Creep of silver bromide at high temperture

Abstract The transient and steady-state creep rate of single crystal and polycrystalline specimens of AgBr, stressed in compression from 6 to 150 g/mm2, has been investigated between 300° and 410°C, with the emphasis on the steady-state creep of single crystals. The effects on the creep rate of orientation, of hydrostatic confining pressure, and of impurities were studied. Single crystals deformed by slip, though with rather weak conditions on possible slip systems. The steady-state results were reproducible to within about 15 per cent. At higher stresses, for crystals with axis in the [001] direction, the steady-state creep rate was fitted to the empirical formula ϵ = C exp {− Q RT} exp {Bσ 1 2 /RT} , with C = 2.8 X 1017min−1, Q = 69.1 kg-cal/mol, B = 1.21 (kg-cal/mol) (g/mm 2 ) 1 2 , σ = compressive stress. For [111] crystals, σ can be replaced by 3 4 σ ; for other orientations the rates were intermediate. At lower stresses the rate decreased more sharply with decreasing stress. The steady-state rate was depressed strongly by high pressure, by the factor exp {−pΔV RT} , with ΔV = 38 ± 3 cm3/mol. The effect of impurities in concentrations of about 10−3 was in general to decrease the creep rate, S− being more effective than Cd++ or Cl- in this respect. Mott's theory of diffusion-limited creep appears to give a satisfactory interpretation of the temperature, stress, and pressure dependence of the steady-state rate for pure crystals. ab|fr|Les vitesses de fluage transitoire et de fluage constant d'echantillons monocristallins et polycristallins de AgBr, soumis a des tensions de compression variant de 6 a 150g/mm2, ont ete investiguees entre 300°et 400°C, avec un accent sur le fluage constant de monocristaux. On a etudie les effets des variables suivantes sur la vitesse de fluage: orientation, pression hydrostatique et impuretes. Les monocristaux se deformaient par glissement, quoiqu'il n'y ait pas eu de conditions bien determinees concernant les systemes de glissement possibles. Les resultats du fluage constant etaient reproductibles a 15 pour cent pres. Aux tensions plus elevees et dans le cas de cristaux dont l'axe correspondait a la direction [001], le fluage constant a pu etre exprime par la formule empirique ϵ = C exp {−Q RT} exp {Bσ 1 2 RT} , ou C = 2.8 X 1017min−1, Q = 69.1 kg-cal/mol, B = (kg-cal/mol) (g/mm 2 ) 1 2 , σ = la tension de compression. Dans le cas de cristaux dont l'axe coincide avec la direction [111], σ peut etre remplace par 3 4 σ ; pour d'autres orientations les vitesses etaient comprises entre ces valeurs. Aux plus basses tensions, la vitesse diminuait plus rapidement avec la diminution de la tension. La vitesse de fluage constant etait fortement abaissee par de hautes pressions suivant le facteur exp {− pΔV RT} , ou ΔV = 38 ± 3 cm3/mol. L'effet des impuretes aux concentrations d'environ 10−3 etait en general d'abaisser la vitesse de fluage; S− etait plus efficace que Cd++ ou Cl−. La theorie de Mott du fluage limite par la diffusion, parait donner une interpretation satisfaisante de la dependance du fluage constant de la temperature, de la tension et de la pression, dans le cas de cristaux purs.