Estimation of the effect of redox treatment on microstructure and tendency to brittle fracture of anode materials of YSZ–NiO(Ni) system

Abstract

The effect of reduction treatment in a high-temperature (600 °C) hydrogen-containing environment on the microstructure and tendency to brittle fracture of YSZ-NiO(Ni) materials for solid oxide fuel cell anodes has been studied. To assess the crack growth resistance of the ceramics, the Vickers indentation technique was adapted, which allowed estimating the microhardness and fracture toughness of the material in the complex. The requirements for high porosity of the anodes to ensure functional properties show that the strength may be an insufficient characteristic of the bearing capacity of the anode. More structurally sensitive characteristics are needed to assess its crack growth resistance. The average levels of microhardness of YSZ-NiO ceramics in the as-sintered state and YSZ-NiO(Ni) cermets(2.0 GPa and 0.8 GPa, respectively) and their fracture toughness (3.75 MPa•m 1/2 and 2.9 MPa•m 1/2 , respectively) were experimentally determined. It was found that the microstructure of YSZ-NiO(Ni) cermet after redox treatment is formed by a YSZ ceramic skeleton with refined Ni-phase grains combined in a network, which provides increased electrical conductivity. Along with higher porosity of the cermet, its fracture toughness is not lower than that of the one-time reduced cermet due to the implementation of the bridging toughening mechanism of fracture.The proposed treatment method allowed forming the microstructure of the anode material, resistant to crack propagation under mechanical load. The propensity of the anode material to brittle fracture on the basis of evaluation of its crack growth resistance and analysis of the microstructure and fracture micromechanism was substantiated. This result is interesting from a theoretical point of view. From a practical point of view, the developed technique allows determining the conditions of redox treatment in the technology of manufacturing fuel cell anodes

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia

“…In these works, the formulas for calculating the K Ic values contain both physical and mechanical parameters, as well as empirical coefficients. Due to the comparison of the K Ic values calculated by these formulas with those obtained by conventional methods of fracture mechanics, we recently concluded [53] that the following formula presented by the authors of the work [51] best fits the characterization of the ZrO 2 -Y 2 O 3 ceramics:…”

“…In the work [53], a dependence of the microhardness of yttria-stabilized zirconia (ZrO 2 -8 mol% Y 2 O 3 ) on the indentation load, known as the indentation size effect [57], was revealed. For this material, the average values of microhardness decreased with increasing indentation load from 0.49 N to 9.81 N. Additionally, a tendency was observed with the yield of microhardness values on the plateau at indentation loads in a range of 4.91 N to 9.81 N. It was concluded that the values of fracture toughness and microhardness obtained in this range of indentation loads are invariant.…”

The Effect of Yttria Content on Microstructure, Strength, and Fracture Behavior of Yttria-Stabilized Zirconia

“…ZrO 2 -based ceramics are widely used in biomedical applications (particularly for teeth crowns, bridges, implant fixtures, and dental prostheses) [ 1 , 2 , 3 ], energy generation [ 4 , 5 ], chemical industry [ 6 , 7 ], and the manufacturing of various machine components [ 8 , 9 , 10 , 11 ]. Doping with Y 2 O 3 improves strength, toughness, and wear resistance [ 12 ], thus opening a possibility of application in orthopedics for hip-joint heads [ 13 , 14 ].…”

THE EFFECT OF ULTRA-FINE ALLOYING ELEMENTS ON THE PHASE COMPOSITION, MICROSTRUCTURE, HIGH-TEMPERATURE STRENGTH AND FRACTURE TOUGHNESS OF Ti–Si–X AND Ti–Cr–X COMPOSITES

“…To characterize crack growth resistance of materials [82][83][84][85][86], a fracture toughness characteristic, namely, the critical stress intensity factor (SIF) KIc is often used. One of the simplest methods of estimation of the fracture toughness is an indentation method implementing a variety of formulas for calculating the SIF [87][88][89][90][91][92][93][94][95][96]. For a lot of materials, the KIc values calculated by some of these formulas are consistent with those obtained by conventional methods of fracture mechanics [78,96,97].…”

“…One of the simplest methods of estimation of the fracture toughness is an indentation method implementing a variety of formulas for calculating the SIF [87][88][89][90][91][92][93][94][95][96]. For a lot of materials, the KIc values calculated by some of these formulas are consistent with those obtained by conventional methods of fracture mechanics [78,96,97]. Among the last ones, a single-edge notch beam (SENB) test [98][99][100] is widely used to estimate fracture toughness of ceramic and composite materials.…”