Fig. (4) Top view of sapphire substrates subjected to 45 min contact with the melts at 1250 °C: (A) with Ni-40.5at.%Nb melt, (B) with Au-7.5at.%Nb melt, 1- the surface, which was not in the contact with the melt, 2- the perimeter of the wetting, 3- the wetting zone, 4- the edge of the Au-7.5at.%Nb drop.