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 study consisted in assessing the influence of surface and volume modification on the characteristics of high-temperature creep of
castings made of waste products of nickel-based superalloys IN 713C and the MAR-247. The results of high-temperature creep tests
performed under conditions of two variants of research were analysed. The characteristics of creep according to variant I were obtained on
the basis of earlier studies of these alloys with the parameters T=982o
C, σ=150MPa [1]. Variant II included carrying out creep tests of
alloy IN713C with the parameters T=760o
C, σ =400MPa and alloy MAR247 with the parameters: T=982o
C, σ=200MPa.Developed creep
characteristics were compared with the results of these alloys with the parameters according to variant I of the study. It was observed that
the conditions of experiments carried out depending upon the value of the creep test temperature and stress with the creep stability depends
on the size of the macrograin (I variant of the studies) or such influence was not observed (II variant of the studies). Stability of samples
with coarse structure in variant I of creep tests was significantly higher than the samples with fragmented grain. It was found that the
observed stability conditions are dependent on the dominant deformation mechanisms under creep tests carried out - diffusion mechanism
in variant I and a dislocation mechanism in variant II of the study. The conditions for the formation and growth of the cracks in the tested
materials, including the morphological characteristics of their macro-and microstructure were tested.
The paper presents the results of research on the determination of the effect of pouring temperature on the macrostructure of the castings
subjected to complex (surface and volume) modification and double filtration. Tested castings were made of post-production scrap (gating
system parts) of IN-713C superalloy. Tests included the evaluation of the number of grains per 1 mm2
, mean grain surface area, shape
factor and tensile strength. Casting temperature below 1470 °C positively influenced the modification effect. The grains were finer and the
mechanical properties increased, especially for castings with thicker walls. On the other hand, manufacture of thin walled castings of high
quality require pouring temperature above 1480 °C.
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.
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 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.