In a recent work,1 we have reported the optimization of the spark plasma sintering (SPS) parameters to obtain dense nanostructured 3Y‐TZP ceramics. Following this, the present work attempts to answer some specific issues: (a) whether ZrO2‐based composites with ZrB2 reinforcements can be densified under the optimal SPS conditions for TZP matrix densification (b) whether improved hardness can be obtained in the composites, when 30 vol% ZrB2 is incorporated and (c) whether the toughness can be tailored by varying the ZrO2–matrix stabilization as well as retaining finer ZrO2 grains. In the present contribution, the SPS experiments are carried out at 1200°C for 5 min under vacuum at a heating rate of 600 K/min. The SPS processing route enables retaining of the finer t‐ZrO2 grains (100–300 nm) and the ZrO2–ZrB2 composite developed exhibits optimum hardness up to 14 GPa. Careful analysis of the indentation data provides a range of toughness values in the composites (up to 11 MPa·m1/2), based on Y2O3 stabilization in the ZrO2 matrix. The influence of varying yttria content, t‐ZrO2 transformability, and microstructure on the properties obtained is discussed. In addition to active contribution from the transformation‐toughening mechanism, crack deflection by hard second phase brings about appreciable increment in the toughness of the nanocomposites.
In the present work, the fretting wear (mode I, linear relative tangential displacement, constant normal load) of a newly developed nanocomposite is investigated with varying load (2-10 N) and test duration (10 000-100 000 cycles). A detailed morphological investigation of worn surface is carried out using a Stylus surface profilometer, optical microscope, SEM, and electron probe microanalyser (EPMA). A clear transition in friction and wear behavior with load is observed. Based on the worn surface topography and wear debris analysis, the wear mechanisms are proposed. The extremely low wear rate (10 À8 mm 3 /N . m) along with low wear depth (o1 lm) indicates high wear resistance of nanoceramic composites. The high fretting wear resistance of the nanocomposites as well as the observed tribological properties are discussed in terms of material properties, abrasion, and tribochemical wear phenomenon. (B5 MPa Á m 1/2 ). XRD investigation on the WC-6 wt% ZrO 2 nanoceramic composites indicated the predominant presence of tetragonal ZrO 2 and WC. No reaction product is detected. An 691 J ournal
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