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.
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.
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.
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.
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′.