鎢與各種碳化物組成之3000°C高溫熔融複材研究

Fused 3000°C Super-Kelvin Composites of W and Various Carbides

莊晴凱(Chuang, Ching Kai)

指導教授 ： 陳瑞凱 ； 吳振名

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

傳統的燒結碳化物，以鐵、鈷、鎳等傳統低熔點的一般金屬與碳化物燒結而成。本實驗室的熔融碳化物，以耐火金屬及其合金，取代傳統一般金屬作為膠結相，並將碳化物強化相引進熵與元數的概念，藉以增進整體複材，在高溫以及室溫的性質。且耐火金屬熔融碳化物以熔煉為製程，除了有快速、低成本、百分之百緻密度的特性外，在極高溫領域，也能維持複材良好的機械性質。
本研究以鎢做為膠結相。強化相先以七種熔點較高，且具有高硬度及高強度的過渡金屬碳化物，分別是TiC, ZrC, HfC, VC, NbC, TaC, WC，做成七種一元膠結相對一元碳化物之鎢膠結碳化物，研究其性質。次將鎢與TiC，以不同的原子百分率做成各種配比，藉以觀察不同配比複材的機械性質與微結構。觀察到鎢佔原子百分比40 %至70 %的試片皆具應用價值。再將機械性質表現較好的試片相互添加做變量，期待除了本身的性質外，還能有固溶強化及高熵效應，結果是以TiC, NbC, TaC, WC做為強化相，互相添加的試片，有較優越的機械性質。本研究以XRD分析結構，以SEM觀察金相、以EDS及EPMA分析成分，也使用ESCA分析複材的鍵結，並測量了室溫硬度、室溫破裂韌性，再將較具代表性的試片做高溫硬度、磨耗試驗以及高溫磨耗試驗。
鎢膠結熔融碳化物有典型的熔融後凝固的樹枝晶與樹枝間晶結構，大部分同時存在鎢的一個BCC固溶體及一個因組合熵導致形成的多元金屬FCC固溶碳化物結構。含40 at.% W複材的室溫硬度範圍，可由1100 HV分佈至2200 HV，破裂韌性也由最低的6 MPa m1/2分布至最高的13 MPa m1/2，這些可透過改變W所佔的原子百分率，改變試片的硬度與破裂韌性。與氧化鋁砂輪帶在6 kgf下對磨，磨耗阻抗最高可達156 m/mm3，在適當的複材破裂韌性下，磨耗阻抗與硬度呈現正相關。已量測過的試片在1000℃高溫下硬度約分佈於800 HV至1400 HV，1100℃下則落於700 HV至1200 HV。挑選製作車刀的兩個複材，在相同的0.5 mm小進刀量輕車削條件下，切削表現略優於比較的商用超硬合金所製作的車刀; 在相同的2.5 mm與4 mm大進刀量重車削條件下，比較商用超硬合金有更好的表現。
綜合以上，本研究的材料在廣大的領域皆有發展潛力。除了可用於高功率、高溫下的車刀、磨料、鑽頭等，也可焊或鍍於其他工件上達到保護的效果，更有機會用於航太工業的引擎、隔熱板、噴嘴等高溫部位，甚至在軍事方面，也可用於砲彈或是飛彈的彈頭、裝甲、砲管等需要耐高溫及高強度的部位。

關鍵字

高溫熔融複材

並列摘要

Conventional sintered carbides (CSCs) are composed of non-refractory metal(s), Co, Ni, or Fe, and carbide(s), while the invented refractory metal fused carbides (RMFCs) in this laboratory are composed of refractory metals and their alloys (as binders) and carbides (as strengtheners) that are mixed in liquid phase and solidified, instead of sintered process. By introducing the configurational entropy in the carbides in RMFCs, the new composites have improved ambient and elevated temperature properties such as 100% relative density and good mechanical properties at super high temperatures and also have merits such as rapid speed and cost effective for manufacturing.
This study takes tungsten as the binder. Seven strengtheners utilized are TiC, ZrC, HfC, VC, NbC, TaC, and WC that are transition metal carbides of high hardness and of high strength. Seven one binder-one strengenther composites are firstly made to investigate their properties. The next are W-xTiC, where x is the mole ratios, to observe the effect of x on mechanical properties and microstructure of the fused composites (W fused carbides, WFCs). The observation results show that good mechanical properties occur for x at the interval of 30 at% ≤ x ≤ 60 at%. The third step is to increase the number of strengtheners that show better properties in the first step, and the results are composites with mixed strengtheners of TiC, NbC, TaC, and WC that have superior mechanical properties. With the assistance of XRD to investigate crystal strcture; SEM to observe microstructure; EDS and EPMA to analyze composition; and ESCA to analyze bond structure; as well as tests such as ambient temperature hardness and toughness, elevated temperature hardness, and both ambient and elevated temperature abrasion tests, the properties of tungsten fused carbides (WFCs) in this study are researched.
WFCs have the typical melted-solidified dendrite-interdendrite microstructure that has almost both a BCC solid solution of W and an FCC solid solution carbide, which is a one multimetal carbide due to the configurational entropy mixing effect. Ambient temperature hardness of WFCs that contain 40 at% W ranges from 1100 Hv to 2200 HV, while toughness at room temperature ranges from 6 MPa m1/2 to 13 MPa m1/2. Both hardness and toughness of WFCs can be adjusted by changing the x value.
The abrasion test with 6 kgf loading and ground with Al2O3 belt show a very high value of abrasion resistance of 156 m/mm3. At a proper toughness the abrasion resistance of WFCs has positive relation to their hardness. Tested speimens show 1000oC-hardness of 800 HV to 1400 HV, while they show 1100 oC-hardness of 700 HV to 1200 HV. Small depth of 0.5 mm in turning show two WFCs have tool life slightly larger than commercial WC-Co, while large depths of 2.5 mm and 4 mm show the same two WFCs have much larger tool life than the same WC-Co.
In summary, in a vast application field WFCs have great developing potential not only in high power and high temperature tool, wear resistant, and drill materials in bulky, welding, or coating form, but possibly in high temperature parts in aerospace engines, thermal insulators, sprayers and even in military applications such as high temperature parts of artilery or rocket bomb, armer, and heavy duty gun barrel.

並列關鍵字

Fused 3000°C Super-Kelvin Composites

參考文獻

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