The size dependent strength of Fe, Nb and V micropillars at room and low temperature

Theoretical Evidence for the Single-Ended-Source Controlled Yield Strengths of Micropillar FCC and BCC Metal Single Crystals

“…As already clarified in the pioneering research on BCC metals by Schneider et al, 10) absolute value of the exponent m becomes smaller as T c becomes higher. Also as already shown by Yilmaz et al 15) whose results are included in Fig. 2, for the results for BCC crystals with T c value at about room temperature, the size dependence of the strength is almost the same as those of FCC crystals, which has been interpreted due to the common feature of high mobility of dislocations for both edge and screw characters without affected by the Peierls potential for screw dislocation.…”

“…They attempted to rationalize the results by assuming that the flow stress consists of additive contributions of the friction term and the bow-out term of forest cutting process, both of which are strain-rate dependent. Yilmaz et al 15) selected three BCC crystals, Fe, Nb and V, of which T c is commonly about 300 K, and investigated size dependent strength of their micropillar specimens at 296 K and at 193 K, where strength was defined by 4% flow stress. At room temperature, the size dependent initial flow stresses for three BCC crystals are almost the same as those of FCC crystals with the size dependent exponent of around ¹0.6, while at 193 K the exponent is around ¹0.3.…”

“…Here, we confirmed that the data scatter in these experiments is relatively small, comparing with that of the critical yield stress or the flow stresses at 0.21%. Those selected experimental data are W, 10) Mo, 10) Ta, 11) V, 12) Nb 10) and the data by Yilmaz et al 15) for Fe, Nb and V, which are plotted in Fig. 2.…”

“…2) On the other hand, thanks to the development of micromachining technique of focused ion beam (FIB) milling, tiny test samples with diameters from a few micrometers down to a few hundred nanometers became available. Since the pioneering research by Uchic, Dimiduk, Florando and Nix 3) on the compression experiments in 2004 on micropillar samples of Ni and Ni 3 AlTa single crystals with the diameter from 0.5 to a few tens of micrometers, produced by the FIB milling process, mechanical tests on FIB processed submicron sized specimens became quite popular: from 2005 to 2020, the target crystals were mainly face-centered-cubic (FCC) single crystals of Au, 4) Ni, 5) Cu 6) and Al, 7) and from 2007 to 2019, body-centered-cubic (BCC) single crystals of Mo, 8,9) W, Mo and Nb, 10) W, Mo, Ta and Nb, 11) V, 12) Fe 13,14) and Fe, Nb, and V, 15) commonly with the ©100ª axial orientation, and also hexagonal-close-packed metals of Ti 16) and Mg 17) and some intermetallic compounds. An important difference between grown whisker crystals and nano-sized crystals fabricated by the FIB milling process is that in contrast to almost dislocation free whisker wires, FIB milling processed micro-pillars contain rather high density of dislocations of the order of 10 13 m ¹2 18) which are most probably introduced as the damage of FIB milling.…”

Наноиндентирование И Механические Свойства Материалов В Субмикро- И Наношкале. Недавние Результаты И Достижения (О Б З О Р)

“…Tm -температура плавления.в этом случае величина n не превышала 0.2 по модулю[126]. В высокоэнтропийных сплавах CrMnFeCoNi и FeCoNiCuPd величина n составляла n = −0.48 и n = −0.31 соответственно[127], что близко к n для некоторых металлов с ОЦК-решеткой.На величину n существенно влияет температура испытания T[128,129]. С ее понижением от комнатной T R до T = −80 • C величина n в ОЦК-металлах падала (по модулю) в 1.5−2.5 раза (в Fe с -0.63 до -0.25, в Nb с -0.58 до -0.31, в V с -0.56 до -0.39)[129]…”