【摘要】 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。更多还原

【Abstract】 By means of creep properties measurement and microstructure observation of as-cast,solution,solution and aging states alloy,the influence of heat treatment on microstructure and creep properties of TiAl-Nb alloy was studied.Results show that the microstructure of as-cast TiAl-Nb alloy consists of the γ /α2phases with the lamellar feature.The boundaries with the irregular jagged configuration are located in between the different oriented lamellar phases,and the single γ phase with non-lamellar feature is distributed in the region near the boundaries.After solution + aged treatment,the alloy obtains the microstructure with uniform and regular lamellar γ /α2phases,and eliminates the single γ phase with non-lamellar feature in the boundary region,which may improve the creep resistance of alloy.Under the applied stress of 200 MPa at 800 ℃,the creep lifetime of as-cast TiAl-Nb alloy is measured to be 147 h,and the one of the alloy after solution + aged treatment is enhanced to 297 h.During creep at 800-840 ℃,the creep activation energy of the alloy after solution and aged treatment is measured to be Q = 432 kJ /mol.During creep,the creep strain of as-cast alloy occurs mainly in the boundary region with single γ phase.While,the cracks in the heat treated alloy during creep are firstly initiated in the grain boundaries which is parallel to the lamellar γ /α2phases along the 45 !relative to the stress axis,and propagated along the boundaries up to the occurrence of creep fracture.更多还原