Baykov Institute of Metallurgy and Materials Science of the Russian Academy of Sciences, Moscow, Russia:

S. B. Rumyantseva, Junior Researcher, e-mail: sbvarlamova@gmail.com

United Engine Corporation JSC, Moscow, Russia:

B. A. Rumyantsev, Principal Specialist, Candidate of Technical Sciences

Bauman Moscow State Technical University, Moscow, Russia:

V. N. Simonov, Professor, Doctor of Technical Sciences

VKh4Sh (Kh65NVFT) stands for a chromium-nickel alloy that is currently used to make combustion chambers for smaller spacecrafts. Due to a high level of oxygen, this alloy has low plasticity at room temperature, which affects its processability. At the same time, the alloy demonstrated high plasticity at a test temperature of 1,100 ^oC, which constrains its use as a refractory material. Some researchers attempted to make the alloy more heat-resistant by doping it with such refractory metals as Ta, Nb, Hf, Zr. But the chemical analysis showed no presence of Hf or Zr or they were found at minimum detectable concentration. Later, a process was described when different deoxidizers had been used for a VKh4Sh type alloy, and there are data that show that the concentration of oxygen decreased from 300–500 to 40–50 ppm while hafnium and zirconium were successfully absorbed. Therefore, the aim of this research is to understand how a lower level of oxygen and doping with refractory metals (Ta, Nb, Hf, Zr) change the mechanical properties and the microstructure of this heatresistant chromium-nickel alloy. The structure of the following chromiumnickel alloys was studied with the help of a scanning electron microscope and an attachment designed for energy dispersive microanalysis: Alloy I (base) produced using the conventional process without doping; Alloy II doped with refractory metals: 0.15 Ta – 0.15 Nb – 0.05 Hf – 0.05 Zr; Alloy III produced using a process that involves double vacuum remelting with magnesium deoxidation and doping with 0.15 Ta – 0.15 Nb – 0.1 Hf – 0.1 Zr. A series of mechanical tests was carried out with the alloys at the temperatures of 20, 900 and 1,100 ^oC. Through experiments, it was established that at 1,100 ^oC the tensile strength of Alloy III increased by 42% compared with Alloy I and by 20% compared with Alloy II, while the elongation of Alloy III dropped by 86% compared with Alloy I and by 25% compared with Alloy II. A microstructural study of the specimens after the tests showed an enhanced structural stability of Alloy III, which is associated with a lower coagulation rate of the phase particles.

1. Ault G. M. Requirements to high-temperature materials for spaceships. Heat-resistant materials. Translated from English by A. S. Sobolev and F. S. Novik. Moscow : Metallurgiya, 1969. pp. 41–65.
2. Voronin G. M., Kishkin S. T., Panasyuk I. O., Podiachev V. N. Refractory alloys in air- and spacecrafts. Aviation materials at the turn of 21^st century. Moscow : VIAM, 1994. pp. 264–273.
3. Conrath E., Berthod P. Microstructures of binary Cr – xNi alloys (0  Ni  50 wt. %) in their as-cast state and after high temperature exposure. Materials at High Temperatures. 2016. Vol. 33, Iss. 2. pp. 189–197. DOI: 10.1080/09603409.2016.1144317.
4. Mironenko V. N., Aronin A. S., Aristov I. M., Shmytko I. M., Trushnikova A. S. Structure and fracture mechanism of a two-phase chromiumnickel alloy during high-temperature deformation. Fizika metallov i metallo vedenie. 2016. Vol. 117, No. 9. pp. 969–976.
5. Butrim V. N. Some solutions for the production of semi-finished steel products made of two-phase chromium-nickel alloy. Problemy chernoy metallurgii i materialovedeniya. 2017. No. 2. pp. 5–19.
6. Beresnev A. G., Razumovskiy V. I., Lozovoy A. Yu. Developing the theory of alloying to create a new generation of heat-resistant nickel alloys produced by powder metallurgy processes. Teoriya legkikh splavov. 2012. Iss. 2. pp. 52–61.
7. Razumovskii V. I., Lozovoi A. Y., Razumovskii I. M. First-principlesaided design of a new Ni-base superalloy: Influence of transition metal alloying elements on grain boundary and bulk cohesion. Acta Materialia. 2015. Vol. 82. pp. 369–377.
8. Butrim V. N., Beresnev A. G., Trushnikova A. S., Razumovskii I. M., Razumovskii V. I. Effect of а number of transition metals on the cohesive properties of Cr – Ni-base alloys. Materials Science Forum. 2017. Vol. 879. pp. 1980–1986.
9. Butrim V. N., Razumovskiy I. M., Kashirtsev V. N., Beresnev A. G., Trushnikova A. S. et al. Chromating alloy and method of alloy melting. Patent RF, No. 2620405. Applied: 24.03.2016. Published: 25.05.2017. Bulletin No. 15.
10. Varlamova S., Trushnikova A., Rumyantsev B., Butrim V., Simonov V. Improvement of chemical composition, structure and mechanical properties of heat-resistant chromium-nickel alloy. IOP Conference Series: Materials Science and Engineering. 2018. Vol. 347. 012007.
11. Rumyantseva S. B., Rumyantsev B. A., Simonov V. N., Sprygin G. S., Kashirtsev V. N. Choosing an optimum deoxidation process for the chromi um-nickel alloy Kh65NVFT doped with refractory metals. Elektrometallurgiya. 2020. No. 1. pp. 9–17.
12. Krell J., Röttger A., Theisen W. Chromium-nickel-alloys for wear application at elevated temperature. Wear. 2019. pp. 432–433. 102924.
13. Butrim V. N. Optimized chromium-nickel alloys for spacecrafts. Composite materials constructions. 2017. No. 2. pp. 26–38.
14. Razumovskiy I. M., Beresnev A. G., Razumovskiy V. I., Logacheva A. I. Doping of heat-resistant alloys with transition metals with high cohesive energy: A universal system. Konstruktsionnye i funktsionalnye materialy. 2014. No. 1. pp. 33–36.
15. Razumovskii I. M., Ruban A. V., Razumovskii V. I., Logunov A. V., Larionov V. N. et al. New generation of Ni-based superalloys designed on the basis of first-principles calculations. Material Science Engineering: A. 2008. Vol. 497, Iss. 1-2. pp. 18–24.