Micromechanical properties of single crystals and polycrystals of pure α-titanium: anisotropy of microhardness, size effect, effect of the temperature (77–300 K)
S.V. Lubenets, A.V. Rusakova, L.S. Fomenko, and V.A. Moskalenko
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Received June 16, 2017
Anisotropy of microhardness of pure α-Ti single crystals, indentation size effect in single crystals, course grained (CG) pure and nanocrystalline (NC) VT1-0 titanium, and the temperature dependences of microhardness of single crystals and CG Ti in the temperature range 77–300 K have been studied. Minimum value of hardness was revealed when indenting into the basal plane (0001). The indentation size effect (ISE) appeared clear at the indentation of the soft high purity iodide titanium while it is the least pronounced in the nano-crystalline VT1-0 titanium sample. It has been demonstrated that the ISE can be described in the geometrically necessary dislocations model (GND) following from the theory for strain gradient plasticity. The true value of hardness of all materials and others parameters of the GND model have been determined. The temperature dependence of microhardness well agrees with the notion on the controlling role of Peierls relief in the thermally activated dislocation plastic deformation of pure titanium as it has been demonstrated and well-grounded before at the macroscopic tensile investigations at the low temperature range. The activation energy and activation volume of dislocation motion in the strained region beneath indenter have been estimated.
PACS: 62.25.+g Mechanical properties of nanoscale materials; PACS: 62.20.Qp Friction, tribology, and hardness; PACS: 68.35.Gy Mechanical properties, surface strains.
Key words: pure α-titanium, single crystals, cryorolling, anisotropy of microhardness, indentation size effect, ge-ometrically necessary dislocations, temperature dependence of microhardness, low temperatures.