Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint A critical note on nanoscale plasticity in 20 ZTA ceramics Payel Maiti a , Manjima Bhattacharya a,b , Pradip Sekhar Das a,c , Jiten Ghosh a , Anoop Kumar Mukhopadhyay a,d,∗ a Advanced Mechanical and Materials Characterization Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, 700032, India b Department of Engineering Science and Humanities, Siliguri Institute of Technology, Techno India Group, Hill Cart Road, P.O. Sukna, Siliguri, 734009, India c Fuel Cell and Battery Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, 700032, India d Department of Physics, School of Basic Sciences, Faculty of Science, Manipal University Jaipur, Jaipur, 303007, Rajasthan, India ARTICLE INFO Keywords: Zirconia toughened alumina Micro pop-in Shear deformation bands Microcracks ABSTRACT The present work reports the very first observations on initiation of nanoscale plastic events in 20 ZTA (Zirconia Toughened Alumina) ceramics. The nanomechanical properties as well as the intrinsic contact deformation resistance of the present ZTA ceramic are studied here as a function of low loads (i.e., 10–1000 mN). Here we report for the very first time, the detailed mechanisms on the genesis of ‘micro pop-in’ events that characterize the nanoscale plasticity initiation in the 20 ZTA ceramics. These new results along with field emission scanning electron microscopy (FESEM) based evidences confirm that the combined contributions from the maximum shear stress generated underneath the nanoindenter, the formations of shear bands and localized microcracking play significant roles in the initiation of nanoscale plastic events in the 20 ZTA ceramics. 1. Introduction Human quest for better structural ceramics in both bulk and coating forms continues to grow with more vigour than ever before [1–5]. In the domain of structural ceramics, the zirconia based ceramics have gathered special attention due to their high hardness, toughness, flex- ural strength, Young's modulus, melting temperature as well as che- mical inertness [6–14]. In particular, the Zirconia Toughened Alumina (ZTA) ceramics possess the unique advantages of high hardness and chemical inertness of alumina along with the beneficial toughening due to the presence of zirconia in the alumina matrix. It is reported that the high toughness is obtained by the tetragonal to monoclinic phase transformation of zirconia that prevents propagation of cracks in ZTA ceramics [15–20]. Thus, the ZTA ceramics have wide applications that include cryogenic domain [21], biomedical implants [18–20], micro- wave sintering [22], machinable dental ceramics [23] and armours [24]. Such high end applications of ZTA involve contact induced de- formations and fractures. As any kind of fracture or damage that is encountered by a material at the macro-structural length scale, actually initiates at the microstructural length scale of the material; the de- termination of nanomechanical properties and the study of the corre- sponding deformation mechanisms at the microstructural length scale of ZTA ceramics is of significant importance. In recent times, nanoindentation has emerged as an important technique in determining the mechanical properties at the micro- structural length scale of a material [15,21,25–48]. Interestingly a huge variety of ceramics exhibit nanoscale plasticity events characterized by the well-known micro pop-in events [25–48]. Unfortunately, however; the total quantum of work on mechanisms behind the initiation of na- noscale plasticity events in particularly the 20 ZTA ceramics is far from significant, if at all. This absence of knowledge base frames the scope of the present work. For instance, the micro pop-ins is proposed to be linked with the radial/median cracks during nanoindentation in the case of ZTA and alumina toughened zirconia (ATZ) ceramics [20]. The micro pop-ins occurs due to diffusion creep in the case of ZnO nanorods [25]. For MgO ceramics, the occurrence of micro pop-ins is linked to the dislocation nucleation [26,27] while micro pop-ins in CaZrO 2 –MgO ceramic com- posites is attributed to disconnection of grains under the indenter and associated microcracking [28]. However, multiplication of dislocation loops and their subsequent movement by cross-slipping from one plane to other plane is suggested to cause micro pop-ins in GaN single crystals [29]. Further, it is also proposed that micro pop-ins occur due to dis- location nucleation in polycrystalline ZrB 2 [30]. On the contrary, the nanoscale plastic micro pop-ins is suggested to occur due to homo- geneous lattice distortion and relaxation in SiC ceramics [31]. https://doi.org/10.1016/j.ceramint.2019.05.189 Received 18 April 2019; Received in revised form 17 May 2019; Accepted 17 May 2019 ∗ Corresponding author. Department of Physics, School of Basic Sciences, Faculty of Science and Dean, Faculty of Science, Manipal University Jaipur, Jaipur, 303007, Rajasthan, India. E-mail addresses: anoopkumar.mukhopadhyay@jaipur.manipal.edu, mukhopadhyay.anoop@gmail.com, anoop123.1958@gmail.com (A.K. Mukhopadhyay). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2019 Published by Elsevier Ltd. Please cite this article as: Payel Maiti, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.05.189