The invention concerns a method wherein the substrate (5) to be coated is immersed in an autocatalytic chemical deposit bath (4), for example nickel, contained in a stainless steel vessel (1) and wherein can be optionally mixed a suspended MCrAlY alloy, so as to form a metal deposit (nickel) wherein are optionally included powder particles. The invention is characterised in that, to provide a prolonged operation of the bath, it consists in measuring with a voltmeter (8) the difference of potential between the substrate (5) and a reference electrode (6) immersed in the bath (4), and in imposing between the substrate (5) and the vessel (1) an electric current produced by a generator (10), said current being adjusted by a regulator (11) so as to maintain said potential difference at a selected value.