A-sialon

Fig. 12. (a) A cross section of multiple coatings of TiN on TiC on a silicon nitride-based tool material (b) multicoatings on a SiAlON-based tool material. 

AS3. Ekstrom T (1997) a-SiAlON and a// -SiAlON composites Recent research. In Babini GN, Haviar M, Sajgalik P (eds) Engineering Ceramics 96 Higher Reliability through Processing, Kluwer Academic Publications, The Netherlands, p 147... 

Mandal H, Hoffmann MJ (2000) Novel Developments in a-SiAlON Ceramics. In Sajgalik P, Lences Z (eds) Engineering Ceramics Multifunctional Properties-New Perspectives. Trans Tech Publications Ltd, Switzerland, p 131... 

Shen Z, Nygren M (2000) Nd-Doped a-Sialon and Related Phases Stability and Compatibility. In Hampshire S, Pomeroy MJ (eds) Nitrides and Oxynitrides. Trans Tech Publications Ltd, Switzerland, p 191... 

Fig. 6.9). Hardness values increased gradually from 16 GPa to about 19 GPa, shifting from the P-SiAlON-rich region to the a-SiAlON-rich one (Fig. 6.10). However, the gradient layer was longer in this sample, which may be due to easier diffusion of species in a larger amount of liquid phase in B3. 

In another study, Mandal and co-workers produced functionally graded SiAION ceramics using the powder bed method.50 In their study, P-SiAlON compacts were embedded in two different homogeneously mixed powder bed compositions, a-SiA10N (100 wt%) and A1N BN (50 50 wt%). The effects of powder bed composition and pressure on the formation of a-SiAlON on the compact surface were investigated. 

Changes in the amount of P-SiAlON from the surface of the samples for green and presintered compacts are shown in Figs 6.22 and 6.23, respectively, after sintering in a-SiAlON and A1N-BN powder beds. Both figures clearly illustrate that the A1N-BN powder bed is more effective for the formation of a-SiA10N at the surface than the a-SiAlON powder bed. Formation of an a-SiAlON-rich layer on the component surface is due to the transfer of a-SiAlON-forming ions from the powder bed. This transfer could be in various... 

Zhao, R., Cheng, Y.B. (1996), Decomposition of Sm a-SiAlON phases during post sintering heat treatment , J. Eur. Ceram. Soc., 16, 1001. 

Mandal, H., Thompson, D.P., Liu, Q., Gao, L. (1997), High temperature stability of a-SiAlON ceramics containing glass additions , Eur. J. Solid. State. Inorg. Chem., 34, 179. 

Xu, X., Mei, S., Ferreira, J.M.F. (2003), Fabrication of a-SiAlON sheets by tape casting and pressureless sintering , Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, Portugal, www.mrs.org/publications/jmr/jmra/2003/ jun/012.html. 

This phenomenon has been postulated as an explanation for the compressive superplastic deformation of a SiAlON which undergoes a transition from n = 1 (Newtonian behaviour) to n = 0.5 for a characteristic critical stress (<7C) independent of both temperature and composition of the secondary phase.35... 

Toughening mechanisms in a/p-sialon composites are similar to those operative in second-phase particle reinforced composites, but, rather than the deliberate addition of a second phase, a/P-sialon composites are fabricated by simultaneous crystallisation of the two solid solutions a- and P-sialon from a eutectic composition liquid. This requires careful design of the starting composition which is usually located within the (a + P)-sialon region of the a-sialon plane as illustrated in Fig. 18.1. 

Schematic illustration of a- and P-sialon phase regions on the a-sialon plane (M metal cation with a valence of 3+). 

Table 18.1 Effects of starting powder, composition on phase present, microstructure and mechanical properties of a-sialons...

Reprinted from J. Mater. Sci., 36(14), Yu Z B, Thompson D P and Bhatti A R, Selfreinforcement in Li-a-sialon ceramics, Fig. 2, 3343-3353, (2001). Copyright 2001, with kind permission of Kluwer Academic Publishers. 

As shown in Table 18.2, both the volume content of Cf and the sintering temperature affect the properties and fracture behaviour of Cf/a-sialon... 

Synergistic roles of carbon fibres and Zr02 particles in strengthening and toughening Li-a-sialon composites, 225-235 (2002). Copyright 2002, with permission of Elsevier). 

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