INTERNAL-FRICTION IN DIRECTED-CRYSTALLIZATION (CU-SN)-NB ALLOYS

The distinctive features of the low-frequency internal friction Q(-1)( T) of (Cu-Sn)-Nb composites at high temperatures (up to 400 degrees C) are investigated for strains in die range 10(-5) - 10(-4). Considerab le hysteresis of Q(-1)(T) in the heating-cooling cycle is recorded, in cluding the presence of a minimum at similar to 175 degrees C when the sample is heated to 400 degrees C and two peaks P-2 (at 280 degrees C ) and P-1 (at similar to 100 degrees C) when the sample is cooled from 400 degrees C. The activation energy of the anomalous internal fricti on background (up to 175 degrees C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which gover n the peak P-2) are calculated, and the value and temperature dependen ce of the yield point of the bronze matrix (which govern the peak P-1) are estimated. (C) 1998 American Institute of Physics. [S1063-7842(98 )02311-3].