摘要"結(jié)合劑的類型和含量對聚晶金剛石的性能有很大的影響。以5μm金剛石為原材料,選用MAX相中的Ti3AlC2為結(jié)合劑,在5.5GPa、1500℃下制備不同Ti3AlC2含量的聚晶金剛石,分析了Ti3AlC2的含量對聚晶金剛石的物相、顯微結(jié)構(gòu)及力學(xué)性能的影響。結(jié)果表明:Ti3AlC2在高溫高壓下會(huì)完全分解形成TiC和Al-Ti合金,并與金剛石反應(yīng)生成Al4C3和TiC等物相,且TiC和Al4C3均勻分布在金剛石顆粒間并與金剛石緊密黏結(jié)在一起,從而提升聚晶金剛石的力學(xué)性能。當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為20%時(shí),聚晶金剛石的相對密度、維氏硬度和磨耗比均達(dá)到最大值,分別為99.3%、54.0GPa和5733.3;當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為25%時(shí),聚晶金剛石的斷裂韌性達(dá)到最大值5.23MPa·m1/2。
關(guān)鍵詞 聚晶金剛石;Ti 3 AlC 2 ;高溫高壓;力學(xué)性能
中圖分類號 TQ164; TG74 文獻(xiàn)標(biāo)志碼 A
文章編號 1006-852X(2024)06-0725-08
DOI 碼 10.13394/j.cnki.jgszz.2023.0234
收稿日期 2023-11-07 修回日期 2024-01-10
在超硬材料中,聚晶金剛石(polycrystallinediamond,PCD)因具有金剛石的高硬度、高耐磨和高導(dǎo)熱等特性成為科學(xué)研究的熱點(diǎn)[1-2]。聚晶金剛石刀具具有高硬度、高耐磨、高導(dǎo)熱、高工效、高使用壽命和高加工質(zhì)量的優(yōu)勢,在機(jī)械、地質(zhì)、石油開采、建筑、航空航天、汽車和電子信息等行業(yè)中發(fā)揮著極為重要的作用[3-6]。
在PCD燒結(jié)時(shí),通常需要選擇適當(dāng)?shù)慕Y(jié)合劑,結(jié)合劑材料有金屬型、陶瓷型和金屬+陶瓷型[7-8]。單相結(jié)合劑制備的聚晶金剛石性能單一,通常選用復(fù)合型的金屬陶瓷結(jié)合劑或者新型結(jié)合劑材料來調(diào)控聚晶金剛石的綜合性能[9-10]。新型陶瓷MAX相結(jié)合劑(包括Ti3SiC2、Ti3AlC2等)由于其特殊的結(jié)構(gòu),兼具金屬與陶瓷的雙重性能優(yōu)點(diǎn)[11]。其中,Ti3AlC2在高溫下會(huì)分解,對其在高溫高壓條件下的分解過程進(jìn)行研究,有助于進(jìn)一步解釋制備聚晶金剛石時(shí)體系中發(fā)生的反應(yīng)[12-13]。朱春城等[14]研究了Ti3AlC2在氬氣環(huán)境中的高溫?zé)岱€(wěn)定性,發(fā)現(xiàn)在升溫過程中,Ti3AlC2沒有明顯的熱效應(yīng),但在1370°C附近存在一個(gè)吸熱峰,表明Ti3AlC2在此溫度附近發(fā)生分解反應(yīng);研究還發(fā)現(xiàn)Ti3AlC2中的Al原子不穩(wěn)定,在大氣壓下隨著溫度升高,Al原子會(huì)逐漸擴(kuò)散出來。李子揚(yáng)等[15]研究發(fā)現(xiàn),在5GPa下,溫度達(dá)到800℃時(shí)Ti3AlC2分解產(chǎn)生了Al3Ti、TiC和少量的TiAlx相;且隨著溫度的進(jìn)一步升高,TiAlx衍射峰的強(qiáng)度逐漸降低,并在1500℃時(shí)完全消失。HOU等[16]研究發(fā)現(xiàn),在制備金屬基金剛石復(fù)合材料時(shí),添加質(zhì)量分?jǐn)?shù)為25%的Ti3AlC2能提高材料的力學(xué)性能,這種改進(jìn)可能是由于金剛石誘導(dǎo)TiyAlC分解并形成Al填充孔隙,促進(jìn)了組織的致密化;同時(shí),Al元素與金剛石發(fā)生反應(yīng),在金剛石表面形成AlCx過渡層,提高了樣品與基體之間的結(jié)合力。
在目前研究的MAX相中,Ti3AlC2是抗氧化性最強(qiáng)、質(zhì)量最輕的材料之一[17-18]。由于Ti3AlC2發(fā)現(xiàn)得較晚,且比Ti3SiC2合成困難,目前以Ti3AlC2作為結(jié)合劑應(yīng)用于聚晶金剛石的研究較少。因此,本研究中以金剛石為原料,選用典型MAX相Ti3AlC2為結(jié)合劑,采用高溫高壓法制備聚晶金剛石復(fù)合材料,研究Ti3AlC2含量變化對聚晶金剛石材料的顯微結(jié)構(gòu)、物相組成和力學(xué)性能的影響,以期獲得高性能的聚晶金剛石復(fù)合材料。
1實(shí)驗(yàn)
1.1實(shí)驗(yàn)原料及聚晶金剛石合成
實(shí)驗(yàn)原料為金剛石粉體(基本顆粒尺寸為5μm,純度為99.9%,柘城惠豐鉆石股份有限公司生產(chǎn))、Ti3AlC2粉體(基本顆粒尺寸為60μm,純度為98%,錦州海鑫金屬材料有限公司生產(chǎn))。選用的Ti3AlC2結(jié)合劑和金剛石的配方如表1所示,Ti3AlC2的質(zhì)量分?jǐn)?shù)從10%升高到30%,相應(yīng)的金剛石質(zhì)量分?jǐn)?shù)從90%降低到70%。
實(shí)驗(yàn)前首先將金剛石粉體進(jìn)行凈化處理,將其放入體積分?jǐn)?shù)為30%的稀鹽酸溶液中煮30min后洗凈,再將酸處理后的金剛石粉體放入體積分?jǐn)?shù)為30%的NaOH溶液中煮30min洗凈,最后經(jīng)過蒸餾水水洗和無水乙醇洗凈后,放入60℃真空干燥箱中干燥24h備用;將金剛石粉體和Ti3AlC2粉體按照表1所示的配方稱重、混合,放入硬質(zhì)合金球磨罐中球磨6h,轉(zhuǎn)速為300r/min,球料質(zhì)量比為3∶1,然后真空干燥;將干燥后的混合粉體放入?11.32mm×4.2mm的鉬杯中壓制成形(壓力10MPa,保壓120s),將組裝后的試塊放入180℃的烘箱中干燥30min。利用六面頂壓機(jī)在高溫高壓下燒結(jié)樣品,其燒結(jié)工藝曲線如圖1所示,采用先升壓再升溫,先降溫再降壓的步驟。高溫高壓燒結(jié)工藝參數(shù):燒結(jié)壓力為5.5GPa,燒結(jié)溫度為1500℃,保溫時(shí)間為6min。5組實(shí)驗(yàn)采用統(tǒng)一燒結(jié)工藝,得到聚晶金剛石復(fù)合材料,再經(jīng)過研磨和拋光等工序?qū)ζ溥M(jìn)行材料性能檢測。
1.2性能檢測
使用美國FEI公司FEIINSPECTF50型掃描電子顯微鏡(SEM)對聚晶金剛石樣品的微觀形貌進(jìn)行分析,觀察金剛石與結(jié)合劑的結(jié)合狀態(tài),并用掃描電鏡附帶的能譜儀測試分析聚晶金剛石燒結(jié)體中各元素的分布情況;使用A8ADVANCE型X射線衍射儀(XRD,λ=0.15406nm,Germany,掃描速度為10°/min,掃描范圍為20°~90°)對聚晶金剛石樣品和原料的物相進(jìn)行分析,確定其物相組成;采用阿基米德原理測量樣品密度;使用FM-ARS900顯微硬度測試儀測定樣品的維氏硬度(載荷為9.81N,保載10s),根據(jù)裂紋長度和材料的硬度及彈性模量使用式(1)計(jì)算斷裂韌性。斷裂韌性公式為[19]:
2結(jié)果與分析
圖2為金剛石和Ti3AlC2的SEM圖。其中,圖2a為金剛石破碎料形貌圖。由圖2a可知:金剛石粉體的顆粒大小均勻,晶粒尺寸范圍為3~8μm,平均晶粒尺寸約為5μm,形狀不規(guī)則,更易于高溫高壓燒結(jié)。圖2b所示為Ti3AlC2的形貌圖,其表現(xiàn)為層狀結(jié)構(gòu)。
2.1XRD分析
圖3為用不同Ti3AlC2質(zhì)量分?jǐn)?shù)制備PCD的XRD。由圖3可知:PCD主要由金剛石、TiC和Al4C3組成,且每個(gè)樣品中都沒有檢測到Ti3AlC2相,因此,認(rèn)為Ti3AlC2完全分解。Ti3AlC2中Ti?C之間是強(qiáng)共價(jià)鍵連接,而Ti?Al之間是弱金屬鍵連接[21]。此外,Ti3AlC2為亞穩(wěn)相,而TiC在高壓高溫下穩(wěn)定[22]。因此,Ti3AlC2分解為TiC和Al-Ti合金,Al-Ti與金剛石反應(yīng)生成TiC和Al4C3。圖3中TiC與Al4C3衍射峰的存在也證實(shí)了這一發(fā)現(xiàn)。當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)相對較低時(shí)(10%和15%),樣品中主要物相為金剛石、少量的TiC和Al4C3。隨著Ti3AlC2含量升高,生成物TiC和Al4C3的衍射峰增強(qiáng)。新生成的TiC、Al4C3作為黏結(jié)材料,將對PCD的力學(xué)性能與顯微結(jié)構(gòu)產(chǎn)生巨大影響。
Ti3AlC2(l)→TiC(s)+TiAl(4)
4TiAl(l)+7C(s)→Al4C3(s)+4TiC(s)(5)
2.2SEM分析
圖4所示是Ti3AlC2不同質(zhì)量分?jǐn)?shù)時(shí)的PCD顯微結(jié)構(gòu)。在圖4中較暗的部分為金剛石顆粒,較亮的部分為結(jié)合劑。當(dāng)結(jié)合劑質(zhì)量分?jǐn)?shù)為10%(圖4a)和15%(圖4b)時(shí),PCD表面存在少量的孔洞和裂紋;當(dāng)結(jié)合劑質(zhì)量分?jǐn)?shù)為20%(圖4c)時(shí),金剛石被結(jié)合劑緊緊包裹,顆粒之間無明顯孔洞,晶型完整,無碎裂現(xiàn)象,金剛石排列緊密分布均勻,相互結(jié)合比較好,具有較好的致密性,說明PCD燒結(jié)體合成工藝控制較好;當(dāng)結(jié)合劑質(zhì)量分?jǐn)?shù)為25%(圖4d)和30%(圖4e)時(shí),多余的結(jié)合劑出現(xiàn)聚集并且使金剛石相互分散出現(xiàn)孔洞。而且,在這幾種條件下均未發(fā)現(xiàn)層狀結(jié)構(gòu)的Ti3AlC2晶粒,這一結(jié)果與XRD分析的結(jié)果一致。在高溫高壓下,Ti3AlC2含量升高會(huì)分解出更多的Al-Ti合金液相,增強(qiáng)了金剛石及生成的硬質(zhì)相在體系中的流動(dòng)和均勻分布,同時(shí),Ti3AlC2分解后的產(chǎn)物與金剛石在高溫高壓下發(fā)生反應(yīng),形成具有強(qiáng)共價(jià)鍵的TiC和Al4C3,改善了金剛石顆粒之間的結(jié)合狀態(tài),從而提升PCD的綜合力學(xué)性能。
在SEM的分析中,當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為15%、20%和25%時(shí),PCD中金剛石與結(jié)合劑的結(jié)合狀態(tài)較好,所以對它們的元素分布進(jìn)行檢測,具體的線掃描的能譜圖如圖5所示,均在金剛石顆粒和金剛石顆粒之間的界面附近觀察到了Ti元素或Al元素的含量升高。結(jié)果表明在燒結(jié)過程中元素?cái)U(kuò)散到金剛石顆粒中,增強(qiáng)了金剛石與結(jié)合劑的潤濕性。在金剛石?金剛石間隙中,C元素的相對含量降低,Ti元素和Al元素的相對含量升高。因此,結(jié)合XRD分析,認(rèn)為在金剛石與金剛石的界面處形成了Al4C3和TiC。
2.3相對密度與磨耗比分析
圖6所示為Ti3AlC2不同質(zhì)量分?jǐn)?shù)時(shí)PCD的相對密度和磨耗比。相對密度呈現(xiàn)先上升后下降的趨勢,樣品的相對密度通常不僅與燒結(jié)條件相關(guān),還與結(jié)合劑的種類有關(guān)。一方面,在高溫高壓下燒結(jié)驅(qū)動(dòng)力增強(qiáng),樣品的相對密度會(huì)隨之上升;另一方面,在高溫高壓下,Ti3AlC2含量升高會(huì)分解出更多的液相合金,增強(qiáng)了金剛石及生成的硬質(zhì)相在體系中的流動(dòng)和均勻分布。因此,PCD的相對密度上升。但當(dāng)結(jié)合劑含量高到足夠完全包裹金剛石時(shí),繼續(xù)提高結(jié)合劑含量反而會(huì)惡化PCD的力學(xué)性能。圖6中PCD的磨耗比與相對密度呈現(xiàn)相同的趨勢,2條曲線都呈現(xiàn)先上升后下降的趨勢。當(dāng)添加的Ti3AlC2質(zhì)量分?jǐn)?shù)為20%時(shí),PCD的磨耗比達(dá)到最大值5733.3。當(dāng)結(jié)合劑添加量過高時(shí),金剛石與結(jié)合劑間的結(jié)合性能變差,同時(shí)磨耗比下降,在電鏡圖片中觀察到PCD復(fù)合材料出現(xiàn)了結(jié)合劑的聚集和孔隙等現(xiàn)象(圖4d和圖4e),解釋了其力學(xué)性能的惡化。
2.4維氏硬度與斷裂韌性分析
圖7所示為Ti3AlC2不同質(zhì)量分?jǐn)?shù)時(shí)燒結(jié)的PCD的維氏硬度與斷裂韌性。由圖7可知:隨著Ti3AlC2質(zhì)量分?jǐn)?shù)的升高,PCD的維氏硬度和斷裂韌性都呈現(xiàn)出先上升后下降的趨勢。在PCD燒結(jié)體中,硬度最大的物質(zhì)是金剛石,但PCD硬度不僅與金剛石等硬質(zhì)相的含量有關(guān),還與燒結(jié)體中各物質(zhì)的結(jié)合狀態(tài)有關(guān)。當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為15%時(shí),PCD的硬度達(dá)到48.3GPa,斷裂韌性為4.60MPa·m1/2,體系中有更多的金剛石,但是由于結(jié)合劑含量低,金剛石相互接觸產(chǎn)生孔隙,會(huì)降低PCD的力學(xué)性能;當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為20%時(shí),PCD的硬度達(dá)到最大值54.0GPa;PCD的斷裂韌性在Ti3AlC2質(zhì)量分?jǐn)?shù)為25%時(shí)達(dá)到最大值,為5.23MPa·m1/2;當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)>20%時(shí),燒結(jié)體內(nèi)結(jié)合劑含量過高會(huì)導(dǎo)致PCD的相對密度下降,從而引起樣品的維氏硬度降低。
3結(jié)論
以顆粒尺寸為5μm的金剛石為原材料,Ti3AlC2為結(jié)合劑,在5.5GPa、1500℃、6min下制備聚晶金剛石,研究了Ti3AlC2含量變化對PCD的結(jié)構(gòu)和性能的影響。
(1)Ti3AlC2在高溫高壓下完全分解并與金剛石發(fā)生反應(yīng),燒結(jié)體中主要有金剛石、TiC和Al4C3。結(jié)合劑與金剛石反應(yīng)形成TiC和Al4C3,將TiC和Al4C3作為中介相結(jié)合,使金剛石顆粒牢固地黏結(jié)在一起,成為致密化的組織結(jié)構(gòu)。
(2)適量的結(jié)合劑使金剛石與黏結(jié)材料均勻分布,PCD燒結(jié)體更致密。當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為20%時(shí),PCD的相對密度、維氏硬度和磨耗比均達(dá)到最大值,分別為99.3%、54.0GPa和5733.3;當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)為25%時(shí),PCD的斷裂韌性達(dá)到最大值5.23MPa·m1/2;當(dāng)Ti3AlC2質(zhì)量分?jǐn)?shù)達(dá)到25%和30%時(shí),燒結(jié)體中過多的結(jié)合劑和金剛石出現(xiàn)聚集和孔隙,使PCD樣品的相對密度、硬度和磨耗比下降。
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作者簡介
通信作者: 栗正新,男,1964 年生,教授、碩士生導(dǎo)師。主要研究方向:金剛石功能材料、先進(jìn)超硬和普通磨料磨具、計(jì)算機(jī)模擬仿真和磨削技術(shù)等。
E-mail:zhengxin_li@haut.edu.cn
(編輯:趙興昊)
Effect of Ti 3 AlC 2 "content on properties of polycrystalline diamond
ZHANG Qunfei, XIAO Changjiang, TANG Lihui, ZHENG Haoyu, LI Zhengxin
(School of Materials Science and Engineering, Henan University of Technology, ZhengZhou 450001, China)
Abstract
Objectives: In superhard materials, polycrystalline diamond (PCD) has become a hot topic in scientific re-search because it inherits the advantages such as high hardness, high wear resistance, and high thermal conductivityfrom diamond. The type and content of the binder have a great influence on the properties of polycrystalline diamond.Methods: The microstructure of polycrystalline diamond samples is analyzed by FEI INSPECT F50 scanning electronmicroscope (SEM) of FEI Company in the United States, and the bonding state between diamond and binder is ob-served. The distribution of each element in the polycrystalline diamond sintered body is tested and analyzed by an en-ergy dispersive spectrometer attached to the scanning electron microscope. An A8 ADVANCE X-ray diffractometer(XRD, λ = 0.154 06 nm, Germany, scanning speed: 10°/ min, scanning range: 20°~90°) is used to analyze the phase ofpolycrystalline diamond samples and raw materials to determine their phase composition. The sample density is meas-ured by Archimedes' principle. The Vickers hardness of the sample is measured using a FM-ARS900 microhardness tester(load: 9.81 N, holding time: 10s). The fracture toughness is calculated using the fracture toughness formula according tothe crack length, the hardness, and the elastic modulus of the material. Results: It can be concluded from XRD analysisthat PCD is mainly composed of diamond, TiC, and Al 4 C 3 , and that the Ti 3 AlC 2 phase is not detected in any sample.Therefore, Ti 3 AlC 2 is considered to have been completely decomposed. The Ti-C bond in Ti 3 AlC 2 is a strong covalentbond, while the Ti-Al bond is a weak metallic bond. In addition, Ti 3 AlC 2 is a metastable phase, while TiC is stable athigh pressure and high temperature. Therefore, Ti 3 AlC 2 is decomposed into TiC and Al-Ti alloy, and Al-Ti reacts withdiamond to form TiC and Al 4 C 3 . The existence of TiC and Al 4 C 3 diffraction peaks also confirms this finding. From theSEM analysis, it can be concluded that when the binder content is 10% and 15%, there are a small number of holes andcracks on the surface of PCD; when the binder content is 20%, the diamond is tightly wrapped by the binder, and thereare no obvious holes between the particles. The crystal form is complete without any fragmentation, and the diamond isarranged closely and distributed evenly, with better combination and compactness, indicating that the synthesis processof the PCD sintered body is well controlled. When the binder content is 25% and 30%, the excess binder appears to ag-gregate and cause dispersed diamonds and more holes. Moreover, no Ti 3 AlC 2 grains with a layered structure were foundunder these conditions, which was consistent with the results of XRD analysis. Under high temperature and high pres-sure, the increase in Ti 3 AlC 2 content will decompose more Al-Ti alloy into the liquid phase, which enhances the flowand uniform distribution of diamond and the generated hard phases in the system. At the same time, the product ofTi 3 AlC 2 decomposition reacts with diamond under high temperature and high pressure to form TiC and Al 4 C 3 withstrong covalent bonds, which improves the bonding state between diamond particles, thus improving the comprehensivemechanical properties of PCD. The relative density shows a trend of increasing first and then decreasing. When theamount of binder is too much, the bonding performance between diamond and binder becomes worse, and the wear ra-tio decreases. In the electron microscope image, it is observed that the aggregation and porosity of the binder appear inthe PCD composites, which explains the deterioration of mechanical properties. With the increase of Ti 3 AlC 2 content,the Vickers hardness and fracture toughness of PCD increase first and then decrease. When the mass fraction of Ti 3 AlC 2is 20%, the hardness of PCD reaches the maximum value of 54.0 GPa. The fracture toughness of PCD reaches the max-imum value of 5.23 MPa·m1/2 when the mass fraction of Ti3 AlC 2 is 25%. When the mass fraction of Ti 3 AlC 2 is more than 20%, the high content of binder in the sintered body will lead to a decrease in the relative density of PCD, resulting in adecrease in the Vickers hardness of the sample. Conclusions :Polycrystalline diamond is prepared at 5.5 GPa, 1 500°C, and 6 minutes by using diamond with a particle size of 5 μm as raw material and Ti 3 AlC 2 as the binder. The effect ofTi 3 AlC 2 content on the structure and properties of PCD is studied. Ti 3 AlC 2 completely decomposes and reacts with dia-mond under high temperature and high pressure. Diamond, TiC, and Al 4 C 3 are the main components in the sinteredbody. The binder reacts with diamond to form TiC and Al 4 C 3 . Through the combination of TiC and Al 4 C 3 as intermedi-ates, the diamond particles are firmly bonded together to form a dense microstructure. An appropriate amount of bindermakes the diamond and the bonding material evenly distributed, and the PCD sintered body becomes denser. When themass fraction of Ti 3 AlC 2 is 20%, the relative density, Vickers hardness, and wear ratio of PCD reach maximum values of99.3%, 54.0 GPa and 5 733.3, respectively. When the mass fraction of Ti 3 AlC 2 is 25%, the fracture toughness of PCDreaches the maximum value of 5.23 MPa·m1/2 . When the Ti3 AlC 2 content reaches 25% and 30%, the density, hardness,and wear ratio of the PCD samples decrease due to the excessive aggregation and pores of the binder and diamond in thesintered body.Key
words
polycrystalline diamond;Ti 3 AlC 2 ;high temperature and high pressure;mechanical properties