B对一种高Al+Ti镍基高温合金氧化行为的影响

Effect of B on the high temperature oxidation behavior of a nickel-base superalloy with high Al and Ti contents

摘要:

采用真空感应炉制备了不同B含量的U720Li合金铸锭并对其进行了均匀化处理，研究了B对均匀化态U720Li合金1100 ℃恒温氧化行为的影响。结果表明，经高温均匀化处理后不同B含量合金基体中的B均发生了严重损耗，表明在1100 ℃以上空气中热暴露时B会向氧化皮中迅速扩散；增加B含量降低了合金的氧化速率，减小了氧化膜附近基体中孔洞的体积分数及γ′分解区的厚度；高B和低B合金的氧化膜均分为3层：最外层主要由疏松的(Ni/Co)O、TiO2和复杂尖晶石化合物构成，中间层主要为Cr2O3，最内层是不连续的Al2O3+TiO2层。B提高均匀化态U720Li合金抗氧化性的主要原因是，增加B含量显著增加了Cr2O3层的厚度并改善其连续性，使其具有更强的保护性。

Abstract:

Three U720Li ingots with different B contents were produced by vacuum induction melting and afterwards they were fully homogenized. The effect of B on the isothermal oxidation behavior of as-homogenized U720Li alloy at 1100 ℃ was investigated by a discontinuous increasing weight method. After the homogenization treatment, extremely serious B depletion from the alloy matrix was found by ICP-AES, indicating that B could diffuse rapidly towards the oxide scale during high temperature air exposure (above 1100 ℃). The B addition decreased the oxidation rate and reduced the volume fraction of pores and the thickness of γ′ depleted layer. The scales formed on both low B and high B alloys consist of three layers, loose outer layer composed of (Ni/Co)O, TiO2 and complex spinel, compact intermediate layer is mainly Cr2O3 and discrete internal oxides are Al2O3+TiO2. It is deemed that B improves the oxidation resistance mainly by promoting the formation of a more continuous and protective Cr2O3 intermediate layer.