| 摘要: | 本研究以電鍍方式將石墨烯共鍍於奈米雙晶銀鍍層，系統性探討石墨烯含量對鍍層微觀結構、機械性質與磨耗行為之影響。實驗結果顯示，當石墨烯添加濃度超過 375 ppm 且分散不良時，實際共鍍濃度反而下降。適量石墨烯雖不改變 奈米雙晶鍍層既有的奈米雙晶結構，卻能有效抑制柱狀晶粒縱向成長，使平均柱長縮短約 27%；橫向晶寬（≈ 0.40 μm）與雙晶片層間距（≈ 60 nm）則幾乎不受影響。晶粒細化與石墨烯之散佈強化相乘，使鍍層硬度提升至 2.03 GPa。
磨潤測試顯示，石墨烯共鍍奈米雙晶鍍層於「插拔磨耗」與「球-盤滑動磨耗」兩種模式下皆展現最佳抗磨性能。插拔測試中，經 130 循環後，未摻石墨烯之奈米雙晶與奈米晶摩擦力皆超過 4.0 kgf；石墨烯共鍍奈米雙晶鍍層則穩定維持約 1.8 kgf，證明石墨烯可抑制摩擦力上升與表面損傷累積。磨痕形貌亦顯示，與奈米晶鍍層常見之壓平、裂紋與局部剝離相比，石墨烯共鍍奈米雙晶鍍層僅有細微刮痕與少量移除，且下方雙晶結構大致保持完整，主因在於兩種微結構之表面能密度差異，導致的摩擦機制不同。
在球-盤滑動磨耗中，石墨烯共鍍奈米雙晶鍍層同樣展現其穩定性：奈米晶鍍層之摩擦係數迅速上升，雙晶銀與石墨烯共鍍奈米雙晶鍍層則分別穩定於 0.341 與 0.274。一般雙晶銀鍍層的磨溝寬度僅約奈米晶鍍層的一半，石墨烯共鍍進一步微幅降低磨耗係數。白光干涉檢測顯示雙晶為結構表面無明顯磨損；FIB 截面證實，磨耗後之雙晶銀微結構逐漸分化為「細化奈米晶／解雙晶／柱狀晶」三區域。計算結果指出，外部作功主要以差排能形式儲存並隨循環累積，導致區域應力堆積與再分布，使塑性變形區域逐步加深，而石墨烯的共鍍將有助於應力分散，能抑制塑性變形並使變形區域更加均勻。
綜合而言，石墨烯共鍍在不破壞奈米雙晶結構的前提下，顯著提升雙晶銀鍍層之硬度與耐磨性。經最佳化添加量後的石墨烯共鍍奈米雙晶鍍層可於高接觸應力下的反覆插拔與持續滑動條件中展現卓越抗磨能力，顯示其在電氣接點等長期耐磨應用領域具備高度潛力。
;This study incorporates graphene into electrodeposited nanotwinned silver (nt-Ag) films and systematically investigates how co-deposition affects the film’s microstructure, mechanical properties, and tribological behavior. When the nominal graphene concentration exceeds 375 ppm, poor dispersion causes the actual co-deposited amount to decrease. Properly dispersed graphene does not disturb the intrinsic nanotwinned architecture of the Ag film, yet it markedly suppresses the longitudinal growth of columnar grains, shortening the average column length by ~27 %. In contrast, the column width (~0.40 µm) and twin lamella spacing (~60 nm) remain almost unchanged. Grain refinement, combined with the dispersion-strengthening effect of graphene, raises the film hardness to 2.03 GPa.
Tribological tests demonstrate that graphene/nt-Ag composite films deliver the best wear resistance in both pin-insertion and ball-on-disk sliding modes. After 130 insertion–withdrawal cycles, the friction forces of graphene-free nt-Ag and nanocrystalline silver (nc-Ag) films peak above 4.0 kgf, whereas the graphene-containing film stabilizes at ~1.8 kgf, highlighting graphene’s ability to curb frictional escalation and surface damage. Microscale observations of the wear scars reveal that, unlike the nc-Ag film—which shows flattening, cracking, and local delamination—the graphene-modified film exhibits only fine scratches and limited spallation, with most of its underlying twin structure intact. These differences stem mainly from the distinct interfacial energy densities of the two microstructures.
In ball-on-disk tests, the superiority of the twin structure is equally clear: the coefficient of friction of nc-Ag films rises quickly, whereas nt-Ag and graphene/nt-Ag films remain steady at 0.341 and 0.274, respectively. The wear-track width on nt-Ag films is only about half that on nc-Ag films, and graphene co-deposition further enhances the wear resistance coefficient slightly. White-light interferometry shows no obvious surface damage on twin-structured films, and FIB cross-sections confirm that post-test twin structure evolves into three zones—refined nanocrystalline, detwinned, and columnar regions. Calculations indicate that the external work done during sliding is stored predominantly as dislocation energy; its accumulation with repeated cycles builds up local stress, triggers stress redistribution, and gradually deepens the plastically deformed region. Moreover, graphene co-deposition facilitates stress redistribution, suppresses plastic deformation, and renders the deformed region more uniform.
Overall, graphene co-deposition significantly enhances the hardness and wear resistance of nt-Ag films without compromising their twin structure. The optimized graphene/nt-Ag composite film exhibits outstanding anti-wear performance under repeated high-load insertion and continuous sliding, underscoring its promise for long-life electrical contacts and other demanding tribological applications. |
