Abstract: In the practice of the sputter ion plating of refractory metals or refractory metal compounds on substrates to form smooth dense substantially porous-free coatings a method whereby the substrate bias potential can be reduced, thereby reducing the generation of substrate heat, is provided wherein the source material consists of a refractory metal or a refractory metal compound and one or more further metals. The further metal may be another refractory metal. Typical refractory and further metals are tungsten and tantalum.The source material may suitably be a bundle of wires consisting of wires of the refractory metal or metal compound and wires of the further metal.For predetermined glow discharge conditions of source and substrate potentials and ionizable gas pressure, the source material preferably consists of the refractory metal or metal compound and the further metal in proportions to form a solid solution on the substrate.The ionizable gas should be an inert gas of high atomic number.