自蔓延燃燒合成法制備分層及梯度結構的Ni-Al/金剛石復合材料研究

盧家鋒,張鳳林,楊志峰,周玉梅

自蔓延燃燒合成法制備分層及梯度結構的Ni-Al/金剛石復合材料研究

盧家鋒,張鳳林,楊志峰,周玉梅

(廣東工業(yè)大學機電工程學院,廣州 510006)

采用自蔓延燃燒合成法制備了分層及梯度結構的Ni-Al/金剛石復合材料。研究了多層及金剛石粒度梯度結構對Ni-Al/金剛石復合材料其自蔓延反應過程及微觀相貌的影響。結果表明：隨著分層數(shù)的增加,自蔓延反應的燃燒波速度下降；自蔓延反應在金剛石粒度梯度結構的燃燒波速率比其在金剛石分層結構的速率快。微觀形貌分析表明,自蔓延反應使得釬料合金Ni-Cr與金剛石生成了強碳化合物Cr3C2和Cr7C3,增強了金剛石和合金粉末基體的結合力。

自蔓延燃燒合成；分層SHS結構；梯度SHS結構；Ni-Al金屬間化合物；金剛石

金剛石具有硬度高,熱導率高,耐腐蝕性能良好等優(yōu)點,使得其被廣泛地應用于各種超硬材料工具制備中[11]。金剛石工具常用的制造方法有:真空熱壓燒結法,電鍍法以及高溫釬焊法等。[7,16,17]其中高溫釬焊法能使金剛石與Ni-Cr或者Cu-Sn-Ti釬料合金產(chǎn)生高強度的化學結合[4,5],所制備的金剛石工具有較高的出刃高度,大大提高了金剛石工具的工作效率[8]。

自蔓延高溫合成法(SHS)可以在短時間內(nèi)對材料進行快速致密化。此外,自蔓延高溫合成法適合于制備具有多層結構的材料。如以TiC或MoC為粘結劑制備的梯度金剛石復合材料[1,9],以Ti-B和金剛石制備的具有多層功能梯度結構的材料(FGM)[12-14]。在我們之前的研究中,基于Ni-Al金屬間化合物體系,用自蔓延的方法制備了一個金剛石磨具,但是通過磨削實驗發(fā)現(xiàn),自蔓延反應后金剛石磨粒的抗壓強度下降了約20%[24]。此外,我們還發(fā)現(xiàn)在Ni-Al金屬間化合物體系中加入Ni-Cr-P, Cu合金粉末和B元素能降低自蔓延反應中燃燒波的速率,使得反應更穩(wěn)定,并且能改善反應產(chǎn)物的微觀結構形貌[10,15,23]。

在本試驗中用自蔓延方法制備了分層和梯度結構的Ni-Al/金剛石復合材料,并且研究了分層數(shù)量和梯度結構對自蔓延反應過程和復合材料微觀形貌的影響,為優(yōu)化金剛石工具的結構和材料設計提供了依據(jù)。

1 實驗方法

本文所用的原料如表1所示,其中Ni、Al、B粉末采購于北京中金研新材料有限公司。金剛石采購于ElementSix公司,粒徑為60/70目、120/140目、325/400目。

表1 試驗原料的特性Table 1 Characteristics of the raw materials

多層結構分為Ni-Al層和金剛石層。其中Ni-Al層的成分包括Ni粉、Al粉(化學計量比為Ni∶Al =1∶1),以及60 wt.%的稀釋劑,稀釋劑的成分為60 wt.%Ni-Cr,35wt.%Cu和5wt.%B。金剛石層的成分:目數(shù)為325/400的金剛石,60 wt.%的稀釋劑。將Ni-Al層和金剛石層材料分別用行星式球磨機進行球磨混合,其中球磨機的轉速為150 r/min,時間為6 h,球料比為5∶1。Ni-Al/金剛石復合材料多層結構如圖1所示,具體分層參數(shù)如表2所示。

圖1 自蔓延反應多層結構示意圖Fig.1 Schematic diagram of multilayer design of self-propagating reaction

表2 分層結構具體參數(shù)Table 2 The specific parameters of layered structure

如圖2所示,金剛石粒度梯度結構分為四個,每個梯度高度為5 mm,最上面為Ni-Al層;其余的為金剛石層,金剛石層金剛石的濃度為5wt.%。將多層結構和梯度結構的Ni-Al/金剛石混合料放到Φ8 ×15mm的圓柱形磨具中冷壓成型,壓強為60 MPa。最后,自蔓延反應,反應通過一根直徑為0.28 mm的鎢絲引燃,并在一個真空度為0.1 Pa的爐內(nèi)進行,反應如圖3所示。

圖2 自蔓延反應粒度梯度結構示意圖Fig.2 Schematic diagram of particle gradient structure of self-propagating reaction

圖3 自蔓延反應合成和冷壓模具示意圖Fig.3 The schematic diagram of SHS and the cold pressing mold

SHS反應速率通過彩色攝像機以25 frames/s拍攝并計算。將反應后的樣品表面及縱切面用金剛石砂紙和研磨膏進行拋光,然后用體積分數(shù)為1∶1∶1的硝酸,鹽酸,酒精腐蝕液進行腐蝕。采用型號為HITACH S3400的電子掃面顯微鏡分析樣品的斷口形貌,并利用X射線能譜儀對SHS基體、金剛石與SHS基體界面等做元素的線分布分析。

2 實驗結果與討論

2.1 多層結構對SHS過程的影響

如圖4所示,隨著Ni-Al/金剛石層數(shù)的增加, SHS過程的燃燒波速率下降。這是因為層數(shù)越多,稀釋劑的含量就越多,稀釋劑中Ni-Cr合金融化時吸收了大部分Ni-Al自蔓延反應的熱量,使得燃燒波速率下降,反應變得更慢。B、TiC和VN也能在自蔓延反應中產(chǎn)生相似的效果[20-22]。

圖4 層數(shù)對燃燒波速率的影響Fig.4 Inflence of the number of layer on combustion velocity

3、4、6和10層結構的SHS過程如圖5、6、7、8所示?？梢园l(fā)現(xiàn),對于3層結構的SHS過程其平均燃燒波速率為15 mm/s。在0.48 s到0.88 s之間的速率是不均勻的,越往后面其速率越快,這可能是因為隨著反應的進行,底部的物料得到了一定的預加熱作用。

圖5 3層結構樣品的SHS過程Fig.5 Images of SHS process of three-layer structure sample

從圖6可以看出,4層結構樣品的SHS過程穩(wěn)定,燃燒波的速率為14.42 mm/s,反應后樣品的形狀保持良好。如圖7所示,6層結構樣品的燃燒波速率為13.89 mm/s,此外可以明顯地看出燃燒波在金剛石層的速率要比在Ni-Al層的速率小。圖8是10層結構樣品的SHS過程,其反應時間為1.52 s,燃燒波的速率為9.87mm/s,反應火焰呈淡黃色。

2.2 多層結構Ni-Al/金剛石微觀結構

多層結構Ni-Al/金剛石微觀相貌如圖9(b)所示。在Ni-Al層可以看到自蔓延高溫合成反應常見的微孔結構;而在金剛石層,可以看到Ni-Cr釬料合金和Ni-Al緊緊的包覆著金剛石,為金剛石提供了較大的把持力。

圖6 4層結構樣品的SHS過程Fig.6 Images of SHS process of four-layer structure sample

圖7 6層結構樣品的SHS過程Fig.7 Images of SHS process of six-layer structure sample

圖8 10層結構樣品的SHS過程Fig.8 Images of SHS process of ten-layer structure sample

圖9 4層結構示意圖及微觀形貌(a),Ni-Al層微觀相貌,(b)金剛石層微觀形貌(c)Fig.9 The schematic diagram of four-layer structure and microscopic appearance(a),SEM images of Ni-Al layer, (b)microscopic appearance of diamond layer(c)

圖10為多層結構Ni-Al/金剛石復合材料的X射線衍射圖,圖中主峰為NiAl、Ni-Cr、Cr3C2和Cr7C3。因為Ni-Al自蔓延高溫合成反應在溫度達到750℃時,鋁已經(jīng)融化而鎳還沒有,反應屬于過鋁的狀態(tài),首先生成NiAl3,隨著反應的進行,溫度不斷升高,然后出現(xiàn)Ni2Al3,最后才生成NiAl,這表明反應已完全進行[2]。

2.3 金剛石粒度梯度結構對SHS過程的影響

金剛石粒度梯度結構SHS過程如圖11所示?？梢钥吹阶月臃磻獮榉€(wěn)態(tài)燃燒模式,燃燒波的速率為55.56 mm/s。燃燒波在梯度結構反應中速度比在多層結構中傳播的速度要快。這是因為金剛石粒度梯度結構中稀釋劑相對于多層結構少,故燃燒波的傳播受到的影響較小。

2.4 金剛石粒度梯度結構Ni-Al/金剛石微觀結構

每個梯度的微觀形貌如圖12所示。可以看到金剛石嵌入到Ni-Al基體中,被Ni-Al緊緊地包覆著,表明金剛石與Ni-Al結合強度較好。從圖13的線掃描可以看到Cr元素富集在金剛石的表面,這和其他釬焊金剛石工具的研究發(fā)現(xiàn)一致[3,6,19]。這是因為在高溫條件下金剛石易與Cr元素形成強碳化合物如Cr3C2和Cr7C3[18]。同時也解釋了圖10出現(xiàn)Cr3C2和Cr7C3物相的原因。

圖10 3層結構樣品的X射線衍射圖Fig.10 X-ray diffraction patterns of three-layer structure sample

圖11 金剛石粒度梯度結構SHS過程Fig.11 Images of SHS process of diamond particle gradient structure

圖12 金剛石粒度梯度結構示意圖及微觀形貌(a),金剛石和合金基體SEM,325/400目、(b)120/140目(c)、60/70目(c)Fig.12 The schematic diagram of diamond particle gradient structure and microscopic appearance(a),SEM images of the diamond and alloy matrix,325/400 meshs(b),120/140 meshs(c),60/70 meshs(d)

圖13 金剛石粒度梯度(325/400)EDX線掃描區(qū)域SEM(a),EDX線掃描區(qū)域BSEM(b), EDX碳的線掃描結果(c)、鉻(d)、鎳(e)、鋁(f)Fig.13 SEM of EDX line scanning area of diamond particle gradient(325/400)(a),BSEM images of EDX line scanning area(b),line scanning result of EDX of C(c),Cr(d),Ni(e),Al(f)

3 結 論

多層結構及金剛石粒度梯度結構的Ni-Al/金剛石自蔓延反應是穩(wěn)態(tài)燃燒的過程。在多層結構中,隨著層數(shù)的增加,燃燒波的速率降低,燒波在Ni-Al層中的傳播速度比在金剛石層中快;金剛石與Ni-Al的結合良好,自蔓延反應使得釬料合金Ni-Cr與金剛石生成了強碳化合物Cr3C2和Cr7C3。

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Study of Layered and Gradient Structural Ni-Al/Diamond Composite Prepared by SHS Method

LU Jia-feng,ZHANG Feng-lin,YANG Zhi-feng,ZHOU Yu-mei
(School of Mechanical and Electronic Engineering,Guangdong University of Technology,Guangzhou,China 510006)

The layered and gradient structural Ni-Al/diamond composite has been prepared by SHS method.The influence of the multilayer nature and the diamond particle size gradient structure on the self-propagating reaction process and microscopic appearance of Ni-Al/diamond composite has been studied.Result shows that as the number of layers increases,the combustion wave velocity of the self-propagating reaction decreases;the combustion wave velocity of the self-propagating reaction in the diamond particle gradient structure is higher than that in the diamond layered structure.The microscopic appearance analysis result shows that strong carbon compounds,Cr3C2and Cr7C3,were created by solder alloy Ni-Cr and diamond through self-propagating reaction,which strenghens the adhesion of diamond and the alloy powder matrix.

SHS;Layered SHS structure;gradient SHS structure;Ni-Al intermetallics; diamond

TQ164

A

1673-1433(2017)04-0019-08

2016-11-15

項目獲得國家自然科學基金(51275096)、廣東省自然科學基金(2015A030313491)和廣東省科技計劃(2013B010204025)資助

盧家鋒(1988-),男,在讀研究生,從事超硬材料及磨料磨具研究。

張鳳林(1972-),男,博士,教授,主要研究方向為超硬材料工具制造硬脆材料加工及仿真。E-mail:zhangfl@gdut.edu

盧家鋒,張鳳林,楊志峰,等.自蔓延燃燒合成法制備分層及梯度結構的Ni-Al/金剛石復合材料研究[J].超硬材料工程,2017,29(4):19-26.