Temperature dependences of the contact angle ͑T͒ between ͑i͒ specially grown tilt grain boundaries ͑GBs͒ in Al and the Zn-rich melt; ͑ii͒ tilt GBs in Zn and the Al-rich melt; and ͑iii͒ tilt GBs in Zn and the Al-based solid solution ͑Al͒Љ were measured using scanning electron microscopy and light microscopy. decreases with increasing T in all cases and reaches zero ͑complete wetting͒ at a certain temperature T w in cases ͑i͒ and ͑ii͒. The wetting transformation for Al GBs is discontinuous ͑first order͒: ͑T͒ dependence is convex, d / dT has a break at T w , and ϳ͓͑T − T w ͒ / T w ͔ 1/2 . The wetting transformation for Zn GBs is continuous: ͑T͒ dependence is concave, d / dT is continuous at T w , and ϳ͓͑T − T w ͒ / T w ͔ 3/2 . For the Zn GBs in contact with a second solid phase ͑Al͒Љ, ͑T͒ dependence is concave and ϳ͓͑T − T w ͒ / T w ͔ 3/2 for the extrapolated T w . The observed change from the discontinuous wetting transition for GBs in a metal with a higher melting point ͑Al͒ to the continuous one for GBs in a metal with a lower melting point ͑Zn͒ is explained using the approach proposed in ͓Pandit et al., Phys. Rev. B 26, 5112 ͑1982͔͒. The validity of this approach and critical exponent of 3/2 may indicate that GB wetting in the Zn-rich alloys is governed by the long-range forces.
Similar to free surfaces, the grain boundaries (GBs) in metals, semiconductors and insulators can contain flat (faceted) and curved (rough) portions. In the majority of cases, facets are parallel to the most densely packed planes of coincidence sites lattice formed by two lattices of abutting grains. Facets disappear with the increasing temperature (faceting-roughening transition) and the increasing angular distance from coincidence misorientation. The temperature of GB faceting-roughening transition T R decreases with the increasing inverse density of coincidence sites R. In case of fixed R, T R decreases with the decreasing density of coincidence sites in the GB plane.The intersection line (ridge) between facets or between facets and curved (rough) portions of surfaces can be of first order (two different tangents in the contact point) or of second order (common tangent, continuous transitions). The rough (curved) portions of GB can also form the firstorder rough-to-rough ridges (with two tangents). GB facets control the transition from normal to abnormal grain growth and strongly influence the GB migration, diffusion, wetting, fracture and electrical conductivity.
The Ti-Fe alloys are quite important among various Ti-based alloys doped with b-stabilisers. Severe plastic deformation by the high pressure torsion (HPT) leads to the strong grain refinement in Ti-Fe alloys. The high-pressure vTi-phase appears during HPT of the Ti-1 wt.% Fe alloy. However, the vTi does not appear after uniaxial compression at the same pressure, without torsion. vTi remains quenched after pressure release and disappears by heating around 140-150°C. However, the further alloying with iron suppresses the formation of vTi-phase. As a result, vTi does not appear after HPT in the Ti-10 wt.% Fe alloy.
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