二元至六元碳化物與耐火金屬組成之 3000°C超高溫熔融複材研究

Fused 3000°C Super-Kelvin Composites of Binary to Senary Carbides with Refractory Metals

曾淯澤(Tseng, Yu Tse)

指導教授 ： 吳振名 ； 陳瑞凱

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

本研究碳化物與耐火金屬超高溫熔融複材，係碳化物與耐火金屬，透過真空電弧熔煉，液態膠結、凝固而成的複材，故稱為 Refractory Metal Fused Carbides。與傳統藉鈷或鎳金屬之液相，燒結而成的不具高熔點的碳化物相比，本研究新型塊狀複材，能夠同時兼具高熔點、高硬度及高韌性的特性。
本研究使用耐火金屬鉬、鎢、鉭、錸與過渡金屬格隙型碳化物TiC, ZrC, HfC, VC, NbC, TaC, WC，以不同的比例，調配出多種含一至二元耐火金屬，與含ㄧ至四元碳化物所組成的複材，探討其室溫硬度、高溫硬度、韌性、耐磨耗、耐蝕、電阻率等性質，並佐以SEM、XRD、EPMA等儀器分析，以期此複材有優良的表現。
本研究複材為典型熔融後凝固之樹枝晶與樹枝間晶結構。整體室溫硬度落在800至2100 HV；室溫破裂韌性落在2.7至15.2 MPa m1/2。
為了要瞭解各碳化物對此複材的影響，先以鉬作為膠結相，分別結合上述的碳化物，觀察到由TiC, ZrC, HfC三者分別組成的複材，有MC相的生成；而含VC, WC者促進M2C相的產生；含NbC, TaC者使MC與 M2C相同時出現；而在一系列同時具有MC與 M2C的試片，可觀察到複材較能兼顧硬度與韌性；而若以Re為膠結相，在與W進行變量時，會有硬且脆的介金屬相Re3W出現，使整體硬度快速提升，韌性明顯下降；以Ta為膠結相時，會有雙晶形貌出現在微結構上，隨著W添加量的上升，雙晶才消失。
以氧化鋁砂輪帶，六公斤荷重，進行Pin-On-Belt磨耗試驗，在相近的硬度與韌性下，膠結相為純鉬基的試片，較純鎢基的為差，僅約其50 %，因此將膠結相進行鉬與鎢二元添加，使其能夠提供更多的強度， 相同的方式也應用於Re基及Ta基系列複材。
本研究複材在無切削液的重車削中，表現較商用WC-Co優異，這凸顯了本研究複材在高溫環境下使用更具優勢。在仿海水的環境下，抗蝕能力也較商用WC-Co優秀。1100oC高溫硬度落在680至1200 HV，較商用超硬合金優秀，值得注意的是本研究熔融複材塊材緻密度為100%。
本研究耐火金屬膠結熔融碳化物複材較傳統商用燒結瓷金，在高溫使用環境下具有更佳的機械性質；可應用於水泥工業與金屬工業之軋輥的硬面焊材、反應爐耐高溫部件、火箭或噴射引擎之耐火材料；除此之外，亦可針對不同的使用需求進行成分調配，在應用上具有更佳的彈性。

關鍵字

碳化物與耐火金屬高溫熔融複材

並列摘要

Super high temperature fused carbide-refractory metal composites in this study are arc-melted carbides and refractory metals (RMs) together and are solidified to form the so-called “refractory metal fused carbides” (RMFCs). Compared with the conventional liquid phase sintered carbides that possess lower melting point such as in the component Co or Ni, bulk RMFCs have the properties of high solidus temperature, high hardness, and high toughness.
This study adopts refractory metals, such as Mo, W, Ta, and Re, and transition metal interstitial carbides, such as TiC, ZrC, HfC, VC, NbC, TaC, and WC to form RMFCs of one to two RMs and one to four carbides with different proportions and to investigate ambient- and elevated-temperature hardness, toughness, wear resistance, corrosion resistance, and electrical resistivity. By the assistant analyses of SEM, XRD, and EPMA, RMFCs are hoped to have excellent properties in elevated temperature hardness, toughness, wear resistance, and corrosion resistance.
Microstructure of RMFCs is a typical melted and solidified dendrite-interdendrite structure. Their ambient hardness and toughness fall in between 800 HV to 2100 HV and 2.7 MPa m1/2 to 15.2 MPa m1/2, respectively.
In order to understand the effect of the individual presence of various carbides on RMFCs, this study firstly uses Mo as a binder. It is observed that Mo-TiC, Mo-ZrC, and Mo-HfC have appearance of MC; Mo-VC and Mo-WC appearance of M2C; and Mo-NbC and Mo-TaC appearance of both MC and M2C. Another important conclusion is that there is a good combination of hardness and toughness in duplex MC-M2C-containing Mo-NbC and Mo-TaC. When both Re and W are used as binders, there is an intermetallic Re3W that results in rapid increase in hardness and obviously decrease in toughness of the composites. When both Ta and W are binders, twin morphology appears in microstructure till the content of W being higher. The pin-on-belt abrasion test of 6 kg loading with Al2O3 belt shows that with nearly the same hardness and toughness W-cardide composites have two times of abrasion resistance higher than that of Mo-cardide composites. Thus both W and Mo are used to supply more strength and hardness of RMFCs. The study in the cases of Re- and Ta-containing composite systems is in the same way as in the case of Mo-bearing system.
In dry and heavy turning test the composites in this study is much better than commercial WC-Co. This result significantly appears the superior property in turning at high temperatures. The corrosion resistance of the composites in 3.5 wt% NaCl sea water like aqueous solution is also superior to that of commercial WC-Co. Hardness at 1100oC in RMFCs falls in between 680 HV and 1200 HV; it is better than that of conventional hardmetals. Note that the relative density of bulk RMFCs is 100%.
RMFCs have better elevated temperature mechanical properties than the conventional sintered hardmetals. This makes it suitable for applications in cement and metal industries for hardfacing rolls, high temperature parts in reactors, and refractory materials of rockets and turbine engines. Note that the degrees of freedom in designing RMFCs for different applications are also large.

並列關鍵字

Fused Super-Kelvin Composites of Binary to Senary Carbides with Refractory Metals

參考文獻

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