| 摘要: | 本研究係以二硫化鉬為核心，以無電鍍法將鎳包覆於二硫化鉬外部，製備鎳-二硫化鉬粉末，並配合高速燃氣熔射在1020低碳鋼基材上進行鎳-二硫化鉬熔射塗層製備，透過各種材料檢測技術 (如SEM/EDS、ICP-AES、XRD、硬度值及附著力等) 進行鎳-二硫化鉬複合粉末及熔射塗層之外觀、結構、成分、硬度、附著力等材料性質探討。並依據ASTM G99規範，於乾摩擦情況下以球-圓盤磨耗實驗來進行鎳-二硫化鉬熔射塗層耐磨性能評估。
實驗結果證明本法確實可製備以鎳為基底、二硫化鉬為分散相之鎳-二硫化鉬熔射塗層，且其磨耗機理係由二硫化鉬作為固體潤滑劑，屬低摩擦複合塗層；惟熔射過程中產生高溫，部分二硫化鉬燒失，以致鎳-二硫化鉬熔射塗層中二硫化鉬含量降低。依據磨耗試驗Ⅰ結果分析，在低負荷下 (< 15 N) ，鎳-二硫化鉬熔射塗層重量損失甚微，隨著負荷增加 (> 30 N) ，鎳-二硫化鉬熔射塗層的重量損失則快速增加。另比較純鎳熔射塗層與鎳-二硫化鉬熔射塗層之平均磨耗率，純鎳較鎳-二硫化鉬熔射塗層高出40倍，顯示添加二硫化鉬之鎳-二硫化鉬熔射塗層耐磨性顯著提升。
另為研究鎳-二硫化鉬熔射塗層歷經高溫環境後之材料性質與減摩性能，在完成鎳-二硫化鉬熔射塗層後，將鎳-二硫化鉬熔射塗層試片置入數位溫控高溫爐，完成不同熱處理溫度製程後，執行磨耗實驗。結果顯示，鎳-二硫化鉬熔射塗層熱處理達500°C時，二硫化鉬氧化生成二氧化鉬晶體，且晶體生長係經汽化-冷凝機制，先從鎳-二硫化鉬熔射塗層內部汽化後在外部凝結生長出二氧化鉬晶體。此過程造成鎳-二硫化鉬熔射塗層孔隙率增大，結構趨於鬆散，導致大大降低鎳-二硫化鉬熔射塗層的硬度、結合強度與增加鎳-二硫化鉬熔射塗層的耐磨耗量，故高溫操作溫度應避免超過500°C。;In this study, the wear resistance of thermally sprayed Ni-MoS2 composite coatings on an AISI 1020 steel substrate was investigated. Ni-MoS2 composite powder (size: 60-90 μm) containing 25 wt.% of dispersed MoS2 was prepared by electroless plating. Ni-MoS2 composite coatings were then prepared by HVOF thermal spraying. The coatings were characterized by structural, surface morphologies and compositional analyses by means of microhardness tests, SEM/EDS, XRD, and ICP-AES. For the evaluation of their anti-wear properties, the composites were subjected to ball-on-disk dry wear tests based on the ASTM G99 standard at room temperature.
Experimental results showed that some of the MoS2 content dispersed in the Ni-based composite coating burnt away during the high-temperature spraying process, thereby reducing the MoS2 concentration in the coating. In the wear test, the weight loss in the Ni-MoS2 composite coating was minimal under a low load (< 15 N) but increased rapidly with increasing load (> 30 N). The average wear rate of the coatings was found to be ~1/40 times that of a pure Ni coating, showing that the wear resistance of the composite coatings was significantly improved by MoS2 addition.
The coatings were then subjected to heat treatments. Various surface inspection techniques including hardness test, scanning electron microscopy, and X-ray fluorescence were then used to characterize the composition and mechanical properties of the composite HVOF coating. In addition, ball-on-disc tests were carried out under dry abrasive conditions, on specimens that were heat treated at different temperatures, according to the ASTM G99 standard. The wear of each specimen was observed and recorded, and the measurements were used to provide a comprehensive assessment of the coating’s wear resistance. When the Ni-MoS2 composite coating was heat treated at 500°C, the growth of MoO2 crystals evaporates from the inward, and condenses as the protruding oxide crystals on the surface, which led to an increase in porosity and structural looseness. Consequently, the hardness and structural strength of the coating decreased significantly, which dramatically decrease its wear resistance. |
