International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Abstract: Thermo-reactive diffusion (TRD) coatings are formed on conventionally cast Ti6Al4V alloy using the pack cementation process to improve its surface characteristics. Aluminizing, siliconizing, and molybdenizing treatments are carried out at 700 °C, 1000 °C, and 900 °C, respectively, for 2 h using Al, Si, and Mo powder packs containing NH₄Cl as the activator and Al₂O₃ as the inert filler. The resulting coatings are systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) to investigate phase evolution, coating morphology, and elemental distribution. XRD analyses confirmed the formation of Ti–Al intermetallics (TiAl, TiAl₂, TiAl₃), Ti–Si silicides (TiSi, TiSi₂, Ti₅Si₃), and Mo-enriched Ti solid-solution phases within the coatings. Cross-sectional SEM observations have revealed continuous and well-adhered diffusion layers with thicknesses of approximately 20 μm for the aluminized coating and 50 μm for the molybdenized coating, while the siliconized layer (40 μm) exhibits a graded multilayer silicide structure. EDS elemental mappings have demonstrated inward diffusion of the deposited species and outward diffusion of substrate elements, confirming diffusion-controlled coating growth. The formation of metallurgically bonded reaction layers with compositional gradients is expected to substantially enhance the surface hardness, wear resistance, and high-temperature performance of the Ti6Al4V alloy. The results demonstrate that thermo-reactive diffusion by pack cementation provides an effective and controllable route for tailoring the surface microstructure of cast Ti6Al4V through appropriate selection of coating chemistry and processing conditions.

The possibilities of Fe-Al intermetallic system production by vacuum sintering and impact consolidation of powder bodies, as well as the influence of the regimes of the methods used on the structure and properties of iron aluminides were studied in the article. Mixture of iron and aluminum powders were used for fabrication of iron aluminide Fe₃Al. The powder samples were compacted and vacuum sintered at temperatures of 1250, 1350, 1400 and 1450 °C, and also using hot forging at a temperature of 1050 °C and 1150 °C. It is shown, that the increase of density is observed only at a temperature of 1400 °C. At sintering temperature of 1450 °C the samples reach a density of 6,35 g/cm³, which is 94% of the theoretical value. Only the use of hot forging makes it possible to obtain nonporous samples. It is shown, that bending strength, fracture toughness and hardness increase with increase of sintering temperature, but higher values of this parameters have the samples, produced with use of hot forging.

The capabilities of powder hot forging for manufacturing of Fe₃Al intermetallics and effect of forging and following thermal treatment routines on their structure and properties had been investigated. Fe₃Al intermetallic powders were produced by means of thermal synthesis at 1000°С in vacuum from a mixture of Fe and Al elemental powders. Hot forging of consolidated preforms had been carried out from 1000, 1050, 1100 and 1150°С and afterwards the hot forged preforms were subjected to supplementary sintering in vacuum at 1100÷1450°С. It is foud, that thermal synthesis of Fe + 14% Al powder mixture results in formation of Fe₃Al phase. Sintering of hot forged specimens result in increasing of strength and crack growth resistance, which values enhance with increasing of sintering temperature. Otherwise the hardness of hot forged intermetallics decreases after their sintering. The influence of modes of treatment on the structure and properties of the materials was investigated. It has been established that the strength and fracture toughness of the intermetallics obtained from milled blend after hot forging had the higher values as compared with the alloy made from the batch without its milling.