铸态TiAl-Nb合金的组织结构与蠕变性能

Microstructure and Creep Behavior of As-Cast TiAl-Nb Alloy

摘要:

摘要：通过蠕变性能测试和组织形貌观察，研究了铸态TiAl-Nb合金在近890-910篊温度区间的蠕变行为。结果表明，铸态TiAl-Nb合金的组织结构主要由层片状r/a2两相组成，不同取向r/a2两相层片状组织之间存在不规则锯齿状形态的晶界，该锯齿状非层片晶界由单一r相组成。在高温蠕变期间，合金具有较好的蠕变抗力和较长的蠕变寿命；合金在蠕变期间的变形机制是大量位错以位错列的形式剪切层片状r/a2两相，其中，大量位错在基体中滑移，发生反应可形成位错网，促进位错的攀移，可减缓应力集中，改善合金的蠕变抗力。与a2-Ti3Al相比,r相有较弱的强度，因此，蠕变期间合金中的裂纹易于在与应力轴呈45?角、且与层状结构相平行的晶界处萌生与扩展，直至蠕变断裂是合金在蠕变期间的断裂机制；其中，与层状结构相平行的断口呈光滑面口，而与层状结构呈一定角度的断裂表面存在撕裂棱，为较高强度的a2-Ti3Al相阻碍裂纹扩展所致。

Abstract:

Abstract：By means of creep properties measurement and microstructure observation, an investigation has been made into the microstructure and creep properties of as-cast TiAl-Nb alloy in the temperature ranges of 800--910篊. Results show that the microstructure of as-cast TiAl-Nb alloy consists of r/a2 phases with the lamellar feature. The boundaries with the irregular jagged configuration are located in between the different oriented lamellar phases, and the single r is distributed in the region near the boundaries. The creep lifetime of as-cast TiAl-Nb alloy is measured to be 237 h under the applied stress of 120 MPa at 900 篊, and the creep lifetime of the alloy is measured to be 307 h under the applied stress of 220 MPa at 800篊. The deformation mechanism of alloy during creep is dislocation slipping within the lamellar r/a2 phases, and the boundaries between the lamellar r/a2 phases may hinder dislocation slipping. During steady state creep, the lamellar r/a2 phases in the alloy may be contorted due to the double orientation slipping of dislocations. In the latter stage of the creep, the micro-crack may be initiated and propagated along the grain boundaries being perpendicular or at about 45?angles relative to the stress axis, under the action of maximum shear stress, up to the occurrence of creep fracture, which is thought to be the fracture mechanism of alloy during creep.