Strain Rate Dependence of Tensile Behavior and Environmental Effect in Zirconia Ceramics

Abstract

The tensile strength of four kinds of zirconia ceramics (two kinds of Y-TZP with different grain sizes, Mg-PSZ and Ce-TZP) has been investigated for a wide range of strain rates (3ϫ10 Ϫ9 -1.0ϫ10 Ϫ1 s Ϫ1) in both air and vacuum. The obviously unique strain rate dependence was observed in Y-TZPs and Mg-PSZ, which have anelastic properties. On the other hand, such strain rate dependence was not observed over the whole range of strain rates for Ce-TZP, which does not exhibit anelasticity. For all of the samples investigated, there was no significant difference between both values of tensile fracture strength in air and vacuum. It was found that a decrease in strength with decreasing strain rate should not be associated with the static fatigue growth of microcracks nucleated during loading. It was concluded that the extent of the occurrence and the exhaustion of anelasticity predominantly controls the tensile strength of zirconia ceramics.KEY WORDS: anelasticity; ADOV; ceramics; fatigue; fracture and fracture toughness. materials are degraded in hydrogen environment. 11,12) However, the extent of the strength degradation or static fatigue in hydrogen is lower than that in air, as reported in alumina and zirconia ceramics.11,12) Therefore, it is much more important to examine the mechanical behavior in air from the view point of clarifying the environmental effect in the ceramic materials loaded. There are quite a few reports that discuss the strain rate effect in zirconia ceramics. 4,6,7) Moreover, these studies have been carried out under compression testing, with the discussion focusing on tensile crack growth. [2][3][4][5][6][7] In this study, we conducted dynamic tensile testing over a wide range of strain rates for four kinds of zirconia ceramics, which have different mechanical properties, transformability, anelastic properties 9,10,13-18) and so on. Dynamic fracture testing was also carried out in vacuum in order to verify the true effect of subcritical microcrack growth on the strain rate dependence of tensile fracture strength. Possible Mechanism of Anelasticity in Zirconia CeramicsIn our recent work, 17,18) we have investigated anelastic behavior in some kinds of zirconia ceramics. Figure 2 shows the anelastic behavior in four kinds of materials (Y-TZP, Y-FSZ, Mg-PSZ and Ce-TZP) at 100 MPa and loadholding time of 10 h.18) This figure indicates that anelastic strain is produced in the Y 2 O 3 -ZrO 2 and MgO-ZrO 2 systems, but almost not in the CeO 2 -ZrO 2 system, irrespectively of the kind of crystallographic phase. This anelastic phenomenon appears even at extremely low stress level (Ͻ100 MPa) and produces time-dependent and recoverable strain.9,10) Therefore, such a unique behavior cannot be explained by conventional mechanism, for example, stress-induced phase transformation, [19][20][21] ferroelastic domain switching, [22][23][24][25] microcracking [26][27][28] and so on. It is well known that the large amount of oxygen vacancy is introduced in matrix of the Y 2 O 3 -ZrO 2 and MgO-ZrO 2 systems in order...

Continuum mechanics simulations of NiO/Ni–YSZ composites during reduction and re-oxidation

“…This type of behaviour is well known in crystalline solids [15,16] and has been reported to be significant in tetragonal zirconia polycrystals (TZP) [17][18][19][20]. Due to the high temperatures, however, the viscosity parameter can be expected to be quite high.…”

Manufacturing and deformation behavior of alumina and zirconia helical springs at room temperature

“…Later, oxygen vacancies were proposed as a reason for anelasticity. 24,27,28 The latter theory is supported by the observed differences in the anelasticity of Y-TZP and Ce-TZP springs. If stabilizing ions with a valence different from that of Zr 4+ are incorporated into the zirconia lattice, as is the case in Y-stabilized TZP materials by incorporating Y 3+ ions, oxygen vacancies are created to maintain electroneutrality.…”

“…An anelastic behavior on 3Y-TZP was first demonstrated in the literature by Pan and Horibe [21][22][23] using strain gauges on flexural specimens. In a multitude of further experiments with similar experimental setup, the influence of stress intensity, deformation rate, and loading mode on the anelastic behavior of various TZP and PSZ materials was investigated by Matsuzawa and other scientists at Waseda University in Tokyo [24][25][26][27][28][29][30] in the following years. It was found that the anelastic characteristic affects phase transformation, crack growth, and ultimately the mechanical properties of TZP ceramics.…”

“…In Ref. [24], the effect of strain rate on fracture strength was investigated on various zirconia materials in tensile test. For Y-TZP with submicron microstructure, the fracture strength increases with increasing strain rate.…”

Effect of microscale shear stresses on the martensitic phase transformation of nanocrystalline tetragonal zirconia powders

“…Moreover, all these previous studies were limited on doped-zirconia, such as yttria-stabilized zirconia (YSZ) and ceria-stabilized zirconia (CSZ). [27][28][29] To our knowledge, effect of microscale shear stress on the martensitic phase transformation of nanocrystalline t-ZrO 2 has never been reported.…”