第一次報(bào)告--張成智

1、博學(xué) 睿思 勤勉 致知 報(bào)告人：張成智2015年4月10日不連續(xù)鍍鉻石墨石墨纖維增強(qiáng)銅基復(fù)合材料的微觀結(jié)構(gòu)和熱力學(xué)性能的研究 先碳中心學(xué)術(shù)報(bào)告會(huì)先碳中心學(xué)術(shù)報(bào)告會(huì)Microstructure and thermal properties of copper matrix composites reinforced by chromium-coated discontinuous graphite fibers博學(xué) 睿思 勤勉 致知實(shí)驗(yàn)2 21 13 3介紹結(jié)果與討論Contents第1頁(yè) 目錄（目錄（Content）4 4結(jié)論博學(xué) 睿思 勤勉 致知 前言（前言（Foreword）第2頁(yè) 粉末冶

2、金（powder metallurgy）PM process：powder mixturecompact（obtain green compact） sintering（densification） 粉末冶金:是制取金屬粉末或用金屬粉末（或金屬粉末與非金屬粉末的混合物）作為原料，經(jīng)過(guò)成形和燒結(jié)，制造金屬材料、復(fù)合材料以及各種類(lèi)型制品的工藝技術(shù)。一般球磨博學(xué) 睿思 勤勉 致知 前言（前言（Foreword）第3頁(yè)熱壓燒結(jié)：將干燥粉料充填入模型內(nèi)，再?gòu)膯屋S方向邊加壓邊加熱，使成型和燒結(jié)同時(shí)完成的一種燒結(jié)方法。優(yōu)點(diǎn)：熱壓燒結(jié)由于加熱加壓同時(shí)進(jìn)行，粉料處于熱塑性狀態(tài)，有助于顆粒的接觸擴(kuò)散、流動(dòng)傳質(zhì)過(guò)程

3、的進(jìn)行，因而成型壓力僅為冷壓的1/10；還能降低燒結(jié)溫度，縮短燒結(jié)時(shí)間，從而抵制晶粒長(zhǎng)大，得到晶粒細(xì)小、致密度高和機(jī)械、電學(xué)性能良好的產(chǎn)品。缺點(diǎn)：過(guò)程及設(shè)備復(fù)雜，生產(chǎn)控制要求嚴(yán)，模具材料要求高，能源消耗大，生產(chǎn)效率較低，生產(chǎn)成本高。 熱壓燒結(jié)（hot-pressing sintering）博學(xué) 睿思 勤勉 致知 2、介紹（、介紹（Introduction）第4頁(yè) Materials serving as heat sinks of such electronic devices should have a high thermal conductivity to rapidly dissipa

4、te heat and a low coefficient of thermal expansion (CTE) to effectively minimize thermal stresses. Combining such graphite fibers with high thermal conductive copper in an appropriate way, it is expected to obtain the graphite fiber/Cu composites with high thermal conductivity, low CTE, good machina

5、bility and reasonable cost.粉末冶金可生產(chǎn)梯度散熱材料。散熱片材料(Materials serving as heat sinks)博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第5頁(yè) In the present work, such milled graphite fibers are compounded with Cu powders by hot-pressing sintering. In order to improve the interfacial bonding, chromium, a carbide-forming eleme

6、nt, is coated on the surface of these fibers through chemical vapor deposition (CVD) technique. The microstructure of the resultant Cr-coated graphite fiber/Cu composites are examined by X-ray diffraction, scanning/transmission electron microscopes, and the effects of arrangement,chromium metallizat

7、ion and content of the fiber on the thermal properties in terms of thermal conductivity and CTE are discussed.3.1 實(shí)驗(yàn)過(guò)程(Experiment)博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第6頁(yè)3.2 原料(Raw materials)The milled form of mesophase pitch-based graphite fibers (XN100 type) used in this work was purchased from Nippon

8、Graphite Fiber Corporation.博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第7頁(yè)3.2 原料(Raw materials)The Cu powders used are the gas-atomized spherical Cu powders, having a mean particle size of 14 mm and a purity 99.9%, supplied by General Research Institute for Nonferrous Metals, Beijing, China.博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)

9、（Experiment）第8頁(yè)3.3 石墨纖維的Cr金屬化(Chromium metallization of graphite fibers) CrCl3：provide chromium resource，CrH3：as reducing agent . graphite fibers：CrCl3：CrH3 at a weight ratio of 100：15：4 . The mixture was placed into a deposition chamber of CVD apparatus. The main reaction in current CVD process can

10、 be expressed as: CrCl3（g）+CrH3(s)Cr(s)+3HCl(g) These generated reactive gaseous Cr atoms deposited on the surface of the graphite fibers, forming Cr coating.The average thickness of the Cr coating on the fibers is about 150 nm (SEM圖)博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第9頁(yè)3.4 復(fù)合材料的合成(Consolidation of co

11、mposites)The Cu powders with varying contents of Cr-coated graphite -fibers (35, 40, 45, 50 and 55 vol%) were dry mixed at room temperature by using a 3-D vibratory mill for 8 h with rotary speed of 2500 rpm. Vacuum hot-pressing sintering system (Model HighMulti 5000, Fujidempa Kogyo Co. Ltd., Japan

12、) was used to synthesize the Cr-coated graphite fiber/Cu composites.A sheet of graphite felt was placed between the punch and the powders as well as between the die and the powders for easy removal.博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第10頁(yè)3.5 復(fù)合材料的性能(Characterization) Bulk density：the water immersion met

13、hod based on Archimedes law and compared with the theoretical density. The morphology and fracture surface：LEO-1450 SEM. The phases：X-ray diffraction (XRD) conducted on Siemens D5000 diffractometer using Cu Ka radiation. Interface area ： LEO JSM-7001F field emission (FE)-SEM and JEM-2100 transmissio

14、n electron microscopy (TEM).博學(xué) 睿思 勤勉 致知 3、實(shí)驗(yàn)（、實(shí)驗(yàn)（Experiment）第11頁(yè)3.5 復(fù)合材料的性能(Characterization) =Thermal conductivityComposite density：water immersion methodThermal diffusivity：differential scanning calorimetry Heat capacity C：a laser flash apparatusCoefficient of thermal expansion (CTE)：PerkineElmer

15、TMA7 dilatometer in temperature range 20-2500C . 博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第12頁(yè)4.1 復(fù)合材料的微觀結(jié)構(gòu)(Microstructure of the composites)Density measurements show a post-sintering densification of96.5% Fig.2 The graphite fibers are homogeneously distributed in the Cu matrix. There is al

16、most no specific degradation of the fibers, separated interfaces, or evident pores can be observed. Moreover, the densification process leads to a preferential orientation of the fibers in the plane (X-Y) perpendicular to the pressing direction (Z). Their properties will be highly anisotropic.博學(xué) 睿思

17、勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第12頁(yè)4.1 復(fù)合材料的微觀結(jié)構(gòu)(Microstructure of the composites)博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第13頁(yè)4.1 復(fù)合材料的微觀結(jié)構(gòu)(Microstructure of the composites)Fig. 4(a) presents FE-SEM micrograph of the interface area ob-tained from the composite with 50 vol% fib

18、ers. A continuousinterlayer of a contrast (dark gray) different from those of graphitefiber (black gray) and Cu matrix (light gray), about 130 nm thick on the average, is clearly visible in the second electron (SE) mode. Combined the results from XRD analysis, it can be verified that this interlayer

19、 is the chromium carbide layer. 博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第14頁(yè)4.1 復(fù)合材料的微觀結(jié)構(gòu)(Microstructure of the composites)At this scale of observation, the overall morphology of this interface region exhibits a neat profile, where the thin and uniform Cr3C2 interlayer is tightly adhered t

20、o both the fiber and Cu matrix. Moreover, the detailed observation of the Cr3C2/graphite fiber interface was determined by TEM in Fig. 4(b) 博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第15頁(yè)4.2 纖維排列對(duì)熱力學(xué)性能的影響(Effect of ber arrangement on thermal properties)Obviously, such planar arrangement of th

21、e fibers makes the axial high thermal conductivity and low CTE of the fibers have a much higher degree of utilization in the X-Y direction than that in the Z direction of the composites.博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第16頁(yè)4.3 纖維Cr金屬化對(duì)熱力學(xué)性能的影響(Effect of fiber chromium metallization

22、on thermal properties)Fig. 5 presents the TEM micrograph of the interface of the uncoated composite. the adhesion between graphite fiber and Cu matrix is very weak, because some nano-sized interfacial gaps are often observed. According to the C/Cu phase diagram, the C solubility in Cu is negligible.

23、 copper is known to be chemically inert with respect to carbon. The chemical incompatibility of carbon and copper can result in a weak mechanical interfacial bonding between graphite ber and Cu matrix, therefore to severely reduce the thermal conductivity of the uncoated composite. 博學(xué) 睿思 勤勉 致知 4、結(jié)果與

24、討論（、結(jié)果與討論（Results and discussion）第17頁(yè)4.3 纖維Cr金屬化對(duì)熱力學(xué)性能的影響(Effect of fiber chromium metallization on thermal properties)An improved interfacial adhesion, by contrast, was obtained due to the formation of a continuous Cr3C2 interlayer，but the Cr3C2 itself has a very low thermal conductivity. which is

25、much lower than that of the graphite fiber or copper, so Under the premise of ensuring the ability to form a good combination between graphite fiber and Cu matrix, the thickness of the layer should be as small as possible. Nevertheless, the optimum thickness for the layer or the prior Cr coating nee

26、ds to be further studied in the following work.博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第18頁(yè)4.3 纖維Cr金屬化對(duì)熱力學(xué)性能的影響(Effect of fiber chromium metallization on thermal properties)A large number of studies about the thermal expansion behaviors ofcomposites have shown that the CTEs of composites a

27、re not onlydetermined by the thermal expansions of reinforcement and matrix themselves, but also by the restriction of reinforcement to the thermal expansion of matrix through interfaces . Fig. 6 gives the SEM fracture images of the both uncoated and Cr-coated composites with 50 vol% bers. The fract

28、ure surfaces are parallel to Z direction.博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第19頁(yè)4.3 纖維Cr金屬化對(duì)熱力學(xué)性能的影響(Effect of fiber chromium metallization on thermal properties)From the above discussions, it can be concluded that using chromium metalized graphite fiber, the formed interlayer with a

29、strong adhesion force with the fiber and copper caused the interface structure of the graphite fiber/Cu composite to change from mechanical bonding into metallurgical bonding, thus the heat and load transfer abilities between the fiber and Cu matrix can be improved, which are effective for enhancing

30、 thermal conductivity and reducing CTE of the composites.博學(xué) 睿思 勤勉 致知 4、結(jié)果與討論（、結(jié)果與討論（Results and discussion）第20頁(yè)4.4 纖維含量對(duì)熱力學(xué)性能的影響(Effect of fiber content on thermal roperties) when the fiber content exceeds 50 vol%, the thermal conductivity of the composite began to decline and difficulties to the densification. This can be attributed to the decreased densities of the composites. As we all know, pores are harmful to the thermal conductivity. This is probably due to the fact that fibers are more easily to adja