NOVELTY - Protecting corrosion on a metallic substrate (10) involves use of a binary coating (12) including a layer of at least first and second different metallic elements in the form of titanium (Ti) and chromium (Cr) as a top layer or an underlayer (14). The metallic substrate comprises any one of iron, steel, aluminum or an aluminum alloy, magnesium or a magnesium alloy, brass, copper, Zamak (RTM: zinc, aluminium, magnesium and copper components) or any die-cast material.    USE - For protecting corrosion on a metallic substrate comprising iron, steel, aluminum or an aluminum alloy, magnesium or a magnesium alloy or brass or copper or Zamak or any die-cast material from at least one of oxidation, sulfidation, acid corrosion and alkali corrosion, including saline corrosion; and for protecting corrosion of a material used in a corrosive industrial environment such as in a chemical reaction apparatus or in a galvanic apparatus or on an electrically conductive element in a battery or fuel cell (claimed).    ADVANTAGE - The TiCr underlayer, when used with top layer system of a wear resistant material having a columnar structure can improve the mechanical properties, since it breaks the columnar structure of the top layer system and gives a desirable smoother top surface (less cauliflower like) which in turn yields better wear resistance against mechanical wear, especially against abrasive wear. The TiCr binary coating, with or without a top layer or top layer system, has excellent properties as a corrosion protective layer.    DETAILED DESCRIPTION - Protecting corrosion on a metallic substrate (10) involves use of a binary coating (12) including a layer of at least first and second different metallic elements in the form of titanium (Ti) and chromium (Cr) as a top layer or an underlayer (14). The metallic substrate comprises any one of iron, steel, aluminum or an aluminum alloy, magnesium or a magnesium alloy, brass, copper, Zamak (RTM: zinc, aluminium, magnesium and copper components) or any die-cast material. The coating comprises either a layer of titanium chromium (TiCr) with constant composition or a graded TiCr layer, e.g. a base layer (adhesion layer) of Cr and a layer of graded composition consisting of Cr and Ti with the proportion of Ti in the layer increasing from the interface with the base layer to a proportion of Ti greater than that of Cr at the boundary of the graded layer remote from the base layer. The proportion of Ti at the boundary comprises 90-100% excluding impurities. The boundary of the graded layer comprises a free surface of the coated substrate. The boundary of the graded layer forms an interface to at least one further layer forming a top coating or top coating system, respectively. The binary coating is present in at least one of amorphous and/or nanocrystalline form. The binary coating has a thickness of 50 nm to 10 mu m. The thickness of the Cr base layer is 10-100 nm, and the thickness of the graded layer is 40 nm to 10 mu m. The coating is deposited by a plasma vapor deposition (PVD) process and/or by plasma assisted chemical vapor deposition (CVD) process (PACVD). The PVD process is one of magnetron sputtering, a high power impulse magnetron sputtering (HIPIMS) process, another ion assisted sputtering process, and a plasma assisted vapor deposition process. The deposition process for the top layer or some or all of the layers of a top layer system are selected from PVD processes, CVD processes, plasma assisted PVD processes, plasma assisted CVD processes, electron beam vapor deposition processes, galvanic processes, powder coating processes, dying processes, chemical processes and painting processes. The coating and optionally any top layer or top layer system has been subjected to a thermal treatment such as an annealing operation or to a chemical treatment such as an oxidation treatment.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional through a substrate provided with the binary coating.    Substrate (10)    Binary coating (12)    Top layer or underlayer (14)    Adhesion layer (16)