Metal-coated polymer articles containing structural substantially porosity-free, fine-grained and/or amorphous metallic coatings/layers optionally containing solid particulates dispersed therein on polymer substrates, are disclosed. The substantially porosity-free metallic coatings/layers/patches are applied to polymer or polymer composite substrates to provide, enhance or restore vacuum/pressure integrity and fluid sealing functions. Due to the excellent adhesion between the metallic coating and the polymer article satisfactory thermal cycling performance is achieved. The invention can also be employed as a repair/refurbishment technique. The fine-grained and/or amorphous metallic coatings are particularly suited for strong and lightweight articles, precision molds, sporting goods, aerospace and automotive parts and other components exposed to thermal cycling and stress created by erosion and impact damage.