Creep deformation of ultrafine grained Ni/sub 75/B/sub 17/Si/sub 8/

Ultrafine grained, polycrystalline materials can be prepared by annealing of melt spun amorphous ribbons under controlled conditions. A grain size of 6.5-12 . 10/sup -5/ mm was attained in ribbons of Ni/sub 75/B/sub 17/Si/sub 8/, annealed at 6000C for 15 min, with a heating rate of 0.01-1 K/s. The samples were creep tested at low stresses (<400 kg/cm/sup 2/) and temperatures between 500 and 6150C. Coble creep, with an activation energy of 4 eV, was the dominant mechanism of deformation at low stress, and below 5750C. At higher stress the rate controlling mechanism became dislocation climb. The transition was temperature and grain size dependent. Above 5750C, the dominant mechanism was a nondiffusion controlled process