А. A. Baikov Institute of Metallurgy and Materials Science¹, Moscow, Russia ; National University of Science and Technology “MISiS”², Moscow, Russia:

T. K. Akopyan, Researcher^1,2, e-mail: aktorgom@gmail.com

National University of Science and Technology “MISiS”, Moscow, Russia:
N. A. Belov, Deputy Director of Engineering Center “Casting Technologies and Materials”, Professor of a Chair of Casting Technologies and Metal Art
A. S. Aleshchenko, Assistant Professor of a Chair of Metal Forming
N. O. Korotkova, Post-Graduate Student

The phase composition and structure of the TNM type γ-alloys have been analyzed applied to the hot isostatic pressing (HIP) temperature, using both computational and experimental methods. The thermodynamic analysis of the investigated -alloys (TNM (% (at.): 42.99 Al, 4.52 Nb and 1.07 Mo) and TNM+ (% (аt.): 43.01 Al, 4.31 Nb, 1.02 Mo, 0.9 Cr and 0.92 Zr), has been performed using the Thermo-Calc software and has revealed that the temperature of 1250 ^оC can be considered as optimal for HIP-treatment, from the position of their phase relationship at this temperature. The experimental studies of the alloys microstructure in as-cast state and after conventional vacuum annealing at 1250 ^оC have showed that γ/α₂-colonies which were formed as a result of the eutectoid decomposition of the α-phase are the main structural component. The particles of the β- and γ-phases are identified at the boundaries of these colonies. The HIP-treatment of the basic TNM alloy at 1250 ^оC and overpressure of 170 MPa does not lead to quantitative changes in the phase composition in comparison to the vacuum annealing, however, coarsening of the eutectic colonies is observed. The HIP-treatment of the TNM+ alloy leads to significant changes of phase relationship as compared to the vacuum annealing, in particular, the amount of γ-phase increases substantially (from 15 to 51 % (vol.), while the amount of -phase decreases from 65 to 17 % (vol.). The hardness (HV 10) of TNM alloy after HIP and conventional annealing is not different, and is about 385 units. The high content of γ-phase in the TNM+ alloy after HIPtreatment reduces its hardness by ~30 units as compared with vacuum annealing, and it makes approximately 330 units. The uniaxial compression tests of alloys after HIP-treatment have showed that the yield stress (σ_0.2) of TNM alloy is slightly higher than that of TNM+ alloy (840 MPa against 787 MPa). This result is also explained by the increased amount of soft γ-phase in the TNM+ alloy. Minimum standard deviation of yield strength is noted for both alloys, which is connected with a positive effect on the HIP-treatment on the mechanical properties reproducibility.
The work has been conducted under support of the Russian Foundation of Basic Research, the grant for the scientidic project No. 16-33-01108 “Development of physical and chemical grounds for control of phase composition, structure and properties of the prospective alloys based on titanium aluminides”.

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