A process for the thermochemical treatment of the surface of metallic pieces, in a plasma reactor having a reaction chamber provided with: a support carrying the metallic pieces; a system of anode and cathode having one of its electrodes (2a, 3a) associated with a pulsating DC power supply; an inlet of ionizable gas load; an inlet of liquid or gas precursor; and an outlet for exhaustion of gas load, comprising the steps of: a) connecting the anode to a first electrode and to a ground and connecting the cathode to the support, operating as the other electrode of the system of anode and cathode, and to a negative potential of the pulsating DC power supply; b) statically positioning the metallic pieces on the support associated with the cathode in the interior of the reaction chamber; c) surrounding the support and the metallic pieces with an ionizable gas load supplied to the reaction chamber through the inlet; d) heating the interior of the reaction chamber to a working temperature; e) applying to the cathode, associated with the support and with the metallic pieces, an electric discharge in order to cause the formation of a gas plasma of ions having a high kinetic energy surrounding the metallic pieces and the support; f) admitting a flow of liquid or gas precursor in at least one tubular cracking chamber having at least one end open to the interior of the reaction chamber and being associated with a high voltage energy source; g) applying a potential difference between the at least one tubular cracking chamber and the anode of the system of anode and cathode for dissociating the molecules of the precursor admitted into said tubular cracking chamber, releasing, to the interior of the reaction chamber, the atoms of the alloy elements to be ionically bombarded against the surfaces of the metallic pieces negatively polarized by the pulsating DC power supply; and h) providing the exhaustion of the gas load from the interior of the reaction chamber, the process being characterized in that the tubular cracking chamber is subjected to the working temperature in the interior of the reaction chamber. a) connecting the anode to a first electrode and to a ground and connecting the cathode to the support, operating as the other electrode of the system of anode and cathode, and to a negative potential of the pulsating DC power supply; b) statically positioning the metallic pieces on the support associated with the cathode in the interior of the reaction chamber; c) surrounding the support and the metallic pieces with an ionizable gas load supplied to the reaction chamber through the inlet; d) heating the interior of the reaction chamber to a working temperature; e) applying to the cathode, associated with the support and with the metallic pieces, an electric discharge in order to cause the formation of a gas plasma of ions having a high kinetic energy surrounding the metallic pieces and the support; f) admitting a flow of liquid or gas precursor in at least one tubular cracking chamber having at least one end open to the interior of the reaction chamber and being associated with a high voltage energy source; g) applying a potential difference between the at least one tubular cracking chamber and the anode of the system of anode and cathode for dissociating the molecules of the precursor admitted into said tubular cracking chamber, releasing, to the interior of the reaction chamber, the atoms of the alloy elements to be ionically bombarded against the surfaces of the metallic pieces negatively polarized by the pulsating DC power supply; and h) providing the exhaustion of the gas load from the interior of the reaction chamber,