Oxide Scale Stress Determination by Raman Spectroscopy Application to the NiCr/Cr2O3 System and Influence of Yttrium
Oxide Scale Stress Determination by Raman Spectroscopy Application to the NiCr/Cr2O3 System and Influence of Yttrium
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DOI：
10.1016/s1359-6462(98)00079-7
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发表时间：
1998-05
影响因子：
6
通讯作者：
G. Calvarin;A. Huntz;A. H. Goff;S. Joiret;M. Bernard
中科院分区：
文献类型：
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作者：
G. Calvarin;A. Huntz;A. H. Goff;S. Joiret;M. Bernard
镍基合金作为耐热材料的性能在很大程度上取决于其抗氧化性。由于形成了保护性的Cr2O3层，阻止了镍离子向氧化垢/气体界面的扩散，防止了NiO垢的快速生长，从而使Ni-Cr合金具有较强的抗氧化性。然而，在高温下或温度变化过程中产生的应力会导致水垢破裂、屈曲和剥落，使底层金属重新氧化。在氧化过程中遇到的应力可以大致分为氧化温度下的生长应力或冷却过程中产生的热应力。生长应力的一个重要来源是金属氧化过程中的体积变化，其特征是PBR，即氧化物的摩尔体积与衬底中等效金属的摩尔体积之比。在大多数情况下，氧化物的体积大于它所结合的金属（PBR 1），因此氧化物晶格的收缩尤其发生在金属-氧化物边界。因此，在金属和金属合金表面形成的氧化层在水垢生长过程中产生压应力。这种效应尤其适用于生长受向内阴离子扩散控制的鳞片。热应力是由于鳞片和基体之间的膨胀不匹配造成的，被认为比生长应力重要得多，生长应力可以通过基体和鳞片的弹粘塑性变形来松弛。如果应力达到临界值，则会导致尺度破裂。因此，为了预测合金的长期行为，有必要了解氧化膜中应力产生的起源过程。因此，氧化层残余应力的测定为这类合金的寿命预测提供了重要的信息。
The performance of nickel-based alloys as heat resistant materials is strongly dependant on their oxidation resistance. A strong resistance to oxidation of Ni-Cr alloys is expected due to the formation of a protective Cr2O3 layer which blocks the diffusion of nickel ions to the oxide scale/gas interface and prevents from fast growth of a NiO scale.Nevertheless, stresses which are created during scale growth at high temperature, or during temperature changes can lead to scale fracture, buckling and spallation, subjecting the underlying metal to renewed oxidation. Stresses encountered during the oxidation process can be broadly categorized as either growth stresses at the oxidation temperature, or thermal stresses developed during cooling. An important source of growth stress is the volume change during oxidation of the metal, characterized by the Pilling-Bedworth ratio (PBR), which is the ratio of the oxide molar volume to the molar volume of the equivalent metal in the substrate. In most cases, the oxide has a larger volume than the metal to which it is bonded (PBR 1) such that contraction of the oxide lattice occurs particularly at the metal-oxide boundary. Thus, compressive stresses are generated in the oxide layer formed at the surface of metals and metallic alloys, during the scale growth. This effect is particularly true for scales whose growth is controlled by inward anionic diffusion. Thermal stresses are due to the expansion mismatch between the scale and the substrate and are considered to be much more important than growth stresses which can be relaxed by elasto-viscoplastic deformation of both the substrate and the scale. Stresses, if they reach a critical value, lead to fracture of the scale. Thus, it is necessary to understand the processes at the origin of stress generation in oxide films in order to predict the long term behaviour of alloys. Determination of residual stresses in oxide scales therefore provides important information for the life time prediction of such alloys.