Interfacial reaction and cracking mechanism on oxidation of metal carbides

研究了过渡金属碳化物（MeC, Me=Ti, Zr, Hf, Nb）在4 ~ 16 kPa的氧分压和400 ~ 800℃的温度范围内的氧化过程。从动力学角度和对氧化物/碳化物界面的SEM和TEM观察解释了氧化机理。摘要如下：TiC的氧化通过扩散控制过程分四个步骤进行。裂纹是由碳化氧/亚氧化钛形成的。氧化ZrC产生两个氧化垢区1和2。1区为相对无孔垢，含14 ~ 23 at%。2区孔隙多，裂纹大，含碳量为7% ~ 10%。1区尺度早期呈抛物线增厚，之后保持不变。2区尺度深度随时间线性增加。HfC的氧化行为与ZrC非常相似。NbC的氧化是通过相边界控制过程发生的，这是由于具有柱状颗粒的多孔鳞片与晶体表面垂直造成的。

Oxidation of transition metal carbide (MeC, Me=Ti, Zr, Hf, Nb) was studied at an oxygen partial pressure of 4 - 16 kPa and in a temperature range of 400 to 800ﾟC, using the powder and single crystal samples. The oxidation mechanism was explained from a kinetic viewpoint and on SEM and TEM observation of the oxide/carbide interfaces. The summary was as follows ;Oxidatin of TiC proceeded by a diffusion-controlled process in four steps. Cracking occurred by formation of oxycarbide/titanium suboxide. Oxidation of ZrC produced two oxide scale zones 1 and 2. Zone 1 showed relatively pore-free scale containing 14 - 23 at%. Zone 2 contained many pores and large cracks with a carbon content of 7 - 10 at%. Zone 1 scale thickened parabolically in an early period, then is kept constant. In contrast, depth of zone 2 scale increased linearly with time. Oxidation behavior of HfC was quite similar to that of ZrC.Oxidation of NbC occurred by a phase boundary-controlled process which resulted from the porous scales having colmnar grains normal to the crystal surface.