Accession Number : AD0023614


Title :   SOME OBSERVATIONS ON GRAIN BOUNDARY SHEARING DURING CREEP


Corporate Author : CALIFORNIA UNIV BERKELEY MATERIALS RESEARCH LAB


Personal Author(s) : Fazan, Bernard ; Sherby, Oleg D ; Dorn, John E


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/023614.pdf


Report Date : 15 Nov 1953


Pagination or Media Count : 24


Abstract : Quantitative measurements of the contribution of grain boundary shearing to the creep process were made for high-purity Al in the temperature range 610 deg to 747 deg K under a stress of 250 psi. Grain boundary shearing followed the same functional relationship as the total creep strain, namely, Eg. b. = f(theta), where Eg.b = creep strain due to the grain boundary shearing and theta = te-delta Hg.b/RT(where t = time under stress delta, delta Hg.b. = activation energy for grain boundary shearing, R = gas constant, and T = absolute temperature). The activation energy for grain boundary shearing was essentially the same as that for the total creep process (about 36,000 cal/mole) . The contribution of grain boundary shearing to the creep strain followed the same primary and secondary stages as exhibited by the total creep strain. Extensive polygonization was observed in the vicinity of grain boundaries. Observations suggested that grain boundary shearing occurs by crystallographic mechanisms of deformation arising from bending and shearing of grain projections in the vicinity of the true relaxed grain boundary. The relative contribution of grain boundary shearing to the total creep strain is shown to be independent of the test temperature, but it increases as the creep stress decreases.


Descriptors :   *STRAIN(MECHANICS) , *GRAIN BOUNDARIES , *CREEP , SECONDARY , DEFORMATION , ACTIVATION ENERGY , GASES , STRESSES , CRYSTALLOGRAPHY , TEMPERATURE , MEASUREMENT , POLYGONS


Subject Categories : Mechanics
      Metallurgy and Metallography


Distribution Statement : APPROVED FOR PUBLIC RELEASE