鎳鎢合金電鍍

Abstract

鎳鎢合金鍍層具有高硬度、耐磨耗的優良機械性質使其為一替代六價硬鉻製程的潛力材料，本文討論了鎳鎢電解液中各個成分的功用以及鎳鎢合金的共鍍機構，同時探討了鍍液pH值對於鍍層鎢含量以及鍍層性質的影響。藉由脈衝和脈衝反轉電流的引入，能夠調整鍍層內應力，特別是脈衝反轉電流能夠大大地降低鍍層內應力，鍍出高品質無裂紋的鍍層，而脈衝反轉電流的增加使得鍍層鎢含量下降，鍍層結晶性變好，晶粒變大，透過脈衝電源和pH值的調整，便能有效控制鍍層鎢含量及晶粒大小。 在熱處理之後，奈米結晶的鎳鎢合金強度能夠再度提升，但過高的退火溫度將使得再結晶與晶粒成長發生，導致鍍層硬度下降，透過適當的熱處理溫度和熱處理時間，能夠有效提升鍍層硬度，而其退火之後的強化現象則和晶界結構的改變以及材料塑性變形機構的轉變有關。除此之外，在脈衝電鍍之後施以直流電電鍍能夠改善鍍層表面平整性，但是鍍層抗蝕性則因為鎢金屬的活性效應並不能同時提升。

Ni-W alloy electrodeposits are being chosen as the candidate of the replacement of hard chromium due to its good mechanical properties such as high hardness and wear resistance. The effect of electrolyte composition and the co-deposition mechanism are discussed first, and then the effect of pH on the microstructure and W content of the deposit has been studied. By additional adjustment of current form, stress measurement experiments shows that pulse and reverse pulse currents reduce the internal stress of the deposit, especially the reversed pulse current; thus, low internal stress and crack-free Ni-W layers are synthesized. However, the tungsten content decreases with increasing reverse pulse current; meanwhile, the crystallinity and surface morphology of the deposit change. In general, the grain size of the deposit increases with decreasing W content. Through the adjustment of pH value and reverse pulse current, the grain size and W content can be controlled. The hardness of Ni-W electrodeposits increases after heat treatment at mild temperatures, but decreases after high-temperature treatment. This decrease is due to recrystallization and grain growth. Consequently, the Ni-W layers are strengthened after proper heat treatments, which lead to the change in grain boundary structure and plastic deformation mechanisms. DC current plating on top of the reverse pulse plated deposit reduces the surface roughness due to pre-existing irregularities on the surface. However, the resultant corrosion properties show insignificant improvement because of the active W element in the deposit.