Mechanical Performance of 3Y-TZP/Ni Composites: Tensile, Bending, and Uniaxial Fatigue Tests
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T. Tanimoto Shonan Institute of Technology, Tsujido-Nishikaigan, Fujisawa, Kanagawa 251, Japan (Received 26 April 2001; accepted 22 March 2002)
Dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP/Ni) homogeneous composites were prepared by a wet-processing route with metal concentration ranging from 0 to 40 vol%. Cyclic fatigue stress/life, tensile and bending strength, and fracture toughness were investigated in 3Y-TZP monolithic samples and 3Y-TZP/Ni composites. It was found that the addition of Ni particles to the 3Y-TZP matrix produced an embrittlement effect in the composites, decreasing the mechanical properties. This fact was attributed to the weak bonding between the Ni and 3Y-TZP particles in samples sintered in a reductive atmosphere. Additionally, the presence of Ni particles decreases the cyclic tensile fatigue of the composites probably by an environmentally assisted slow crack growth. I. INTRODUCTION
Zirconia ceramics are materials with fundamental properties responsible for the development of both functional and structural ceramic1 of interest for engineers and designers.2– 4 These properties include high flexural strength (f ⳱ 700 to 1500 MPa), high fracture toughness (KIC ⳱ 5 to 10 MPa ⭈ m1/2), high hardness (HV ⳱ 12 GPa), wear resistance, good frictional behavior, modulus of elasticity and coefficient of thermal expansion similar to several metals (Ni, steel, etc.), relatively high dielectric constant (⑀ ⳱ 12.5 at 2 MHz, room temperature), low thermal conductivity (2.094 W/m ⭈ K at 1300 °C), and corrosion resistance in acids and alkalis. These ceramics are also non-magnetic and serve as good electrical insulators. In spite of the wide field of applications of zirconia ceramics in their pure form, conductive particles incorporated in such an insulating matrix give new materials with appealing properties. In the present investigation, nickel was selected as the electrical conductive material because of its reasonably close match in coefficient of thermal expansion and elastic modulus with zirconia5 (␣Ni ⳱ 13.3 × 10−6 °C−1; ENi ⳱ 206 GPa). Nickel and zirconia are compatible at sintering because the sintering temperature of zirconia is lower than the melting point of nickel (Tm ⳱ 1455 °C). Additionally, nickel is a ferromagnetic material and may open new possibilities for functional applications. ZrO2/Ni represents a two-phase composite system containing a non-noble metal component that does not react with the insulating component. In a)
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J. Mater. Res., Vol. 17, No. 7, Jul 2002 Downloaded: 14 Mar 2015
diffusion bonding studies, no reaction product or intermediate phase was observed in sandwich structures of Ni foil and bulk zirconia.6 These cermets find important and critical applications in several emerging technologies (aerospace, energy, sensors, etc.) because of their appropriate combination of mechanical, electrical and magnetic properties. This system is of interest for flow sensors and temper
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