电沉积Ni-Mo镀层不同温度退火前后微观组织与力学性能研究

Investigation of Microstructure and Mechanical Properties of Electrodeposited Ni-Mo Films Before and After Annealing at Different Temperature

目的提高Ni基镀层的高温热稳定性与硬度。方法在酸性条件下,通过直流电沉积的方式,在黄铜基体表面制备不同Mo含量的Ni-Mo镀层,研究不同浓度的二水钼酸钠(20、40、60 g/L)以及不同温度的退火处理(300、400、500℃)对Ni-Mo镀层微观组织及硬度的影响规律。通过XRD、SEM、EDS以及纳米压痕仪等设备对镀层的微观组织与性能进行表征。结果随着镀液中钼酸钠含量的增加,镀层中Mo含量也会逐渐提高,晶粒尺寸减小,结晶度下降。随着退火温度的提高,晶粒尺寸增大,镀层开始从非晶态向晶态转变。同时物相分析表明,镀层中Ni、Mo是以固溶体的形式存在,起到了固溶强化的作用,增加了材料的硬度。通过纳米压痕试验,发现镀层的硬度随着钼含量的增加而提高。Mo含量较低时,镀层硬度随着退火温度的升高而降低;Mo含量较高时,镀层硬度随着退火温度的升高出现先升高后降低;但两种情况下镀层的硬度均远高于基体铜片。结论与沉积态相比,经300℃退火处理后,Ni-Mo镀层硬度未呈现显著变化;500℃退火处理后,镀层硬度则有所降低。因此,Mo元素的加入可以提高Ni基镀层的热稳定性与力学性能。

The work aims to improve the thermal stability and hardness of Ni based coating.Ni-Mo coatings with different Mo content were prepared on the surface of brass substrate by direct current electrodeposition under acid condition.The influences of different concentrations of sodium molybdate dihydrate(20,40,60 g/L)and different annealing treatment(300,400,500℃)on the microstructure and hardness of Ni-Mo coating were investigated.The microstructure and properties of the coatings were characterized by XRD,SEM,EDS and nano-indentation tester.With the increment of the contents of sodium molybdate,the contents of Mo in the coating increased gradually and the grain size was refined with the reduction of crystallinity.Upon post annealing at elevated temperature,the grain sizes of Ni-Mo coatings were coarsened and the phases were transformed from amorphous to crystalline.Meanwhile,the XRD results showed that Mo elements were dissolved in Ni matrix in the form of Ni(Mo)solid solution,presenting solution strengthening in the coatings with the increment of Mo contents.In addition,the hardness of the coating was reduced with the increase of annealing temperature,while hardness of the coating was enhanced first and then dropped at higher Mo contents.However,the hardness of the coating in both situations was far higher than that of the copper matrix.Compared with as-deposited samples,the hardness of Ni-Mo coatings changed slightly upon annealing at 300℃,and reduced significantly at 500℃.Thus,it is concluded that the addition of Mo can improve the thermal stability and mechanical properties of Ni-based coatings.