Variable Controled Temperature Gradient Effect on the Features of Structure, Phase Composition, Properties of High-Temperature Superalloys in Their Directional Solidification

Authors: Kablov E.N., Bondarenko Yu.A., Echin A.B. Published: 06.12.2016
Published in issue: #6(111)/2016  

DOI: 10.18698/0236-3941-2016-6-43-61

Category: Metallurgy and Science of Materials | Chapter: Metal Science, Thermal Processing of Metals and Alloys  
Keywords: directional solidification, temperature gradient, a nickel single crystal superalloy, reinforcing gamma’-phase, gamma/gamma’ eutectic, dendrite segregation, micro-porosity, short-term strength, long-term strength

The paper presents the research into the conditions of directional solidification with a variable controlled gradient. In our work first, we determined the factors influencing the temperature gradient at the growth front . We found that the most significant method is to remove the crystallization heat by radiation or convection cooling when the mould is immersed into the liquid metal coolant. When examining this process, we discovered important factors: temperature in the heating furnace, the liquid metal coolant temperature, heat shields, separating the heating zone from the cooling zone, the thermal conductivity of the ceramic mould. The study offers the method for the experimental evaluation of the temperature gradient values at the growth front by thermocouples. Findings of experimental studies conducted on the single-crystal samples with crystallographic orientation CLC of Recontaining VZHM3 alloy, show that by controlling the temperature gradient values (G = 20, 50, 100, 150 and 200°C/cm) we can significantly influence the size of the structural superalloy components. Metallurgical studies carried out by optical and electron microscopy showed that with the increase in the temperature gradient with 20°C/cm to 200°C/cm, the interdendritic distance halves from 310 microns to 130 microns, the size of the reinforcing particles γ'-phase in axes and mezhosnom space is reduced by 3 times, the particle size of the eutectic γ-γ' is reduced by more than 2 times, the volume fraction of microporosity is reduced by more than 10 times. By the method of least squares we obtained the regularities of changes of structural components VZHM3 alloy, which are presented in the form of equations. With increasing temperature gradient alloy, single crystal casting properties of cast samples VZHM3 values of tensile strength at 20°C increase in ~1.5 times, while 980°C - by 10-20%, the time to failure at 1100°C and σ=120 MPa increases more than 2 times. This work is within the framework of an integrated research area 9.5: Directional crystallization (with variable controlled gradient) of high-temperature superalloys ("Strategic trends in development of materials and technologies for their processing for the period up to 2030") and is aimed at creating the concept of "The advanced engine".


[1] Kablov E.N. Innovative developments of FSUE "VIAM" SSC of RF on realization of "Strategic directions of the development of materials and technologies of their processing for the period until 2030". Aviatsionnye materialy i tekhnologii [Aviation Materials and Technologies], 2015, no. 1, pp. 3-33 (in Russ.).

[2] Kablov E.N., ed. Litye lopatki gazoturbinnykh dvigateley: splavy, tekhnologii, pokrytiya [Cast blades of gas-turbine engine: alloys, technologies, coatings]. Moscow, Nauka Publ., 2006. 632 p.

[3] Versnyder F.L., Guard R.W. Directional grain structure for high temperature strength. Trans. ASM, 1960, vol. 52, pp. 485-493.

[4] Petrov D.A. Splavy tsvetnykh metallov: K analizu nekotorykh storon metoda napravlennoy kristallizatsii [Non-ferrous alloys: analysis of some features of directional crystallization technique]. Moscow, Nauka Publ., 1972, pp. 76-81.

[5] Kurts V., Zam P.R. Napravlennaya kristallizatsiya evtekticheskikh materialov [Directional crystallization of eutectic materials]. Moscow, Metallurgiya Publ., 1980. 272 p.

[6] Versnyder F.L., Shank M.E. The development of columnar grain and single crystal high temperature materials through directional solidification. Mater. Sci. and Eng., 1970, vol. 6, no. 4, pp. 213-247. DOI: 10.1016/0025-5416(70)90050-9

[7] Giamei A.F. and Kear B.H. On the nature of freckles in nickel-base superalloys. Met. Trans., 1970, vol. 1, no. 8., pp. 2185-2192. DOI: 10.1007/BF02643434

[8] Giamei A.F., Tschinkel J.G. Liquid metal cooling: a new solidification technique. Met. Trans. A, 1976, vol. 7, no. 9, pp. 1427-1434. DOI: 10.1007/BF02658829

[9] Giamei A.F., Kraft E.H., Lemkey F.D. New trends in materials processing // Amer. Soc. for Metals. 1976, pp. 48-98.

[10] Tschinkel J.G., Giamei A.F. Apparatus for casting of directionally solidified articles. U.S. Patent No. 3.763.926, 1971.

[11] Kablov E.N., Pankratov V.A. Turbine blades incubator. Nauka i zhizn’, 1991, no. 8, pp. 62-64 (in Russ.).

[12] Bondarenko Yu.A., Kablov E.N., Morozova G.I. Effect of high-gradient directed crystallization on the structure and phase composition of a high-temperature alloy of the type rene-N5. MiTOM, 1999, no. 2, pp. 15-18. (Eng. version of journal: Metal Science and Heat Treatment, 1999, vol. 41, no. 2, pp. 61-64. DOI: 10.1007/BF02468315)

[13] Kablov E.N., Bondarenko Yu.A. Producing monocrystal blades for gas turbine engine by means of high-gradient directional crystallization. Aviatsionnaya promyshlennost’ [Aviation Industry], 2000, no. 1, pp. 53-56 (in Russ.).

[14] Kablov E.N., Bondarenko Yu.A., Kablov D.E. Particularities of <001> single crystals structure and heat-resistant properties of high-rhenium ni-base superalloy, produced under the high-gradient directed solidification conditions. Aviatsionnye materialy i tekhnologii [Aviation Materials and Technologies], 2011, no. 4, pp. 25-31 (in Russ.).

[15] Bondarenko Yu.A., Kablov E.N. directional crystallization of heat-resistant alloys with increased temperature gradient. MiTOM, 2002, no. 7, pp. 20-23 (in Russ.).

[16] Bondarenko Yu.A., Echin A.B., Surova V.A., Narskiy A.R. On the directional solidification using heat-resistant alloys. Liteynoe proizvodstvo [Foundry. Technologies and Equipment], 2011, no. 5, pp. 36-39 (in Russ.).

[17] Kablov E.N., Bondarenko Yu.A., Echin A.B., Surova V.A. Advancement of the directional crystallization process of GTE blades of superalloys with the single-crystal and composition structures. Aviatsionnye materialy i tekhnologii [Aviation materials and technologies], 2012, no. 1, pp. 3-8 (in Russ.).

[18] Bondarenko Yu.A., Echin A.B., Surova V.A., Narskiy A.R. Influence of directional crystallization conditions on the structure of parts of the gas-turbine engine blade type. Liteynoe proizvodstvo [Foundry. Technologies and Equipment], 2012, no. 7, pp. 14-16 (in Russ.).

[19] Echin A.B., Bondarenko Yu.A. Modern equipment for turbine blades production designed with a glance of high-gradient directional crystallization process. Trudy VIAM [Proceedings of VIAM], 2014, no. 12. DOI: 10.18577/2307-6046-2014-0-12-3-3

[20] Bondarenko Yu.A., Echin A.B., Surova V.A., Narskiy A.R. Effect of temperature gradient on heat-resistant alloy structure in event of its crystallization. Liteyshchik Rossii, 2014, no. 5, pp. 24-28 (in Russ.).

[21] Kablov E.N., Bondarenko Yu.A., Echin A.B., Surova V.A. Ustroystvo dlya polucheniya otlivok s napravlennoy i monokristallicheskoy strukturoy [Equipment for producing casting with directional and monocrystal structure]. Patent RF № 2398653, 2009 (in Russ.).

[22] Petrushin N.V., Svetlov I.L., Ospennikova O.G. Liteynye zharoprochnye nikelevye splavy. Vse materialy. Entsiklopedicheskiy spravochnik [Heat-resistant Ni-base casting alloys. In: All materials. Encyclopedia], 2012, no. 5, pp. 15-19 (in Russ.).

[23] Echin A.B., Bondarenko Yu.A., Narskiy A.R. Influence of variable temperature gradient on refinement of dendritic structure of Re-containing super alloy. Liteynoe proizvodstvo [Foundry. Technologies and Equipment], 2015, no. 10, pp. 33-36 (in Russ.).

[24] Svetlov I.L., Kuleshova E.A., Monastyrskiy V.P. Effect of directional crystallization on phase composition and dispersability of Ni-base alloys structure. Metally, 1990, no. 1, pp. 86-93 (in Russ.).