張紀(jì)福,劉艷梅,張濤,柯培玲,張翔宇,丁洋,Kim Kwang Ho,王鐵鋼
摩擦磨損與潤滑
還原性氣氛制備Zr-B-N納米復(fù)合涂層的結(jié)構(gòu)及性能分析
張紀(jì)福1,劉艷梅1,張濤1,柯培玲2,張翔宇1,丁洋1,Kim Kwang Ho3,王鐵鋼1
(1.天津職業(yè)技術(shù)師范大學(xué) 天津市高速切削與精密加工重點實驗室,天津 300222;2.中國科學(xué)院寧波材料技術(shù)與工程研究所 中國科學(xué)院海洋新材料與應(yīng)用技術(shù)重點實驗室,浙江 寧波 315201;3. Global Frontier R&D Center for Hybrid Interface Materials, Pusan National University, Busan 609-735, South Korea)
制備高純度、超硬、高耐磨的Zr-B-N納米復(fù)合涂層。在反應(yīng)氣體中摻入還原性氣體H2,利用氫元素強還原性去除真空室以及反應(yīng)氣氛中殘留的O雜質(zhì),采用脈沖直流磁控濺射技術(shù),通過調(diào)節(jié)N2+H2混合氣體流量制備高純度Zr-B-N涂層。利用掃描電鏡、納米壓痕儀、摩擦磨損試驗機等設(shè)備對涂層的微觀結(jié)構(gòu)、力學(xué)性能和摩擦性能進行測試,并分析其變化機理。隨著N2+H2流量的增加,Zr-B-N涂層內(nèi)N含量在N2+H2流量為10 mL/min時達到最高。從截面形貌可以看出,涂層結(jié)構(gòu)由粗大的柱狀晶逐步轉(zhuǎn)變?yōu)椴A罴毿≈鶢罹ЫY(jié)構(gòu),涂層更加致密,呈現(xiàn)典型的納米復(fù)合結(jié)構(gòu)。微量H元素的摻入,減少了涂層制備過程中O相關(guān)化學(xué)鍵的生成,制備出的Zr-B-N涂層晶粒的生長環(huán)境得到改善。在N2+H2流量為 10 mL/min時,涂層的硬度和彈性模量達到最大值40.26 GPa和532.98 GPa,臨界載荷最大約為60.1 N,摩擦系數(shù)較小,為0.72,磨損率在此時最低,為1.12×10–5mm3/(N·m)。當(dāng)N2+H2流量為10 mL/min時,制備出了超硬Zr-B-N納米復(fù)合涂層。適量氫元素的摻入,充分去除真空室內(nèi)氧雜質(zhì),改善了涂層中晶粒的生長環(huán)境,有效地提高涂層的硬度及摩擦磨損性能。
還原性反應(yīng)氣氛;Zr-B-N涂層;磁控濺射;納米復(fù)合涂層;微觀結(jié)構(gòu);力學(xué)性能
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材料涉及現(xiàn)代社會各個領(lǐng)域,特別是對機械加工、航空航天、汽車、醫(yī)療等行業(yè)的快速發(fā)展起著至關(guān)重要的作用[1-4]。硼化鋯是一種有金屬與陶瓷雙重特性的強共價鍵耐高溫材料。ZrB2呈六角晶體結(jié)構(gòu),具有高硬度、高熔點(3 246 ℃)、優(yōu)異的熱導(dǎo)率(65~135 W·m–1·K–1)和較強的抗腐蝕性等優(yōu)點,已成為航空航天、微電子和切削刀具等領(lǐng)域新的發(fā)展方向[5-6]。
Stewart等[7]探究了硼化鋯基薄膜中晶體的生長機理及微觀結(jié)構(gòu)演變規(guī)律,促進了高溫薄膜電子學(xué)的應(yīng)用。Bunshah等[8]利用電子束蒸發(fā)技術(shù)在不同溫度下制備出一系列ZrB2薄膜,當(dāng)沉積溫度達到900 ℃時,薄膜的硬度提升到最大值3 000 kg/mm2。為提升薄膜性能,Pierson等[9]采用PECVD技術(shù)在鋯合金表面沉積出ZrB2涂層,研究發(fā)現(xiàn),于580 ℃制備的涂層中含有納米ZrB2晶體及非晶態(tài)Zr-B-O化合物。之后他們在反應(yīng)氣體中混入氧氣,利用磁控濺射鍍膜技術(shù)探究了不同O2含量對Zr-B-O薄膜物相和組織結(jié)構(gòu)的影響。試驗表明,即使微量氧氣的混入,也會生成明顯的非晶組織,致使薄膜內(nèi)應(yīng)力和硬度下降,且隨O2含量的增加,微觀組織由ZrB2–xO固溶體逐漸演變?yōu)閆rO2和B2O3非晶相。
盡管大量文獻對硼化鋯基薄膜進行了理論性研究[10-12],如ZrB2-SiC復(fù)合材料具有高溫耐腐蝕性能[13-14],N元素的摻入將改善硼化鋯基薄膜的韌性[15]等,但試驗中缺乏還原性氣氛對磁控濺射法制備ZrB2過程影響的研究內(nèi)容。研究發(fā)現(xiàn),利用濺射法制備硼氮化物薄膜過程中,由于O極易與B反應(yīng)生成軟質(zhì)B2O3,嚴重降低薄膜性能,而O常來自于鍍膜室內(nèi)殘留的氣體或反應(yīng)氣體N2中的雜質(zhì),后者因采用物理分離法制取,故不可避免存在O雜質(zhì)。在反應(yīng)沉積過程中,利用具有還原性的H2去除鍍膜室內(nèi)的O雜質(zhì),有望進一步提高薄膜質(zhì)量和純度。故本課題采用磁控濺射技術(shù),在不同還原性氣體流量下沉積一系列Zr-B-N薄膜,系統(tǒng)性研究還原性氣體流量對薄膜力學(xué)性能和微觀結(jié)構(gòu)的影響,加速硼氮化物薄膜的實用化進程。
試驗采用脈沖磁控濺射技術(shù)進行鍍膜。所用基體材料為單晶硅片(50 mm×6 mm×0.67 mm)、304不銹鋼(30 mm×25 mm×1 mm)和硬質(zhì)合金(30 mm×30 mm× 5 mm),氣體為Ar(純度為99.999%)、N2+H2(氣體體積比為9︰1)。試驗前,需將基體材料在MP-2D型雙盤金相磨拋機上進行鏡面拋光、研磨等前處理,并分別用酒精、丙酮溶液浸泡后,超聲清洗20 min,去除表面雜物,再經(jīng)高純氮氣充分干燥后,將基片懸掛在樣品架上。工藝流程如圖1所示。
圖1 工藝流程
Fig.l Process flow diagram
對真空室抽真空以及加熱,使真空室內(nèi)壓強達到3.5×10–3Pa以下,溫度達到400 ℃,并保持穩(wěn)定。通入Ar的同時,設(shè)置脈沖偏壓為–800 V,占空比為87%。對基片輝光刻蝕15 min,開啟ZrB2靶,離子轟擊清洗基片8 min。通入Ar與N2+H2,開啟Cr靶,設(shè)置脈沖偏壓為–150 V,沉積CrN過渡層,旨在改善膜/基結(jié)合力。具體工藝參數(shù)見表1。
采用SU8010型冷場發(fā)射掃描電子顯微鏡觀察涂層的微觀形貌,EPMA-1610型電子探針分析涂層化學(xué)成分,D8-Discovery X射線衍射儀分析涂層的物相組成,選用Cu靶單色Kα射線輻射,最大電流為80 mA,最高電壓為60 kV,最高功率為2.2 kW,掃描速度為0.02 (°)/s,步長為0.01°,波長為0.154 nm,衍射角(2)掃描范圍為20°~80°。采用Anton Paar TTX- NHT-3型納米壓痕儀測量涂層的硬度和彈性模量,設(shè)置施加載荷為10 mN。采用Anton Paar RST-3型劃痕測試儀測量膜/基結(jié)合力,設(shè)置劃痕長度為3 mm,劃痕速度為6 mm/min,勻速施加法向載荷0~80 N,記錄涂層破裂位置(c2)。采用Anton Paar THT型銷盤式摩擦磨損試驗機測試涂層的摩擦性能,對摩副選取直徑為6 mm的Al2O3球,磨痕半徑為6 mm,線速度為0.1 m/s,法向載荷為1 N,每個樣品旋轉(zhuǎn)2 000轉(zhuǎn)。
表1 還原性氣氛下制備Zr-B-N納米復(fù)合涂層工藝參數(shù)
Tab.1 Process parameters for the preparation of Zr-B-N nanocomposite coatings in reductive atmosphere
不同N2+H2流量下制備的Zr-B-N涂層的化學(xué)成分如圖2所示。由圖2可知,隨著真空室內(nèi)反應(yīng)氣體流量增加,涂層中N元素含量先顯著上升,再逐漸趨于穩(wěn)定;B元素含量先急劇下降,后趨于緩慢;Zr元素含量整體變化不大。在ZrB2涂層中,B含量高于Zr含量,但反應(yīng)氣體的加入使Zr含量高于B含量。這是由于N元素的加入易與B反應(yīng)生成輕質(zhì)BN顆粒,其平均自由程遠低于Zr+,使得單位時間內(nèi)達到基體表面的Zr+增多,致使涂層內(nèi)Zr含量偏高。相關(guān)研究[16]表明,BN相在Ti-B-N涂層內(nèi)以非晶形式存在,Ti-B-N涂層具有典型的納米復(fù)合結(jié)構(gòu)。本試驗研制的Zr-B-N涂層也具有納米復(fù)合結(jié)構(gòu),由于B與N的結(jié)合能低,大量B與N反應(yīng),生成非晶BN相。Zr原子序數(shù)較大,其離子在負偏壓電場作用下向基體做加速運動,行程中受其他粒子碰撞的影響較小,故涂層中Zr含量波動不大。隨著N2+H2的持續(xù)增多,靶表面鈍化現(xiàn)象加劇,致密的鈍化膜降低了靶材濺射效率,使涂層內(nèi)N含量漸漸趨于穩(wěn)定[17]。
圖2 不同N2+H2流量下制備的Zr-B-N涂層的化學(xué)成分
圖3為不同N2+H2流量下制備的Zr-B-N涂層的XRD圖譜。隨著N2+H2流量的增加,涂層中(001)、(100)與(002)晶面的ZrB2相衍射峰強度均有不同程度的改變,(101)晶面衍射峰強度未發(fā)生明顯變化,反應(yīng)氣體流量的增加未使其生長取向發(fā)生變化,衍射峰無明顯偏移。在圖2中沒有發(fā)現(xiàn)氮化物相的衍射峰,這表明N元素主要以非晶態(tài)的形式存在于涂層中。在含氮較高的Zr-B-N涂層中,ZrB2相的(001)和(002)晶面衍射峰明顯減弱、寬化,可能歸因于大量N與B或Zr原子反應(yīng)生成軟質(zhì)非晶BN或ZrN,非晶層限制了ZrB2晶粒的生長,阻礙了ZrB2相各晶面的結(jié)晶,衍射峰寬化[18-19]。劉爽[20]通過建立缺陷超胞模型分析了TiBN薄膜中可能存在的點缺陷,發(fā)現(xiàn)在此薄膜中BN的形成能最低,最先形成Ti(B,N)置換固溶體,當(dāng)薄膜中B與N含量增多后,會形成非晶。Deng等[21]采用直流磁控濺射技術(shù)制備TiB(N)涂層時發(fā)現(xiàn),隨著N2流量的增加,涂層中(001)與(002)晶面的結(jié)晶逐漸轉(zhuǎn)變?yōu)闊o定形的微結(jié)構(gòu),涂層的硬度、彈性模量和耐磨性等都得到明顯的改善,與本次試驗結(jié)果較為相似。本試驗制備ZrBN涂層是根據(jù)能量最低原理,優(yōu)先形成能量較低的非晶,而BN所需結(jié)晶溫度或動能較高,故本次XRD衍射圖中沒有出現(xiàn)BN晶相。在反應(yīng)氣體流量為15 mL/min時,衍射峰增強,這可能是沉積離子遷移率受靶材表面鈍化的影響造成的。由于反應(yīng)氣體N2增多后,結(jié)晶程度升高,使晶粒團簇堆積,此時沉積離子的動能較低,離子吸附能力較弱,沉積后失去了擴散能力,晶體的形核速率慢,致使薄膜晶粒尺寸增大,衍射峰增強。
為定量評估不同N2+H2流量下制備Zr-B-N涂層的微觀結(jié)構(gòu),采用謝樂公式計算平均晶粒尺寸,見式(1)。
式中:λ為波長;B為衍射峰的半高寬;θ為相應(yīng)的布拉格角。經(jīng)計算,未通入N2+H2反應(yīng)氣體時,涂層中晶粒尺寸最大為6.8 nm。隨著N2+H2氣體流量的增多,晶粒細化。當(dāng)反應(yīng)氣體流量為10 mL/min時,晶粒尺寸最小約3.9 nm。繼續(xù)增加反應(yīng)氣體流量至15 mL/min,晶粒尺寸又增加至約5.5 nm。
不同N2+H2流量下制備的Zr-B-N涂層的表面形貌如圖4所示。可以發(fā)現(xiàn),在反應(yīng)室未通入N2+H2時,沉積涂層表面具有較多的顆粒物(熔滴造成),且尺寸較大。隨著N2+H2的不斷加入,涂層的表面顆粒物邊界由清晰轉(zhuǎn)變得模糊,顆粒尺寸逐漸減小。當(dāng)N2+H2流量加至10 mL/min時,涂層表面最平整致密,沒有明顯的大顆粒物和針孔等缺陷存在,涂層沉積較為均勻。沉積ZrB2涂層時,由于腔體中存在氧雜質(zhì),使靶面異常放電,靶材電流增大,導(dǎo)致靶面易產(chǎn)生小熔池,較多液滴沒有離化而直接從靶面飛出,部分液滴在電場中與電子相撞,尺寸減小后,沉積到基體表面,部分液滴則直接沉積到基體表面,使涂層表面顆粒物增多,表面粗糙度增大。隨著反應(yīng)室中H2+N2的不斷加入,大量非晶BN與晶體聚合,非晶相的高界面聚合能限制了晶粒的生長,如圖4b—d所示。另外,大量氮氣吸附于基體和靶材表面時,基體與靶面不斷產(chǎn)生氮化物,靶面鈍化,使離子的散射能量和自由行程減小,造成涂層表面的瘤狀物和液滴減少,Bujak等[22]證實了這一現(xiàn)象。沉積離子遷移率受靶材表面鈍化的影響,由于反應(yīng)氣體N2大量增加后,結(jié)晶程度升高,使晶粒團簇堆積。此時沉積離子的動能較低,離子吸附能力較弱,沉積后失去了擴散能力,晶體的形核速率慢,致使涂層晶粒尺寸增大,涂層表面缺陷增多,如圖4e所示。
不同N2+H2流量下制備的Zr-B-N涂層的截面形貌如圖5所示,膜/基分界清晰。從圖5a觀察到,經(jīng)過磁控濺射技術(shù)制備出的ZrB2涂層,結(jié)構(gòu)致密,無明顯宏觀缺陷,下層呈現(xiàn)較為粗大的柱狀晶結(jié)構(gòu)。隨著反應(yīng)氣體的增多,表面顆粒物減少的同時,截面表現(xiàn)出柱狀晶逐漸細化的現(xiàn)象,涂層慢慢轉(zhuǎn)變?yōu)榫鶆蛑旅艿闹鶢钗⒂^結(jié)構(gòu),又逐漸形成向玻璃狀結(jié)構(gòu)轉(zhuǎn)變的細小柱狀晶結(jié)構(gòu),如圖5b—d所示。結(jié)合圖3涂層的XRD圖譜可知,此時Zr-B-N涂層在(001)和(002)晶面處呈現(xiàn)出微弱的ZrB2衍射峰,未檢測到N元素的存在,N元素以非晶的形式存在涂層中,形成非晶相包裹納米晶的納米復(fù)合結(jié)構(gòu)充分細化晶粒,涂層結(jié)構(gòu)較為致密[23]。當(dāng)N2+H2流量達到15 mL/min時,涂層演變成玻璃狀與等軸晶相互轉(zhuǎn)變的微觀結(jié)構(gòu),如圖5e所示。結(jié)合圖3涂層的XRD圖譜可知,此時衍射峰強度增加,表明此時Zr-B-N涂層中結(jié)晶程度升高。這可能是由于靶材表面產(chǎn)物的增多,使其鈍化,濺射粒子所含能量減小,在基體表面遷移運動受限,晶粒團簇堆積,與圖4c表面形貌的結(jié)果相吻合。在所有涂層中,沒有發(fā)現(xiàn)明顯的針孔等缺陷存在,這表明全部涂層結(jié)構(gòu)致密。
圖4 不同N2+H2流量下制備Zr-B-N涂層的表面形貌
圖5 不同N2+H2流量下制備Zr-B-N涂層的截面形貌
不同N2+H2流量下制備的Zr-B-N涂層的硬度與彈性模量如圖6所示??梢钥闯?,涂層的硬度與彈性模量呈現(xiàn)相同的變化趨勢,隨著N2+H2流量的增加,先增大、后減小。未通入反應(yīng)氣體時,沉積的ZrB2硬度和彈性模量分別為38.6 GPa和515.27 GPa。在N2+H2流量為10 mL/min時,分別取得最大值40.26 GPa和532.98 GPa。試驗前期未摻入H2,僅采用N2作為反應(yīng)氣體制備Zr-B-N涂層時,隨著N2流量的增多,涂層的硬度均未超過35 GPa,可能是由于界面氧雜質(zhì)與納米尺度界面交互作用引發(fā)微缺陷,而本試驗還原性氣體的摻入充分還原了真空室內(nèi)的氧雜質(zhì),使涂層硬度得到提高。通過涂層化學(xué)成分測試結(jié)果可知,隨著N2+H2流量從0 mL/min逐漸增加至10 mL/min的過程中,Zr-B-N涂層中所含N元素含量也逐漸增加,B元素含量逐漸下降,Zr元素含量較為穩(wěn)定,且由XRD測試結(jié)果可知,涂層中僅檢測到ZrB2相衍射峰。這是由于隨著N2+H2流量的增加,Zr-B-N涂層中的N元素并未與金屬Zr結(jié)合,而是與靶材濺射出的B元素優(yōu)先結(jié)合,生成大量非晶BN。同時,還原性氣體的加入不斷還原真空室內(nèi)氧雜質(zhì),減少了涂層制備過程中O相關(guān)化學(xué)鍵的生成,制備出的Zr-B-N涂層晶粒的生長環(huán)境得到改善,涂層呈現(xiàn)細小的柱狀晶結(jié)構(gòu)。由截面形貌也可看出,N2+H2流量為10 mL/min時,晶粒組織更加致密,此時硬度與彈性模量取得最大值。
圖6 不同N2+H2流量下制備Zr-B-N涂層的硬度與彈性模量
/和3/*2也是反映涂層力學(xué)性能的重要指標(biāo),在一定程度上分別代表涂層的抗彈性變形和抗塑性變形能力。Leyland等[24]認為,/值越大,涂層往往表現(xiàn)出更好的韌性。Musil 等[25]發(fā)現(xiàn),涂層具有較高/值的同時,彈性模量越低,涂層具有越優(yōu)異的摩擦性能。Chang等[26]認為,涂層的3/*2比值與涂層的耐磨性成正比,3/*2的增加有望提高涂層的彈性回復(fù)率,改善涂層的韌性。由圖7可見,Zr-B-N涂層的/和3/*2呈現(xiàn)相似的變化趨勢,隨著N2+H2的通入,制備出的Zr-B-N涂層的/和3/*2值均高于ZrB2涂層。當(dāng)N2+H2流量為10 mL/min時,/和3/*2值達到最大,分別為0.078、0.2 GPa,推測此時Zr-B-N涂層具有較好的耐磨損性能和韌性,需要進一步實驗求證。
圖7 不同N2+H2流量下制備Zr-B-N涂層的H/E和H3/E*2
不同N2+H2流量下制備的Zr-B-N涂層的劃痕形貌如圖8所示。可以看出,通入N2+H2后,涂層的膜/基結(jié)合力有不同程度的提升。涂層的膜/基結(jié)合力受諸多因素的影響,結(jié)合微觀形貌、硬度和彈性模量分析,經(jīng)充分去除氧雜質(zhì)后,制備出的高純度Zr-B-N涂層具有致密的納米復(fù)合結(jié)構(gòu)。涂層內(nèi)部缺陷的減少,以及/和3/*2值的提升,使Zr-B-N涂層在N2+H2流量為10 mL/min時,臨界載荷達最大值60.1 N,大量的兩相界面有效阻擋了裂紋的萌生和擴展,在劃痕邊界處未發(fā)生涂層大面積剝落現(xiàn)象。
圖8 不同N2+H2流量下制備Zr-B-N涂層的劃痕形貌
不同N2+H2流量下制備的Zr-B-N涂層的磨痕形貌如圖9所示。由圖9可以看出,涂層形貌均比較光滑,磨痕邊緣連續(xù),且存在磨屑堆積,主要表現(xiàn)為磨粒磨損。未通入N2+H2反應(yīng)氣體時和N2+H2流量為7 mL/min時,磨痕寬度較寬。N2+H2流量為10 mL/min時,磨痕寬度最窄,且此時磨屑較少,磨損較輕。不同N2+H2流量下制備涂層的磨損情況與涂層內(nèi)部結(jié)構(gòu)的致密性有較大聯(lián)系,良好的結(jié)構(gòu)致密性使涂層具有較少的內(nèi)部缺陷。外部施加載荷時,涂層抵抗裂紋的形成與擴展的能力越強,使涂層在摩擦磨損試驗中不易脫落產(chǎn)生磨屑,有效地緩解了磨屑在對摩副間的粘著磨損,提高了涂層的耐磨損性能。根據(jù)圖5可知,Zr-B-N涂層在10 mL/min時具有細小的柱狀晶結(jié)構(gòu),且無明顯缺陷,同時此時涂層硬度、彈性模量、/值最高,涂層具有較好的韌性,使其更不易剝落,表現(xiàn)出良好的摩擦磨損性能。
圖9 不同N2+H2流量下制備Zr-B-N涂層的磨痕形貌
不同N2+H2流量下制備的Zr-B-N涂層的平均摩擦系數(shù)和磨損率如圖10、11所示。由圖10可見,隨著N2+H2流量的增加,Zr-B-N涂層的平均摩擦系數(shù)呈現(xiàn)先增大、后減小、再增大的趨勢。N2+H2流量較小時,涂層中的ZrB2硬質(zhì)相多,涂層脆性大,摩擦過程中硬質(zhì)相易發(fā)生脆性剝落,并參與對摩副界面摩擦,使摩擦系數(shù)增大,磨損率提高。如圖9所示,N2+H2流量為4 mL/min時,磨損形貌呈現(xiàn)犁溝狀,此時磨損較為嚴重,可能是由于涂層脆性剝落以及對摩件中脫落的硬質(zhì)顆粒參與磨損所致。進一步增加N2+H2流量至10 mL/min,涂層中軟質(zhì)相的增多,包裹硬質(zhì)相,涂層結(jié)構(gòu)由粗大柱狀晶轉(zhuǎn)變?yōu)榧毿≈鶢罹ЫY(jié)構(gòu),隨著涂層結(jié)構(gòu)的致密,磨痕變窄,磨屑減少,同時摩擦系數(shù)變小為0.72,磨損率在此時最低為1.12× 10–5mm3/(N·m)。
圖10 不同N2+H2流量下制備Zr-B-N涂層的平均摩擦系數(shù)
圖11 不同N2+H2流量下制備Zr-B-N涂層的磨損率
1)反應(yīng)氣體的加入使膜層中的B原子數(shù)減少,B與N生成的BN相對分子量小,自由程大,使膜層中B的含量較低,質(zhì)量較大的Zr原子含量較均勻。隨著N2的持續(xù)增多,靶面鈍化現(xiàn)象逐步加重,涂層逐漸處于氮飽和狀態(tài)。
2)根據(jù)XRD圖分析可知,Zr-B-N涂層內(nèi)主要由沿(001)晶面擇優(yōu)生長的hcp-ZrB2晶粒組成,沒有觀察到氮化物的衍射峰,這表明N元素主要以非晶的形式存在于Zr-B-N涂層中。氮氣含量的增多,使薄膜表面的大顆粒物與液滴明顯減少,表面光滑致密,涂層結(jié)構(gòu)由粗大的柱狀晶轉(zhuǎn)變?yōu)橹旅艿牟A罴毿≈鶢罹ЫY(jié)構(gòu)。
3)微量H元素的摻入,充分還原了真空室內(nèi)氧雜質(zhì),制備出的Zr-B-N涂層晶粒的生長環(huán)境得到改善,當(dāng)N2+H2流量為10 mL/min時,制備的Zr-B-N涂層的硬度和彈性模量達到最大值40.26 GPa和532.98 GPa。此時涂層的臨界載荷也最大,約為60.1 N,摩擦系數(shù)為0.72,磨損率也最低,約為1.12×10–5mm3/(N·m)。
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Structure and Properties of Zr-B-N Nanocomposite Coatings Prepared in Reducing Reactive Atmosphere
1,1,1,2,1,1,3,1
(1. Tianjin Key Laboratory of High Speed Cutting and Precision Manufacturing, Tianjin University of Technology and Education, Tianjin 300222, China; 2. Key Laboratory of Marine Materials and Related Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Zhejiang Ningbo 315201, China; 3. Global Frontier R&D Center for Hybrid Interface Materials, Pusan National University, Busan 609-735, South Korea)
ZrB2coatings have been widely used in industrial fields due to their interesting intrinsic characteristics, such as high melting point, high hardness, excellent oxidation resistance and corrosion resistance, etc. However, they are still restricted to apply on the cutting tool surface owing to their high brittleness. The addition of nitrogen atoms is expected to cause a further improvement on the film toughness through forming nanocomposite microstructure, namely the nanocrystallines ZrN or ZrB2are surrounded by amorphous BN phase. Usually, high purity nitrogen used as reactive gas is produced by physical liquid phase separation method. It is inevitable that small amount of oxygen impurity is remained in it. Because boron is easy to react with oxygen to form amorphous boron oxide. As a result, a large amount of amorphous boron oxide and boron nitride phases existing in the coatings severely affects their mechanical properties. To resolve the above problem, the oxygen impurities in the Zr-B-N coating must be removed. In this work, a new method to prepare high-purity, super-hard and highly wear-resistant Zr-B-N nanocomposite coatings was proposed. Namely, an appropriate amount of reducing hydrogen was mixed into the reactive gas during the coating deposition. Through reduction reaction, the combination of oxygen with elements other than hydrogen would be prohibited, and the oxygen impurities in the vacuum chamber could be removed. Therefore, the purity of the Zr-B-N coating and its related properties could also be improved. In addition, the use of reducing gas in the process of reactive deposition also lowered the technological requirements of coating equipment. A large amount of vacuum pumping time was saved. The coating efficiency was improved and the production cost is reduced.
The pulsed direct current magnetron sputtering technique was used to fabricate a series of Zr-B-N coatings. The coating composition and microstructure were adjusted by using different N2+H2flow rates. For comparison, the ZrB2coating was also prepared no reactive gas used. The mechanical properties, microstructure and tribological properties of the Zr-B-N coatings were systematically investigated. Their variety laws and relative influence mechanisms were deeply analyzed. The surface morphology, chemical composition, hardness, elastic modulus, friction coefficient and wear rate of the coatings were tested by SEM, XRD, EPMA, nano-indenter and tribometer, respectively. The results showed that with the increase of N2+H2flow rate, the N content in the Zr-B-N coating firstly increased rapidly, and then tended to be stable. As the N2+H2flow rate was 10 mL/min, N content reached the highest. The cross-sectional morphology showed that the coating structure gradually changed from coarse columnar crystals to glassy fine columnar crystals, and the coating became denser showing a typical nanocomposite structure. The doping of trace H elements reduced the generation of O-related chemical bonds during the coating preparation. The growth environment of the Zr-B-N coating was also improved. The hardness and elastic modulus of the coatings reached a maximum value of 40.26 GPa and 532.98 GPa at a N2+H2flow rate of 10 mL/min. In this case, the critical load of the coating was about 60.1 N, the friction coefficient was 0.72 and the wear rate reached 1.12×10–5mm3/(N·m). A conclusion can be drawn that the properly mixing hydrogen into reactive gas removes oxygen impurities in the vacuum chamber, and improves the growth environment of the coating. The resulted coating hardness and tribological performance are significantly improved.
reducing reactive atmosphere; Zr-B-N coating; magnetron sputtering; nanocomposite coating; microstructure; mechanical property
2021-08-30;
2021-11-29
ZHANG Ji-fu (1997-), Male, Postgraduate, Research focus: tool coatings.
劉艷梅(1976—),女,碩士,副教授,主要研究方向為硬質(zhì)薄膜。
LIU Yan-mei (1976-), Female, Master, Associate professor, Research focus: hard films.
王鐵鋼(1978—),男,博士,教授,主要研究方向為刀具涂層技術(shù)。
WANG Tie-gang (1978-), Male, Doctor, Professor, Research focus: tool coatings.
張紀(jì)福, 劉艷梅, 張濤, 等. 還原性氣氛制備Zr-B-N納米復(fù)合涂層的結(jié)構(gòu)及性能分析[J]. 表面技術(shù), 2022, 51(9): 83-90.
TG156.88;TB114.2
A
1001-3660(2022)09-0083-08
10.16490/j.cnki.issn.1001-3660.2022.09.000
2021–08–30;
2021–11–29
國家自然科學(xué)基金(51301181, 51875555);天津市科技重大專項(18ZXJMTG00050);天津市自然科學(xué)基金(19JCYBJC17100);天津市科技特派員項目(20YDTPJC01460)
Fund:The National Nature Science Foundation of China (51301181, 51875555); Tianjin Science and Technology Major Project (18ZXJMTG00050); Tianjin Natural Science Foundation (19JCYBJC17100); Special Commissioner Project of Tianjin Science & Technology (20YDTPJC01460)
張紀(jì)福(1997—),男,碩士研究生,主要研究方向為刀具涂層技術(shù)。
ZHANG Ji-fu, LIU Yan-mei, ZHANG Tao, et al. Structure and Properties of Zr-B-N Nanocomposite Coatings Prepared in Reducing Reactive Atmosphere[J]. Surface Technology, 2022, 51(9): 83-90.
責(zé)任編輯:劉世忠