In this investigation, the formation of oxide scales on different Co-Ni based superalloys of γ–γ′ type was analyzed. Co-20Ni-7Al-7W (at. %) alloy as well as its W-free modifications based on Co-Ni-Al-Mo-Nb and Co-Ni-Al-Ta systems was analyzed under conditions of high temperature oxidation at 800 and 900°C. Therefore, the alloys were isothermally oxidized at selected temperatures for 100 h in laboratory furnace. Afterwards, the oxidation products were evaluated by means of X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The performed tests showed that W-free alloys exhibit worse oxidation resistance compared to those of Co-Ni-Al-W alloys. After oxidation at 900°C, all alloys were prone of oxide spallation. The scales characterized by oxide peeling were mostly composed of complex Co-based oxides, including CoWO4, CoTa2O6, Co2Mo3O8, CoNb2O6.

In this study, the effects of adding niobium and vanadium to Fe-based oxide dispersion strengthened alloys are confirmed. The composition of alloys are Fe-20Cr-1Al-0.5Ti-0.5Y2O3 and Fe-20Cr-1Al-0.5Ti-0.3V-0.2Nb-0.5Y2O3. The alloy powders are manufactured by using a planetary mill, and these powders are molded by using a magnetic pulsed compaction. Thereafter, the powders are sintered in a tube furnace to obtain sintered specimens.

The added elements exist in the form of a solid solution in the Fe matrix and suppress the grain growth. These results are confirmed via X-ray diffraction and scanning electron microscopy analyses of the phase and microstructure of alloys. In addition, it was confirmed that the addition of elements, improved the hardness property of Fe-based oxide dispersion strengthened alloys.

Impact of surface and volume modification and double filtration during pouring the moulds on basic mechanical properties and creep resistance of nickel superalloys IN-713C and MAR-247 in conditions of accelerated creep of castings made of post-production scrap of these alloys is evaluated in this paper. The conditions of initiation and propagation of cracks in the specimens were analysed with consideration of stereological properties of material macro- and microstructure. It has been proven that in the conditions of hightemperature creep at 980°C and at stress σ = 150 MPa, creep resistance of superalloy MAR-247 is more than 10 times higher than the creep resistance of IN-713C alloy. In case of IN-713C alloy, the creep resistance negligibly depends on macrograin sizes. But, the macrograin size considerably affects the time to failure of specimens made of alloy MAR-247. Creep resistance of specimens made of coarse grain material was 20% higher than the resistance of fine grain materials.

Products of complex geometry, aerodynamic shape and high quality surface finishes are among the most difficult to produce by using stamping methods. When additionally materials with special properties are intended, the task of determining their technological character becomes difficult to solve without the use of physical and numerical methods of process modeling. The paper presents the results of modeling the process of producing a single tube of the jet engine tubular diffuser subassembly. This is a product representative of such a complex geometry one. The charge material for this element requires resistance to operating conditions at elevated temperature and high durability. Therefore, an Inconel type nickel superalloy was proposed for the charge material. In the solution of designing the method of producing a single diffuser tube task, the capabilities of the AutoGrid automatic strain analyzer and the FEM simulation software Eta / Dynaform 5.9 were combined. Numerical simulations of different variants of the manufacturing process of the diffuser tube were made using the Eta / Dynaform 5.9 software. The results of forming simulations became the basis for the alternative technological cycle design of this drawpiece.

Since fatigue cracks nucleate and initiate generally at the surface of the rotary components such as blades and discs, the surface condition is the most important factor affecting the fatigue life. Surface scratches are suitable sites for stress concentrations and therefore the nucleation stage of fatigue cracks will be shortened. In the present work, the influence of surface roughness on the low cycle fatigue life behavior of nickel-based superalloy Rene®80 at the temperature of 900°C was evaluated. Results of low cycle fatigue tests (LCF) under strain-controlled condition at 900°C for R = _εmin/εmax = 0 and strain rate of 2×10 ^–3 s ^–1, at a total strain range of 1.2% showed an inverse relationship between fatigue strength and surface roughness of the specimens. In this study, increasing the surface roughness of Rene®80 from 0.2 μm to 5.4 μm led to the decline in the final LCF life from 127 cycles to 53 cycles which indicated a 58.3% reduction in fatigue life at the same condition. Fractography evaluation also exhibited that fatigue cracks initiated from the notch in the rough specimens, whereas in the smooth specimen fatigue cracks nucleated from the internal imperfections and carbides.

Paper presents the results of evaluation of heat resistance and specific heat capacity of MAR-M-200, MAR-M-247 and Rene 80 nickel

superalloys. Heat resistance was evaluated using cyclic method. Every cycle included heating in 1100°C for 23 hours and cooling for 1

hour in air. Microstructure of the scale was observed using electron microscope. Specific heat capacity was measured using DSC

calorimeter. It was found that under conditions of cyclically changing temperature alloy MAR-M-247 exhibits highest heat resistance.

Formed oxide scale is heterophasic mixture of alloying elements, under which an internal oxidation zone was present. MAR-M-200 alloy

has higher specific heat capacity compared to MAR-M-247. For tested alloys in the temperature range from 550°C to 800°C precipitation

processes (γ′, γ′′) are probably occurring, resulting in a sudden increase in the observed heat capacity.

Superalloys show a good combination of mechanical strength and resistance to surface degradation under the influence of chemically

active environments at high temperature. They are characterized by very high heat and creep resistance. Their main application is in gas

turbines, chemical industry, and in all those cases where resistance to creep and the aggressive corrosion environment is required. Modern

jet engines could never come into use if not for progress in the development of superalloys. Superalloys are based on iron, nickel and

cobalt. The most common and the most interesting group includes superalloys based on nickel. They carry loads at temperatures well in

excess of the eighty percent of the melting point. This group includes the H282 alloy, whose nominal chemical composition is as follows

(wt%): Ni - base, Fe - max. 1.5%, Al - 1.5% Ti - 2.1%, C - 0.06% Co - 10% Cr - 20% Mo - 8.5%. This study shows the results of thermal

analysis of the H282 alloy performed on a cast step block with different wall thickness. Using the results of measurements, changes in the

temperature of H282 alloy during its solidification were determined, and the relationship dT / dt = f (t) was derived. The results of the

measurements taken at different points in the cast step block allowed identifying a number of thermal characteristics of the investigated

alloy and linking the size of the dendrites formed in a metal matrix (DAS) with the thermal effect of solidification. It was found that the

time of solidification prolonged from less than ome minute at 10 mm wall thickness to over seven minutes at the wall thickness of 44 mm

doubled the value of DAS.

Nickel alloys belong to the group of most resistant materials when used under the extreme operating conditions, including chemically

aggressive environment, high temperature, and high loads applied over a long period of time. Although in the global technology market

one can find several standard cast nickel alloys, the vast majority of components operating in machines and equipment are made from

alloys processed by the costly metalworking operations. Analysis of the available literature and own studies have shown that the use of

casting technology in the manufacture of components from nickel alloys poses a lot of difficulty. This is due to the adverse technological

properties of these alloys, like poor fluidity, high casting shrinkage, and above all, high reactivity of liquid metal with the atmospheric air

over the bath and with the ceramic material of both the crucible and foundry mold. The scale of these problems increases with the expected

growth of performance properties which these alloys should offer to the user.

This article presents the results of studies of physico-chemical interactions that occur between theH282alloy melt and selected refractory

ceramic materials commonly used in foundry. Own methodology for conducting micro-melts on a laboratory scale was elaborated and

discussed. The results obtained have revealed that the alumina-based ceramics exhibits greater reactivity in contact with the H282 alloy

melt than the materials based on zirconium compounds. In the conducted experiments, the ceramic materials based on zirconium silicate

have proved to be a much better choice than the zirconia-silica mixture. Regardless of the type of the ceramic materials used, the time and

temperature of their contact with the nickel alloy melt should always be limited to an absolutely necessary minimum required by the

technological regime.

The paper presents the results of studies to determine the effect of complex surface and bulk modification and double filtration during mould pouring on the stereological parameters of macrostructure and mechanical properties of castings made from the post-production waste IN-713C and the MAR-247 nickel alloys. The evaluation covered the number of grains per 1mm2 of the sample surface area, the average area of grains and the shape index, hardness HB, tensile strength and resistance to high temperature creep. The results indicate the possibility of controlling the stereological parameters of macrostructure through application of several variants of the modification, controlling in this way also different low- and high-temperature properties. The positive effect of double filtration of the alloy during mould pouring on the metallurgical quality and mechanical properties of castings has also been emphasized.

The paper presents the results of research on the impact of impurities in the feed ingots (master heat) on the precipitation of impurities in

the ATD thermal analysis probe castings. This impurities occur mostly inside shrinkage cavities and in interdendritic space. Additionally,

insufficient filtration of liquid alloy during pouring promotes the transfer of impurities into the casting. The technology of melting

superalloys in vacuum furnace prevents the removal of slag from the surface of molten metal. Because of that, the effective method of

quality assessment of feed ingots in order to evaluate the existence of impurities is needed. The effectiveness of ATD analysis in

evaluation of purity of feed ingots was researched. In addition the similarities of non-metallic inclusions in feed ingots and in castings

were observed.

The γ/γ′ Co-based alloys are a new class of cobalt superalloys, which are characterized by remarkable high temperature strength owing to strengthening by γ′-Co3(Al, X) phases. In this investigation, the effect of cerium addition on oxidation behavior of model Co-Al-W alloys was studied. The introduction of Ce aimed at improvement of the oxidation resistance of γ′-forming Co-based superalloys. The minor additions of cerium (0.1, 0.5 at.%) were added to the base alloy Co-9Al-9W. The alloys were prepared via induction vacuum melting (VIM). Further, a primary microstructure of the alloys was analyzed with particular regard to a segregation of Ce. The thermogravimetric analysis (TG) under non-isothermal conditions was used to preliminary estimate the oxidation behavior of alloys at different temperatures. During experiment, differential thermal analysis (DTA) was performed simultaneously. After this test, cyclic oxidation expermients was carried out at 800°C for 500 h. In as-cast state, Ce segregates to interdendritic areas and forms intermetallic phases. The effect connected with melting of interdendritic precipitates was observed at 1160°C. Ce-containing alloys were less prone of oxide spallation. Moreover, oxidation rate of these alloys substantially decreased after 100h of oxidation, whereas mass of the sample corresponding to base alloy continued to increase.

High temperature vacuum brazing is a well-known and commonly used method for joining of nickel based elements and subassemblies of gas turbines, both for stationary and aviation applications. Despite the fact that currently used brazing filler metals meet stringent requirements of aviation and energetic industries, a lot of effort is spent on improving operational properties of the joints through modification of chemical composition or brazing process parameters. This paper aims for both of these aspects – its purpose is evaluation of the impact of filler metal composition, brazing gap width and process conditions on the microstructure of joints between sheet metal elements made of Hastelloy X nickel superalloy. Two different Ni-based filler materials (BNi-2 and Amdry 915) were investigated, based on the results of light and scanning electron microscopy evaluations, energy dispersive X-ray spectroscopy and hardness measurements.

CM247LC alloy was manufactured by using selective laser melting (SLM) process, one of the laser powder bed fusion ­(L-PBF) methods. The hot isostatic pressing (HIP) process was additionally conducted on the SLM-built CM247LC to control its microstructures and defects. The high temperature oxidation property was investigated, and it was compared with conventional DS247LC sample (reference) prepared via the directional solidification process. The L-PBF HIP sample showed blocky-type MC carbides generated along the grain boundary with average size of about 200 nm. A semi-spherical primary γ' phase of size 0.4-1.0 μm was also observed inside the grains. Moreover, the DS247LC sample displayed a coarse eutectic γ' phase and many script-type MC carbides. Furthermore, cuboidal-type γ' with an average size of about 0.5 μm was detected. High-temperature oxidation tests were conducted at 1000°C and 1100°C for 24 hours. The results at 1100°C oxidation temperature showed that the measured oxidation weight gains for HIP and DS247LC were 1.96 mg/cm2 and 2.26 mg/cm2, respectively, indicating the superior high-temperature oxidation resistance of the L-PBF HIP sample. Based on the above results, a high-temperature oxidation mechanism of the CM247LC alloys manufactured by the SLM process and the directional solidification process has been proposed.

An optimum route to fabricate the Ni-based superalloy with homogeneous dispersion of Y2O3 particles is investigated. Ni-based ODS powder was prepared by high-energy ball milling of gas-atomized alloy powders and Y2O3 particles treated with a high-pressure homogenizer. Decrease in particle size and improvement of dispersion stability were observed by high-pressure homogenization of as-received Y2O3 particles, presumably by the powerful cavitation forces and by collisions of the particles. Microstructural analysis for the ball-milled powder mixtures reveal that Ni-based ODS powders prepared from high-pressure homogenization of Y2O3 particles exhibited more fine and uniform distribution of Ni and Y elements compared to the as-received powder. These results suggested that high-pressure homogenization process is useful for producing Ni-based superalloy with homogeneously dispersed oxide particles.

This study explores the hydrogen embrittlement behaviour of two Ni-based superalloys using electrochemical hydrogen charging. Two types of tensile specimens with different geometry for the Haynes 617 and Hastelloy X alloys were electrochemically hydrogen-charged, and then a slow strain rate test was conducted to investigate the hydrogen embrittlement behaviour. Unlike the ASTM standard specimens, two-step dog-bone specimens with a higher surface-area-to-volume ratio showed higher sensitivity to hydrogen embrittlement because hydrogen atoms are distributed mostly on the surface area. On the other hand, the Haynes 617 alloy had a lower hydrogen embrittlement resistance than that of the Hastelloy X alloy due to its relatively large grain size and the presence of precipitates at grain boundaries. The Haynes 617 alloy primarily showed an intergranular fracture mode with cracks from the slip band, whereas the Hastelloy X alloy exhibited a combination of transgranular and intergranular fracture behavior under hydrogen-charged conditions.

This study aimed to investigate the metallographic structure and the impact of the heat treatment process on the MAR-M247 superalloy, a high-temperature nickel-based superalloy commonly used in turbine blades. The heat treatment process can potentially influence the mechanical properties of the MAR-M247 superalloy at different temperatures. A strength simulation analysis of gas turbine blades should include the variations in the mechanical properties of the material. The effect of heat treatment on grain size was investigated by metallographic experiments, and numerical calculations of material mechanical properties were conducted. The mechanical property parameters necessary for finite element analysis of turbine blades were determined. Finally, a finite element simulation model of the blade was established based on these mechanical property parameters, and strength analysis was performed. The simulation results provided the stress distribution and the strength of the turbine blade.

The paper presents results of calorimetric studies of foundry nickel superalloys: IN100, IN713C, Mar - M247 and ŻS6 U. Particular attention was paid to determination of phase transiti ons temperatures during heating and cooling. The samples were heated to a temperature of 1500°C with a rate of 10°C ⋅ min – 1 and then held at this temperature for 5 min. After a complete melting, the samples were cooled with the same rat e. Argon with a purity of 99.99% constituted the protective atmosphere. The sample was placed in an alundum crucible with a capacity of 0.45 cm 3 . Temperature and heat calibration was carried out based on the mel ting point of high- purity Ni. The tests were carried out by the differential scanning calorimetry (DSC) using a Multi HTC high -temperature calorimeter from Setaram. Based on the DSC curves, the following temperatures were determined: solidus and liquidus, dissolution and precipitation of the γ ’ phase, MC carbides and melting of the γ ’ /γ eutectic. In the temperature range of 100 -1100°C, specific heat capacity of the investigated superalloys was determined. It was found that the IN713C and IN100 alloys exhibit a higher specific heat while compared to the Mar - M247 and ŻS6 U alloys.

The analysis of influence of mould withdrawal rate on the solidification process of CMSX-4 single crystal castings produced by Bridgman

method was presented in this paper. The predicted values of temperature gradient, solidification and cooling rate, were determined at the

longitudinal section of casting blade withdrawn at rate from 1 to 6mm/min using ProCAST software. It was found that the increase of

withdrawal rate of ceramic mould results in the decrease of temperature gradient and the growth of cooling rate, along blade height. Based

on results of solidification parameter G/R (temperature gradient/solidification rate), maximum withdrawal rate of ceramic mould

(3.5 mm/min), which ensures lower susceptibility to formation process of new grain defects in single crystal, was established. It was

proved that these defects can be formed in the bottom part of casting at withdrawal rate of 4 mm/min. The increase of withdrawal rate to 5

and 6 mm/min results in additional growth of susceptibility of defects formation along the whole height of airfoil.

Paper presents the assessment of impact of heat treatment on durability in low-cycle fatigue conditions (under constant load) in castings

made using post-production scrap of MAR-247 and IN-713C superalloys. Castings were obtained using modification and filtration

methods. Additionally, casting made of MAR-247 were subjected to heat treatment consisting of solution treatment and subsequent aging.

During low-cycle fatigue test the cyclic creep process were observed. It was demonstrated that the fine-grained samples have significantly

higher durability in test conditions and , at the same time, lower values of plastic deformation to rupture Δϵpl. It has been also proven that

durability of fine-grained MAR-247 samples can be further raised by about 60% using aforementioned heat treatment.

The primary microstructure of new Co-based superalloy of Co-20Ni-7Al-7W (at.%) type was showed in this article. The alloy was manufactured by induction melting in vacuum furnaces. This alloy is a part of new group of high-temperature materials based on Co solid solution and strengthened by coherent L12 phase similar to Ni-based superalloys with γʹ phase. The final form of Coss/L12 microstructure is obtained after fully heat treatment included homogenization, solutionizing and aging processes. But first step of heat treatment thermal parameters determination is characterization of primary microstructure of alloys after casting process with special attentions on segregations of alloying elements in solid solution and presences of structural elements such as eutectic areas, and other phases precipitations. In analysed case the relatively high homogeneity of chemical composition was expected especially in the case of W distribution, what was confirmed be SEM/EDS analysis in dendritic and interdendritic areas.

The paper presents the results of evaluation of the metallurgical quality of master heat ingots and of the identification of non-metallic inclusions (oxides of Al., Zr, Hf, Cr, etc.), which have been found in the shrinkage cavities formed in these ingots. The inclusions penetrate into the liquid alloy, and on pouring of mould are transferred to the casting, especially when the filtering system is not sufficiently effective. The specific nature of the melting process of nickel and cobalt alloys, carried out in vacuum induction furnaces, excludes the possibility of alloy refining and slag removal from the melt surface. Therefore, to improve the quality of castings (parts of aircraft engines), it is so important to evaluate the quality of ingots before charging them into the crucible of an induction furnace. It has been proved that one of the methods for rapid quality evaluation is an ATD analysis of the sample solidification process, where samples are taken from different areas of the master heat ingot. The evaluation is based on a set of parameters plotted on the graph of the dT/dt derivative curve during the last stage of the solidification process in a range from TEut to Tsol.

Paper presents the results of ATD and DSC analysis of two superalloys used in casting of aircraft engine parts. The main aim of the

research was to obtain the solidification parameters, especially Tsol and Tliq, knowledge of which is important for proper selection of

casting and heat treatment parameters. Assessment of the metallurgical quality (presence of impurities) of the feed ingots is also a very

important step in production of castings. It was found that some of the feed ingots delivered by the superalloy producers are contaminated

by oxides located in shrinkage defects. The ATD analysis allows for quite precise interpretation of first stages of solidification at which

solid phases with low values of latent heat of solidification are formed from the liquid. Using DSC analysis it is possible to measure

precisely the heat values accompanying the phase changes during cooling and heating which, with knowledge of phase composition,

permits to calculate the enthalpy of formation of specific phases like γ or γ′.