纯镍材N6及其焊缝在3种腐蚀介质中的腐蚀

Corrosion of Pure Nickel N6 and Welding Seam in Different Corrosive Medium

腐蚀介质储运容器的焊缝易受腐蚀,是影响其使用寿命的主要因素,过去对之研究报道较少,更缺乏系统性的报道。对N6纯镍材进行了等离子焊接,分别浸入质量分数均为10%的H_2SO_4,NaOH,FeCl_3溶液中,进行常温静态腐蚀;采用现代表面分析技术研究了其腐蚀机理。结果表明:在3种腐蚀介质中,N6纯镍材的耐蚀性明显优于自熔焊焊缝,因为熔池在凝固过程中易出现缺陷,导致焊缝纯净度和组织均匀性变差;焊缝组织为粗大的柱状晶,致使焊缝耐蚀性变差; N6纯镍材及自熔焊焊缝在10%FeCl_3溶液中的腐蚀速率远高于在10%H_2SO_4和10%NaOH溶液中的,因为溶液中的Cl^-活化作用破坏了其动态平衡,促使溶解过程转为优势; FeCl_3水解过程中生成酸,既有氧去极化腐蚀作用,又有氢去极化腐蚀作用;非金属夹杂物Al_2O_3与基体界面处优先溶解,促使腐蚀加剧。

Pure nickel N6 was welded by plasma arc welding( PAW). Pure nickel N6 after welding was immersed in 10%H2SO4,10%NaOH and 10%FeCl3 corrosion medium at room temperature respectively. Subsequently,the corrosion mechanism of specimens in different corrosive medium was further analyzed. Results showed that in all three kinds of corrosive medium,pure nickel N6 possessed better corrosion resistance than self-fusible welding seam,because the defects easily formed in weld crater during solidifying process,which could make the purity of welding seam and uniformity of microstructure worse. Moreover,the welding seam was main composed of coarse columnar crystal,leading to the decrease of welding seam. The corrosion rates of pure nickel and welding seam in 10% FeCl3 solution were much higher than those in 10%H2SO4solution and 10% Na OH solution,because the activation effect of Cl-in solution could destroy the dynamic balance and further promote the dissolution process to be dominant. Meanwhile,some acid formed in the process of hydrolysis process of FeCl3,which possessed not only the effect of depolarization corrosion of oxygen but also the depolarization corrosion of hydrogen. The nonmetallic Al2O3 inclusion and the substrate interface were prior to be dissolved,which aggravated the corrosion.