Effect of the foem of loading on the degree of manifestation of the adsorption-induced loss of strength and ductility in metals

Abstract

It has been shown by a number of authors that the extent to which the e f fec ts of s t rength reduction, b r i t t l enes s development , and ea sy d i spers ion appea r in solids under the influence of adsorp t ion-ac t ive med ia (including the case of solid me ta l s in the p re sence of meta l l i c mel ts ) depends ve ry cons iderably on a n u m b e r of fac to rs , such as the chemica l composi t ion of the solid and liquid phases , the t rue s t ruc tu re of the solid, and the conditions of deformat ion and f r ac tu re (in pa r t i cu la r , the c h a r a c t e r and intensity of the applied mechan ica l forces) [1-5]. The pa r t s played by these fac tors v a r y cons iderably . The chemica l c o m posi t ion (and hence the c h a r a c t e r of the in te ra tomic interact ions) de te rmines the actual poss ib i l i ty of a m o r e or l ess s eve re reduct ion in the f ree sur face energy taking place at the boundary between the solid and the med ium (i.e., the poss ib i l i ty of e a s i e r f rac tu re , and the r e a r r a n g e m e n t of the in te ra tomic bonds in the solid under the influence of the medium), which is the pr inc ipa l n e c e s s a r y condition for the s t reng threducing effects of adsorpt ion under considera t ion . However , only under ce r ta in conditions do these e f fects appea r to any m a r k e d extent . Thus the embr i t t l emen t due to the action of a mol ten meta l encountered in a pa r t i cu l a r b inary s y s t em on subject ing the s amples to tens i le t e s t s usual ly fails to appear under conditions of compres s ion ; the effect is s t imula ted by s t r e s s r a i s e r s (notches), the use of specif ic fa i r ly high r a t e s of deformat ion, cyc l ica l (fatigue} ef fec ts , and so on. In view of this si tuation exis t ing data as to the influence of var ious mel t s on the s t rength of solid me ta l s (now e x t r e m e l y abundant) r ema ins l a rge ly incomplete and con t rad ic to ry . Thus, for example , lead is found [6] to have no influence on the s t rength of single c r y s t a l s of zinc subjected to tensi le s t r a in at 15% min-~; for much higher deformat ion veloci t ies [7] single c r y s t a l s of zinc a re embr i t t l ed in the p re sence of mol ten lead. Analogously, mol ten t in e m b r i t t l e s polyc rys ta l l ine lead subjected to rapid bending [8] but has no effect on its ductility for slow bending [9]. These examples show how much the conditions of deformat ion affect the extent to which the adsorpt ioninduced loss of s t rength and ductil i ty appea r s in solid me ta l s under the act ion of the surrounding medium.