研究了纯 Na_2SO_4,10%NaCl+90%Na_2SO_4和20%NaCl+80%Na_2SO_4三种盐沉积对 GH37镍基合金在750—850℃范围内蠕变性能的影响.结果表明前两种盐对蠕变性能无明显影响,而20%NaCl+80%Na_2SO_4混合盐当沉积量达到3mg/cm~2时严重地缩短蠕变断裂时间,并降低蠕变断裂延伸率.沉积在合金表面的20%NaCl+80%Na_2SO_4混合盐破坏了氧化膜 Cr_2O_3的保护作用,在合金表层同时发生均匀腐蚀和沿晶腐蚀,在基体一侧产生贫 Cr 带,同时氧和硫沿晶界侵入,外力作用下发生沿晶开裂.表层沿晶裂纹和体内蠕变产生的沿晶裂纹相互联结大大地缩短了蠕变第二阶段的时间,导致过早断裂.
The creep fracture behaviour of Ni-base alloy GH37 sustained under various loads was studied in three salt depositions:Na_2SO_4,10% NaCl+90% Na_2SO_4 or 20% NaCl+80% Na_2SO_4 at 750—850℃.No remarkable attack was observed in either Na_2SO_4 or 10% NaCl+90% Na_2SO_4,but a violent reduction in life of creep rupture and in creep elongation was expected while in 20% NaCl+80% Na_2SO_4 deposited at rate up to 3 mg/cm~2.The deposition of mixed salts 20% NaCl+80% Na_2SO_4 may destroy the protective oxide film on the alloy surface,meanwhile, may also erode evenly both surface and grain boundaries,and a Cr-depleted layer and intergrartular crackings under stress may be resulted.Therefore,the period of second stage creep is much shortened by interaction of the intergranular crack- ing at surface layer together with internal creep,and the alloy fails prematurely.
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