Thermal treatment process capable of reducing microsegregation of directionally-solidified high-niobium TiAl alloy

Abstract

The invention provides a thermal treatment process capable of reducing the microsegregation of directionally-solidified high-niobium TiAl alloy. The high-niobium TiAl alloy containing trace elements such as W, B, Y, Mn and the like is prepared from the following components by atomic percent: 44-46% of Ti, 6-9% of Al, 0-2% of Nb, 0-0.5% of W and Mn, and the balance of B and Y; and a fastener ingot is obtained by virtue of electric arc melting, the fastener ingot is sucked and cast into an alloy test bar, and a directionally-solidified high-niobium TiAl alloy sample is prepared by utilizing a Bridgeman method. A directional solidification technology is utilized, so that alloy grains grow along a forced direction, the transversal grain boundary is eliminated, and the high-temperature property is improved, but as the cast high-niobium TiAl alloy has structural defects caused by ubiquitous S segregation, beta segregation and alpha segregation, the mechanical property of the alloy is finally influenced. According to the invention, heat preservation is carried out on the directionally-solidified sample at the temperature of 1250-1290 DEG C for 6-24 hours, and when the sample is cooled to 890-910 DEG C along with a furnace, heat preservation is carried out for 30-35 minutes, thus the beta segregation and the alpha segregation are greatly reduced, simultaneously recrystallization and grain growth phenomena do not appear, and the mechanical property of the alloy is effectively improved. The process provided by the invention is simple and reliable in method, low in cost and strong in practicability; and the obtained high-strength, high-toughness and directionally-solidified high-niobium TiAl alloy has a wide application prospect in the aerospace field.

Description

technical field [0001] The invention belongs to the field of high-performance alloy material preparation, and in particular relates to a heat treatment process for reducing micro-segregation of directional solidified high-niobium titanium-aluminum alloy. Background technique [0002] Titanium-aluminum (TiAl)-based alloys have become a high-temperature structure for aerospace and automotive engines due to their low density, high specific strength and specific elastic modulus, high-temperature strength and stiffness, and good creep and oxidation resistance. parts with very competitive materials. Compared with ordinary TiAl-based alloys, the addition of high-melting-point refractory metal Nb to high-niobium TiAl alloys improves the high-temperature strength of the alloy, improves high-temperature creep resistance and oxidation resistance, and increases the service temperature of the alloy by 60- 100oC, taking into account the low density of ordinary TiAl alloys. The density o...

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Problems solved by technology

Studies have shown that high-temperature annealing for 12-24h above the α phase transition temperature (1350oC-1400oC) can simultaneously eliminate S segregation, β segregation, and α segregation in directionally solidified high-niobium TiAl alloys, but recrystallization and grain growth occur. Large phenomenon, which ultimately affects the comprehensive mechanical properties of directionally solidified TiAl alloys. At the same time, the increase of heat treatment temperature also greatly increases the equipment requirements and energy consumption (The effect of heat treatment on S-segregation in the structure of large-scale cast high-Nb-TiAl alloys, Aviation Journal of Materials Science, 28-32, 27, 2007)

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