磷含量对化学镀Ni-W-P合金热处理晶化及电化学行为的影响

Effects of phosphorus contents on annealing crystallization and electrochemical behavior of electroless deposited Ni-W-P coatings

用化学沉积法制备了非晶态和混晶态两种Ni-4.9%W-P合金(P含量为11.26%及5.98%)。通过XRD定量分析技术研究了P含量对镀层退火晶化的影响,获得了晶粒尺寸、晶格应变及晶化程度等显微组织特征。通过极化曲线和交流阻抗测试,并采用SEM对镀层腐蚀前后的形貌观察,分析了镀层的电化学腐蚀行为。不同处理态镀层在0.5 mol H2SO4溶液中的极化测试表明,其腐蚀形式为均匀腐蚀,腐蚀机理主要取决于P含量及热处理晶化获得的显微组织结构;在3.5%NaCl溶液中的EIS测试表明,其腐蚀行为表现为点蚀,腐蚀机理在很大程度上受到镀层缺陷的影响,尤其是镀层中存在的孔洞,孔洞的数量越多,尺寸越大,就越容易发生点蚀。

Two kinds of Ni-4. 9% W-xP （x is 11.26% and 5.98% , respectively）coatings were prepared by electroless deposited method. Effects of phosphorous content on microstructural characteristics, including degree of crystallization, grain size and lattice strain of the coatings before and after annealing treatment were investigated by a quantitative XRD analysis technology. Electrochemical corrosion behaviour of the coatings was analysed by measurements of polarization curves and electrochemical impedance spectra and observation of SEM for the coating surface morphology before and after corrosion. The polarization tests of the coatings under different heat treatment conditions in 0. 5 mol H2SO4 solution show that their corrosion is uniform corrosion. The corrosion mechanism mainly depends on phosphorous contents and microstrueture of the coatings after heat treatment. The EIS measurements of the coatings in 3.5% NaC1 solution indicate that their corrosion is pitting corrosion. The corrosion mechanism mostly affected by defects, especially the porosity in the coatings. The more the number of pores are and the larger the size is, the easier the pitting corrosion occurs.