Institute of Fundamental Technological Research

Direct Metal Laser Sintered Haynes 282 specimens as well as wrought ones were subjected to high-temperature exposure at 1000 °C for 100h in air to compare their oxidation behaviour. The specimens were removed from the furnace after 1h, 5h, 25h, 50h and 100h to reveal and study oxidation mechanisms through morphological and cross-sectional examination by using scanning electron microscopy with energy dispersive spectroscopy attachment and X-ray diffraction. Microstructural studies revealed that the oxidation kinetics, determined by changes in thickness scale and depth of aluminium diffusion zone, were mainly driven by the formation of Cr2O3 for the wrought material, and TiO2 for DMLS one. The wrought material was characterized by the oxidation rate equal to 0.96 and followed the logarithmic law. On the other hand, DMLS-manufactured Haynes 282 exhibited oxidation rate of 0.90 and follows the linear law for the thickness scale considerations. However, when the depth of aluminium diffusion was investigated, it had an oxidation rate of 0.87 and followed cubic law.

The development of powder metallurgy methods in recent years has caused traditional casting methods to be replaced in many industrial applications. Using such methods, it is possible to obtain parts having the required geometry after a process that saves both manufacturing costs and time. However, there are many material issues that decrease the functionality of these methods, including mechanical properties anisotropy and greater susceptibility to cracking due to chemical segregation. The main aim of the current article is to analyze these issues in depth for two powder metallurgy manufacturing processes: laser powder bed fusion (LPBF) and hot-pressing (HP) methods—selected for the experiment because they are in widespread use. Microstructure and mechanical tests were performed in the main manufacturing directions, X and Z. The results show that in both powder metallurgy methods, anisotropy was an issue, although it seems that the problem was more significant for the samples produced via LPBF SLM technique, which displayed only half the elongation in the building direction (18%) compared with the perpendicular direction (almost 38%). However, it should be noted that the fracture toughness of LPBF shows high values in the main directions, higher even than those of the HP and wrought samples. Additionally, the highest level of homogeneity even in comparison with wrought sample, was observed for the HP sintered samples with equiaxed grains with visible twin boundaries. The tensile properties, mainly strength and elongation, were the highest for HP material. Overall, from a practical standpoint, the results showed that HP sintering is the best method in terms of homogeneity based on microstructural and mechanical properties.

Haynes 282 nickel alloy, LPBF, HP, SEM , Static tensile test

The fatigue response and high-temperature corrosion resistance of Inconel 740 nickel alloy in its as-received state, and the same material with aluminized surface layer, were investigated. The aluminized layer was applied by using the chemical vapor deposition process with the participation of AlCl3 vapors under a hydrogen protective atmosphere at a temperature of 1040°C for 8 h and internal pressure of 150 hPa. The microstructure of the aluminized layer was characterized through scanning electron microscopy and x-ray energy dispersive spectroscopy analysis. It was found that Inconel 740 with an aluminized surface exhibited an improved hardness and fatigue response of 100 MPa in the whole range of stress amplitudes from 350 MPa to 650 MPa. Additionally, the application of the aluminization process enhanced service life as well as the corrosion resistance of the alloy in question and effectively protected it against high-temperature corrosion.

In this paper, three different directions of 0°, 45° and 90° were used to manufacture the Haynes 282 alloy bars by using the Direct Metal Laser Sintering (DMLS) method. The additively manufactured specimens as well as these of the wrought Haynes 282 were subsequently subjected to comparative fatigue tests in the range of stress amplitude from ±400 MPa to ±800 MPa. The AM process enhanced the fatigue response of the nickel-based alloy in question by 200 MPa. Furthermore, it was found, that the printing direction does not affect the fatigue response of additively manufactured specimens significantly as minor differences in service life were observed for the entire stress amplitude range adopted. Finally, fatigue damage measure φ and fatigue damage parameter D approaches were used to reveal the dynamics of damage development and to monitor damage development due to fatigue.

Haynes 282, nickel alloys, fatigue, additive manufacturing, Direct Metal Laser Sintering (DMLS)

The paper presents a comparison of microhardness, fatigue and high temperature corrosion of Inconel 740H nickel alloy in its as-received state and the same material with nitrided surface layers. The nitrided layers were produced using traditional glow discharge nitriding (specimens nitriding on the cathode potential) and an active screen (specimens nitriding at the plasma potential). A microstructure of the layers was characterized through the scanning electron microscopy, X-ray energy dispersive spectroscopy and X-ray diffraction analysis. Mechanical properties of the nitrided Inconel 740H alloy were examined using microhardness measurements and standard fatigue tests. It was found that Inconel 740H with a nitrided surface exhibited an improved fatigue response of 50 MPa in the whole range of stress amplitudes from 350 to 650 MPa and almost 325% increase of hardness for plasma modified surface and 250% for cathode modified surface. Additionally, the application of cathode nitriding enhanced the corrosion resistance of the alloy in question and effectively protected it against a high temperature oxidation.

nitriding, nickel alloys, coatings, fatigue, corrosion

In this paper, a novel method for high temperature fatigue strength assessment of nickel superalloy turbine blades after operation at different times (303 and 473 h) was presented. The studies included destructive testing (fatigue testing at temperature 950 °C under cyclic bending load), non-destructive testing (Fluorescent Penetrant Inspection and Eddy Current method), and finite element modelling. High temperature fatigue tests were performed within load range from 5200 to 6600 N using a special self-designed blade grip attached to the conventional testing machine. The experimental results were compared with the finite element model generated from the ANSYS software. It was found that failure of turbine blades occurred in the area with the highest stress concertation, which was accurately predicted by the finite element (FE) model.

nickel superalloys, high temperature fatigue, finite element (FE) modelling, eddy current

Thermomechanical conditions in which the elements of modern aircraft engines work, require the use of protective coatings. The coatings increase the creep strength and also the local thermal stress in the near-surface areas due to the differing thermal expansion of particular material layers. For this reason it is necessary to develop a method for evaluating the operating properties of nickel superalloys with the aluminide layer, taking into consideration the surface processes related to the thermo-mechanical fatigue, taking place during the operation. In the presented work the assessment of the influence of the aluminium-coated layer, deposited on the nickel alloy specimens in the chemical deposition process (CVD) on the changes of the damage parameter in cyclic load conditions was carried out. The damage parameter was defined as a total strain in consecutive load cycles. The dynamics of damage development was analysed for two specimen lots (4 with the layer and 4 without it) displaying axial symmetry with a narrowing in the measured section. The results obtained were correlated with the results of fractography studies using SEM. The results obtained were used for the determination of the relationship between the damage parameter being the sum of the average strain and the strain amplitude, and the number of cycles, until the specimen is destroyed.

Alumina Layer, Fatigue Damage, Super Nickel Alloy

The paper presents the results of studies on the structure and properties of the AlNi type diffusion layers fabricated on the IN 740 nickel alloy by chemical vapor deposition using aluminium chloride (AlCl3), introduced into a hydrogen atmosphere. The layers were examined by light microscopy and scanning electron microscopy. Their chemical composition was examined by EDS, and the phase composition - using a Bruker D8 X-ray diffractometer with CuKa radiation. Fatigue tests were carried out in Inconel 740 sample, in the initial state and covered with the diffusion intermetallic AlNi layers. The strength under dynamic load was examined using a MTS 858 testing machine using symmetric load cycles repeated at a frequency of 20 Hz. The stress amplitude was 550 MPa. Corrosion resistance tests were performed employing potentiodynamic methods, in 0.1M Na2SO4 solution, at ambient temperature. It is shown that the layers improve the fatigue resistance and corrosion resistance of the Inconel 740 substrate.

Inconel 740, CVD, Aluminide layer, High-cycle fatigue, corrosion resistance