划痕诱发的镍基合金应力腐蚀裂尖扩展驱动力分析

Analysis on Crack Driving Force at Stress Corrosion Cracking Tip Induced by Scratch in Nickel-based Alloy

摘要:

镍基合金通常被用于制造压水堆蒸汽发生器的传热管。但是,传热管表面凹坑和划痕诱发的应力腐蚀开裂(SCC)更具有突发性和严重性并对核电站的安全可靠性有很大影响。为了解表面划伤导致的不同氧化物形貌对镍基合金应力腐蚀行为的影响,模拟了膜致应力下镍基合金划伤裂纹尖端的局部应力应变场。结果表明,楔形力是引发SCC裂纹扩展的主要驱动力。划痕裂纹前端的氧化物越厚,楔形力越大,并会增大SCC裂纹扩展速率。裂尖氧化物的形成导致了压应力、压应变和负的应变速率,并会阻碍半椭圆裂纹尖端上部和下部的SCC裂纹扩展。

Abstract:

Nickel-based alloys are commonly used to fabricate transfer tubes of pressurized water vapor generators. However, the stress corrosion cracking (SCC) induced by surface pits and scratches of the tubes is more sudden and has great influence on the safety and reliability of nuclear power plant. To understand the effects of the oxide morphology on the crack tip of scratched surface on SCC behavior of nickel-based alloy, the local stress-strain field at scratched crack tip in the presence of film-induced stress is simulated. Results show that wedge force is the major crack driving force that causes the SCC growth. Greater oxide thickness of scratch crack will give rise to wedge force and lead to an increase in SCC crack growth rate (CGR). The formation of oxide at crack tip will induce compressive stress, compressive strain and negative strain gradient, and thus retard the SCC propagation in the upper and lower part of the semi-ellipticalScrack front.