Method for producing a titanium nitride coating on the surface of a titanium or titanium alloy substrate

Abstract

A method for producing a titanium nitride coating on the surface of a titanium or titanium alloy substrate may include: a) immersing the titanium or titanium alloy substrate as an electrode in a non-aqueous electrolyte comprising an ionic liquid having nitrogen ions in the presence of a counter electrode; and b) activating an electrochemical process of nitriding the substrate by applying an electric potential between the electrode, and the counter electrode, to generate an anodic electric current to decompose the nitrogen ions by releasing the nitrogen contained therein. The liberated nitrogen penetrates the titanium or titanium alloy substrate until it leads to the conversion to titanium nitride of a surface layer of the substrate, thereby generating a nitrided diffusion surface layer that forms a nitrided surface coating. The electric potential and/or the anodic electric current are modulated in time according to the desired thickness for the nitrided surface coating.

1 - 27 . (canceled) 
     
     
         28 . A method for producing a titanium nitride coating on the surface of a titanium or titanium alloy substrate, comprising the following steps:
 a) immersing the titanium or titanium alloy substrate as an electrode in a non-aqueous electrolyte consisting of an ionic liquid at room temperature, comprising nitrogen ions, in the presence of a counter electrode; and   b) activating an electrochemical nitriding process of the substrate, by applying an electric potential between an electrode, acting as an anode, and the counter electrode, acting as a cathode, so as to generate an anodic electric current at least sufficient to decompose the nitrogen ions releasing the nitrogen contained therein, the released nitrogen penetrating by diffusion into the titanium or titanium alloy substrate until leading to the conversion of a surface layer of said substrate into titanium nitride, thereby generating a nitrided diffusion surface layer constituting a nitrided surface coating for the substrate,   wherein said electric potential and/or said anodic electric current are modulated in time as a function of the thickness to be obtained for said nitrided surface coating.   
     
     
         29 . The method according to  claim 28 , wherein said non-aqueous electrolyte is at a temperature of less than 250° C., preferably less than 200° C., and even more preferably at room temperature. 
     
     
         30 . The method according to  claim 28 , wherein said nitrided surface coating consists of sub-stoichiometric TiNx titanium nitride, where 0≤x≤0.3, said sub-stoichiometric titanium nitride having a degree of crystallinity lower than the degree of crystallinity of stoichiometric TiN titanium nitride. 
     
     
         31 . The method according to  claim 28 , wherein said nitrided surface coating has an average thickness between 0.040 and 5 μm obtainable by prolonging said step b) of activating an electrochemical nitriding process for a period of time between 5 and 45 minutes. 
     
     
         32 . The method according to  claim 28 , wherein said electrochemical process comprises two consecutive steps:
 a first galvanostatic step, in which an electric potential is applied which is modulated in time so as to generate an anodic electric current having a value on average equal to a predefined base current density, until a predefined threshold electric potential is reached; and   a second potentiostatic step, in which an electric potential is applied on average equal to a predefined base electric potential, maintaining it until at least reaching an anodic current having a predefined threshold current density.   
     
     
         33 . The method according to  claim 32 , wherein during said first galvanostatic step the anodic electric current is maintained on average equal to said predefined base current density in a constant manner or in a pulsed pattern. 
     
     
         34 . The method according to  claim 32 , wherein during said second potentiostatic step the electric potential is maintained on average equal to said predefined base electric potential in a constant manner or in a pulsed pattern, preferably in a pulsed pattern. 
     
     
         35 . The method according to  claim 32 , wherein said predefined base current density is between 0.025 to 0.5 mA/cm2. 
     
     
         36 . The method according to  claim 32 , wherein said predefined threshold electric potential is between 2 and 12V, and preferably between 4 and 10V, even more preferably equal to 5V. 
     
     
         37 . The method according to  claim 32 , wherein said predefined base electric potential is between 8 and 50V, and is preferably 10V. 
     
     
         38 . The method according to  claim 32 , wherein said predefined threshold current density is between 20 and 80 μA/cm2, and preferably 50 μA/cm2. 
     
     
         39 . The method according to  claim 32 , wherein said second potentiostatic step has a duration of at least 5 minutes, regardless of the threshold current density value. 
     
     
         40 . The method according to  claim 28 , wherein said ionic liquid at room temperature comprises nitrogen anions. 
     
     
         41 . The method according to  claim 28 , wherein said ionic liquid at room temperature consists of pyrrolidinium, imidazolium and/or morpholinium cations and dicyanamide and/or tricyanomethanide anions, wherein preferably the pyrrolidinium, imidazolium and morpholinium cations are functionalized with radical groups chosen from the group consisting of: methyl, ethyl, propyl and butyl, preferably methyl, ethyl and propyl. 
     
     
         42 . The method according to  claim 41 , wherein said ionic liquid at room temperature is selected from the group consisting of 1-propyl-1-methylpyrrolidinium dicyanamide, 1-ethyl-1-methylpyrrolidinium dicyanamide, 1-propyl-1-methylimidazolium dicyanamide, 1-ethyl-1-methylimidazolium dicyanamide and 1-Ethyl-3-methylmorpholinium dicyanamide. 
     
     
         43 . The method according to  claim 28 , wherein said ionic liquid at room temperature comprises bis(trifluoromethylsulfonyl)imide or bis(fluorosulfonyl)imide anions. 
     
     
         44 . The method according to  claim 28 , wherein said ionic liquid at room temperature is selected from the group consisting of:
 Tributylmethylammonium bis(trifluoromethylsulfonyl)immide; Butyltrimethylammonium bis(trifluoromethylsulfonyl)immide; Choline bis(trifluoromethylsulfonyl)immide; 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl)immide; 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)immide; 1-Methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)immide; 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)immide; Tributylmethylphosphonium bis(trifluoromethylsulfonyl)immide; Diethylmethylsulfonium bis(trifluoromethylsulfonyl)immide.   
     
     
         45 . The method according to  claim 28 , wherein said ionic liquid at room temperature is selected from the group consisting of:
 1-Ethyl-3-methylimidazolium nitrate; and 1-Methyl-1-propylpiperidinium tetrafluoroborate.   
     
     
         46 . The method according to  claim 28 , wherein said counter electrode consists of a body made of graphite, stainless steel, titanium or aluminum and preferably graphite. 
     
     
         47 . The method according to  claim 28 , wherein said counter electrode consists of a body immersed in said non-aqueous electrolyte or the container of said non-aqueous electrolyte. 
     
     
         48 . The method according to  claim 28 , comprising a pre-treatment step c) of the substrate, to be carried out before said steps a) and b), wherein said pre-treatment consists of removing any traces of grease and/or lubricant-coolant liquid from the surface of the substrate. 
     
     
         49 . The method according to  claim 48 , wherein said pre-treatment of removing any traces of grease and/or lubricating coolant liquid is carried out by immersing the substrate in a polar solvent for a predefined period of time, preferably with the additional application of ultrasound, preferably said immersion being followed by washing with distilled water and subsequent air drying. 
     
     
         50 . The method according to  claim 28 , comprising a post-treatment step d) of the substrate, to be carried out after said steps a) and b), wherein said post-treatment consists of removing any residues of ionic liquid from the nitrided surface of the substrate. 
     
     
         51 . The method according to  claim 50 , wherein said post-treatment of removing any residues of ionic liquid is carried out by immersing the substrate in a polar solvent for a predefined period of time, preferably said immersion being followed by washing with distilled water and subsequent air drying. 
     
     
         52 . An article, comprising at least a portion in titanium or titanium alloy, said portion having a nitrided surface coating consisting of sub-stoichiometric TiNx titanium nitride, where 0≤x≤0.3, said sub-stoichiometric titanium nitride having a degree of crystallinity less than the degree of crystallinity of stoichiometric TiN titanium nitride, wherein said surface coating is integrated into the crystalline matrix of said portion in titanium or titanium alloy. 
     
     
         53 . The article according to  claim 52 , wherein said nitrided surface coating has an average thickness of between 0.040 and 5 μm. 
     
     
         54 . The article according to  claim 52 , wherein said nitrided surface is obtained by subjecting said portion in titanium or titanium alloy to nitriding by
 a) immersing the titanium or titanium alloy substrate as an electrode in a non-aqueous electrolyte consisting of an ionic liquid at room temperature, comprising nitrogen ions, in the presence of a counter electrode; and   b) activating an electrochemical nitriding process of the substrate, by applying an electric potential between an electrode, acting as an anode, and the counter electrode, acting as a cathode, so as to generate an anodic electric current at least sufficient to decompose the nitrogen ions releasing the nitrogen contained therein, the released nitrogen penetrating by diffusion into the titanium or titanium alloy substrate until leading to the conversion of a surface layer of said substrate into titanium nitride, thereby generating a nitrided diffusion surface layer constituting a nitrided surface coating for the substrate,   wherein said electric potential and/or said anodic electric current are modulated in time as a function of the thickness to be obtained for said nitrided surface coating.