材料期刊网

为了优化脉冲电镀镍工艺,采用扫描电子显微镜、X射线衍射仪和显微硬度仪研究了脉宽、脉间、蜂电流密度对镀层的晶粒尺寸、表面形貌、晶体取向和硬度的影响.结果表明,保持峰电流密度和脉间不变,镀层的晶粒尺寸随着脉宽的增加先减小后增加.当脉宽由0.1 ms增至8 ms,晶体取向由(111)织构向(200)织构转变.保持峰电流密度和脉宽不变,当脉间的增加,晶粒尺寸增大,但晶体的取向不变.增加峰电流密度能够显著降低镀层的晶粒尺寸.当峰电流密度由0.2 A/cm~2增至2.0 A/cm~2,晶体取向由随机态向强的(200)织构转变.镀层的硬度与镀层的晶粒尺寸有关,晶粒尺寸较大时,服从Hall-Petch关系,晶粒尺寸较小时,产生纳米效应,反Hall-Petch关系.因此,脉宽、脉间、蜂电流密度均能显著影响镀层的显微硬度.

To optimize the nickel pulse plating process, the scanning electron microscope, X-ray diffraction and microhardness tester were used to determine the influence of pulse on-time, pulse off-time and peak cur-rent density on the grain size, surface morphology, crystal orientation and microhardness of the nickel electro-deposits. The study shows that at constant off-time and peak current density, the crystal size of the deposits in-itially decreases and then starts to increase with the increasing pulse on-time. The crystal oridntation progres-sively changes from a (111) texture at the on-time of 0. 1 ms to a strong (200) texture at the on-time of 8 ms.The increase of pulse off-time at the constant on-time and peak current density results in a progressive increase in crystal size, while the crystal orientation remains unaffected. The increase of peak current density results in considerable refinement in crystal size of the deposits. The crystal orientation progressively changes from an al-most random distribution at the lowest peak current density of 0. 2 A/cm~2 to a strong (200) texture at the peak current density of 2.0 A/cm~2. The microhardness of deposits is related with grain size. When the grain size is large, the microhardness is consistent with Hall-Petch law (HPL). When the grain size is ultrafine, nano-effect will be generated, and the microhardness is against HPL. Therefore, pulse on-time, pulse off-time and peak current density have distinct influence on microhardness of the deposits.