Book of Abstract of
The 8th ASEAN Microscopy Conference & 32nd Microscopy Society of Thailand Annual Conference
28-30 January 2015, Nakhon Pathom, Thailand
Microstructural Observation of Density Changing
Effect on Creep
Dilek Turan1*, Serkan Ulukut 2
1
Department of Airframe and Powerplant Maintenance, Anadolu University, 26480, Eskisehir, Turkey
2
Department of Materials Science and Engineering, Anadolu University, 26480, Eskisehir, Turkey
*Corresponding author, e-mail: dtetik@anadolu.edu.tr
Abstract
Silicon nitride (Si3N4) based materials are used in high temperature applications due to their high strength,
toughness and low density. The mechanical and chemical properties of Si3N4 can be tailored further with the
addition of aluminum and oxygen into the structure, which are called SiAlON materials. Creep rupture is the
major damage form for SiAlON ceramics being used at high temperature. Creep properties of SiAlON ceramics
are determined by the state of secondary phases, i,e. whether it is amorphous or crystalline. The steady state creep
mechanisms of SiAlON ceramics containing amorphous intergranular phase has been attributed to viscous flow,
grain boundary sliding, diffusion and cavities.
In this study, in order to find out the role of microstructure on the creep resistance of SiAlON ceramics. It was
decided to carry out accurate density measurements before and after creep, paying particular attention to
density/strain relationships. The influence of density difference of as-received samples on the creep behavior of
the β-SiAlON materials that contain Er-Sm-Ca multi cation system and 10% SiC as a secondary phase were
investigated. Samples were subjected to four-point bending test in air at the temperature of 1390°C and 100 MPa
flexural stress for 72 hours. Microstructural characterization of the samples were carried out by X-ray diffraction
(XRD) and microscopy techniques (SEM and EDX) before and after creep tests.
Density measurement results of non-heat treated samples were given in Table 1. Test samples were selected
which has got different densities after sintering tests.
Table 1. Density measurement results of non-heat-treated samples
Sample Code
ER-1
ER-3
ER-5
ER-71
ER-74
Er-75
Density(gr/cm3)
m3g/cm3
3,29
3,29
3,29
3,29
3,23
3,20
With increasing density, creep elongation, as well as flexural creep rates of the samples were observed to
increase as shown in Fig. 2. The average rate of creep of high concentration sample 4.26x10-8 s-1, while the
average of the low-concentration sample is measured 4.96x10-9 s-1.
After creep testing, microstructures of the samples were examined with SEM. As shown in Figure 3, there are
three different regions in the samples. Since the creep tests have been performed in air, oxide layer formed on the
surface. On top of the oxide layer (which appears in white and light gray portions) formed by diffusion of
additional sintering silicate glassy phase was found and just below the SiO 2 layer is located. The layer below the
oxide layer are affected by creep. These layers were different for high density and low density of the samples.
Under oxide layer for high density samples, sintering additives create crystallization at grain boundaries which
appears in white. Under this layer, there is another layer which is depleted of sintering additives layer
Under the oxide layer for low density samples grain boundary phase crystallization does not seem to be clustered
in one layer and the grain boundary phase impoverished relatively small area.
References
S. M. Wiederhorn, B.J.Hockey and J. D. French, “Mechanisms of Deformation Of Silicon Nitride And Silicon
Carbide at High Temperature”, J. Am. Ceram. Soc., 19,2273-84 (1999)
A.Carman, E.V.Pereloma, Y. B. Cheng, “Grain Boundary Evolution in Sm-and Nd-SiAlONs during Post Heat
Treatment”, J. Austr. Ceram. Soc. 45, 27-34 (2009).
M. T. Lin, L. Wang, D. Y. Jiang, G.Q. Zhu, J.L. Shi, “High Temperature Bending Creep of a Sm-- SiAlON
Composite” J. Mat. Sci., 37, 655-62 (2002).
Book of Abstract of
The 8th ASEAN Microscopy Conference & 32nd Microscopy Society of Thailand Annual Conference
28-30 January 2015, Nakhon Pathom, Thailand
Figure 1. XRD patterns an
Figure 2. Creep Behavior of non-heat-treated samples for 72 hours to 1390 ° C and 100 MPa
Figure 3. Isıl işlem görmemiş ve 1390°C sıcaklıkta sürünmüş a) 3.29 g/cm3 ve b) 3.20 g/cm3 yoğunluğa sahip
numunelerin 1000 büyütmede alınan SEM görüntüleri