Method for Producing Wear-Resistant and Fatigue-Resistant Edge Layers in Titanium Alloys, and Components Produced Therewith

Abstract

The invention relates to edge layer finishing of functional components, and thereby in particular to a method for producing wear-resistant and fatigue-resistant edge layers in titanium alloys, and components produced therewith. The method according to the invention for producing wear-resistant and fatigue-resistant edge layers in titanium alloys by means of laser gas alloying is essentially characterized in that the laser gas alloying is carried out with a reaction gas that contains or releases interstitially soluble elements in the titanium alloy used, whereby the partial pressure of the reaction gas is selected such that the partial pressure remains below the threshold value above which nitride, carbide, or boride titanium phases are produced. The features according to the invention of the wear-resistant and fatigue-resistant component made of a titanium alloy with a gas-alloyed edge layer essentially are that the wear-resistant edge layer is composed of a fine-grain mixture of α- and β-titanium grains with an interstitially dissolved reaction gas, has a surface hardness H s , measured on the ground surface, of 360 HV0.5≦H s ≦500 HV0.5, or an edge layer microhardness H R , measured on a polished cross section at 0.1 mm below the surface, of 360 HV0.1≦H R ≦560 HV0.1, extends over a depth t R of 0.1 mm≦t R <3.5 mm, and does not contain any nitride, carbide, oxide, or boride phases produced by the reaction gas.

1 . A method for producing wear-resistant and fatigue-resistant edge layers in titanium alloys by high-intensity energy gas alloying, comprising: 
 carrying out high-intensity energy gas alloying in a treatment zone using a reaction gas that contains or releases interstitially soluble elements in the titanium alloy used, and    wherein the partial pressure of the reaction gas is selected such that the partial pressure remains below the threshold value above which nitride, carbide, or boride titanium phases are produced.    
   
   
       2 . The method according to  claim 1 , wherein nitrogen is used as the reaction gas which is interstitially soluble in the titanium alloy, and the nitrogen together with an inert gas is fed to the laser treatment zone.  
   
   
       3 . The method according to  claim 2 , wherein the volumetric proportion V N  of the nitrogen in the working gas mixture is 1%≦V N ≦15%.  
   
   
       4 . The method according to  claim 3 , wherein the volumetric proportion V N  of the nitrogen is selected in the range of 1%≦V N ≦11% for components subjected to particularly high fatigue stress.  
   
   
       5 . The method according to  claim 2 , wherein the volumetric proportion V N  of the nitrogen in the working gas is altered during the processing and is adapted to the localized load conditions and to the ratio of wear to cyclic load.  
   
   
       6 . The method according to  claim 1 , wherein the gas-alloyed edge layer is subjected to an accelerated cooling.  
   
   
       7 . The method according to  claim 6 , wherein the accelerated cooling is achieved by a self-quenching as the result of an external cooling of the untreated portions of the component during the gas alloying.  
   
   
       8 . The method according to claim  6 , wherein the accelerated cooling is achieved by a localized gas cooling subsequent to the treatment zone.  
   
   
       9 . The method according to  claim 1 , wherein the component is mechanically fixed before the high-intensity energy gas alloying and is maintained in the fixed state during the high-intensity energy gas alloying.  
   
   
       10 . The method according to  claim 1 , wherein the fixing and cooling are implemented by the same device.  
   
   
       11 . The method according to  claim 1 , wherein after being cooled to room temperature the gas-alloyed edge layer is mechanically smoothed by vibratory finishing, grinding, and/or polishing.  
   
   
       12 . The method according to  claim 1 , wherein after the component is cooled to room temperature or after a mechanical smoothing by vibratory finishing, grinding, and/or polishing, wherein an aging heat treatment of the entire component is performed at a temperature T A  of 350°≦T A ≦700° C. for an aging period t A  of 2 h≦t A ≦24 h.  
   
   
       13 . The method according to  claim 11 , wherein after the mechanical smoothing a stress-free annealing is subsequently carried out at a temperature T SR  of 300°≦T SR ≦620° C. and a period t SR  of 1 h≦t SR ≦10 h.  
   
   
       14 . The method according to  claim 6 , wherein the gas-alloyed layer is shot-blasted after the cooling from the last heat treatment.  
   
   
       15 . The method according to  claim 1 , wherein a non-vac electron beam unit is used as a high-intensity energy source.  
   
   
       16 . The method according to  claim 1 , wherein a plasma torch is used as a high-intensity energy source.  
   
   
       17 . A wear-resistant and fatigue-resistant component made of a titanium alloy, having a gas-alloyed edge layer formed by carrying out high-intensity energy gas alloying in a treatment zone using a reaction gas that contains or releases interstitially soluble elements in the titanium alloy used, and 
 wherein the partial pressure of the reaction gas being selected such that the partial pressure remains below the threshold value above which nitride, carbide, or boride titanium phases are produced,    such that the wear-resistant edge layer is composed of a fine-grain mixture of α-titanium and β-titanium grains with an interstitially dissolved reaction gas, has a surface hardness H S , measured on the ground surface, of 360 HV0.5≦H S ≦500 HV0.5, or an edge layer microhardness H R , measured at the polished cross section 0.1 mm below the surface, of 360 HV0.1≦H R ≦560 HV0.1, extends over a depth t R  of 0.1 mm≦t R ≦3.5 mm, and    does not contain any nitride, carbide, oxide, or boride phases produced by the reaction gas.    
   
   
       18 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein the wear-resistant edge layer is composed of a track pattern of overlapping individual tracks, and the track overlap rate ü, wherein  
     
       
         
           
             
               
                 
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       and ü is 0.5≦ü≦0.9.  
     
   
   
       19 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein the edge layer is composed of a wide individual track which is produced by oscillating a beam of the high-intensity energy source transverse to a feed direction.  
   
   
       20 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein the component represents a turbine blade subjected to erosion or droplet impingement stress.  
   
   
       21 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 20 , wherein the wear-resistant edge layer includes a leading edge of the blade in a direction of a concave side of the blade and as well as in a direction of a back side of the blade.  
   
   
       22 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 20 , wherein the wear-resistant edge layer is composed of overlapping tracks parallel to the leading edge.  
   
   
       23 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein the sequence of track production is selected in such a way that the tracks are each situated in alternation with the neutral fiber with respect to a bending of the turbine blade in the pliant direction.  
   
   
       24 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 20 , wherein the wear-resistant edge layer is composed of tracks situated transverse to the longitudinal axis of the turbine blade or to the leading edges thereof, the tracks extend around the leading edge, and the oscillation of the beam from the high-intensity energy source is produced about the longitudinal axis of the blade as a result of an oscillating vibratory motion of the turbine blade.  
   
   
       25 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein a track field boundary on the blade foot side runs at an angle of 20-65° with respect to the leading edge.  
   
   
       26 . The wear-resistant and fatigue-resistant component made of a titanium alloy according to  claim 17 , wherein the edge layer hardness is correspondingly adapted according to localized load conditions and a ratio of wear to cyclic load.  
   
   
       27 . The method according to  claim 1 , wherein a laser is used as a high-intensity energy source.