Abstract
The subject of the study was temperature dependence of electrical resistivity of alloys based on Ni-Cr-Al system in liquid and solid state. Objects of research were alloy compositions contained 10 and 15 % of chromium and alloyed by 5 and 10 % of aluminium each. The temperature dependences of electrical resistivity was a characteristic to commercial superalloys. It has been founded that the higher the amount of alloyed elements the lower critical temperature heating up to which leads to the formation of equilibrity and microhomogeneouty of the melt structure and the lower the temperature of hysteresis of electrical resistivity polyterms. Melt state before crystallization has had a significant influence on solidification process and structure of alloys in solid state.
Highlights
The Ni-Cr-Al system occupies a special place in the development of dispersion-hardening nickelbased alloys [1]
- abnormal temperature - the beginning of intensive restructuring of the melt structure; - critical temperature – the temperature, heating to which leads to irreversible restructuring of the structure of the melt; - the temperature range of the intensive reorganization of the melt structure – Δtirs is located between the temperature of the anomaly and the hysteresis temperature of the polytherm, i.e. Δtirs = th - tan; - coefficient of intensive restructuring of the melt structure Cirs = Δρh / Δtirs, where Δρh is the hysteresis value of the polytherm ρ for th; the index of Cirs is used as an analog of the activation energy for express analysis of the structural rearrangement process
The temperature dependences of the electrical resistivity of Ni-Cr-Al alloy system are shown in figure 2
Summary
The Ni-Cr-Al system occupies a special place in the development of dispersion-hardening nickelbased alloys [1]. The distortion of the crystal lattice of solid solutions based on nickel accrues continuously and smoothly with increasing number of alloying components and their concentrations. This is due to the appearance of additional polar bonds in such alloys and the determining factor of phase stability is the electron concentration but not the difference in the dimensions of the atoms [2]. Alloys are strengthened by creating a dispersive heterogeneous structure consisting of a γ-solid solution and a strengthening phase of Ni3Al that is variable in solubility; dispersion hardening is possible because of heat treatment. Chromium is dissolved in small amounts in this phase
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