A Study of the Role of Grain Boundary Cavitation in the Creep-Fatigue Interaction in High Temperature Fatigue.
Abstract
An investigation has been carried out of the processes involved in the nucleation of grain boundary cavities in astroloy. Cavitation was produced by several methods: room temperature straining, straining and annealing, high temperature creep of prestrained astroloy, creep of non-prestrained material. It is concluded from the experimental evidence that the same mechanism is responsible for the initial grain boundary damage in all cases. In astroloy pulled at room temperature, damage shows up as microcracks at the interface pulled at room temperature, damage shows up as microcracks at the interface between carbide and matrix. It is isotropic. During annealing, large residual stresses in the strained material close up cracks on some boundaries, increase and round out the cracks on other boundaries so that damage now appears in the form of voids. Residual stresses have a large effect on the creep life of prestrained astroloy. Their influence can persist over a significant fraction of the creep life. Residual stresses are found to be important even in the creep of non-prestrained astroloy. The density of voids in non-prestrained astroloy seems to be determined by total creep strain; it is independent of creep stress, at least over the range of test conditions studied. A small strain appears to be necessary for the onset of creep cavitation. All of the results noted above can be explained qualitatively on the basis of the stress fields which build up during deformation around non-deforming inclusions whose elastic constants differ from those of the matrix.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 20, 1982
- Accession Number
- ADA121231
Entities
People
- Julia R. Weertman
Organizations
- Northwestern University