1. Processing and characterization of sialon-based ceramic nanocomposites reinforced with SiC and WC nanoparticles for cutting tool and wear resistance applications
Abbas Saeed Hakeem1*, Tahar Laoui1,2, Faheemuddin Patel2, Moath Mohammed Al Malki‏2, Raja Muhammad Awais Khan2
1. Center of Excellence in Nanotechnology, KFUPM, Dhahran 31261, Kingdom of Saudi Arabia
2. Mechanical Engineering Department, KFUPM, Dhahran 31261, Kingdom of Saudi Arabia *
ABSTRACT
Alumina silicate oxynitride sialon nanoceramics were processed by spark plasma sintering (SPS). After wet mixing by probe sonication, the starting powder mixture was sintered by SPS and transformed mainly into  and β-sialon phase(s). Small amount of other phases were found in the sialon matrix but well dispersed nanocrystalline particles. Well mixed powders mixture and SPS sintering promoted adequate reaction among the starting powders with the aid of selected metallic precursors, and improved the sintering ability of the starting powders, so the densification temperature was lowered compared with the conventional sintering techniques (such as hot pressing). -sialon grains with the designed composition were formed directly through precipitation from the homogeneous mixture.
The synthesised samples were characterized using field emission scanning electron microscopy, X-ray diffraction, density by Archimedes method and Vickers hardness method.
SYNTHESIS METHOD
Powder mixtures having composition of (Ca/Ba)Si6Al6O4N12 prepared by probe sonication were sintered via SPS, using overpressure of 10 kPa, by N2 atmosphere, with constant pulsed electric current and frequency duration. Powder mixtures were poured into a cylindrical graphite die (dia. 20 mm) then heated at a rate of 100°C/min to chosen temperature (ranging from 1400 to 1700°C), while applying a constant pressure of 50 MPa. Samples were held at elevated temperature for 30 minutes and then cooled quickly to room temperature.
RESULTS
Table 1. Table shows the synthesized samples and their properties: samples1, 2 and 3 are Ba-sialon and samples 4 to 8 are Ca-sialons
Sample
Si3N4
Additive
 (g/cm3)
Hv10 (GPa) 1
Amorphous
-----
3.425 11 2 Al
3.488 3
Alpha (nano)
3.412 13 4
3.145 14 5 Si
3.106 6
3.138 7
Al+Si
3.153 8
3.029 15
AIM OF THE PROJECT
The aim of the project is to develop a route to synthesize sialon-based ceramics and their nanocomposites, having a great potential in the field of cutting tools and hard materials industry. In this regard, KFUPM is well equipped for conducting promising research in hard materials and nanocomposites including sialons.
Sialon-based ceramics and nanocomposites have been and are still being synthesized in this project via SPS. It was proposed to use ceramic nano-precursors (such as; Si3N4, SiO2, AlN and Al2O3), and metallic precursors (i.e., Ca, Al and Si) which could introduce an innovative way to synthesize sialons at low temperature (at/below 1600C) having similar or improved properties to alumina-silicate oxynitride ceramics. Various compositions of Ba- and Ca-based sialons were synthesized. 1 2 3
-sialon
-sialon 4 6 5
Fig.1. XRD spectra from samples 1 to 6 showing the  and  sialon phases in the synthesized samples. d e f
INTRODUCTION
Sialons are promising hard materials suitable for extreme and harsh environments. These materials have several engineering applications. For the preparation of these ceramics, various combinations of precursors can be used. The key compound in these ceramics is Si3N4 which forms a solid solution. Densification of sialons requires the addition of metal oxides such as CaO, Y2O3 or MgO to form a liquid phase(s), essential for densification and solution-precipitation processes allowing interlocking of the grains in the microstructure.
Fig.2. FESEM micrographs indicating the morphologies of barium and calcium sialons. Micrographs a, b and c are from samples1 to 3 (table 1), and micrographs d, e and f are from samples 4 to 6 (table 1).
CONCLUSIONS
All compositions formed both  and β-sialon phases with or without the introduction of β-Si3N4 in the powder mixtures: however, an increase in the amount of β-phase was noticed when β-Si3N4 was introduced into the starting mixtures at 1400C in case of barium.
All samples were fully densified, but addition of Al and Si metals in the powder mixtures did not shown a remarkable improvement in hardness values. Therefore, the next step is the increase further the amount of both elements to explore their influence on the properties.
Moreover, further work is underway to explore compositions with high nitrogen content in -sialon region.
VALUE FOR THE KINGDOM
It is expected that the positive outcomes of the present study, once completed, will contribute towards development of a technology and know-how that would benefit the current and future industries in the Kingdom in the field of high performance cutting/drilling tools. The innovation of the project lies in the preparation of high strength advanced ceramics by adopting new a synthesis strategy combining the proper selection of the starting powder mixtures (exploring micro- and nano-size particles) followed by consolidation using SPS. Potential companies could include oil and gas industries such Aramco, and water industries such as SWCC. Furthermore, the training of researchers, graduate and undergraduate students, and engineers/technicians involved in this research project is another important outcome and added value to the human resource in the Kingdom.
ACKNOWLEGEMENT
The authors would like to acknowledge the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science & Technology Unit & CENT at King Fahd University of Petroleum & Minerals for funding this work through project No. 12-ADV as part of the National Science, Technology and Innovation Plan (NSTIP).
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