摘要:

The initial strength of (σi) and thermal shock resistances (ΔTcand σr/σi), as determined by quench tests, of Al2O3‐ZrO2composites are increased by increasing amounts of tetragonal ZrO2second phase for contents of up to ∼15 vol%. For composites with ≤9 vol% ZrO2the increases in σrand ΔTcreflect the increase in γICwith addition of ZrO2However, for ZrO2contents>9 vol%, the thermal shock resistances (ΔTcand σr/σi) and σiare also affected by machining‐induced microcracking in the surface of the samples. For ZrO2contents>14 vol%, bulk microcracking can become extensive and result in a degrad

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb09555.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

A weak electrolyte model for the mixed‐alkali effect on electrical conductivity and ionic mobility in glass was developed for the dilute foreign alkali region. The basic assumptions are (a) that alkali transport in single‐alkali glasses is due to a small concentration of mobile species and (A) adding small amounts of foreign alkali suppresses, by mass action, the mobile species concentration. The model was developed explicitly for the case where the mobile species are interstitial cations or cation pairs and was applied to analysis of conductivity data for 0.242(K2O +Na2O)–0.758SiO2glasses in the dilute Na+ region. The analysis allows the fraction of mobile cations in the single‐alkali glass to be calculated. This varies from 0.5% at 25° to 6% at 500°C for 0.242K2O–0.758SiO2glass and is in good agreement with estimates of the extent of dissociation from internal friction data and an ionic jump model of c

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb09556.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The assignment of boundary values for the chemical potential and the calculation of energy‐release rates for the growth of creep cavities along grain boundaries by self‐diffusion are discussed. For simplicity, it is assumed that the boundaries are flat and that surface and grain‐boundary diffusion are the dominant transport mechanisms. As matter diffuses from the void surface into and along the grain boundary, misfit residual stresses are induced to alleviate the high stress concentration ahead of the cavity apex. As a result, the contribution of strain‐energy terms to the chemical potential can be neglected in typical cases. Also, contrary to the Griffith crack‐extension model, the energy dissipation incurred by diffusive removal of material from the cavity surface and deposition in the grain boundary is a major term in the energy transfers associated with cavity growth. The primary energy “sink” in diffusive cavity growth is shown to arise from the work done by the grain‐boundary normal stress when matter is inserted in the near‐tip region by diffusion, not from the loss of strain energy of matter that is removed from the cavity at its tip or from the work of bond separation. Thermodynamic restrictions on the angle formed by the void surfaces at their apex, where they join the grain boundary, are considered. Boundary values for the chemical potential are derived in a manner appropriate for arbitrarily large but elastic distortions of material near the cavity tip and, in contrast to most previous work in the area, the effects of surface tension (i.e. of “surface stress,” as distinct from surface

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb09557.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

This paper surveys recent developments in the calculation of surface energies, surface tensions, defect structure, and related surface phenomena. The way in which theory can complement experiment in understanding the surface behavior of stoichiometric and nonstoichiometric ceramics is discussed.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb09558.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1981.tb09559.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY