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.
In spite of the fact that in most applications, magnesium alloys are intended for operation in environments with room temperature, these
alloys are subject to elevated temperature and oxidizing atmosphere in various stages of preparation (casting, welding, thermal treatment).
At present, the studies focus on development of alloys with magnesium matrix, intended for plastic forming. The paper presents results of
studies on oxidation rate of WE43 and ZRE1 magnesium foundry alloys in dry and humidified atmosphere of N2+1%O2. Measurements of
the oxidation rate were carried out using a Setaram thermobalance in the temperature range of 350-480°C. Corrosion products were
analyzed by SEM-SEI, BSE and EDS. It was found that the oxide layer on the WE43 alloy has a very good resistance to oxidation. The
high protective properties of the layer should be attributed to the presence of yttrium in this alloy. On the other hand, a porous, two-layer
scale with a low adhesion to the substrate forms on the ZRE1 alloy. The increase in the sample mass in dry gas is lower than that in
humidified gas.
With the use of differential scanning calorimetry (DSC), the characteristic temperatures and enthalpy of phase transformations were
defined for commercial AlSi9Cu3 cast alloy (EN AC-46000) that is being used for example for pressurized castings for automotive
industry. During the heating with the speed of 10oCmin-1
two endothermic effects has been observed. The first appears at the temperature
between 495 oC and 534 oC, and the other between 555 oC and 631 oC. With these reactions the phase transformation enthalpy comes up as
+6 J g-1
and +327 J g-1
. During the cooling with the same speed, three endothermic reactions were observed at the temperatures between
584 oC and 471 oC. The total enthalpy of the transitions is – 348 J g-1
.
Complimentary to the calorimetric research, the structural tests (SEM and EDX) were conducted on light microscope Reichert and on
scanning microscope Hitachi S-4200. As it comes out of that, there are dendrites in the structure of α(Al) solution, as well as the eutectic
(β) silicon crystals, and two types of eutectic mixture: double eutectic α(Al)+β(Si) and compound eutectic α+Al2Cu+β.
Tests concerning EN AC 48000 (AlSi12CuNiMg) alloy phase transition covered (ATD) thermal analysis and (DSC) differential scanning
calorimetry specifying characteristic temperatures and enthalpy of transformations. ATD thermal analysis shows that during cooling there
exist: pre-eutectic crystallization effect of Al9Fe2Si phase, double eutectic and crystallization α(Al)+β(Si) and multi-component eutectic
crystallization. During heating, DSC curve showed endothermic effect connected with melting of the eutectic α(Al)+β(Si) and phases:
Al2Cu, Al3Ni, Mg2Si and Al9Fe2Si being its components. The enthalpy of this transformation constitutes approx. +392 J g-1
. During
freezing of the alloy, DSC curve showed two exothermal reactions. One is most likely connected with crystallization of Al9Fe2Si phase
and the second one comes from freezing of the eutectic α(Al)+β(Si). The enthalpy of this transformation constitutes approx. –340 J g-1
.
Calorimetric test was accompanied by structural test (SEM) conducted with the use of optical microscope Reichert and scanning
microscope Hitachi S-4200. There occurred solution's dendrites α(Al), eutectic silicon crystal (β) and two types of eutectic solution: double
eutectic α(Al)+β(Si) and multi-component eutectic α+AlSiCuNiMg+β.
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.