以真空燒結和熱均壓製程改善15 wt%鎳鐵基及15 wt%鈷基碳化鎢合金之腐蝕行為與機械性質

Improvement of the Corrosion Behavior and Mechanical Properties of the WC-15 wt% (Ni, Fe) and WC-15 wt% Co alloys via Vacuum Sintering and HIP Processes

陳松嶺(Song-Ling Chen)

指導教授 ： 張世賢

國立臺北科技大學/工程學院/材料科學與工程研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00295

摘要

碳化鎢複合材料因具優越的機械性質、切削性能及耐磨耗能力，在工業界上常被應用於需要在嚴苛條件下操作的機械工具、鑽鑿工具和耐磨耗零件上。但作為傳統硬質合金的主要黏結劑Co，因其資源短缺且價格昂貴，故尋找Co的替代用品具有重要意義。鈷是現已發現中多數碳化鎢應用的最佳黏結劑金屬，而其他的鐵系金屬(鎳鐵基碳化鎢，鎳和鐵)，則在需要熱硬度、抗熱龜裂或抗腐蝕/抗氧化的特殊場合使用。這類超硬合金因熔點高，大多採用粉末冶金製造，此外；熱均壓技術為一種同時結合了高溫與高壓的熱處理方式，並已被廣泛應用於粉末冶金工業上，以去除工件內部的封閉孔隙與缺陷，來改善材料的機械及物理性質。
本研究主要運用不同的燒結溫度(1250°C, 1300°C, 1350°C及1400°C)，以尋求鈷基(WC-Co)和鎳鐵基碳化鎢合金(WC-Ni, Fe)最佳的燒結溫度。此外，將更進一步比較兩種不同黏結劑(WC-Ni, Fe與WC-Co)對碳化鎢硬質合金性質的差異；試片的製作是利用粉末冶金真空燒結方式，結合熱均壓(1250°C, 100 min, 175 and 120 MPa)製程，析出相的顯微結構微分析是利用SEM、XRD與EDS等技術。另一方面，並以硬度測試和抗彎強度(TRS)量測機械性質，腐蝕電位分析作為耐腐蝕性測試，以及材料破裂韌性(K1C)等，來評估真空燒結及熱均壓製程對於商用製造WC-Ni, Fe硬質合金之可行性。
實驗結果顯示，Ni, Fe基及Co基碳化鎢展現良好之液相燒結，試片幾乎不具孔隙，並表現出優良之機械性質。Ni, Fe基碳化鎢經燒結溫度1400°C，與Co基碳化鎢經燒結溫度1350°C與1400°C燒結1小時之後，其相對密度可達98%，硬度分別達到HRA 84與85以上，而抗折強度分別為2524 MPa與2471 MPa。此外，在抗腐蝕試驗方面，WC-Ni, Fe合金經1400°C燒結後，具有最低之腐蝕電流為1.1111 × 10-5 A，與最高之極化電阻2464.6 Ω•cm2；同時在K1C方面，可以提高至15.1 MPam1/2，此結果顯示WC-Ni, Fe合金具有較佳之耐腐蝕性及電性。

關鍵字

鎳鐵基碳化鎢 ； 熱均壓 ； 真空燒結 ； 腐蝕電位 ； 破裂韌性

並列摘要

Tungsten carbide composites are widely are used in industry for machining tools, mining tools and wear-resistant parts requiring superior mechanical properties, cutting performance and wear-resistant abilities. As the main binder of conventional cemented carbides, Co is rare in storage and expensive; thus, it has made sense to look for a substitute. While cobalt has been found to be the optimal binder metal for most applications, other iron group metals (Ni-Fe based WC, nickel and iron) are employed to a limited extent for specialized applications, e.g., where hot hardness and resistance against thermal cracking or corrosion/oxidation resistance are required. Due to their high melting point, these hard metals are mostly manufactured by the power metallurgy method. In addition, the hot isostatic pressing (HIP) technique is a heat treatment method which combines high temperature and high pressure. Recently, the HIP technique has been widely used in the power metallurgy industry to eliminate the isolated pores and defects on the inside of work-pieces, thus improving the mechanical and physical properties of materials.
In the present research, different sintering temperatures (1250°C, 1300°C, 1350°C and 1400°C) were explored in order to find the optimal parameters of WC-Co and WC-Ni, Fe sintered materials, as well as to compare the different properties of two binders (WC-Ni, Fe and WC-Co) for WC materials. The specimens were fabricated using the vacuum sintering of the powder metallurgy technique combined with the HIP process (1250°C, 100 min, 175 and 120 MPa). The precipitate phases presented in the microstructures were analyzed using SEM, XRD and EDS techniques. In addition, the hardness test and transverse rupture strength (TRS) were used for the mechanical property test, the corrosion potential analysis for the corrosion test and the K1C test for the fracture toughness. Finally, the feasibility of commercial manufacturing WC-Ni, Fe cement carbides via the vacuum sintering and HIP processes was evaluated.
The experimental results showed the WC-Ni, Fe and WC-Co specimens to have good liquid-phase sintering and lower properties, and thus exhibit excellent mechanical properties. The optimal vacuum sintering temperatures of WC-Ni, Fe and WC-Co alloys were 1400°C and 1350°C for 1 h, respectively. The relative density reached 98% and 98.28%, the hardness was over HRA 84 and 85, and the TRS increased to 2524 and 2471 MPa. In addition, the corrosion resistance test results also showed that the 1400°C sintered WC-Ni, Fe alloy had the lowest corrosion current of 1.1111 × 10-5 A and the highest polarization resistance of 2464.6 Ω•cm2 in the 0.15 M HCl solution. Meanwhile, the value of K1C increased to 15.1 MPam1/2. These results showed that the WC-Ni, Fe alloy had the optimal corrosion resistance and electrical properties.

並列關鍵字

Ni-Fe based WC ； HIP ； Vacuum Sintering ； Corrosion Potential ； K1C

參考文獻

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