二元及三元硼化物與碳化物 3000。C高溫熔融複材研究

Binary and Ternary Boride and Carbide 3000oC Super-Kelvin Composite

顏孝書(Yen, Hsiao Shu)

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

本研究二元及三元硼化物與碳化物3000。C高溫熔融複材，為二元及三元硼化物及碳化物，透過熔融方式，與鎢膠結形成之複材，即Binary and ternary boride-carbide 3000°C super-Kelvin fused composites。
傳統瓷金複材為Schröter在1923年提出的專利，主要為透過燒結，將鈷或鎳金屬與WC, TiC與TaC等碳化物結合，形成兼具碳化物高硬度及鈷鎳金屬高韌性之複材，但其液相燒結製程有致命的缺點，即緻密度不足，造成cememted carbides在機械性質以及其他性質，沒有預期的優越。本研究將膠結金屬改為耐火金屬鎢，同時加入過渡金屬硼化物及碳化物，以熔煉為製程，提升緻密度，並創造同時兼具高硬度、高熔點、與高韌性的膠結複材，研究系統分別在只存在碳化物時、與同時存在硼化物與碳化物時，機械性質及微結構的變化，其中，硼化物，選擇價格較低，且熔點硬度較高的TiB2與ZrB2，碳化物則選擇TiC, ZrC, NbC, TaC, WC, HfC與VC，透過各種組合與配比，探討複材硬度、韌性、耐磨耗、腐蝕、高溫硬度、與車削等性質。
本研究高溫熔融複材為典型複合樹枝晶及樹枝間晶凝固型態的結構，整體硬度介於1200至2300 HV之間，KIC韌性介於6至13 MPa m1/2之間。在一元碳化物添加一元硼化物(TiB2或ZrB2)的系統中，碳化物為ZrC與HfC的複材，比其他碳化物的複材，硬度明顯降低，並且韌性提升。一元碳化物添加ZrB2的複材硬度，比背景複材(即單純碳化物複材)的硬度，皆大幅提升。以氧化鋁砂輪帶，進行磨耗測試，加以六公斤荷重與試片對磨，其磨耗阻抗可高達95.6 m/mm3，已接近商用WC-Co試片之120 m/mm3，並觀察到，複材磨耗阻抗與複材硬度呈正相關，也與適當韌性有一定的相關性。本研究複材在1100°C下，仍有800 HV至1300 HV的硬度，可看出其優勢有二：(1)隨著溫度上升，硬度下降的比例，較商用之膠結碳化物小。(2)此系統在高溫下的硬度，明顯高於商用之膠結碳化物。本研究複材因高溫硬度表現良好，而有優良的重車削表現。本研究複材在仿海水腐蝕試驗中，呈現優良抗蝕能力。
綜合以上，本研究之高溫熔融瓷金複材，適用於需要高溫下同時具備高硬度與高韌性的環境，像是超高速車削刀具與硬面焊材，如軋輥等之應用。

關鍵字

熔融複合材料

並列摘要

In this study binary and ternary boride-carbide 3000°C-super-Kelvin fused composites are tungsten-cemented fused boride(s)-carbide(s) with solidus temperatures being higher than 3000°C.
Conventional cermets, sintered WC, TiC and TaC cemented mainly with Co or Ni, were patented by Schröter in 1923. Although these composites possess high hardness of carbides and high toughness of Co and Ni, they have a serious defect of low relative density and, consequently, have no predicted superior mechanical and other related properties due to (liquid phase) sintering. In order to improve high melting point of composites, this study uses tungsten as a binder to cement transition metal carbide(s) and boride(s) and adopts melting process to provide 100% relative density. The effect of presence of merely carbide(s) and presence of both carbide(s) and boride(s) on mechanical properties and microstructure is thus investigated. Choice of TiB2 and ZrB2 is due to their relative inexpensive cost and high melting points, while for carbides are TiC, ZrC, NbC, TaC, WC, HfC and VC by considering their high hardness and high melting points. By means of various combinations as well as compositions of carbide(s) and boride(s), this study investigates hardness of composites at both ambient and elevated temperatures up to 1100oC, and toughness, wear, corrosion, and machinability of composites at ambient temperature.
Super Kelvin fused composites in this study are typically a solidified structure of dendrite-interdendrite type. At ambient temperature these composites possess hardness of 1200 HV to 2300 HV and KIC toughness ranging from 6 MPa m1/2 to 13 MPa m1/2. In one carbide-one boride (TiB2 or ZrB2) composites, the hardness of the composites of ZrC or HfC has significantly lower value than that of the other carbides, while their toughness obviously has higher value than that of the other carbides. In ZrB2 composites of various carbides, the hardness of the composites with ZrB2 is higher than that of the background composites without ZrB2. In the pin-on-belt abrasive wear test with 6 kg loading on the counterpart Al2O3 belt, the wear resistance reaches 95.6 m/mm3, as compared with the value of a commercial hardmetal WC-Co of 120 m/mm3. Another conclusion of this test is that the wear resistance is closely related to the hardness of the composites as well as to their toughness. The hardness of the composites at 1100oC still has value ranging from 800 HV to 1300 HV. These composites have the following two merits over commercial WC-Co; i.e., (1) their lowering temperature coefficient in hardness is lower than that of commercial WC-Co; (2) their elevated temperature hardness is obviously higher than that of commercial WC-Co. With high hardness at elevated temperature, their performance in heavy duty turning machining is thus extraordinarily better than that of commercial WC-Co. Their anticorrosion behavior in 3.5 wt% NaCl artificial sea water linear potentiodynamic polarization test shows a better result than that of commercial WC-Co.
In conclusion, these high temperature fused cermets are suitable for high-temperature environments that require both high hardness and high toughness, such as super high speed machining tools and hard facing applications in repairing rolling rolls.

並列關鍵字

fused composite

參考文獻

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