Microstructure and Properties of Nickel Layers Electrodeposited under Reduced Pressure and Temperature Gradient Conditions

摘要:

前期研究表明，在5 kPa恒负压和35 ℃/65 ℃温度梯度和无添加剂的条件下，能以高达1 mm/h的沉积速度制备出表面光滑、近无沉积缺陷且多项性能优越的镍镀层。本实验则重点研究负压、温度梯度等条件参数对镍沉积层形貌、织构和性能的影响。研究结果显示：负压和温度梯度大小对沉积层的形貌、织构与硬度、耐腐蚀等性能都有一定程度的影响；只有在贴近阴极面的液层处于沸腾状态时才能获得良好的镍沉积层；增大温度梯度和（或）降低沉积槽气压都有利于细化晶粒、提高硬度和耐酸腐蚀性；温度梯度对镍沉积层的织构特征影响作用明显，但负压大小对镍层的择优取向几乎没有影响。镍沉积层上述形貌、织构与性能的变化主要归结于负压电沉积的沸腾驱动传质效应与真空脱气效应

Abstract:

Our previous studies showed that at a considerably high plating speed up to 1 mm/h, the nickel electrodeposits with smooth surface, few deposition defects and some improved properties could be prepared under the conditions of an additive-free bath at a reduced pressure of 5 kPa and a temperature gradient of 35 °C /65 °C. This paper aims at further analyzing the effect of bath pressure and temperature gradient on the surface morphology, the microstructure and the properties of electrodeposited nickel coatings in a subatmospheric environment. Our findings indicate that the surface quality, the microstructure and the properties of the deposited nickel coatings are, to some extent, affected by the applied bath pressure and the temperature gradient; favorable nickel electrodeposits can be only achieved when the electrolyte in the vicinity of cathode surface is in a boiling state. The temperature gradient influences the texture characteristic of nickel deposits, but the bath pressure has few effects on the preferred orientation. Grain-fining, microhardness, and corrosion resistance of nickel deposits are improved with increasing of the temperature-gradient and/or the reducing of bath pressure. These variations are closely relevant with the boiling-driven mass transfer effect and the vacuum-degassing effect during the electrodeposition in a reduced pressure bath.