The reasons for the appearance of dimensional properties of surfaces of coatings obtained under the conditions of induced codeposition of iron group metals with tungsten are investigated. It is shown that the previously described size effect of microhardness and the macroscopic size effect of the corrosion rate discovered and described in this article have the same nature – the formation of surface oxides. Deletion of oxides by abrasive treatment results in an increased corrosion rate and a lack of the size effect of microhardness. The reasons for the formation of oxides surface layers during the induced codeposition of alloys are investigated.