Temperature Dependent Brittle Fracture of Undoped and Impurity Doped Sapphire Fibers

The flexure strength of partially‐stabilized tetragonal ZrO2(Er2O3) single‐crystal monofilaments manufactured by the laser‐heated floating zone method was measured as a function of the environment (air versus water) and temperature (from 25° to 800°C) at loading rates spanning three orders of magnitude to ascertain their susceptibility to the environmental conditions. These mechanical tests were completed with parallel tests on fully annealed monofilaments (to relieve the thermal residual stresses induced during growth) and by detailed analysis of the fracture surfaces using scanning electron microscopy and micro‐Raman spectroscopy. While environmental susceptibility of ZrO2(Y2O3) in previous investigations was always associated with the destabilization of the tetragonal phase, monoclinic phase was not detected on the fracture surfaces of the ZrO2(Er2O3) monofilaments and it was concluded that slow crack growth in this material at high temperature or immersed in water was due to stress corrosion cracking.

Section: Discussionsupporting

confidence: 86%

Stress Corrosion Cracking of Single‐Crystal Tetragonal ZrO₂(Er₂O₃)

Ridruejo

Pastor

LLorca

et al. 2005

“…3). This is in agreement with the evidence of SCG in tetragonal and cubic Y 2 O 3 ‐doped ZrO 2 9,10 as well as in Al 2 O 3 6,7 at intermediate and elevated temperatures.…”

Section: Discussionsupporting

confidence: 91%

“…Moreover, the flexure strength of the monofilaments tested in water or at 400°–800°C increased with the loading rate, and this behavior was accompanied by significant changes in the morphology of the fracture surfaces, which showed evidence of slow crack growth (SCG). These previous results raise the question of the environmental susceptibility of the Er‐PSZ single crystals, particularly at elevated temperature, because it is well known that the mechanical performance at high temperature of some oxide single crystals, such as Al 2 O 3 , has been hindered by the occurrence of SCG due to stress‐corrosion cracking 5 or thermally activated bond rupture 6,7 …”

Section: Introductionmentioning

confidence: 99%

High‐Temperature Tensile Strength of Er₂O₃‐Doped ZrO₂ Single Crystals

Pastor

LLorca

Poza

et al. 2006

The deformation and fracture mechanisms in tension were studied in single‐crystal Er2O3‐doped ZrO2 monofilaments processed by the laser‐heated floating zone method. Tensile tests were carried out between 25° and 1400°C at different loading rates and the dominant deformation and fracture mechanisms were determined from the shape of the stress–strain curves, the morphology of the fracture surfaces, and the evidence provided by monofilaments deformed at high temperature and broken at ambient temperature. The tensile strength presented a minimum at 600°–800°C and it was controlled by the slow growth of a crack from the surface. This mechanism was also dominant in some monofilaments tested at 1000°C and above, while others showed extensive plastic deformation before fracture at these temperatures. The strength of plastically deformed monofilaments was significantly higher than those which failed by slow crack growth due to the marked strain hardening capacity of this material.

“…␣-Al 2 O 3 whiskers also have been prepared by the vapor-phase method, 13 under which a stream of moist hydrogen is passed over aluminum powder at 1300°-1500°C. 15 Pedestal growth, also known as float-zone growth, is similar to the Czochralski method: The melt is formed on the tip of the feed-stock ceramic rod and held together by the surface tension of the melt. In addition, c-axis ␣-Al 2 O 3 has been produced by the laser-heated pedestal-growth (LHPG) method.…”

Section: Introductionmentioning

confidence: 99%

Method for Production of α‐Alumina Whiskers via Vapor‐Liquid‐Solid Deposition

Valcárcel

Cerecedo

Guitián

2003

α‐alumina (α‐Al2O3, corundum) fibers exhibit high thermal and chemical stability, as well as good mechanical properties, even at high temperatures. Such characteristics make them good candidates for use in composites. Nevertheless, very few methods of producing α‐Al2O3 fibers are available. In the present work, we describe a method that uses aluminum pieces deposited on SiO2 powder, in an argon atmosphere, at temperatures in the range 1300°–1600°C. The α‐Al2O3 fibers are obtained via vapor‐liquid‐solid deposition. The novel addition of nickel and cobalt (or their oxides) allows the use of temperatures >1500°C, resulting in improved fiber production. We demonstrate that the metals do not contaminate the fibers produced in this way. Finally, we also estimate the tensile strength of the Al2O3 fibers produced through this method.