This paper presents the results of measurements of liquid metal fluidity and linear shrinkage of nickel alloy IN-713C in vacuum induction
melting furnace Balzers VSG-2. Because of limited volume of the furnace chamber special models for technological trials were designed
and constructed to fit in the mould of dimensions 170x95x100mm. Two different designs of test models were proposed: horizontal round
rods and modified spiral. Preliminary studies were carried out for alloys Al-Si. Horizontal round rods test was useful for evaluation of
fluidity of hypoeutectic silumin, however in case of nickel superalloy the mould cavity was completely filled in each test because of high
required pouring temperature. Positive results were obtained from the modified spiral test for all alloys used in the research. Relationship
between the linear shrinkage for the test rod and a specific indicator of contraction defined on a spiral was observed.
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.
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.