Titanium alloy having high ductility, fatigue strength and rigidity and method of manufacturing same

Abstract

A titanium alloy is provided wherein metal boride is uniformly crystallized and/or precipitated in the matrix. The heating temperature in the finishing hot working is set smaller than the β transus temperature by not less than 10° C., thereby causing the matrix to include an equiaxial α structure in a rate of not less than 40 vol %. This titanium alloy has excellent properties, i.e., high rigidity, ductility and fatigue strength, which are all required for structural components, and therefore can be widely applied to a mechanical component such as an engine of an automobile, a structural component in an aircraft as well as a component for a high speed rail vehicle.

1 . A titanium alloy having a high ductility, fatigue strength and rigidity, wherein said titanium alloy includes B: 0.5-3.0% in mass %, and metal boride is uniformly crystallized and/or precipitated in the matrix, and wherein the matrix includes an equiaxial α structure in a rate of not less than 40 vol %.  
     
     
         2 . A titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 1 , wherein said titanium alloy is either of α type or of α+β type.  
     
     
         3 . A titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 1 , wherein said titanium alloy further includes Al: 5.5-10%, oxygen (O): 0.07-0.25%, C: not more than 0.1%, H: not more than 0.05% and N: not more than 0.1% in mss %.  
     
     
         4 . A titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 3 , wherein said titanium alloy further includes one or more than two of Sn, Zr and Hf in not more than 20% in mass % in amount and/or one or more than two of β phase stabilizing elements in not more than 10% of V equivalent given by the below equation (a):  
       
         
           
             
               
                 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       equivalent 
                     
                     = 
                     
                       V 
                       + 
                       
                         
                           15 
                           10 
                         
                          
                         Mo 
                       
                       + 
                       
                         
                           15 
                           6.3 
                         
                          
                         Cr 
                       
                       + 
                       
                         
                           15 
                           4.0 
                         
                          
                         Fe 
                       
                       + 
                       
                         
                           15 
                           36 
                         
                          
                         Nb 
                       
                       + 
                       
                         
                           15 
                           9 
                         
                          
                         Ni 
                       
                       + 
                       
                         
                           15 
                           25 
                         
                          
                         W 
                       
                     
                   
                 
                 
                   
                     ( 
                     a 
                     ) 
                   
                 
               
             
           
           
           
               
           
         
       
     
     
         5 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity, wherein said titanium alloy includes B: 0.5-3.0% in mass %, and metal boride is uniformly crystallized and/or precipitated in the matrix, and wherein the heating temperature in the finishing hot working is set smaller than the β transus temperature by not less than 10° C.  
     
     
         6 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 5 , wherein the solution treatment is carried out within a temperature range between (the β transus temperature−350° C.) and (the β transus temperature−10° C.).  
     
     
         7 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 6 , wherein the aging treatment is further carried out.  
     
     
         8 . A method for manufacturing titanium alloy having a high ductility, fatigue strength and rigidity, wherein said titanium alloy includes B: 0.5-3.0%, Al: 5.5-10%, oxygen (O): 0.07-0.25%, C: not more than 0.1%, H: not more than 0.05% and N: not more than 0.1% in mass %, and metal boride is uniformly crystallized and/or precipitated in the matrix, and wherein the heating temperature in the finishing hot working is set smaller than the β transus temperature by not less than 10° C.  
     
     
         9 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 8 , wherein the solution treatment is carried out within a temperature range between (the β transus temperature−350° C.) and (the β transus temperature−10° C.).  
     
     
         10 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 9 , wherein the aging treatment is further carried out.  
     
     
         11 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity, wherein said titanium alloy includes B: 0.5-3.0%, Al: 5.5-10%, oxygen (O): 0.07-0.25%, C: not more than 0.1%, H: not more than 0.05% and N: not more than 0.1% in mass %, and further includes one or more than two of Sn, Zr and Hf in not more than 20% in mass % in amount and/or one or more than two of β phase stabilizing elements in not more than 10% of V equivalent given by the below equation (a), and wherein the heating temperature in the finishing hot working is set smaller than the β transus temperature by not less than 10° C.:  
       
         
           
             
               
                 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       equivalent 
                     
                     = 
                     
                       V 
                       + 
                       
                         
                           15 
                           10 
                         
                          
                         Mo 
                       
                       + 
                       
                         
                           15 
                           6.3 
                         
                          
                         Cr 
                       
                       + 
                       
                         
                           15 
                           4.0 
                         
                          
                         Fe 
                       
                       + 
                       
                         
                           15 
                           36 
                         
                          
                         Nb 
                       
                       + 
                       
                         
                           15 
                           9 
                         
                          
                         Ni 
                       
                       + 
                       
                         
                           15 
                           25 
                         
                          
                         W 
                       
                     
                   
                 
                 
                   
                     ( 
                     a 
                     ) 
                   
                 
               
             
           
           
           
               
           
         
       
     
     
         12 . A method for manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 11 , wherein the solution treatment is carried out within a temperature range between (the β transus temperature−350° C.) and (the β transus temperature−10° C.).  
     
     
         13 . A method of manufacturing a titanium alloy having a high ductility, fatigue strength and rigidity according to  claim 12 , wherein the aging treatment is further carried out.