弯曲形变及热处理对纯镍N6焊缝晶界特征分布及腐蚀行为的影响

Effect of Bending Deformation and Heat Treatment on Grain Boundary Characteristic Distribution and Corrosion Behavior for Pure Nickel N6 Weld

摘要:

对纯镍N6等离子弧焊缝进行“U”形弯曲形变及热处理加工，借助电子背散射衍射（EBSD）和取向成像显微技术（OIM）对比分析Non-GBE、GBE样品晶界特征分布(GBCD)及对腐蚀行为的影响。结果表明：焊缝经“U”形弯曲形变+900℃退火10min后，低ΣCSL晶界比例提高到54.1%，并形成具有Σ3n取向关系的大尺寸晶粒团簇；退火过程中再结晶形核点增加，晶粒尺寸下降到146 um。GBE样品耐蚀性高于Non-GBE样品，GBE样品（0.2113 A·m-2）自腐蚀电流密小于Non-GBE样品（0.8138 A·m-2），且GBE样品的容抗弧半径、阻抗模值|Z|、相位角θ均大于对应Non-GBE样品。两种样品表面均发生了点蚀，腐蚀行为概括为：腐蚀初期，C1-破坏样品表面局部区域钝化膜形成点蚀坑。随浸泡时间延长，阳极金属附近Ni2+浓度达到饱和或过饱和状态，Ni2+与膜层中结合水反应生成Ni(OH)2，部分Ni(OH)2脱水分解为NiO，组成的腐蚀产物膜沉积在样品表面，阻止Cl-穿过腐蚀产物渗透到样品表面，点蚀受到控制。

Abstract:

The pure nickel N6 plasma arc weld was subject to U-shaped bending deformation heat treatment.The grain boundary characteristic distribution (GBCD) of Non GBE and GBE samples and its influence on corrosion behavior were studied by grain boundary character distribution (EBSD) and orientation image microscopy (OIM). The results show that the proportion of lowΣCSL grain boundaries increase to more than 54.1% by the TMP after U-shaped bending deformation and subsequent annealing at 900℃ for 10 min, and simultaneously the large-size highly-twinned grain-cluster microstructure is formed.The recrystallization nucleation point increased and the grain size decreased to 146 um during annealing.The corrosion resistance of GBE sample is higher than that of Non GBE sample. The self corrosion current density of GBE sample is less than that of Non GBE sample, and the capacitive arc radius, impedance modulus and phase angle of GBE sample are greater than those of corresponding Non GBE samples.Pitting corrosion occurr on the surface of samples.The passivation film on the surface of the coating is destroyed by C1-in the solution and forms pitting pits at the initial stage.With the prolongation of immersion time, the concentration of Ni2+near the anode metal reaches saturation or supersaturation. the bound water in the corrosion product film reacts with Ni2+ forms Ni(OH)2, and then the Ni(OH)2 are dehydrated and decomposed into NiO.Corrosion products cover the surface of the sample and form a corrosion product film, which are composed of NiO and Ni(OH)2. The corrosion product film has a protective effect,which prevents Cl- from penetrating through the corrosion products to the sample surface and the pitting is controlled.