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′.
Paper presents the results of research on modified surface grain refinement method used in investment casting of hollow, thin-walled parts
made of nickel based superalloys. In the current technology, the refining inoculant is applied to the surface of the wax pattern and then, it
is transferred to the ceramic mould surface during dewaxing. Because of its chemical activity the inoculant may react with the liquid metal
which can cause defects on the external surface of the cast part. The method proposed in the paper aims to reduce the risk of external
surface defects by applying the grain refiner only to the ceramic core which shapes the internal surface of the hollow casting. In case of
thin-walled parts the grain refinement effect is visible throughout the thickness of the walls. The method is meant to be used when internal
surface finish is less important, like for example, aircraft engine turbine blades, where the hollowing of the cast is mainly used to lower the
weight and aid in cooling during operation.
The paper presents the results of studies on the development of correlation of solidification parameters and chemical composition of nickel
superalloy IN-713C, which is used i.a. on aircraft engine turbine blades. Previous test results indicate significant differences in
solidification parameters of the alloy, especially the temperatures Tliq and Tsol for each batch of ingots supplied by the manufacturer.
Knowledge of such a relationship has important practical significance, because of the ability to asses and correct the temperatures
of casting and heat treatment of casts on the basis of chemical composition. Using the statistical analysis it was found that the temperature
of the solidification beginning Tliq is mostly influenced by the addition of carbon (similar to iron alloys). The additions of Al and Nb have
smaller but still significant impact. Other alloying components do not have significant effect on Tliq. The temperature Teut is mostly
affected by Ni, Ti and Nb. The temperature Tsol is not in any direct correlation with the chemical composition, which is consistent with
previous research. The temperature Tsol depends primarily on the presence of non-metallic inclusions present in feed materials and
introduced during the melting and casting processes.
In current casting technology of cored, thin walled castings, the modifying coating is applied on the surface of wax pattern and, after the
removal of the wax, is transferred to inner mould surface. This way the modification leading to grain refinement occur on the surface of
the casting. In thin walled castings the modification effect can also be seen on the other (external) side of the casting. Proper reproduction
of details in thin walled castings require high pouring temperature which intensify the chemical reactions on the mould – molten metal
interface. This may lead to degradation of the surface of the castings. The core modification process is thought to circumvent this problem.
The modifying coating is applied to the surface of the core. The degradation of internal surface of the casting is less relevant. The most
important factor in this technology is “trough” modification – obtaining fine grained structure on the surface opposite to the surface
reproduced by the core.
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 paper presents the results concerning impact of modification (volume and surface techniques), pouring temperature and mould
temperature on stereological parameters of macrostructure in IN713C castings made using post-production scrap. The ability to adjust the
grain size is one of the main issues in the manufacturing of different nickel superalloy castings used in aircraft engines. By increasing the
grain size one can increase the mechanical properties, like diffusion creep resistance, in higher temperatures. The fine grained castings. on
the other hand, have higher mechanical properties in lower temperatures and higher resistance to thermal fatigue. The test moulds used in
this study, supplied by Pratt and Whitney Rzeszow, are ordinarily used to cast the samples for tensile stress testing. Volume modification
was carried out using the patented filter containing cobalt aluminate. The macrostructure was described using the number of grains per
mm2
, mean grain surface area and shape index. Obtained results show strong relationship between the modification technique, pouring
temperature and grain size. There was no significant impact of mould temperature on macrostructure.