La对Ni-Cr-W-Mo耐热合金1173K恒温氧化行为的影响

研究了不同La含量Ni-Cr-W-Mo耐热合金的1173 K恒温氧化行为.结果表明:La能明显提高合金的抗氧化能力.不同La含量合金的抗氧化性能从劣到优依次为:La含量为0%、0.048%、0.026%、0.087%.添加超过0.026%的合金由于析出La化合物,使La的固溶量未呈线性增加,而在0.048%处出现拐点.氧化中由于La化物不参与氧化,因此合金的抗氧化能力主要取决于La在合金中的实际固溶量,固溶的La形成LaCrO3是La提高合金抗氧化能力的主要原因.LaCrO3在氧化物晶界处的偏聚阻碍了Cr3+的扩散,并可作为MnCr2O4异制形核的核心,促进细小的MnCr2O4生成并弥散分布于Cr2O3之间,形成混合氧化膜,提高了氧化膜的粘附性,亦成为提高抗氧化能力的因素.

Effects of La on isothermal oxidation behavior of a Ni-Cr-W-Mo heat-resistant alloy at 1173 K

The effect of rare earth element La addition on the isothermal oxidation behavior of a Ni--Cr--W--Mo superalloy was investigated. The results showed that the oxidation resistance can be effectively improved by the addition of La element. The improving degree with the La addition from the worst to the best is 0.0%, 0.048%, 0.026%, 0.087%. For the testing alloys, 0.026% La is considered as the optimum amount. It has been found that La--riched phase precipitates with more than 0.02% La addition, and soluted La in the matrix does not increase linearly with the increasing of La addition. The amount of soluted La is considered as the main reason for the improving of oxidation resistance. Diffusion of the Cr³⁺  was impended by LaCrO₃ segregated on the interface of oxide scale. LaCrO₃  as heterogeneous nucleating of MnCr₂O₄, promoted the nucleation of the fine MnCr₂O₄ grains among the Cr₂O₃, forming smooth multi--oxide scale without voids, so that the bounding force
between oxide scale and matrix was increased.