Structural changes and properties of molybdenum upon cold and cryogenic deformation under pressure

Abstract

The structure and hardness of a molybdenum single crystal with an (110) orientation, which was deformed by high pressure torsion at 290 and 80 K, are investigated. Such deformation mechanism as dislo cation slip that is characteristic of materials with a high stacking fault energy works also during cryogenic deformation: twinning does not occur. At both temperatures, the single crystal transforms into a polycrystal line state at a true strain e ≈ 2. Up to the maximum achievable true strains, no uniform in size submicrocrys talline structure forms in molybdenum.

Study of Cryogenic Rolling of FCC Metals with Different Stacking Fault Energies

“…On one hand, planar slip is the predominant mode of deformation in metals at room temperature, leading to the development of dislocation cells arrangement for high SFE materials (aluminum), as well as planar arrays of dislocations for materials with lower SFE (like copper and silver). On the other hand, as stated by Gapontseva et al 5 , deformations at low temperatures, even for intermediate and high SFE materials, results in higher dislocation density, promote twinning deformation and as consequence, the materials present higher strength combined with good ductility and tend to have smaller grain size. [4][5][6][7][8] In the present work, commercially pure samples of aluminum (Al), copper (Cu) and silver (Ag) were rolled at room and cryogenic temperatures until approximately 99% of overall thickness reduction, or equivalent strains (ε) between 3.23 and 4.13, in order to detect structural changes.…”

The effect of annealing on micro-hardness of molybdenum single crystals

“…In this connection, it should be noted that the (Peierls [43]) barriers for dislocation movement are comprised of both thermal and athermal components [44]. The former depends upon the mechanical energy given to the system during plastic deformation [45], while the latter is associated with the thermal energy supplied to the material [44]. For dislocation to move, the available energy must be sufficient enough to overcome the Peierls barriers.…”

Microstructure and Microhardness Evolution in Pure Molybdenum Processed by High‐Pressure Torsion

“…Nevertheless, HPT has an important advantage because experiments on a magnesium alloy showed that it is generally feasible to conduct HPT processing at a relatively lower temperature than ECAP, including at room temperature (RT), because of the large hydrostatic pressure that is imposed on the sample during the processing operation. [21] For refractory metals, reports are now available on the processing of W by ECAP or HPT over a range of temperatures from 673 to 1273 K, [22][23][24][25] the processing of Ta by ECAP at RT [26][27][28][29][30][31] or at 1173 or 1473 K [32] and HPT at RT, [33][34][35][36][37] the processing of V by HPT at RT, [38][39][40] and the processing of Mo by ECAP or HPT at temperatures from 623 to 1073 K [41][42][43][44][45][46][47][48] and HPT at both RT [38,[49][50][51][52][53][54][55][56][57] and a cryogenic temperature of 80 K. [54,56] Although several reports are now available on the processing of Mo by HPT, there have been no systematic studies of the concurrent evolution of microstructural refinement and hardness in pure molybdenum as are available, for example, in conventional fcc metals such as aluminum, …”

“…Nevertheless, HPT has an important advantage because experiments on a magnesium alloy showed that it is generally feasible to conduct HPT processing at a relatively lower temperature than ECAP, including at room temperature (RT), because of the large hydrostatic pressure that is imposed on the sample during the processing operation . For refractory metals, reports are now available on the processing of W by ECAP or HPT over a range of temperatures from 673 to 1273 K, the processing of Ta by ECAP at RT or at 1173 or 1473 K and HPT at RT, the processing of V by HPT at RT, and the processing of Mo by ECAP or HPT at temperatures from 623 to 1073 K and HPT at both RT and a cryogenic temperature of 80 K …”