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<p>Alloys based on γ-TiAl with 44 and 47 at.% Al, doped with 4 at.% Nb, 1 at.% Mo, 0.5 at.% Cr, and 0.1 at.% B, were melted in an arc furnace from pure materials. Their structure, phase transformation temperature, and deformation mechanism were studied using the results of tensile tests at elevated temperatures. Optimal Al/Ti ratios were determined and effective heat treatment parameters were established to ensure high mechanical properties. Scanning electron microscopy found that grains in the as-cast and annealed alloys with 44 at.% Al consisted of α<sub>2</sub> + γ lamellar colonies. The grain boundaries contained the β<sub>0</sub> phase and γ globules, which disappeared during annealing to transform into γ lamellae. The as-cast and annealed alloy samples with 47 at.% Al consisted of α<sub>2</sub> + γ lamellar colonies and the β<sub>0</sub> phase at the grain boundaries. X-ray diffraction revealed that the alloys with 47 at.% Al had 30–40% more γ phase than those with 44 at.% Al. The cubic β<sub>0</sub> phase content differed little. The alloys with higher aluminum content were shown to be more ductile at all test temperatures. They exhibited higher elastic modulus and fracture toughness but significantly lower yield stress. The fracture stress was comparable, weakly depended on temperature, and ranged from 1100 to 1300 MPa. For both groups of alloys, strength parameters remained quite high throughout the test temperature range (20–750°C). At room temperature, the hardening rate of the alloys with 44 at.% Al was three times that of the alloys with 47 at.% Al. In the brittle–ductile transition region, these alloys showed increased sensitivity of ultimate strain to strain rate. For the Ti<sub>47.5</sub>Al<sub>47</sub>Nb<sub>4</sub>Cr<sub>0.5</sub>Mo<sub>1</sub> alloy tested at 650°C, a decrease in the strain rate by only one order of magnitude led to an almost threefold increase in ductility. The distinctive behavior of the studied intermetallics is attributed to the pronounced strain-rate sensitivity of relaxation processes, determining the mechanism of dislocation motion over the temperature range of brittle–ductile transition.</p>

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Structure and Properties of γ-TiAl Alloys Doped with Niobium, Molybdenum, Chromium, and Boron

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • A.A. Bondar,
  • O.O. Bilous,
  • Yu.M. Podrezov,
  • S.O. Firstov,
  • N.I. Tsyganenko,
  • V.M. Voblikov,
  • O.M. Myslyvchenko,
  • V.I. Danylenko

摘要

Alloys based on γ-TiAl with 44 and 47 at.% Al, doped with 4 at.% Nb, 1 at.% Mo, 0.5 at.% Cr, and 0.1 at.% B, were melted in an arc furnace from pure materials. Their structure, phase transformation temperature, and deformation mechanism were studied using the results of tensile tests at elevated temperatures. Optimal Al/Ti ratios were determined and effective heat treatment parameters were established to ensure high mechanical properties. Scanning electron microscopy found that grains in the as-cast and annealed alloys with 44 at.% Al consisted of α2 + γ lamellar colonies. The grain boundaries contained the β0 phase and γ globules, which disappeared during annealing to transform into γ lamellae. The as-cast and annealed alloy samples with 47 at.% Al consisted of α2 + γ lamellar colonies and the β0 phase at the grain boundaries. X-ray diffraction revealed that the alloys with 47 at.% Al had 30–40% more γ phase than those with 44 at.% Al. The cubic β0 phase content differed little. The alloys with higher aluminum content were shown to be more ductile at all test temperatures. They exhibited higher elastic modulus and fracture toughness but significantly lower yield stress. The fracture stress was comparable, weakly depended on temperature, and ranged from 1100 to 1300 MPa. For both groups of alloys, strength parameters remained quite high throughout the test temperature range (20–750°C). At room temperature, the hardening rate of the alloys with 44 at.% Al was three times that of the alloys with 47 at.% Al. In the brittle–ductile transition region, these alloys showed increased sensitivity of ultimate strain to strain rate. For the Ti47.5Al47Nb4Cr0.5Mo1 alloy tested at 650°C, a decrease in the strain rate by only one order of magnitude led to an almost threefold increase in ductility. The distinctive behavior of the studied intermetallics is attributed to the pronounced strain-rate sensitivity of relaxation processes, determining the mechanism of dislocation motion over the temperature range of brittle–ductile transition.