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.
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.