Surface hardening of group iv metals

Abstract

The present invention relates to a method of case hardening a Group IV metal or a Group IV metal alloy and to components hardened in the method. The method comprising the steps of: providing a workpiece of a Group IV metal or a Group IV metal alloy, the workpiece being in its final shape; nitriding the workpiece in a nitriding atmosphere comprising NHs as a nitriding species at a first temperature in the range of 450° C. to 750° C. for a nitriding duration of at least 16 hours to provide a hydrogen containing diffusion zone; removing hydrogen from the hydrogen containing diffusion zone at a second temperature of up to 750° C. and a partial pressure of H 2 of up to 10 −4 mbar over a hydrogen removal duration of at least 4 hours to provide a hydrogen depleted diffusion zone. The method and the component are useful for implants, in particular dental implants.

1 . A method of case hardening a Group IV metal or a Group IV metal alloy, the method comprising the steps of:
 providing a workpiece of a Group IV metal or a Group IV metal alloy, the workpiece being in its final shape,   nitriding the workpiece in a nitriding atmosphere comprising NH 3  as a nitriding species at a first temperature in the range of 450° C. to 750° C. and a partial pressure of NH 3  in the range of 0.5 bar to 2 bar for a nitriding duration of at least 0.1 hour to provide a hydrogen containing diffusion zone, and   removing hydrogen from the hydrogen containing diffusion zone at a second temperature in the range of 600° C. to 750° C. and a partial pressure of H 2  (pH 2 ) of up to 10 −4  mbar over a hydrogen removal duration of at least 4 hours to provide a hydrogen depleted diffusion zone.   
     
     
         2 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the nitriding atmosphere does not comprise oxidising species. 
     
     
         3 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the first temperature is in the range of 580° C. to 700° C. 
     
     
         4 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the total pressure in the step of removing hydrogen from the hydrogen containing diffusion zone is up to 10 −4  mbar. 
     
     
         5 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the Group IV metal is zirconium or a Group IV metal alloy containing at least 2 wt % zirconium. 
     
     
         6 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the second temperature in the range of 600° C. to 700° C. 
     
     
         7 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the Group IV metal is titanium or a titanium-based alloy not containing zirconium. 
     
     
         8 . A component of zirconium or a Group IV metal alloy containing at least 2 wt % zirconium, the component having a core hardness and a nitrogen containing diffusion zone extending from a surface of the component to a depth from the surface, where the microhardness is equal to the core hardness plus 50 HV 0.005 , the component having a hardness in the range of 1000 HV 0.005  to 1500 HV 0.005  at a depth from the surface of 2.5 μm, as measured according to the DIN EN ISO 6507 standard, which component does not comprise a nitride layer. 
     
     
         9 . A component of titanium or a titanium-based alloy not containing zirconium, the component having a surface hardness in the range of 700 HV 0.005  to 2000 HV 0.005 , a core hardness and a nitrogen containing diffusion zone extending from a surface of the component to a depth from the surface, where the microhardness is equal to the core hardness plus 50 HV 0.005 , as measured according to the DIN EN ISO 6507 standard, the component having a surface nitride layer of Ti 2 N. 
     
     
         10 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the surface does not comprise TiN. 
     
     
         11 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the layer of Ti 2 N is identified using X-ray diffraction analysis. 
     
     
         12 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the component has a microhardness in the range of 700 HV 0.005  to 1200 HV 0.005  at a depth from the surface of 2.5 μm. 
     
     
         13 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the absence of TiN is identified using X-ray diffraction analysis. 
     
     
         14 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the surface of the component does not comprise an oxide layer, except from nanometre scale oxide layers formed naturally on the surface of Group IV metals in contact with air. 
     
     
         15 . The component of titanium or a titanium-based alloy not containing zirconium according to  claim 9 , wherein the component has a mirror polish appearance defined as a surface with an arithmetical mean deviation (Ra) roughness of <0.1 μm in accordance with the ISO 1302:2002 standard. 
     
     
         16 . (canceled) 
     
     
         17 . The component of zirconium or a Group IV metal alloy containing at least 2 wt % zirconium according to  claim 8 , wherein the absence of TiN is identified using X-ray diffraction analysis. 
     
     
         18 . The component of zirconium or a Group IV metal alloy containing at least 2 wt % zirconium according to  claim 8 , wherein the surface of the component does not comprise an oxide layer, except from nanometre scale oxide layers formed naturally on the surface of Group IV metals in contact with air. 
     
     
         19 . The component of zirconium or a Group IV metal alloy containing at least 2 wt % zirconium according to  claim 8 , wherein the component has a mirror polish appearance defined as a surface with an arithmetical mean deviation (Ra) roughness of <0.1 μm in accordance with the ISO 1302:2002 standard. 
     
     
         20 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 1 , wherein the first temperature is in the range of 450° C. to 580° C. and the nitriding duration is in the range of 24 hours to 200 hours. 
     
     
         21 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 3 , wherein the nitriding duration is in the range of 0.5 hours to 100 hours. 
     
     
         22 . The method of case hardening a Group IV metal or a Group IV metal alloy according to  claim 6 , wherein the hydrogen removal duration is in the range of 12 hours to 200 hours.