Ta氧化膜开裂的临界应力

本工作将测量金属氧化膜内应力的单面弯曲法和检测氧化膜破裂的声发射技术相结合,建立了金属氧化膜开裂临界应力的测试装置。即从声发射信号判定氧化膜第一次开裂的时间,并由相应的氧化偏转曲线求得氧化膜开裂临界立力。纯 Ta 试样的测量结果表明,在500℃、550℃、600℃1atm O_2中,Ta 氧化膜开裂的临界应力分别为:23.3、38.5、18.4×10~6kgf/m~2。不论Ta 遵循直线型还是抛物线型氧化规律,只要时间足够长,恒温氧化中膜都会破裂;且破裂的临界应力和膜的疏密程度及开裂方式有关。

THE MEASUREMENT OF THE CRITICAL CRACKING STRESSES OF THE OXIDE SCALE DURING THE OXIDATION OF TANTALUM

The bending method can be used to measure the stresses of the oxide scale directly in-situ during high temperature oxidation.In com- bination with the acoustic emission technique it was used to measure the critical stresses of the oxide scale of tantalum.The acoustic emis- sion can sensitively monitor ventical and parallel cracks of the oxide scale,while the weight gain curves only give information about vent- ical cracks.During the oxidation of tantalum at 500℃,550℃,600℃ in 1 arm O_2,the cracking stresses(σ_(max,c) represented by the maximum stresses)are 23.3,38.5,18,4×10~6 kgf/m~2 respectively.The cracking stresses are dependent on the oxidation temperature.SEM,X-ray diffra- ction analysis and optical microscopy show that this result is related to the density and type of cracking of the oxide scale.The less denser the oxide is,the smaller the critical stress is.The stresses causing blister-like cracks are larger than the stresses causing cracks along the grain boundaries.In a word,the oxide scale cracking not only depends on stresses,but also on other mechanical properties,