Cr颗粒尺寸对Ni-Cr复合镀层750℃热腐蚀性能影响

Effect of Cr particle size on hot corrosion resistance of co-deposited Ni-Cr composite coatings at 750 ℃

采用复合电镀技术,通过向普通电镀溶液中分别加入平均粒度为40 nm和1-5μm的Cr粉的方法在Ni基材上制备了一种金属Ni基纳米Cr粒子弥散的Ni-Cr纳米复合镀层和一种微米Cr粒子弥散的Ni-Cr复合镀层。混合盐（75 wt%Na2SO4＋25wt%NaCl）750℃热腐蚀行为结果表明：与微米Cr粒子弥散的Ni-12.4 wt%Cr复合镀层相比,Ni-11wt%Cr纳米复合镀层表现出更好的耐腐蚀性能。SEM/EDAX、XRD和TEM分析表明,在相同的Cr颗粒含量条件下,Cr颗粒尺寸的降低提高了Ni-Cr复合镀层的抗腐蚀性能,这是因为Cr颗粒尺寸的降低和基体Ni晶粒的细化增加了单位面积内的Cr2O3形核率,缩短不同Cr2O3核间的距离,与此同时基体Ni晶粒的细化有利于保护性氧化物形成元素Cr沿晶界向腐蚀前沿的快速扩散,从而加速了保护性Cr2O3膜的快速形成。

Ni-Cr composite coatings with Cr nanoparticles（termed as ENCCs Ni-Cr） and Cr microparticles（termed as EMCCs Ni-Cr） were developed by co-electrodeposition in nickel plating bath with different contents of Cr particles in average size of 40 nm and 1～5 μm,respectively.The hot-corrosion behavior of ENCC Ni-11wt% Cr and EMCC Ni-12.4 wt% Cr coatings in the salt of 75 wt% Na2SO4 and 25 wt%NaCl at 750 ℃ was studied.The results show that the ENCC Ni-11wt% Cr coating exhibits superior corrosion resistance compared to the EMCC Ni-12.4 wt%Cr coating.SEM/EDAX,XRD and TEM results indicate that at a given Cr particles content,the finer of the co-deposited Cr particles,the better of the hot corrosion performance.The effect is ascribed to the fast formation of a continuous chrome film on the ENCCs Ni-Cr coating.This is due to that the large amount of grain boundares and interface of chromium nanopaticles and nickel matrix is favourable for nucleation of chrome and fast linking of the chrome nuclei as a result of enhanced diffusion of Cr along grain boundaries.