Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint New observations and critical assessments of incipient plasticity events and indentation size efect in nanoindentation of ceramic nanocomposites Payel Maiti a , Jiten Ghosh a , Anoop Kumar Mukhopadhyay a,b,∗ a Advanced Mechanical and Materials Characterization Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata, 700032, India b Department of Physics, School of Basic Sciences, Faculty of Science, Manipal University Jaipur, Jaipur, 303007, Rajasthan, India ARTICLEINFO Keywords: Zirconia toughened alumina Incipient plasticity events Shear deformation bands Microcracks ABSTRACT The ceramic nanocomposites (CNCs) like zirconia toughened alumina (ZTA) ceramics are important futuristic materials for structural and functional applications in advanced strategic systems, structural components, bio- medical prostheses and devices. In all structural materials including the ZTA CNCs, the very early stages of plastic deformation i.e., the incipient plasticity events (IPE) are most important to be understood so that the microstructure and mechanical properties can be tuned to suit a given end application. Here we report for the frst time the mechanisms of IPE in the nanoindentation experiments conducted at 10–1000mN loads in the 40 ZTACNCs.Here40ZTACNCstandsfor40vol%of3mol%Yttriapartiallystabilizedzirconiatoughenedalumina (40ZTA) CNC. The role of load ranges in variations of the IPE related parameters in the 40 ZTA CNCs is also studied. Further, an attempt is made to assess how the amount of zirconia content in ZTA CNCs afects the variations of the IPE related parameters. Through the extensive usage of feld emission scanning electron mi- croscopy (FESEM) and theoretical estimations, eforts are also directed to check out the linkage, if any, between the localized shear deformation and/or microcracking with the IPE events that occur in the present CNCs. In addition, a new concept of damage resistance is introduced for the first time in the present work to explain the presence of a strong indentation size efect (ISE) in the 40 ZTA CNCs. Finally, an attempt is also directed to understand how the indentation load (P) controls the relative size of interaction zones of dislocation loops as well as the damage resistance and thereby, engineer the acuteness of the ISE in ZTA CNCs. The implication of these fndings in futuristic design of especially the ZTA CNCs for various applications is also discussed. 1. Introduction The occurrence of incipient plasticity events (IPE) refers to the very early stage of plastic deformation initiation. It gives rise to localized ser- rationsand/ordiscontinuousstepsintheload(P)versusdepth(h)and/ or displacement plots obtained during nanoindentation experiments [1]. Since, in terms of structural health assessment it is extremely im- portant to understand early stages of plastic deformation, this research feld on genesis of IPE spans across a wide variety of advanced struc- tural and functional materials e.g., high entropy alloys [1], Cu nano- crystal [2], LiTaO 3 and LiNbO 3 single crystals [3], GaN [4], diamond [5], Si crystal [6],4HSiC[7], colloidal glasses [8] and multi-principal element metallic alloys [9] and many other important materials [10]. Thus, the IPE can happen in both load controlled and displacement controlled nanoindentation experiments. In absence of IPE the P-h curveisexpectedtobesmooth.InpresenceofIPEtheP-hplotsmakesa transition from elastic deformation to plastic deformation. The elastic deformation is recoverable and hence, reversible. But the plastic de- formation is irrecoverable and hence, irreversible. However, the me- chanism and/or mechanisms operative behind the genesis of IPE in especially zirconian based ceramics (ZBCs) and/or advanced ceramic nanocomposites (CNCs) like the zirconia toughened alumina (ZTA); is yet to be unambiguously established [1–10]. The huge current thrust on research in ZBCs and ZTA is linked to their wide application range from e.g., advanced dielectric coatings to e.g., thermal barrier coatings etc. [11–21]. All these applications in- volve surface contact. So, a signifcant amount of research is done to improve hardness and fracture toughness of ZTA [22–27]. In terms of assessing the structural integrity at the microstructural length scale at or in the vicinity of the surface the nanoindentation technique has emergedasoneofthemostimportant,recent,versatilecharacterization techniquesthatcanbeappliedtoawidevarietyofstructural,functional https://doi.org/10.1016/j.ceramint.2019.10.019 Received 6 August 2019; Received in revised form 20 September 2019; Accepted 2 October 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 (A.K. Mukhopadhyay). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Payel Maiti, Jiten Ghosh and Anoop Kumar Mukhopadhyay, Ceramics International, https://doi.org/10.1016/j.ceramint.2019.10.019