High-Temperature Plastic Deformation of Polycrystalline Beryllium Oxide

Barmore, W. L.; Vandervoort, R.R.

doi:10.1111/j.1151-2916.1965.tb14648.x

Cited by 35 publications

(9 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Activation Energy Q The activation energy is large (100 kcal mole-a), but similar values have been observed in creep [5] and sintering [13] experiments in BeO. Most published values of activation energies for cation and anion self-diffusion in BeO fall in the range 50 to 60 kcal mole -1 [14][15][16] however, there is evidence to suggest that these values are associated with impurity effects.…”

Section: Mean Values Of the Apparent Activation Volumesupporting

confidence: 57%

“…Fig. 3 shows a 284 The present data cannot be interpreted in terms of a creep law with the first power of the stress (/3 = 1 over the stress range in the beam) such as has been suggested from higher temperature creep data [5].…”

Section: Resultsmentioning

confidence: 88%

“…In certain cases, for example elastic deflection in four-point bending, these distributions are known and a simple relation exists between measured and required values; in creep deformation, however, these distributions are complex and generally unknown and simplifying assumptions must be made. It is often assumed that the stress distribution in creep is identical to that for elastic deflection [5]; under certain conditions of creep this may be an accurate description but in general it leads to significant errors [7]. In the present case it was decided to attempt a more general solution to the problem of relaxation in a beam under four-point bending and to apply this to a study of stress relaxation in BeO.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Stress relaxation in beryllia

Walker¹,

Rotsey²,

Wood³

1971

J Mater Sci

View full text Add to dashboard Cite

Beryllia beams were loaded at temperature in four-point bending to a deflection of 0.001 in. or 0.002 in. and the decrease in load necessary to maintain the deflection constant was measured as a function of time. The beryllia was fine-grained, in the range ~-~ 1 to 7 Fm, and the porosity varied between 3 and 21 ~. The test conditions covered a temperature range of 850 to 1240~ experiments took from 10 min to 8 h: the loads used produced initial maximum outer fibre stresses of the order 3000 to 6000 psi.A method was developed for calculating the stress distribution in a beam at any time and this was used to analyse the results. The stress relaxation process was found to be stress-activated, and the conversion of elastic to plastic strain could be expressed as a creep law having the formThe activation energy was 100 • 2 kcal mole-' and the activation volume was large, probably of the order of 103 atoms. The rate constant ko was approximately proportional to the fraction of intergranular porosity and inversely proportional to the cube of the grain diameter. It is suggested that the mechanism of grain boundary sliding is consistent with the observations.

show abstract

Section: Mean Values Of the Apparent Activation Volumesupporting

confidence: 57%

Section: Resultsmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Stress relaxation in beryllia

Walker¹,

Rotsey²,

Wood³

1971

J Mater Sci

View full text Add to dashboard Cite

show abstract

“…Additionally, dislocations were shown to contribute to deformation of polycrystalline ceramics at high temperatures (e.g., >1000 • C). [10][11][12][13][14][79][80][81] Furthermore, it was demonstrated that dislocations could even increase the toughness of ceramics. 36,82,83…”

Section: Fundamental Aspects Of Dislocations In Ceramicsmentioning

confidence: 99%

“…In consequence, ideas can remain within their fields while there are few overarching reviews so far. For example, knowledge on room temperature plasticity of a whole range of ceramic single crystals [6][7][8][9] or plasticity of polycrystals at elevated temperature [10][11][12][13][14][15] is currently not wide spread.…”

Section: Introductionmentioning

confidence: 99%

60 years of dislocations in ceramics: A conceptual framework for dislocation mechanics in ceramics

Porz

2022

Int J Ceramic Engine & Sci

View full text Add to dashboard Cite

High‐tech ceramics are typically engineered by controlling point defects and interfaces while one‐dimensional dislocations have found much less attention so far. Nevertheless, their impact on almost any functional property and the sudden ease to fabricate them with novel synthesis methods, such as rapid densification, brings spotlight attention to dislocations as design dimension. Although the typical brittleness of ceramics insinuates the irrelevance of dislocations for mechanical behavior, abundant literature is spread over materials, decades, and disciplines, however, often unconnected. Here, a conceptual framework for dislocation mechanics in ceramics separated into five logical aspects, (1) fundamental mobility, (2) obstacles to motion, (3) limitation by necessity of nucleation, (4) motion complexity, and (5) avoidance of competing mechanisms, brings oversight into the complex behavior. In consequence, quicker identification of the limiting step allows to estimate the potential involved more precisely and to identify open research questions with greater ease. An introduction to dislocations and the functionality involved, a look back over the last six decades, and highlights of open question are dedicated to provide a framework and bridge the gap between the attached research fields.

show abstract

Microstructural Features of Scales and Their Likely Influence on Creep Behaviour

Strafford¹

1972

Materials & Corrosion

View full text Add to dashboard Cite

The microstructural features of scales as formed during the high temperature corrosion of metals can vary considerably. Apart from the obvious differences between scales derived from different metals, even with a given metal the microstructure of the scale is affected by factors such as metal purity and the conditions of exposure, namely the duration and temperature of oxidation and the partial pressure of the oxidant in the atmosphere. In particular variations in grain size and morphology, and in the degree and morphology, and in the degree and nature of porosity can occur; in addition in some systems precipitation of a second phase of variable morphology can take place. Some of these differing structural features in scales are discussed and illustrated. It is suggested that such variations in microstructure will considerably affect the mechanical properties of the scales in which they occur. In general few data concerning mechanical properties, in particular plastic deformation characteristics of scales have been published; furthermore little attempt has been made to assess the possible role of such variations in structure. Rather more information is, however, available from the field of ceramics, and this knowledge is critically reviewed. The usefulness and limitations of such information in relation to the interpretation of the creep behaviour of cobalt monoxide scales is illustrated.

show abstract

High-Temperature Plastic Deformation of Polycrystalline Beryllium Oxide

Cited by 35 publications

References 22 publications

Stress relaxation in beryllia

Stress relaxation in beryllia

60 years of dislocations in ceramics: A conceptual framework for dislocation mechanics in ceramics

Microstructural Features of Scales and Their Likely Influence on Creep Behaviour

Contact Info

Product

Resources

About