材料学外文资料翻译

材料学外文资料翻译

DC resistivity of alumina and zirconia sintered with TiC Central Glass and Ceramic Research Institute，Kolkata 700 032，India College of Ceramic Technology，Kolkata 700 010，India

MS received 20 October 2003; revised 11 February 2005 Abstract：Pure alumina and zirconia powders were sintered separately with increasing amount of TiC up to ~ 65 vol.%，as a conducting second phase with an aim to prepare conducting structural ceramics which can be precisely machined by EDM technique. TiC did not help in sintering the parent phase but it decreased the d.c. resistivity of the composite to 1 ohm.cm at ~ 30 vol.% loading. The conductivity is explained by the effective media and percolation theories.

Keywords. Alumina; zirconia; titanium carbide; composite; electrical conductivity; electrical resistivity

1.introduction

Attempts have been made in different directions to improve the mechanical properties of the structural ceramics. Promising among them is a second phase reinforcement in the parent matrix. The ceramics of superior mechanical properties in turn give rise to time consuming finishing processes which are quite expensive. As a solution to this problem，a newer technique of finishing the components at a faster rate and at a relatively reduced cost viz. electro discharge machining (EDM) technique，has been applied in some cases. The technique essentially needs the components to be electrically conducting (resistance < 100ohm-cm). The electrically conducting and compatible second phase materials such as nitrides (TiN)，

borides(TiB2)，carbides (TiC) and silicides (MoSi2，Ti–Si)，the electrical resistivity of which are in the range of 13–50 ×10–6 ohm-cm，may impart conductivity to the matrix. The reinforcing second phase may also improve mechanical properties of the material. The electrical conductivity of the matrix is directly dependent on the size and amount of the conducting second phase grains，in general (Pierson 1996).

Research in this direction was carried out mainly with engineering ceramics like Si3N4，SiC etc (Matkin et al 1972; Bellosi et al 1989; Mclachlan et al 1990; Sawaguchi et al 1991; Nakayama and Kuroshima 1992). Si3N4 when sintered with SiC nanoparticle (Sawaguchi et al 1991) reduced the resistivity of the composite—the effect was remarkable above 10% SiC. Resistance with 25% SiC

was found to be ~ 1 × 107 W cm and the composite behaved like a semiconductor. The critical volume of SiC at the boundaries of sintered Si3N4 grains was 17% and the electrical behaviour of the composite followed the percolation theory. Up to 10%

SiC increased the fracture toughness of the composite. Si3N4 sintered with TiN (Nakayama and Kuroshima 1992) without any other additive

reduced impedance of the composite from ~ 1 ×107 W cm to ~ 1 × 103 W cm when measured in the presence of moisture. A lot of work was done on SiC based material as the use of SiC in electrical/electronic devices is wide， e.g. making heating elements，semiconductors，sensors，varistors，etc. Al2O3 and ZrO2 are two other common structural engineering ceramic materials. Scanty reports are available on increasing electrical conductivity of the materials (Guicciardi 1992; Buerger 1994; Krell et al 1995; Mao et al 1998; Wang et al 1998) or in the related field. Mao and co-workers (1998) worked on cobalt coated Al2O3–TiC composite and measured only the abrasion resistance of the composite. They showed that the role of cobalt coating was important and it was responsible for wear damage. Buerger (1994) used up to 50 wt.% TiC with Al2O3. DC resistivity decreased from 1 × 1012 to ~ 1 ×10–3 W cm with 45% TiC. The conductivity was explained by the model of connectivity of TiC particles. TiC，up to 30 wt.%，increased flexural strength of the composite. Krell and co-workers (1995) used 30% TiC with ZrO2 with or without

TiH2. TiH2 changed the stoichiometry of TiC in the sintered matrix. The grains were free from amorphous phase; the strength and toughness of the composite was similar to 3Y-TZP. Bellosi and co-workers (1989) studied in detail the Al2O3 based composites. They used 20 and 30 vol.% of TiC/TiN or TiB2 and measured the CTE，E-modulus，Vicker’s hardness at 500 g load，fracture toughness，flexural strength up to 800°C，oxidation resistance and D.C. electrical resistivity. The effect of TiN on the above mentioned properties is more compared to the others. tivity decreases to ~ 10–3 ohm.cm with 30 vol.% TiN and the threshold percolation volume is below 20 vol.%. They inferred that the composite may be machined by EDM technique. Wang and co-workers (1999) reportedon D.C. resistivity of Si3N4–TiC composite and their

mechanical properties. They explained the conductivity through percolation theory and calculated the threshold loading of TiC for conductivity to be 18.5 vol.%.

An attempt has been made in this work to study the D.C. electrical behaviour of pure Al2O3 and ZrO2 with addition of TiC and also to optimize the amount of TiC addition. Relevance of decrease of d.c. resistivity of ZrO2 and Al2O3 with TiC was explained with the help of effective media and percolation theories.

2. Experimental

Pure Al2O3 (HTM30，99×5%，avg. particle size，5 mm，Indian Aluminium Co.，Kolkata)，pure ZrO2 (99.9%，avg. particle size，10 mm，Indian Rare Earths Ltd.，Thiruvananthapuram) and TiC (99.0%，avg. particle size，16 mm，H.C. Starck，Goslar，Germany) were taken for preparation of the composites. Each composition (table 1) was mixed in pure isopropyl alcohol for 3 h. The pellets of

18 mm diameter were dry pressed uniaxially at 300 MPa and sintered at 1600°C in pure argon in a graphite resistance heated furnace for 10，30，90 and 180 min. Bulk density of the sintered pellets were measured by water displacement method. X-ray

diffractograph of the samples were taken to detect the major phases and to know if there was any reaction. The samples with low porosity were polished progressively with 60 mm，10 mm，6 mm，3 mm and 1 mm diamond paste for microstructural study. The ground pellets were coated with silver paint，cured and their D.C. resistivity was measured with a precision ohm-meter (Hewlett Packard Resistance Tester) at room temperature.

3. Results and discussion

3.1 Sintering

Sintered density of both Al2O3 and ZrO2 composites with varying percentages of TiC was measured and is plotted in figure 1. The density is compared with the theoretical density of the composites calculated using mixture rule. Sintered density of the composites achieved in the case of Al2O3 (0% TiC) based composition is 78% ( max. 80%)while that in the case of ZrO2 (0% TiC) is 73% because of poorer sinterability of ZrO2 compared to Al2O3 at 1600°C (even in 180 min). Sintering of alumina with TiC addition is，however，poor and the average density reduces to 67% compared to the theoretical value at 55 vol.% TiC. The average sintered density in the case of ZrO2–TiC composites measured over the whole range of TiC addition is ~ 73% while that with Al2O3 drops down slowly with increase of TiC content and achieves an average value of 67% at 55 vol.% TiC content in the composites. TiC in both cases acts as an inert phase and it does not react with the parent phase. TiC acts detrimentally with alumina in forming the composites. The SEM photomicrographs of the composites with 25.68 vol.% TiC–alumina and 33.75 vol.% TiC–zirconia are shown in figures 2a and b. The second phase was seen to be evenly dispersed in the matrix. XRD result shows no reaction between the matrix and the second phase.

3.2 DC electrical resistivity

Figure 3 shows the reduction of d.c. resistivity of the composites with amount of TiC. The fall of resistivity of the composites is similar in nature which reaches a plateau after a critical percolation volume of TiC. The composites

sintered for 180 min had the critical volume of inflexion of resistivity (j c) at 34.0 and 26.3 vol% for ZrO2 and Al2O3，respectively. The fall in d.c. resistivity is sharp for the composites sintered for shorter time and the critical percolation volume is also low compared to the others. Sintering within such a short time is very poor and the fine TiC particles are also well distributed in the matrix，while the composites sintered

for longer time shows more coagulation of TiC in the matrix. Hence the critical percolation volume is more although the matrix is denser than the former. From the microstructures of Al2O3–TiC it is obvious that TiC is more dispersed in the matrix and the effect is reflected in the j c values. The D.C. resistivity reduced to 1 W cm which is favourable for machining the matrix by EDM technique.

The D.C. resistivity of the composites may be explained with the help of percolation theory which explains the conductivity of a composite medium near a metal–insulator transition region. This theory applies，in a strict sense，only when conductivity of the low conducting phase is zero or resistivity of the high conducting phase is zero (Wang et al 1999) ideally. In a real case，the general

effective media (GEM) equation has been postulated (Mclachlan 1988) where conductance of both media (s h and s l) is finite occurrence thus overcoming the limitation of the percolation theory. The equation fits accurately the conductivity

Figure 1. Variation of sintered density of (a) Al2O3–TiC and (b) ZrO2–TiC with amount of TiC sintered at 1600°C at different soaking times.

for a large number of binary composite media.

In a continuous medium，comprising of an insulating medium as the parent

matrix and an electrically conducting second phase，percolation theory predicts that near a conductor–nonconductor transition of the matrix，the resistivity will be given by the percolation equation

r m = k {(1 – j)/jc}t，(1)

where r m is the total resistivity of the composite，j the volume fraction of high conductivity phase，j c the criti cal (percolation) volume fraction for the high conduct ivity phase and t the resistivity exponent whose values range between 1×65 and 2×00 (Balberg 1987). Equation (1) can be written as log r m = log k + t log {(1 –j)/j c}，(2) where k is the proportionality constant.

-

Figure 2. SEM micrograph of (a) 74.3 Al2O3–25.7 vol.% TiC composite and (b) 66.25 ZrO2–33.75 vol.% TiC composit

Table 2. Values of threshold percolation volume (j c) and t of the composites.

Figure 3. Variation of d.c. resistivity of Al2O3 and ZrO2 composites with TiC. The compositions of the matrix for microstructural studies were so selected that they are close to the threshold of the critical percolation volume of the systems to have an idea of the matrix. The threshold volume for such percolation in the systems are，however，dependent on the grain size and amount of the parent and the conducting second phases，shape，size and amount of the pores present in the

matrix. The value of j c seems to be on the higher side in both cases mainly because of the larger particle size of the conducting phase and the presence of pores in the matrix (table 2).

4. Conclusions

(I) TiC was of no help in sintering of alumina and zirconia at 1600°C. Sintered density of alumina，however，increased while that of zirconia decreased with addition of TiC.

(II) The minimum percolation volume of TiC in 180 min sintered alumina was 26.3 vol.% and that of zirconia，34.0 vol.%. This volume decreased when the composites were sintered for shorter time because of non-coagulation of TiC and finer Al2O3.

(III) The D.C. resistivity of both composites were sufficiently low and there is a possibility of machining them by EDM technique as addition of 30 vol.% TiC also improves mechanical properties of the sintered composites，

in general.

Acknowledgements

The work was carried out at the Non-Oxide Ceramic Section，Central Glass and Ceramic Research Institute，Kolkata. The authors are grateful to all the staff members of the section. The authors are also grateful to the Director，CGCRI，Kolkata，for providing facilities

.

References

Balberg I 1987 Phys. Rev. Lett. 1305

Bellosi A et al 1989 Electroconductive Si3N4 based composites，Euroceramics (ed.)

G de with (London: Elsevier Applied Sci.)，Vol 3，pp 3×389–93

Buerger W 1994 Keram Z. 46 547，550

Guicciardi B.de portu 1992 J. Euro. Ceram. Soc. 10 307 Krell A，Blank P，Pippel E and Woltersdorf J 1995 J. Am. Ceram.Soc. 78 2641

Mao D S，Liu X H，Li J，Guo S Y，Zhang X B and Mao Z Y 1998 J. Mater. Sci.

33 5677

Matkin D I，Cavell I W and Dyson J R 1972 Proc. Br. Ceram.Soc. 23 58 Mclachlan D S 1988 J. Phys. C: Solid State Phys. C21 1521

Mclachlan D S，Blaszkiewicz M and Newnham R E 1990 J. Am. Ceram. Soc. 73 2187

Nakayama S and Kuroshima H 1992 J. Ceram. Soc. Japan100 758

Pierson H O 1996 Handbook of refractory carbides and nitrides (USA: Noyes Publ.) Sawaguchi A，Toda K and Niihara K 1991 J. Am. Ceram. Soc.74 1142

Wang H L，Li J B，Li Y and Liu J F 1999 Study of electrical conductivity of

TiC/Si3N4 ceramic composite，Proc. 1st China conf. on high performance ceramics，Beijing，(ed.) D S Yan and Z D Guan (Beijing: Tsinghua University Press) p. 432

氧化铝与氧化锆和TiC烧结的直流电阻率

中央玻璃陶瓷研究所，加尔各答700 032，印度

陶瓷技术学院，加尔各答700 010，印度

2003年10月20日收到，2005年2月11日修订

摘要：纯氧化铝和氧化锆粉末分别与TiC烧结的增加额高达65％，作为一个有准备进行第二阶段达到结构陶瓷的目标，可由电火花精密加工技术完成。TiC不仅无助于烧结阶段，而且它降低了直流复合材料的电阻率1Ω·CM30％左右的负荷。电导率是通过有效的媒介和渗流理论解释的。

关键词：氧化铝；氧化锆；钛碳化物；复合材料；电导率；电阻率。

1.引言

已经在尝试在用不同的方法来提高结构陶瓷的力学性能。它们之间是有希望在第二阶段，发生优越的陶瓷机械固化反应，但引起的特性反应过程很费时，整理过程是相当复杂。作为这个解决问题方案，新技术的一个组成部分，分别以更快的速度和更低的成本整理。电火花加工（EDM）技术，已应用于很多情况下。该技术主要需要的电控制完成，关键部件是导电器（电阻<100Ω ·CM ）。第二阶段的材料是兼容的导电材料，如氮化物（TiN），硼化物（TiB2），碳化物（TiC）和硅化物（MoSi2，Ti—Si），其中电阻率在13～50 ×10 -6 Ω ·CM的范围，可以传导到基体上。第二阶段可能还可以提高材料的机械性能，基体的导电性一般是直接依赖于量的大小和进行第二阶段基体的数量（皮尔逊1996年）。

在这个研究方向进行，而主要是工程陶瓷像氮化硅，碳化硅等（马特金等人1972;贝洛西等人1989;麦克拉克伦等人1990;泽口等1991年; 迈克和库什曼1992年）。当氮化硅与碳化硅烧结复合时电阻率降低（泽口等人1991），该方法比碳化硅显著高于10％。含量为25％碳化硅复合材料的电阻被发现在1 × 10 7 Ω·cm 左右时表现像一个半导体。在硅烧结的界限内氮化硅的临界体积氮化硅晶粒为17％，而复合后的电特性是依照渗透理论高达10％，增加了碳化硅复合材料的韧性。氮化硅与氮化钛烧结（1992年），没有任何其他的添加剂复合，复合阻抗从1 × 10 7Ω·CM降低至1×103Ω·CM，测量前去除水分。对SiC作为基体材料做了很多工作，将SiC使用在电气电子设备材料是很多的，如制造加热元件，半导体传感器，压敏电阻等。氧化铝和氧化锆另外两个共同结构工程陶瓷材料。有很少的报道利于增加材料的导电性（圭霞尔蒂1992年;伯格1994;克雷尔等1995年;毛和同事等人1998;王等1998）或其他相关领域。毛和同事（1998年）工作是研究Al2O3 - TiC复合涂层和测量耐磨复合材料的力学性能。他们研究表明钴涂层的作用是重要的，它对表面磨损破坏有影响。伯格（1994）使用了质量分数50％的碳化钛和三氧化二铝。与45％TiC结合直流电阻率从1 × 1012下降到1 × 10 -3Ω。该导电率变化用连接粒子模型解释。碳化钛，重量达30％，增加了复合材料的抗弯强度。克雷尔和同事（1995）用30％碳化硅和及氧化锆而没有TiH2，

TiH2改变了TiC烧结还原特性。晶粒摆脱了非晶相力，和纤维增强复合材料的3Y-TZP相似。洛西和同事详细研究了以氧化铝为基体的陶瓷复合材料，他们用体积分数为20%和30 % TiC/TiN ，测量了TiB2的热膨胀数、电子模量、维氏硬度500克负荷、断裂韧性、抗弯强度可达800℃、抗氧化性及直流电阻率。锡的效果是在上面提到的性质比别的多。然而，复合材料在800℃以上的氧化电阻研究在国内外是空白，直流电阻率降低到10-3Ω·CM 体积分数为30％TiN和渗流阈值低于20％。他们推断复合材料可通过电火花加工技术加工。王和同事（1999）报告对Si3N4- TiC复合材料的直流电阻率和操作性能。他们通过渗流理论和计算TiC电导率解释。

这项工作已在尝试中，研究纯Al2O3和ZrO 2直流电特性，此外还与基体的数量有关。ZrO2和Al2O3 与TiC复合的关联性的使直流电阻率下降，这些与媒体介质的退化机制和渗流理论有关。

2. 实验

纯铝Al2O3（HTM30，平均99.5%，颗粒大小5微米，印度铝业有限公司，加尔各答），纯氧化锆（平均99.9％，颗粒大小10微米，印度稀土有限公司）和TiC（平均99.0％，颗粒大小16微米，慧聪斯塔克，戈斯拉尔，德国）进行复合。每个组合（表1）在纯酒精混合异丙醇3小时，该球团直径18毫米在300MP单轴干压，用纯氩气石墨电阻，并在1600℃加热炉中烧结10，30，90和180分钟，体积球团的烧结密度用水位移法测定。用X射线透视软管，普莱斯被作为检测的主要阶段，并知道有任何反应。低孔隙度的样本逐渐被打磨60微米、10微米、6微米、3微米和1微米研究金刚石微观结构。表面涂有银颗粒的固化涂料，在室温温度下测其直流电阻测量，精确电阻（惠普电阻测试仪）。

3.结果与讨论

3.1 烧结

测量了烧结Al2O3和ZrO2复合材料的不同百分比密度变化绘制如图1。与理论复合材料的混合使用密度计算规则相比较，以复合材料的烧结密度中的Al2O3（0％的TiC）的含量组成78％（最多80％）而在氧化锆的（0％的TiC）为73％，因为与Al2O3 在1600℃分钟（甚至180分钟）相比氧化锆烧结物较少。氧化锆的平均烧结密ZrO2-TiC复合材料在整个测量范围TiC的添加是73％，而与Al2O3滴下来TiC的含量逐渐增加，并达到了一个极限值67％。复合材料中TiC含量为55％。在这两种情况TiC的行为，它作为一种惰性不与父相反应。TiC的行为与氧化铝复合材料中形成的。复合材料在扫描电镜下的显微照片TiC–氧化铝体积分数为25.68％和TiC -氧化锆的体积分数为33.75％的如图2a和b，第二阶段被认为是均匀分散在基体中。X射线衍射结果显示在第二阶段矩阵之间的没有反应。

3.2 直流电阻率

图3显示了与大量的TiC结合后减少的直流电阻率。该复合材料电阻率的降低与TiC的体积有关，关键的是渗流。该复合材料在烧结180 min时的临界量拐点的电阻率在体积分数分别为34.0％和26.3％的ZrO2和Al2O3。直流电阻率下降主要是由于复合材料的烧结临界渗流体积也比较低其他时间较短。在这么短烧结时间内，矩阵的TiC颗粒分布和优良性很差，而复合材料的烧结时间较长显示更多凝结于TiC基体中。因此，关键的是矩阵密度的渗透量高于前者。Al2O3- TiC 的微观结构的很明显，分散的矩阵和效果反映值的影响。该直流电阻率减少到

1Ω·CM，有利于电火花技术加工。

该复合材料的直流电阻率变化的原因可以用复合材料中渗流导电理论解释其中的金属的过渡区域。这个理论具有严格的适用范围，，只有当电导率低即导电相电阻为零或阶段的高导电是零（王等人1999的理想情况下。在实际情况下，（基拉尔）方程有效的媒介已被假定（克兰1988），在两个媒介的传导性是有限的，从而发生克服渗流理论的局限性，方程适合于电度为大量的元复合媒介。

在连续介质中，括一个绝缘父矩阵和一个在第二阶段的导电行为，渗流理论预测，不久的一导体，靠近绝缘体的过渡矩阵，由渗流方程可得

ρm= k {(1 –j ) /j c}t，

（1）其中ρm是总电阻，体积分数高的导电相，j c是重要的卡尔（渗流）体积分数的，高电导相位和电阻率指数t，其值介于1.与2.00之间（Balberg 1987年）.方程（1）可写为

log ρm = log k + t log {(1 –j) /j c}，

图1. (a) ZrO2-TiC和(b)Al2O3-TiC和大量的TiC 在1600℃温度下和不同烧结时间烧结密度的变化

（

图2.扫描显微镜下(a)体积分数为74.3 %Al2O3-25.7%TiC复合

和（b）体积分数为66.5%ZrO2-33.75%TiC的复合。

表2.阈值(j c)的作用和复合材料的渗流

组分烧结时间（min）TiC的阀值（j c) t值

ZrO210 31.2 0.52 90 33.5 0.10 180 34.0 1.78

Al2O3180 26.3 1.60

（2）其中k是比例常数。微结构研究的成分如此选择，以致于已接近临界值，该系统的关键事渗流体积有一个主要的基体。在系统中渗流阈值是等体积的，然而，大小依赖于本体数量和进行第二次阶段基体中呈现的气孔的形状、大小和数量，在目前的情况下，值j c似乎是在较高的一方，基体气孔的大小两种情况，主要是因为较大的颗粒导电相和孔隙中的存在基体（表2）。

图3 Al2O3和ZrO2分别与TiC复合的直流电阻率的变化

4. 结论

（一）TiC在1600℃对氧化锆和氧化铝的烧结没有什么帮助，然而，氧化铝烧结密度随着氧化锆中TiC的增加而下降。

（二）在180分钟时，TiC与氧化铝烧结的最小渗出体积分数为26.3％，而氧化锆体积分数为34.0 ％。当复合材料缩短了烧结时间，体积分数会下降，因为TiC和更精细的Al2O3没有凝结。

（三）复合材料的直流电阻率足够低，有可能是电火花加工技术在加工它们时，一般来说，补充30％TiC也提高了烧结复合材料的力学性能。

致谢

这项工作是在加尔各答，玻璃和陶瓷中央实验研究所，非氧化物—陶瓷课题组开展的。撰文感谢这里所有工作人员。作者还感谢加尔各答CGCRI的署长提供设施。

参考资料

1 包罗基1987年，物理评论快报，1305

2 贝罗西等人，Si3N4基复合材料（编辑）德国（伦敦：爱思唯尔科技与应用）第3卷，pp 3.

3 89–93

3 伯格·王199

4 陶瓷杂志46 547～550

4 圭霞尔蒂1992 欧洲陶瓷学报10 307

5 克雷尔，和沃尔特斯多夫1995 美国陶瓷学报78 2641

6 毛博士，刘晓华，李洁，郭茜亚，张和毛1998 硕士学报.33 5677

7 马特金，戴森小卡夫尔1972 英国陶瓷学报23 58

8 麦克拉克伦1988 陶瓷科学C21 1521 1521

9 麦克拉克伦副局长，纽纳姆稀1990 美国陶瓷学报73 2187

10 那克亚马1992 日本陶瓷学报100 758

11 皮尔逊1996 耐火碳化物手册-（美国：诺耶斯。）

12 泽口一，户田1991 美国陶瓷学报74 1142

13 Wang H L，li J B和Liu J F ，TiC/Si3O4陶瓷基复合材料导电性能研究，中国第一高性能陶瓷，北京，（主编）燕秘书长ZD系列馆（北京：清华大学出版社）432