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通过对铸态、固溶、固溶+实效处理后的TiAl-Nb合金进行蠕变性能测试及组织形貌观察,研究了不同工艺对合金组织与蠕变性能的影响。结果表明,铸态TiAl-Nb合金的组织由层片状γ/α2两相组成,具有锯齿状不规则形态的晶界位于不同取向的层片状团簇之间,其晶界区域为单一γ相非层片状组织。经1320℃/0.5 h(油冷)+1250℃/8 h(炉冷)后,合金获得了规则、平直且均匀分布的层片状γ/α2两相组织,并消除了近晶界区域的非层片状γ单相,可明显提高合金的蠕变抗力。在800℃/200 MPa蠕变条件下,铸态合金的蠕变寿命是147 h,经固溶+时效处理后,合金的蠕变寿命提高到297 h,在施加800~840℃温度和200~240 MPa应力范围内,测定出热处理态合金在稳态蠕变期间的表观蠕变激活能为432 kJ/mol。在高温蠕变期间,铸态合金的蠕变应变主要发生在近晶界区域的非层片状单一γ相内;蠕变期间,固溶+时效态合金中的裂纹在与应力轴成45!角、且平行于层片状结构的晶界处萌生,并沿晶界扩展,是合金在蠕变期间的主要断裂机制。
The effects of different technology on the microstructure and creep properties of TiAl-Nb alloy were investigated by means of creep test and microstructure observation of the as-cast, solution and solid solution + treated samples. The results show that the microstructure of the as-cast TiAl-Nb alloy is composed of lamellar γ / α2 two phases, and the jagged irregular grain boundaries are located between lamellar clusters with different orientations. The grain boundary region is single γ Non-lamellar structure. After 1320 ℃ / 0.5 h (oil cooling) + 1250 ℃ / 8 h (furnace cooling), a regular, flat and uniform lamellar γ / α2 two-phase structure was obtained and the grain boundary region Non-lamellar γ single phase, can significantly improve the creep resistance of the alloy. Under 800 ℃ / 200 MPa creep condition, the creep life of the as-cast alloy is 147 h. After the solution treatment and aging treatment, the creep life of the alloy is increased to 297 h. Under the condition of 800 ~ 840 ℃ and 200 ~ In the 240 MPa stress range, the apparent creep activation energy of the heat-treated alloy during steady-state creep was determined to be 432 kJ / mol. During creep at high temperatures, the creep strain of the as-cast alloy mainly occurs in the non-lamellar single γ phase in the grain boundary region. During creep, the crack in the solution-aged alloy is 45% of the stress axis Angle, and parallel to the lamellar structure of the grain boundaries at the initiation, and along the grain boundaries, the alloy is the main fracture mechanism during creep.