CYCLIC DEFORMATION OF Nb SINGLE CRYSTALS
单晶铌的循环变形研究

Nb single crystals of both 321] and 110] orientations have been cy-clicly deformed in tension-compression at constant strain rate 8×10~(-4)s~(-1) over arange of plastic strain amplitudes between 10~(-3) and 10~(-4). The cyclic hardening, thechanges in shape of crystals and the asymmetry of stress have been studied. Thehardening curve can be divided into three stages, i. e. first, rapid-hardening andsaturated stage. In the first stage of cyclic hardening curve dominant features of dislocationconfigurations are high density networks and debris loops. In the rapid-hardeningstage the main feature is the formation of dislocation bundles. In the saturateda well defined bundle structure fully develops and between them it is filled withonly screw disloca tions and the imposed strain is accommodated mainly bythe motion of screw dislocations travelling to and from between the bundles.Three-dimention cell, two-dimention cell or bundle structures are summarized as thesaturated structures of bcc metals.