本文關(guān)鍵詞： 碳氫協(xié)同還原 納米鎢粉 納米碳化鎢 揮發(fā)-沉積 階段碳化　出處：《南昌大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：超細/納米晶WC-Co硬質(zhì)合金因兼具高硬度和高強度(即兼有高耐磨性和高韌性的“雙高”性能)而成為硬質(zhì)合金的發(fā)展方向,制備性能優(yōu)良的納米W粉和WC粉是生產(chǎn)超細/納米晶WC-Co硬質(zhì)合金的基礎(chǔ)和關(guān)鍵。本文針對氧化鎢氫還原過程中因揮發(fā)-沉積作用而導(dǎo)致的W粉顆粒快速長大和異常長大的現(xiàn)象,采用碳氫協(xié)同還原法制備納米W粉,然后分別通過階段碳化法和碳氫協(xié)同還原-碳化法制備納米WC粉,并采用低壓燒結(jié)制備超細晶WC-Co硬質(zhì)合金。論文系統(tǒng)研究了納米W粉、WC粉及其燒結(jié)體的制備工藝、性能和機理,具體內(nèi)容如下:1.研究了碳氫協(xié)同還原過程中的物相和形貌演變以及還原工藝參數(shù)W粉性能的影響。結(jié)果表明:還原過程遵循分步還原規(guī)律,非晶前驅(qū)體依次轉(zhuǎn)變?yōu)閃O_(2.9)、WO_(2.72)和WO_2低價中間氧化物,最終還原為α-W,隨著還原過程中發(fā)生晶型轉(zhuǎn)變以及碳與水蒸氣反應(yīng)被消耗,還原產(chǎn)物變得疏松多孔。W粉平均粒徑隨前驅(qū)體配碳比升高而減小,當(dāng)配碳比高于2.6時,殘余碳含量會顯著增加;隨著還原溫度升高,前驅(qū)體中的碳參與反應(yīng)并被消耗,W粉顆粒的長大作用被削弱,還原W粉的平均粒徑和殘?zhí)剂侩S還原溫度升高而減小。配碳比為2.6的前驅(qū)體經(jīng)760 oC還原60 min后,得到平均粒徑56 nm的球形W粉。2.研究了還原方式對W粉形貌、粒度和顯微結(jié)構(gòu)的影響,通過分析不同還原溫度W粉的晶粒長大曲線,提出了碳氫協(xié)同還原制備納米W粉的機理。結(jié)果表明:W粉晶粒的長大速率隨還原溫度升高而變慢,760 oC以上時,還原產(chǎn)生的水蒸氣與碳反應(yīng)生成CO和H_2,顯著降低體系中p[H_2O]/p[H_2],抑制揮發(fā)性水合物WO_2(OH)_2的產(chǎn)生,W粉的主導(dǎo)長大方式也由揮發(fā)-沉積轉(zhuǎn)變?yōu)樵訑U散。還原方式會對W粉的粒徑和形貌產(chǎn)生重要影響,碳氫協(xié)同還原W粉的還原長大機制以固相局部化學(xué)反應(yīng)為主,所得W粉為均勻細小的球形顆粒,結(jié)構(gòu)疏松、分散性良好;普通氫還原W粉的還原長大機制以揮發(fā)-沉積為主,所得W粉顆粒粗大,發(fā)育完全,呈現(xiàn)W本征晶體的多面體形貌。3.以碳氫協(xié)同還原納米W粉和碳黑為原料,采用階段碳化法制備納米WC粉,研究了階段碳化工藝(碳化溫度和保溫時間)對WC粉物相、形貌和粒徑的影響。結(jié)果表明:WC粉的粒徑取決于W粉的碳化速率和長大速率,高的碳化速率和低的長大速率有利于降低粒徑;低溫預(yù)碳化能夠在W粉顆粒表面形成一定厚度的WC層,使顆粒間的接觸狀態(tài)由W/W接觸變?yōu)閃C/WC接觸,抑制碳化初期因W粉顆粒燒結(jié)合并長大而導(dǎo)致的WC粒徑增粗。碳氫協(xié)同還原納米W粉階段碳化的最佳工藝為:預(yù)碳化溫度900 oC,保溫時間60 min,二段碳化溫度1150 oC,保溫時間90 min,平均粒徑56 nm的W粉經(jīng)900 oC+1150 oC階段碳化,得到平均粒徑106 nm的WC粉。4.采用連續(xù)碳氫協(xié)同還原-碳化法制備納米WC粉,研究了前驅(qū)體配碳比對WC粉碳含量的影響,還原、碳化溫度對WC粉形貌和粒徑的影響。結(jié)果表明:WC粉化合碳含量隨前驅(qū)體配碳比升高而逐漸增加,當(dāng)前驅(qū)體配碳比為3.6時,化合碳含量達到理論值6.12%,游離碳含量為0.06%;當(dāng)配碳比高于3.6時,游離碳含量迅速升高。還原-碳化過程中由W向WC的轉(zhuǎn)變具有結(jié)構(gòu)遺傳性,長大系數(shù)在1.4~1.6之間,WC粉的平均粒徑隨還原溫度升高而降低;升高碳化溫度會促進WC粉顆粒的晶界遷移,WC粉的平均粒徑隨碳化溫度升高而增大。碳氫協(xié)同還原-碳化制備納米WC粉的最佳工藝為:前驅(qū)體配碳比3.6,還原溫度760~800 oC,碳化溫度1100~1200 oC;所得WC粉為均勻細小的近球形顆粒,平均粒徑87.3 nm。5.以制備的納米WC粉為原料,采用低壓燒結(jié)技術(shù)制備超細晶WC-Co硬質(zhì)合金,研究了燒結(jié)工藝參數(shù)對WC-Co硬質(zhì)合金顯微組織和力學(xué)性能的影響。結(jié)果表明:隨著燒結(jié)溫度升高和保溫時間延長,燒結(jié)體的致密度增加,平均晶粒尺寸增大,試樣的硬度和抗彎強度也會隨致密度上升而提高;若燒結(jié)溫度過高或保溫時間過長,則會使燒結(jié)體的晶粒發(fā)生異常長大,導(dǎo)致致密度降低,合金力學(xué)性能下降。WC-6Co燒結(jié)的最佳工藝參數(shù)為:燒結(jié)溫度1360 oC,保溫時間60 min,所得硬質(zhì)合金樣品的平均晶粒尺寸為305 nm,為超細晶硬質(zhì)合金,洛氏硬度達到94.6 HRA,抗彎強度達到4450 MPa。
[Abstract]:Ultrafine nanocrystalline WC-Co cemented carbide with high hardness and high strength (i.e. both high wear resistance and high toughness of the "double high" performance) as the development direction of hard alloy, preparation of excellent performance of nano W powder and WC powder is the production of ultrafine / nano crystalline WC-Co hard alloy according to the foundation and the key. W particles caused by evaporation deposition of tungsten oxide by hydrogen reduction process of rapid growth and abnormal growth of the phenomenon, the hydrocarbon co reduction method for preparing nanometer W powder, and then through the stage of carbonization and hydrocarbon preparation of nano WC powder reduction and carbonization of collaborative, ultrafine grained WC-Co hard alloy by low pressure sintering. This dissertation has systematically studied the preparation process of nano W powder, WC powder and sintered body, performance and mechanism, the specific contents are as follows: 1. research of hydrocarbon evolution phase and morphology of the reduction process in cooperative and reduction process parameters of W powder The influence of the performance. The results showed that reduction process follows the fractional reduction of amorphous precursors are converted to WO_ (2.9), WO_ (2.72) and WO_2 low intermediate oxide, eventually reduced to a -W, with the consumption of crystal transformation and carbon and water vapor reaction in the reduction process, the reduction product becomes loose the porous.W powder average particle size with the precursor carbon ratio decreases when the carbon ratio is higher than 2.6, the residual carbon content significantly increased; with the increase of reduction temperature, precursor of carbon and consumed in the reaction, W particles grow up is weakened, the average particle size of W powder reduction and the carbon content decreases with the increase of reduction temperature. Carbon ratio of 2.6 precursor by 760 oC reduction after 60 min spherical W powder.2. average particle size of 56 nm on the morphology of W powder reduction method, effect of particle size and microstructure, through the analysis of different reduction temperature of W powder crystal Grain growth curve, and presents a collaborative mechanism of preparation of nano W powder reduction hydrocarbon. The results showed that the growth rate of W powder grain with the reduction temperature and slower, more than 760 oC, water vapor and carbon reduction reaction of H_2 and CO, significantly decreased p[H_2O]/p[H_2] in the system, WO_2 OH (volatile gas hydrate inhibition) _2, leading W powder by evaporation deposition method to grow up into atomic diffusion. Reduction on W powder particle size and morphology has an important impact on reduction of W powder by reduction of hydrocarbon synergistic growth mechanism with solid local chemical reaction, the W powder as spherical particles, uniform and fine loose structure, good dispersion of W powder; ordinary hydrogen reduction reduction mechanism to grow evaporation deposition, the W powder coarse particles, fully developed,.3. presents the W intrinsic polyhedral morphology of crystals by hydrocarbon synergetic reduction of nano W powder and carbon black as raw materials. Preparation of nanometer WC powder by carbonization of the stage, stage of carbonization process (carbonization temperature and holding time) on WC powder phase, influence the morphology and particle size. The results show that the carbonation rate of WC depends on the size of the powder W powder and growth rate, high rate and low growth rate of carbonation is conducive to to reduce the particle size of WC layer; low temperature carbonization can form a certain thickness on the surface of W particles, the contact state between particles by the W/W contact to WC/WC contact inhibition of W particles during the initial stage of carbonization by sintering the combined growth caused the particle size of WC. The optimum synergistic thickening hydrocarbon reduction of nano W powder phase carbonization for the pre carbonization temperature 900 oC, holding time of 60 min, two oC 1150 carbonization temperature, holding time of 90 min, the average particle size of 56 nm W 900 oC+1150 oC powder with WC powder.4. carbide phase, the average particle size of 106 nm with the continuous reduction of carbon nano - Preparation of hydrocarbon co legalization M WC powder, reduction effect, the carbon ratio of precursor powder of WC carbon content, effect of carbonization temperature on the morphology and particle size of WC powder. The results showed that the carbon content of WC powder combined with precursor carbon ratio increased, the body carbon ratio of 3.6, the combined carbon content the theoretical value of 6.12%, the free carbon content is 0.06%; when the carbon ratio is higher than 3.6, the free carbon content increased rapidly. Reduction and carbonization process from W to WC transformation with genetic structure, growth coefficient between 1.4~1.6, the average particle size of WC powder with the reduction temperature and reduce the temperature rise of carbon; will promote the migration of grain boundary of WC particles, the average particle size of WC powder with the carbonization temperature increasing. The best preparation technology - reduction hydrocarbon co carbonization of nano WC powder as precursor of carbon ratio 3.6, reduction temperature of 760~800 oC 1100~1200 oC, carbonization temperature; the WC near the ball into a uniform fine powder The shape of particles, the average particle size of 87.3 nm.5. in the preparation of nano WC powder as raw material, preparation of ultrafine WC-Co cemented carbide by low pressure sintering technology, studied the effects of sintering parameters on Microstructure and mechanical properties of hard alloy WC-Co. The results showed that with the increase of the sintering temperature and holding time, the density of sintering body increase, the average grain size increases, the hardness and bending strength will be increased with the density increasing; if the sintering temperature is too high or the holding time is too long, will make the grains grow abnormally, resulting in lower density, optimum parameters of mechanical properties of.WC-6Co sintered alloy decrease as sintering temperature of 1360 oC, holding time of 60 min, the average grain size of the hard alloy samples is 305 nm for ultrafine cemented carbide, Rockwell hardness of 94.6 HRA, the flexural strength reached 4450 MPa.

【學(xué)位授予單位】：南昌大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TF123.7;TF125.3

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