Journal of the European Ceramic Society 36 (2016) 3059–3066 Contents lists available at www.sciencedirect.com Journal of the European Ceramic Society jo ur nal home p ag e: www. elsevier.com/locate/jeurceramsoc Nanoindentation induced deformation anisotropy in -Si 3 N 4 ceramic crystals Tamás Csanádi a,∗ , Duˇ san Németh a , Ján Dusza a,b , Zoltán Lenˇ céˇ s c , Pavol ˇ Sajgalík c a Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 04353 Koˇ sice, Slovak Republic b Donát Bánki Faculty of Mechanical and Safety Engineering, Óbuda University, Népszínház utca 8, 1081 Budapest, Hungary c Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 845 36 Bratislava, Slovak Republic a r t i c l e i n f o Article history: Received 30 July 2015 Received in revised form 13 November 2015 Accepted 24 November 2015 Available online 11 December 2015 Keywords: -Si3N4 Indentation modulus Nanohardness EBSD Anisotropy a b s t r a c t The inﬂuence of crystal orientation on nanohardness and indentation modulus of grains in polycrystalline -Si 3 N 4 was studied under nanoindentation at room temperature. The orientation of the individual grains was determined by electron backscatter diffraction (EBSD) prior to the indentation. Signiﬁcant elastic and plastic deformation anisotropy was revealed. The elastic modulus exhibited a decrease for grains oriented from the basal towards the prismatic facets while the nanohardness values showed reversed tendency. The orientation dependence of indentation modulus was predicted by the Vlassak-Nix model and ﬁnite element model (FEM) calculations based on the elastic constants of -Si 3 N 4 single crystal and compared to the experimental results. A theoretical model was proposed to describe the nanohardness anisotropy on the basis of the possible slip systems of -Si 3 N 4 . The calculations for elastic and plastic anisotropy are in good agreement with the experimental results. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction For more than ﬁfty years, silicon nitrite based ceramics are still one of those advanced materials which are in the centre of interest owing to their attractive mechanical properties, such as high hard- ness, strength and wear resistance. These properties are attributed mostly to the high energy covalent bonds which make silicon nitrite possible for wide range of applications such as cutting tools, ball bearings or heat engine parts [1]. Silicon nitride exists in two major crystallographic modiﬁcations,  and . Both have hexagonal struc- ture and -Si 3 N 4 (space group P6 3 /m) is the more stable one due to the  →  phase transformation which occurs at higher temper- atures [1,2]. It is well known that the mechanical and fracture properties of bulk polycrystalline silicon nitride ceramics are strongly inﬂu- enced by the properties of the individual grains and intergranular phases, as well as by the structure of interface between the grains and intergranular phases [3–5]. Therefore, in order to design opti- mized microstructure with enhanced combinations of hardness, toughness and wear resistance, it is important to understand the ∗ Corresponding author. E-mail address: tcsanadi@imr.saske.sk (T. Csanádi). anisotropic deformation behaviour of the individual -Si 3 N 4 crys- tals. Plasticity of macroscopically brittle materials, focusing here only on silicon nitride , is commonly investigated by means of micro-, nanoindentation testing and more recently by micropil- lar compression [6–14]. Table 1 gives a summary of the results of the most relevant studies which aimed to characterize the effect of crystallographic orientation of -Si 3 N 4 single crystal grains on their hardness. One of the ﬁrst attempts to characterize the deformation behaviour and the hardness anisotropy of Si 3 N 4 single crystals were performed by Chakrabotry and Mukerji [6] and Reimanis et al. [7]. They investigated the microhardness of differently oriented crys- tallographic planes in - and -Si 3 N 4 single crystals and reported higher hardness values corresponding to the prismatic plane com- pared to basal facet. Later, similar hardness anisotropy was revealed by Dusza et al. [8,9] in -Si 3 N 4 grains of gas pressure sintered poly- crystalline Si 3 N 4 founding also signiﬁcantly higher hardness values belonging to the prismatic plane than that on the basal one. It is important to emphasize that these investigations are focused on the two extreme crystal orientations, namely on the basal and the prismatic orientations. Up to now, the only relevant paper which attempted to map the general orientation dependence between the basal and the prismatic orientations is the nanoindentation study of Hay et al. [10]. In their work, the inﬂuence of crystal orienta- http://dx.doi.org/10.1016/j.jeurceramsoc.2015.11.028 0955-2219/© 2015 Elsevier Ltd. All rights reserved.