【摘要】：金剛石是自然界中最硬的材料。由于其優(yōu)異的力學(xué)性質(zhì),而被廣泛應(yīng)用在工業(yè)加工、航空航天、地質(zhì)勘探、國防建設(shè)等領(lǐng)域。由于金剛石單晶具有各向異性和較高的脆性,在受到外力沖擊時容易沿(111)解理面解離,從而限制了單晶金剛石在自身加工和抗沖擊等方面的應(yīng)用。納米聚晶金剛石(NPD)具備優(yōu)于天然金剛石的各向同性、良好的韌性、耐磨性和熱穩(wěn)定性等,以及硬度不低于天然金剛石,具有更廣闊的的應(yīng)用空間。無添加劑石墨在高溫高壓下直接轉(zhuǎn)變?yōu)榧{米聚晶金剛石是獲得優(yōu)異力學(xué)性質(zhì)NPD的最理想的途徑。然而,利用石墨直接合成NPD需要極高的壓力和溫度,在較低的溫度和壓力下,石墨只能部分轉(zhuǎn)化為金剛石。此外,制備NPD的前驅(qū)物中,包括玻璃碳、洋蔥碳、炭黑、石墨等,以石墨為前驅(qū)物制備出的NPD所需要的條件最為苛刻,但制備出的NPD硬度最高,并且具有較高的斷裂韌性和高溫抗氧化性。因此,制備優(yōu)質(zhì)的納米石墨前驅(qū)物、探索由石墨直接轉(zhuǎn)化成NPD的實(shí)驗(yàn)條件及其機(jī)理,不僅優(yōu)化合成條件使其能在工業(yè)化生產(chǎn)具有重要的意義,而且對研究石墨與金剛石的相變路徑具備重要的科學(xué)意義。為了研究納米聚晶金剛石的合成,本論文首先對國產(chǎn)六面頂液壓機(jī)高壓裝置和Walker型六-八壓機(jī)的樣品腔體進(jìn)行壓力和溫度的標(biāo)定,并設(shè)計出一套適用于國產(chǎn)六面頂高壓裝置的高壓樣品腔體高溫組裝,溫度可達(dá)2000℃以上,提高了六面頂合成腔極端條件下的穩(wěn)定性能;確定了國產(chǎn)六面頂和Walker型六-八壓機(jī)系統(tǒng)油壓與合成樣品腔壓力之間的關(guān)系,獲得了油壓與實(shí)際腔體壓力的曲線關(guān)系;標(biāo)定了六-八壓機(jī)高壓樣品腔的溫度。為后續(xù)實(shí)驗(yàn)的進(jìn)行提供了壓力和溫度的參考依據(jù)。利用高能球磨制備出納米石墨粉,作為合成納米聚晶金剛石的前驅(qū)物,得到了不同的球磨條件與納米石墨粉粒徑之間的關(guān)系。利用得到的納米石墨粉,在六-八高壓裝置中,高溫高壓合成方法在18 GPa,2100℃到2300℃之間實(shí)現(xiàn)了石墨到金剛石的轉(zhuǎn)變,合成出了納米聚晶金剛石體材料。樣品微區(qū)XRD測試結(jié)果顯示:高溫高壓下,前驅(qū)物燒結(jié)后的樣品在2100℃和2300℃均合成出了立方相的金剛石;前驅(qū)物未燒結(jié)的樣品,雖有立方相金剛石的產(chǎn)生但是XRD測試結(jié)果表明樣品轉(zhuǎn)化不完全。拉曼測試結(jié)果表明樣品中在1330 cm-1處均有拉曼峰,為金剛石一階拉曼譜線。通過掃描電鏡分析結(jié)果顯示合成出的納米金剛石的顆粒在15 nm左右,維氏硬度儀測量結(jié)果表明前驅(qū)物燒結(jié)過的樣品維氏硬度高達(dá)140GPa。這一結(jié)果大于單晶金剛石最大值(120 GPa)近17%。這一結(jié)果再次證實(shí),NPD是一種性能優(yōu)異的超硬材料。
[Abstract]:Diamond is the hardest material in nature. Because of its excellent mechanical properties, it has been widely used in industrial processing, aerospace, geological exploration, national defense construction and other fields. Due to the anisotropy and high brittleness of diamond single crystal, it is easy to dissociate along (111) cleavage surface when it is impacted by external force, which limits its application in self-processing and impact resistance. Nanocrystalline diamond (NPD) is superior to natural diamond in isotropy, good toughness, wear resistance and thermal stability, and its hardness is no less than that of natural diamond. The direct transformation of graphite without additives to nanocrystalline diamond at high temperature and high pressure is the best way to obtain NPD with excellent mechanical properties. However, the direct synthesis of NPD from graphite requires very high pressure and temperature. At low temperature and pressure, graphite can only be partially converted into diamond. In addition, among the precursors for the preparation of NPD, including glass carbon, onion carbon, carbon black, graphite and so on, the conditions required for the preparation of NPD with graphite as precursor were the most severe, but the hardness of NPD was the highest. It also has high fracture toughness and high temperature oxidation resistance. Therefore, it is of great significance to prepare high quality nano-graphite precursors and explore the experimental conditions and mechanism of direct transformation from graphite to NPD, which not only optimizes the synthetic conditions, but also can be used in industrial production. Moreover, it is of great scientific significance to study the phase transition path between graphite and diamond. In order to study the synthesis of nanocrystalline polycrystalline diamond, the pressure and temperature of the high pressure device and the sample chamber of Walker type 6-8 press were calibrated firstly in this paper. A set of high-pressure sample cavities suitable for domestic six-sided top-high pressure device is designed, which can be assembled at a temperature of more than 2000 鈩，

本文編號：2125005