Work hardening and flow stress of ultrapure molybdenum single crystals

The temperature dependence of the flow stress of molybdenum, deduced by means of two independent methods from tensile tests and stress-relaxation measurements on ultrapure single crystals (residual resistivity ratio 4 x 10(5), Schmid factor of the [111]((1) over bar 01) slip system mu = 0.5) in the temperature range 4 K less than or equal to T less than or equal to 460 K, is shown to agree with that obtained by the cyclic-deformation technique. The analysis in terms of the kink-pair theory of screw-dislocation mobility gives the following results. Below (T) over cap = 60 K the elementary slip steps take place on ((1) over bar 01) planes (Peierls stress of the a(0)[111]/2 screw dislocations sigma(P)([110]) = (870 +/- 10)-MPa, formation energy of a pair of isolated kinks 2H(k)([110]) = (0.63 +/- 0.03) eV). At T > (T) over cap slip proceeds by cross slip on ((2) over bar 11 and (1) over bar(1) over bar2) planes (sigma(p)([112]) = (690 +/- 20) MPa, 2H(k)([112]) = (1.27 +/- 0.03) eV). (C) 2001 Elsevier Science B.V. All rights reserved.