Continuous cavity nucleation and creep fracture

Intergranular creep fracture under the stress and temperature conditions experienced by components in service is generally acknowledged as resulting from nucleation and growth of intergranular cavities. Firstly, there seemed to be an approximately linear reciprocal relationship between time-to-fracture and minimum rate of creep deformation. Secondly, cavity growth by stress-directed flow of atoms was shown by Hull and Rimmer to lead to lifetime being inversely proportional to the maximum principal stress providing that all cavities initiated at the start of the test. Recently, it has been demonstrated that the boundary conditions imposed by Hull and Rimmer were unnecessarily restrictive and that more realistic ones result in cavity growth rates being proportional to strain rates. Nevertheless, there is an increasing body of experimental evidence on engineering alloys and also iron which indicates that cavities are not all nucleated in a short time interval, but are nucleated continuously. This paper collates the evidence for the continous nucleation of cavities, places this within the framework of creep fracture modelling and introduces a quantitative assessment of the likely errors of measurement. A model of cavity nucleation based on the stochastic nature of transgranular creep deformation is also discussed.

[1]  Paul Shewmon,et al.  Diffusion in Solids , 2016 .

[2]  M. V. Speight,et al.  Vacancy Potential and Void Growth on Grain Boundaries , 1975 .

[3]  R. Balluffi,et al.  Growth of voids in metals during diffusion and creep , 1957 .

[4]  B. Cane.  Interrelationship between creep deformation and creep rupture in 2¼Cr-1Mo steel , 1979 .

[5]  B. F. Dyson,et al.  Constrained Cavity Growth, Its Use in Quantifying Recent Creep Fracture Results , 1979 .

[6]  B. Dyson.  Constraints on diffusional cavity growth rates , 1976 .

[7]  B. Dyson,et al.  A New Method of Predicting Creep Life , 1972 .

[8]  T. Gibbons,et al.  Influence of trace elements on creep and stress-rupture properties of Nimonic 105 , 1979 .

[9]  M. Speight.  Mass transfer and grain-boundary sliding in diffusion creep , 1975 .

[10]  T. Gladman,et al.  Nucleation and growth of creep cavities in a Type 347 steel , 1980 .

[11]  B. F. Dyson,et al.  Creep of Nimonic 80A in torsion and tension , 1977 .

[12]  Michael F. Ashby,et al.  Intergranular fracture at elevated temperature , 1975 .

[13]  David R Hayhurst,et al.  Creep in Structures , 1981 .

[14]  W. Nix.  Reply to comment on: “On the jogged screw dislocation model for steady state creep” , 1967 .

[15]  D. Hull,et al.  The growth of grain-boundary voids under stress , 1959 .

[16]  B. Hopkins,et al.  The creep cavitation of commercial and high-purity Cr-Mo-V steels , 1976 .

[17]  M. V. Speight,et al.  Creep cavitation by vacancy diffusion in plastically deforming solid , 1978 .

[18]  Deryle W. Lonsdale,et al.  Damage accumulation and microstructural changes occurring during the creep of a 214%Cr1%Mo steel , 1979 .

[19]  Michael F. Ashby,et al.  Intergranular fracture during power-law creep , 1979 .

[20]  D. Woodford.  A Parametric Approach to Creep Damage , 1969 .

[21]  Rishi Raj,et al.  Nucleation of cavities at second phase particles in grain boundaries , 1978 .

[22]  B. Dyson,et al.  Prestrain, Cavitation, and Creep Ductility , 1974 .

[23]  G. W. Greenwood,et al.  The Nucleation and Growth of Cavities in Iron during Deformation at Elevated Temperatures , 1975 .

[24]  G. W. Greenwood.  Cavity nucleation in the early stages of creep , 1969 .

[25]  W. Beeré.  Grain size stability and switching in two phase polycrystals , 1978 .

[26]  Peter Goodhew,et al.  Comments on: “Low energy grain boundaries in metals” by Herrmann, Gleiter and Ba̋ro, Acta Met , 1977 .