Effect of Carbon nanotubes on microstructure of multiphase composite Al2O3 ceramics

Li Xiao qing Xu Ming

1.0 Introduction

With high hardness， wear resistance， corrosion resistance and excellent high-temperature performance， Al2O3 ceramics become of the most widely using， more extensive application. A lot of production ceramic materials are used in aerospace， aviation， engine wear parts， tools， etc [1-3]. At the same time， because of high brittleness and poor uniformity of adverse weaknesses of ceramic materials， the work reliability and safety of ceramic materials are affected. Therefore， it is important to crack down the problem that is how to improve the toughness of Al2O3 ceramics [4]. Carrying out Al2O3 ceramics toughening research has the significant modern meaning and practical application value[5].

In recent years， a large number of research is carried out in order to solve the the high brittleness of Al2O3 ceramic material and enhanced strength and toughness. At present， there are several ways to improve the fracture toughness of Al2O3 ceramics： （1） the particle dispersion toughening； （2） fiber and whisker toughening； （3） zirconia of phase transformation toughening，（4） composite toughening； （5） the toughening， etc[6] .

With the emergence of nanometer materials， nanometer materials are used greatly to improve the fracture toughness of ceramic cutting tool material by a unique volume effect （small size effect）， surface effect， quantum size effect and macroscopic quantum tunneling effect， etc.

Carbon nanotubes has characteristic of small diameter， large length to diameter ratio， and mechanical performance， etc， as a new type of nanometer materials. Since carbon nanotubes is discovered， people still have paid attention on it. As fabrication on technology of carbon nanotubes becomes perfect increasingly， the research of carbon nanotube composite materials has been one of hot topics in the study of its application. People have done a lot of research on its and has obtained certain achievement.

However， using carbon nanotubes reinforced ceramics materials is still on the trial stage. There is no recognized the strengthening and toughening mechanism of nano materials [7]. In this thesis， carbon nanotubes reinforced multiphase composite Al2O3 ceramics was fabricated by hot pressing sintering. At the same time， it is analyzed toughening and strengthening mechanism by means of microstructure observation .

2 Experimental method

2.1 Experimental materials

The Al2O3 powder， TiC powder and carbon nanotubes are all commercially available.The average particle size of Al2O3 particles is 30 nano， its purity was 99. 9%.The average diameter of TiC particles for 2 to 4 microns.The ratio of composition are shown in table 1.

Table 1. Contents of composition

Sample Al2O3

（30 nano） Al2O3

（2-4microns） carbon nanotubes TiC

（2-4microns）

Ni Mo

ACT1 85 5 2 5 0.9 2.1

ACT2 5 85 2 5 0.9 2.1

2.2 The preparation of composite powder

The main steps of the preparation of nano-Al2O3 matrix composite powder is shown in fig 1 [7].

Fig. 1 . main steps of the preparation of nano-Al2O3 matrix composite powder

3 Results and discussions

The fracture morphology of sample is shown as figure 3.

（a） （b）

Fig.3 . sample fracture morphology

In figure 3 ，（a） and （b） are respective the fracture morphology of A and B sample with sintering additives （the fracture of three point bending experiment ）at 1 550 ℃ sintering temperature.Fracture surface of A sample show that there are a lot of hole which left by pulling a large number of grains out ，and distribution of grain size is nonuniform，a large number of carbon nanotubes distribute in the gap.The way of fracture of B sample is the intergranular fracture， distribution of grain size is uniform ，exposed capitulum of Carbon nanotubes in section indicates that carbon nanotubes are pulled broken ，and appear disorderly flake of graphite sediments in the joint of grains.Maybe due to increasing the content of carbon nanotubes ， the chance of making dispersed carbon nanotubes lap， attached together become increasing.So the addition of carbon nanotubes doesn't improve the overall mechanical properties of composites.

4.0 Conclusion

It is carried on many researches of carbon nanotubes as reinforced phase in ceramic matrix. However， the performance of the composite materials is not improved obviously， sometimes even worse. Because Ceramic matrix material is very sensitive to dispersed state of carbon nanotubes and sintering behavior of carbon nanotubes which effects the microstructure and the mechanical properties of ceramic tool materials. Therefore， it is necessary to further study systematically on compound process of adding carbon nanotubes and the influence for interface bonding strength of composites in order to improve the mechanical properties of composites ceramic tool materials which add carbon nanotubes.