Experimental confirmation of high-temperature phase boundaries in the nickel-rich part of Ni-Al-Cr system

Abstract

Precise determination of the course of phase boundaries is particularly important for alloys operating at elevated temperatures. In the case of multi-component materials such as nickel superalloys, computational methods are often used for this purpose. They are based on binary and ternary systems and require reliable experimental data. Commonly used research methods for determining phase boundaries at elevated temperature have a number of limitations and it is difficult to interpret their results without the support of other studies. This work presents a series of experiments to confirm the course of phase boundaries γ′/(γ′ + γ) and (γ′ + γ)/γ in Ni-Al-Cr system, particularly at 600 °C. For this purpose, a series of alloys from Ni-rich part of Ni–Al-Cr ternary system was prepared by vacuum induction melting (VIM) and casting into graphite mold under an argon protective atmosphere. Samples after machining were subjected to compression tests using the Gleeble 3800 thermomechanical simulator at room temperature as well as directly at 600 °C after pre-heating at 1100 °C. Stress–strain curves of various character were obtained and were associated with the appropriate phase structure confirmed by X-ray diffraction (XRD) analysis. The relationship between the phase structure of the studied alloys and their mechanical properties has been proven. Compression results were compared with the results of hardness measurements, high-temperature calorimetric solution method and differential thermal analysis (DTA). The obtained results showed a very good agreement in terms of the course of the γ′/(γ′ + γ) and (γ′ + γ)/γ phase boundary in Ni-Al-Cr system.