and K_1C(49 N)= 7.6 ± 1.6 MPa•m^0.5 (r =11.75 g/cm³). A significant improvement in Young's modulus from 532 GPa to 853 GPa was achieved by adding 20 wt.% SiC and HotP at 1900, 1 h. By sintering mixtures with 30 wt.% SiC using the HP-HT and SPS methods at 1800 °C for 0.13 and 0.05 h, respectively, the following materials were obtained: with Н_V(9.8 N)= 39.4 GPa and K_1C(9.8 N)=6.75 MPa•m^0.5 (HotP) and Н_V(49 N)=25.4±2.1 GPa and K_1C(49 N)=10.8±0.8 MPa•m^0.5 (SPS). The variation in the properties of the materials upon addition of additives is explained by the formation of solid solutions due to the diffusion during sintering of the present elements and different porosity. When adding 30 wt.% SiC after HotP (1900 °C, 1 h), the approximate stoichiometric composition of the matrix phase of the sample estimated by SEM EDX was TaB₂Si_0.5O_0.06.

The results of influence of amount of SiC additives to HfB₂ and the physical chemical characteristics of the additives will be under the discussion. Studies of the resistance to ablation of hot-pressed HfB₂ and HfB₂-SiC samples heated by a gas burner showed that HfB₂ ceramics with the addition of 30 wt.% SiC with average grain sizes of 30-50 μm (powder with fragmented grains with sharp edges with approximate average stoichiometry SiC_1.6O_0.1, and  6_H SiC structure) and 5-10 μm (single-crystal grains with a hypercubic shape, close to spherical, practically free of impurities, with approximate stoichiometry SiC_1.5, b-SiC) have significantly higher thermal resistance – up to temperatures of 2766 and 2780 °C, respectively (mass loss of 0.25 mg/s) than HfB₂ ceramics without additives, samples of which cracked already at 1870 °C. The formation of a framework from SiC when 40 wt.% SiC was added resulted in decrease of resistance to ablation, of Young's modulus, and the material cracking at low temperature during heating in air. The composite made from a mixture of HfB₂ - 30 wt.% b-SiC (5-10 μm) by hot pressing under a pressure of 30 MPa, 1950 °C, 30 min. with a specific gravity of 6.54 g/cm³ demonstrated the highest Vickers microhardness H_V(9.8 N)=38.6±2.5 GPa and fracture toughness, K_1c(9.8 N)=7.7 ± 0.9 MPa m^0.5, Young's modulus 510 GPa. The additions of SiC_6H with sharp fragment grains of 1 μm in size with a lamellar or strongly elongated in one direction grains, with an approximate stoichiometry of SiC_4.6O_0.75 or 3-10 μm with an approximate stoichiometry of SiC_2.3O_0.25 added in the same amount (30 wt.%) were cracked during heating in air at a temperature of 1787 and 1455 °C, respectively.

Our previous study has been shown that treatment of coated conductors (CC) under high pressure - high temperature conditions can lead to further increase of critical current density especially in low magnetic fields [1]. Treatment under 100 bar of oxygen for 3 h of GdBCO_CC via Ag layer (which covered superconducting layer of CC) at 600 °C led to an increase in Jc (77 K, 0 T) from 2.57 to 2.67 MA/cm². The charge carrier density n_H(100 K) increased from 6.55´10²¹ to 6.91´10²¹ cm^-3, and  J_c(5 K, 0 T) =28.94 MA/cm² was observed after the treatment. The increase in J_c (77 K, 0 T) from 2.10 to 2.28 MA/cm² for GdBCO_CC which was oxygenated without Ag layer (etched by acid before oxygenation) was observed after treatment at 300 °C under 100 bar of O₂ for 3 h. In the both cases c-parameter of Gd123 decreased from 1.1735(1) to 1.1731(0) nm. The increase of critical current density is connected with overdoping by oxygen and thus by charge carriers of the superconducting GdBCO layer. Oxygenation under 160 bar pressure at 800 ^oC for 3h of tetragonal YBa₂Cu₃O_x film deposited on single crystalline strontium titanate substrate allowed to obtain critical current density J_c (77 K, 0 T) = 4.09 MA/cm² and J_c(5 K, 0 T) = 38.2 MA/cm². The value of Jc (77 K, 0 T) turned out to be twice as high as when saturated with oxygen under a pressure of 1 bar. As a result of oxygenation, c-parameter of YBa₂Cu₃O_x decreased from 1.1711(2) down to 1.1681(3) nm.  This work was supported in part by the funds from MICIU/AEI/FEDER for SUPERENERTECH (PID2021–127297OB-C21), FUNFUTURE “Severo Ochoa” (CEX2019–000917-S); MUGSUP (UCRAN20088) project from CSIC scientific cooperation with Ukraine; Catalan Government 2021 SGR 00440; and NAS of Ukraine Project III-7-24 (0788).