Second-order faceting - roughening of the tilt grain boundary in zinc

摘要

The faceting of the almost stationary [1010] tilt grain boundary with a misorientation angle θ of 84° in the Zn bi-crystal has been investigated. The shape of the very slow migrating grain boundary has been studied in situ between 350 and 400℃ using polarized light. Two intersecting facets lie in the closely-packed planes of the constrained coincidence sites lattice with coincidence parameter Σ = 15. In the as-grown sample flat grain boundary facets form the sharp first-order ridge with the break of the first derivative {partial deriv}y/{partial deriv}x of the grain boundary shape similar to those observed in our previous works on GB faceting in Zn. However, above 350℃ the sharp first-order ridge is substituted by the smooth grain boundary portion without a {partial deriv}y/{partial deriv}x derivative break similar to that observed in twin grain boundaries in Mo. The transformation of the as-grown first-order grain boundary ridge into continuous one has been observed for the first time. The critical parameter α has been calculated using the grain boundary shape in the transition region. α increases from α =1.7 ±0.07 for 350℃ to α = 1.9 ± 0.07 for 385℃ approaching the α = 2 value predicted in the mean-field Andreev model for the continuous surface roughening.