The presented work deals with the investigation of mechanical tribological properties on Inconel 625 superalloy, which is welded on a 16Mo3 steel pipe. The wall thickness of the basic steel pipe was 7 mm, while the average thickness of the welded layer was 3.5 mm. The coating was made by the cold metal transfer (CMT) method. A supercritical bending of 180° was performed on the material welded in this way while cold. The mechanical properties evaluated were hardness, wear resistance, coefficient of friction (COF) and change in surface roughness for both materials. The UMT Tribolab laboratory equipment was used to measure COF and wear resistance by the Ball-on-flat method, which used a G40 steel pressure ball. The entire process took place at an elevated temperature of 500 °C. The measured results show that the materials after bending are reinforced by plastic deformation, which leads to an increase in hardness and also resistance to wear. Superalloy Inconel 625 shows approximately seven times higher rate of wear compared to steel 16Mo3 due to the creation of local oxidation areas that support the formation of abrasive wear and do not create a solid lubricant, as in the case of steel 16Mo3. Strain hardening leads to a reduction of possible wear on Inconel 625 superalloy as well as on 16Mo3 steel. In the case of the friction process, the places of supercritical bending of the structure showed the greatest resistance to wear compared to the non-deformed structure.

The oxidation behavior of the nickel superalloy Inconel 740H was studied at 750 °C for 100, 250, 500, 1000, and 2000 h in a steam atmosphere. Microstructure observations were performed using scanning electron microscopes and scanning-transmission electron microscope. The phase identification of existing oxidation products was conducted by electron diffraction in transmission electron microscope. The obtained results showed that the microstructure of Inconel 740H was stable during the oxidation process. The kinetic data showed that the superalloy has the ability to form protective oxide layers that are characterized by good adhesion and no tendency to spallation during the test. The oxidation products were mainly composed of external and internal oxides mainly at grain boundaries. The oxides in the external layer were Cr₂O₃, MnTiO_3,, and α-Al₂O₃ after 2000 h of oxidation. Internal oxides were α-Al₂O₃ and TiO₂. The occurrence of discontinuities in the internal oxidation zone was also observed after 500 h of test. It was found that the thickness of the internal oxidation zone was greater than the thickness of the external oxide layer, which proves the strong tendency of the superalloy to form internal oxides after oxidation in the steam atmosphere.

This article presents an assessment of the susceptibility of the WE54 magnesium-based alloy to stress corrosion cracking in an 0.1 M Na₂SO₄ environment. In this work, the basis criterion for assessing the alloy’s behavior under complex mechanical and corrosive loads is the deterioration in its mechanical properties (elongation—ε, %, reduction in area—Z, %, tensile strength—R_m, MPa) along with a fractographic analysis of fracture surfaces. The WE54 magnesium-based alloy was subjected to the slow strain rate test (SSRT) under mechanical loads in corrosive environment (0.1 M Na₂SO₄ solution). The test was carried out in four variants: (a) SSRT in air, (b) cathodic hydrogen charging for 24 h at a current density of 50 mA/cm² followed by SSRT in air, (c) SSRT in a corrosive environment under open-circuit potential conditions, and (d) SSRT in a corrosive environment under cathodic polarization at a current density of 50 mA/cm². In each variant, the content of hydrogen in the alloy was determined. It was demonstrated that under SCC conditions, in the presence of hydrogen, the plastic properties of WE54 decreased significantly, whereas the alloy’s strength properties changed to a smaller degree. The change in the mechanical properties under SCC conditions in a corrosive environment was accompanied by a change in the fracture surface morphology and by the presence of numerous cracks, both on fracture surfaces and in the alloy’s microstructure.

Summary: Pure AISI 316L steel is investigated after solution heat treatment (1050 °C/H₂O) and structural sensitization (650 °C). Two quite different intergranular corrosion tests are used to determine the degree of structural sensitization due to the precipitation of secondary phases along the grain boundaries (mainly the M₂₃C₆ and σ‐phase): the oxalic acid etch test and the electrochemical potentio‐kinetic reactivation test. Generally, the dissolution of chromium‐rich carbides (M₂₃C₆) is provoked by oxalic acid etch tests, whereas the chromium‐depleted zones, in the vicinity of chromium‐rich carbides (M₂₃C₆), are attacked by electrochemical potentio‐kinetic reactivation tests. Both intergranular corrosion tests are used to determine the maximum degree of structural sensitization. Thus structural analysis by carbon replicas reveals the Laves phase, and both the M₂₃C₆ and (Cr,Mo)_x(Fe,Ni)_y phases. The results of intergranular corrosion tests are related to the findings of the structural analysis.