Study on QTi3.5-10graphite slurry

Vol. 14 No. 1Trans. Nonferrous Met. Soc. ChinaFeb. 2004Article ID: 1003 - 6326(2004)01 -0148 -04.Study on QTi3. 5-10graphite slurry' DZHANG Peng(张鹏)'，DU Yun-hui(杜云慧)', LIU Han- wu(刘汉武)'，ZENG Da-ben( 曾大本)”，CUI Jian-zhong( 崔建忠), BA Li-min(巴立民)*( 1. Department of Mechanical Engineering, Beijing Jiaotong University, Beijing 100044， China;2. Department of Mechanical Engineering， Tsinghua University, Beijing 100084, China;3. Metal Forming Department， Northeastern University, Shenyang 110004, China;4. Anshan Automobile Fittings Factory, Anshan 114014, China)Abstract: QTi3. 5-10graphite( mass fraction, %) slurry was prepared using electromagnetic -mechanical stirringtechnology. The distribution of graphite particles in QTi3. 5-10graphite slurry was studied using cold quenchingmethod. The results show that solid fraction of QTi3. 5- l0graphite slurry increases with the decreasing stirring tem-perature. There is a linear relationship between solid fraction and stirring temperature. With increasing solid frac-tion, the rising of graphite particles in slurry is restricted gradually. When the solid fraction is larger than 42.5%，the rising of graphite particles in slurry can be controlled, and QTi3.5-10graphite slurry with uniform distribution ofgraphite particles can be prepared.Key words: QTi3. 5; electromagnetic mechanical stirring; graphite particles; solid fractionCLC number: TD146.2Document code: A1 INTRODUCTIONgraphite particles in copper alloy matrix should bedeveloped.Copper- graphite is an ideal material for theIn this work，QTi3. 5-10graphite slurry wasslide of locomotive electricity-catching bowl1prepared using electromagnetic mechanical stirringGraphite hasexcellent lubricating property-2] .technology. The distribution of graphite particlesCopper alloy such as yellow brass, bronze has per-in QTi3. 5-10graphite slurry was studied and thefect electrical conductivity-3]. Therefore， copper-condition for preparing QTi3. 5- 10graphite slurrygraphite has a very wide application in slide- electri-with uniform distribution of graphite particles wascal field41.obtained.However, the properties of copper alloy andgraphite are very different. The density of copper2 EXPERIMENTALalloy (about 8.8X10-3 kg/m3) is much larger thanthat of graphite (about 2. 2X10-3 kg/m2), and theThe materials used in this experiment isfreezing range of the former about 875-1 085 C isQTi3.5 and the graphite particles size is about 60much lower than that of the latter 3 700 'C[5].μm. QTi3.5 is a copper alloy which contains 3. 5%Graphite particles are always buoyed by copper al--4.0% Ti, and less than 0. 5% impurity (As，Sb,loy liquid, and it is very difficult for graphite parti-Sn, Si, Al, Pb, P, Fe, Bi, Zn, Mn). Its freezing .cles to distribute evenly in molten copper alloy.range is about 890 - 1 070 C(Fig. 1)47，and theAt present， the available way to realize thedensity is about 8. 8X10 -3 kg/m3uniform distribution of graphite particles in copperThe experimental procedures were as fol-alloy matrix is powder metallurgy method-61lows:However, this method includes too many working1) Preparing QTi3. 5 liquid. The temperatureoperations such as powder manufacturing，powderof the liquid was 1 200 C. The liquid must be demixing，high temperature sintering and wastes toogassed.much energy. The cost of product is very high.2) Preparing QTi3.5-10graphite slurry. Fig. 2F urthermore, too more cavities in copper alloy ma-shows the diagram of QTi3. 5- 10graphite slurry-trix deteriorate the properties. Thus the applica-making apparatus ( being patent). It includes threetion of this material is limited. Therefore, a newmail中国煤化工-magnetic stirrer， mmethod to realize the uniform distribution ofchanYHCNMHG.. graphite crucible. E-①Foundation item: Projects (50274047. 50304001) supported by the National Natural Science Foundation of China; project supported byBeijing Jiaotong University FoundationReceived date: 2003 -04 - 15; Accepted date: 2003 -07 - 21Correpondenee.ZHANG Peng, Professor, PhD; Tel: + 86-10-51682226; E mail: zhangp9@ 263. netVol. 14 No. 1Study on QTi3. 5-10graphite slurry ..149●1 200N pole↓Graphite crucibleSlury1 1001 084.5 CS pole ,L+CuTi10001.+2920 C1.+Cu3Ti2O2 900-。855 C875 C 27> 32.5k /4.4|L+CugTf800700x+Cu;Ti|CuzT2+Cu3Ti| CuTi+MaskCugTi2600Cu02030CoolerHeater(aFig. 1 Cu-Ti binary equilibrium diagramA-AUpper cover |Thermocouplelectromagnetic stirrer is made up of three couplesAr gas pipeof electric poles which distribute around the cruci-ble evenly. Its main role is to break up the dendrit-ic crystal in the process of solidification by circular .motion of slurry. Its power is 10 kW. Mechanicaluniform device is a fluid director designed special-ly. It can move up and down by using an assistantelectric device. Its main role is to enlarge the stir-ring intensity and to accelerate the deconcentrationof graphite particles in the whole crucible. Graph-ite crucible is a temperature- adjusting container.Uniform deviceSpigotThere are holes in its wall evenly. These holes(b)contain heaters and coolers so as to adjust the tem-perature of slurry. There is a hole at the bottom ofthe crucible. Its role is to let out the slurry. Be-Fig.2 Diagram of QTi3. 5-10graphitecause the solidus liquidus interval of QTi3.5 is 180slurry- making apparatusC，the solid fraction ( volume fraction)of slurry ismainly controlled by stirring temperature. Theprocess of making QTi3.5-10graphite slurry was asserved directly after cold quenching.4) Conduct SEM experiment to determine thefollows: first， the crucible was preheated up to 1solid fraction of slurry and the distribution of000 "C by using the heaters. After the QTi3. 5 liq-uid (1 200 C) and 60 μm graphite particles weregraphite particles in slurry.put into the crucible，the upper cover was overlaidand Ar gas was inlet through the gas pipe in order3 RESULTS AND DISCUSSIONto prevent the liquid and graphite particles fromoxidizing.' Then， the electromagnetic stirrer and3.1 Relationship between solid fraction and stir-the mechanical uniform device were switched onring temperature of QTi3.5-10graphite slurryand the cooling mediator was pumped into the cool-When the temperature of a metal is lower thaning pipe to cool the liquid until down to the re-its melting point， dendritic crystal can be formedquired temperature. The heaters were switched onand the proportion of this solid metal to the wholeto keep the temperature stable by adjusting themetal is called solid fractionl91. Under the action ofcurrent. The precision of temperature was士0. 5stirring，the dendritic crystal will be broken up andC. After a certain time of stirring at constant tem-gradually change. into solid Darticles which distrib-perature，the slurry with required solid fractionute中国煤化工mly. So the metal be-could be prepared. In this experiment, the stirringcomYHC N M H Glicates the experimen-time was 20 min.tal data ot the sold traction of QTi3. 5-10graphite3) Cold quenching experiment-8]After theslurry at different stirring temperatures. Afterslurry was prepared, the spigot was opened andtheoretical regression analysis， the regressionthe slurry at the bottom of crucible was let out intoquation about solid fraction of QTi3. 5-10graphitewater, atructure of slurry could be reslurry and stirring temperature is●150●Trans. Nonferrous Met. Soc. ChinaFeb. 2004Table 1 Solid volume fraction and .10graphite slurry, the content of graphite particlesstirring temperatureincreases gradually, namely, the rising of graphiteSampleSolid volumeStirring temperature/ Cparticles is restricted constantly. When the solidNo.fraction/ %fraction was larger than 42. 5%，the content ofgraphite particles is 10% basically. It can be seen101 070that when the solid fraction of QTi3. 5- 10graphite23.51 065slurry is larger than 42. 5%，the rising of graphite35.21 060particles is removed, and the graphite particles candistribute evenly in the QTi3. 5-10graphite slurry.41 055Table 2 Solid volume fraction and content of511.11 050graphite particles616. 11 045Sample :Content of graphiteparticles/ %18. 61 040824.31 0352.5926.11 0305.00.51(28.41 0257.51.034. 31 02010.01.736.61 01512.52.41:41.51 010715. 03.21444.7100517.53.748. 71 00020.04.31699522. 54.856.299025.057.198527.55.81961.398030.06.6f.=753.9- 0.706 t(1)32. 57.8where f。 is solid fraction; t is stirring tempera-1535. 08.6ture. The regression coefficient R is 0.998 88，and1037.59.1this proves that Eqn. (1) gives a correct relation-ship between solid fraction and stirring tempera-40.09.8ture of QTi3. 5-10graphite slurry.42. 53.2 Distribution of graphite particles in QTi3. 5-45. 010graphite slurry2(47.5The difference of density between graphite andQTi3.5 will result in the rising of graphite parti-2.50.010. 0cles in molten QTi3. 5-10graphite. The nearer tcthe bottom of slurry， the less the graphite parti-cles. If the distribution of graphite particles in the3.3 Discussionwhole slurry is uniform，the quantity of graphiteUnder the action of strong electromagneticparticles at the bottom of slurry will be 10%.mechanical stirring， graphite particles can get e-Therefore，the content of graphite particles innourealize the distributionslurry at the bottom of crucible was used to deter-in|中国煤化Iditional energy SEmine the distribution of graphite particles in QTi3.s[11TYHCNMHG5- l0graphite slurry. The nearer to 10% of graphite△E= ZoE,particles，the more uniform the distribution ofgraphite particles in the whole slurry.' The experi-where△E; represents additional surface energy,mental data. are. listed in Table 2. It can be seenadditional potential energy, additional kinetic ener-that，witHA秘aasing solid fraction of QTi3. 5-gy and additional buoyancy energy， respectively.Vol.14 No. 1Study on QTi3. 5-10graphite slurry .●151●However, graphite particles will move up to themechanical stirring technology.top of molten QTi3. 5 because of the difference ofdensity between graphite and QTi3. 5. The veloci-CONCLUSIONSty V is[12V=a(ρ1一ρ2)●r2/η(3)where a is a coefficient; ρ1 is the density of1) For QTi3. 5-10graphite, slurry can be pre-QTi3.5; ρ2 is the density of graphite; η is the vis-pared by electromagnetic mechanical stirring tech-cosity of molten QTi3. 5.nology.' The relationship between solid fractionFrom Eqn. (3)，it can be seen that, the smal-and stirring temperature isler the viscosity of molten QTi3. 5，the larger thf。=753. 9-0. 706tvelocity. It is well known that， the higher the2)Withincreasing solid fraction oltemperature of molten metal， the smaller the vis-QTi3.5-10graphite slurry， the rising of graphitecosity. For QTi3.5- l0graphite slurry, when theparticles in slurry reduces gradually. When thesolid fraction is zero， the temperature is the high-solid fraction is larger than 42. 5%，graphite parti-est(1 070 C )，the viscosity is the smallest， andcles can distribute evenly in QTi3. 5- l0graphitethe rising velocity of graphite particles is the lar-slurry. This establishes a useful basis for semi-sol-gest. Therefore， no graphite particles existed atid processing of QTi3. 5- l0graphite.the bottom of slurry stably.However，when the solid fraction is largerREFERENCESthan zero，with increasing solid fraction,the tem-perature decreases, the viscosity increases, and the[1] Wang Z. Application of composite materials in high-rising velocity of graphite particles decreases grad-speed Train[J]. Mater Mecha Eng, 2001, 25(10): 1 -ually. Furthermore， more and more primary4. (in Chinese)QTi3.5 solid particles in slurry hinder the vertical[2] LI S. Graphite [ M]. Bejing: Chemistry Industrymotion of graphite particles. Therefore， the risingPress，1991. 11 - 23. (in Chinese)of graphite particles is limited continuously， and[3] Kovacik J. Electrical conductivity of Cu/ graphite com-the content of graphite particles at the bottom ofposite materials as a function of structural characteris-slurry increases gradually. When the solid fractiontics[J]. Scripta Materialia， 1996, 35(2): 151- 155.reaches about 42.5%，the large viscosity and the[4] Rohatgi P. Metals Handbook[M]. OH: ASM Inter-surrounded primary QTi3. 5 solid particles restrictnational, 1992. 801 - 818.the rising of graphite particles completely. Thus[5]ZHE J. The Welding of Copper and Copper Alloy[M]. Beiing: Chemistry Industry Press， 1979. 9slurry reaches its largest value of 10%，and graph-12. (in Chinese)ite particles distribute in the slurry evenly. Fig. 3[6] Mackay M L. Innovation in powder metallurgy: an en-shows the stereoscan photograph of the sample .gine bearing material [J]. Metal Progress, 1997(6):whose solid fraction is 42. 5%. The dark parts are32 - 36.graphite particles， the white parts are primary[7] CAI J. Metallographical Atlas of Copper and CopperQTi3.5 solid particles. It can be seen that the dis-Alloy[ M]. Bejing: Metallurgical Industry Press,tribution of graphite particles and the primary1983.117- 121. (in Chinese)QTi3.5 solid particles are relatively uniform. This[8] ZHANG P. The influence of solid fraction on gravity .illustratesthatuniformQTi3.5-10graphitesegregation of Sn in AI 20Sn alloy casting[J]. J MaterSci Technol, 2000，16(6): 577-579. .slurry can be prepared by using electromagnetic-[9] Stuart B B. Semi-solid processing [J]. Advanced Ma-terials &. Processes, 1993(1): 36-42.[10] ZHANG P. Semi- solid processing of Al 7graphitecomposite[J]. J Uni Sci Technol Bejjing， 2001, 8(3): 203 - 205.[11] LI J. Study on the mechanism of the mixture of liquidAl with SiCp particles [J]. Special Casting and Non-ferrous Allov, 2001(5): 139 - 142. (in Chinese)[12]中国煤化工lopment of alumina basedMHCNMHGed with particles [J ].soutary, 1000，41: 16- 21. (in Chinese)60 um[13] Merton C F. Behavior of metal alloys in the semi-sol-id state[J]. Trans A. 1991, 5A: 957 - 603.Fig.3 Structure of slurry( Edited by LI Xiang-qun)