本文選題：硬質(zhì)合金　切入點：WC-Co　出處：《華南理工大學》2011年碩士論文　論文類型：學位論文

【摘要】：WC-Co硬質(zhì)合金由于具有極高硬度和在高溫下保持硬度的優(yōu)良力學性能而被廣泛應用于各種工業(yè)領域,隨著科技的發(fā)展,如何進一步提高其強韌性成為人們面臨的一大挑戰(zhàn)。為了提高硬質(zhì)合金的性能,研究者們在合金中添加晶粒長大抑制劑細化WC晶粒,制備納米結構硬質(zhì)合金。本論文首先介紹了硬質(zhì)合金的發(fā)展歷程及主要制備方法、晶粒長大抑制劑的種類及機理。隨后,在以經(jīng)介質(zhì)阻擋放電等離子體(DBDP)輔助高能球磨的添加晶粒長大抑制劑的W-C-Co復合粉體為原料,采取直接法制備硬質(zhì)合金。首先,分析添加晶粒長大抑制劑的W-C-Co復合粉體在球磨過程中的微觀形貌變化;在此基礎上研究了不同燒結工藝對WC-Co硬質(zhì)合金性能的影響,并重點研究了晶粒長大抑制劑的添加量及不同形態(tài)對硬質(zhì)合金力學性能的影響;最后對晶粒長大抑制劑的作用機理進行了初步探索。 研究發(fā)現(xiàn),DBDP輔助高能球磨對添加了晶粒長大抑制劑的W-C-Co混合粉體的作用效果不僅僅是細化單質(zhì)粉體,還使石墨包覆于W顆粒表面,粉體顆粒呈片層狀疊加。DBDP輔助高能球磨對W粉的細化效率呈現(xiàn)出先快后慢的規(guī)律,在經(jīng)過3小時球磨后,其晶粒尺寸大約為23nm。 采用不同工藝的直接法燒結制備含晶粒長大抑制劑的WC-Co硬質(zhì)合金,發(fā)現(xiàn)采用壓力燒結工藝較真空燒結制備出的硬質(zhì)合金其液相Co流動充分,不僅較好的填充了由于氣體逸出而造成的孔洞,還均勻分布于硬質(zhì)相WC之間,起到很好的粘結作用。在1340℃下加載4MPa壓力制備的WC-10Co-0.6VC硬質(zhì)合金,致密度達到99%,洛氏硬度達到HRA91.8,橫向斷裂強度TRS達到3348MPa。通過改變VC的量,可進一步改善組織,提高其力學性能。隨著VC添加量的增加,合金中WC由長條狀變?yōu)楸∑瑺?晶粒細化趨勢明顯;合金的硬度呈現(xiàn)出不斷提高的規(guī)律,而橫向斷裂強度則先升高后降低。經(jīng)綜合比較后認為,采用相同的工藝制備的添加0.9VC制得的WC-Co硬質(zhì)合金具有最佳的力學性能,其硬度達到HRA92.4,橫向斷裂強度TRS約為3600MPa。 為簡化工藝,提高經(jīng)濟性,在W-C-Co混合粉體中直接添加V_2O_5,在燒結過程中W、V_2O_5同時發(fā)生碳化反應,原位生成抑制劑。結果表明,生成的VC對WC的抑制效果更好,比直接添加VC更能抑制WC晶粒在縱向上的生長。 在透射電鏡下觀察到WC晶粒呈薄片狀(厚度小于100nm),并且在WC/WC界面上發(fā)現(xiàn)有VC的聚集。結合SEM圖片,可以認為VC主要是抑制WC晶粒在0001方向的生長。VC的加入細化了WC晶粒,WC晶粒細化,晶界增多,能有效阻礙裂紋的擴散,有利于提高硬質(zhì)合金的橫向斷裂強度;但是當VC在Co中飽和后,多余的VC會以脆性相的形式在晶界上析出,導致其橫向斷裂強度降低。
[Abstract]:WC-Co cemented carbide has been widely used in various industrial fields because of its excellent mechanical properties of extremely high hardness and keeping hardness at high temperature, with the development of science and technology. In order to improve the properties of cemented carbides, researchers added grain growth inhibitors to the alloys to refine WC grains. In this paper, the development of cemented carbides, the main preparation methods, the types and mechanisms of grain growth inhibitors are introduced. Cemented carbides were prepared by direct method from W-C-Co composite powder assisted by dielectric barrier discharge plasma (DBDP) assisted high energy ball milling with grain growth inhibitor. The microstructure changes of W-C-Co composite powders with grain growth inhibitor during ball milling were analyzed, and the effects of different sintering processes on the properties of WC-Co cemented carbides were studied. The effects of the amount of grain growth inhibitor and the different morphology on the mechanical properties of cemented carbide were studied. Finally, the mechanism of grain growth inhibitor was preliminarily explored. It is found that the effect of DBDP assisted high energy ball milling on W-C-Co mixed powder with grain growth inhibitor is not only to refine the powder, but also to make graphite coated on the surface of W particle. After 3 hours ball milling, the grain size of W powder is about 23 nm. WC-Co cemented carbides with grain growth inhibitor were sintered by direct sintering with different processes. It was found that the liquid phase Co flow of cemented carbides prepared by pressure-sintering process was more adequate than that prepared by vacuum sintering. The WC-10Co-0.6VC cemented carbide prepared at 1340 鈩，

本文編號：1562482