Abstract:
Creep resistant titanium alloys containing aluminum, zirconium, molybdenum and germanium plus optional silicon, carbon, tin and niobium.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to titanium base alloys. All percentages are weight percentages. 
     SUMMARY OF THE INVENTION 
     According to the present invention we provide a titanium base alloy consisting of 5.0-7.0% aluminium, 2.0-7.0% zirconium, 0.1-2.5% molybdenum and 0.01-10.0 germanium and optionally one or more of the following elements: tin 2.0-6.0%, niobium 0.1-2.0%, carbon 0.02-0.1% and silicon 0.1-2.0%; the balance being titanium apart from incidental impurities. 
     The aluminium content may be in the range 5.0-6.0% or 5.0-6.5%. 
     The zirconium content may be in the range 2.0-4.0%, 2.0-6.0% or 3.0-7.0%. 
     The molybdenum content may be in the range 0.1-0.6%, 0.25-0.75% or 2.0-2.5%. 
     The germanium content may be in the range 0.01-5.0%, 0.01-0.2%, 0.01-0.5%, 0.1-2.0% or 2.0-5.0%. 
     More particularly, the alloy may consist of 5.3-6.1% aluminium, 3.5-4.5% tin, 3.0-4.0% zirconium, 0.5-1.0% niobium, 0.2-0.7% molybdenum, 0.1-0.5% silicon, 0.03-0.10% carbon and 0.3-3.0% germanium, the balance being titanium apart from incidental impurities. 
     Alternatively, the alloy may consist of 5.3-6.1% aluminium, 3.5-4.5% tin, 3.0-4.0% zirconium, 0.5-1.0% niobium, 0.2-0.7% molybdenum, 0.03-0.10% carbon and 0.3-3.0% germanium, the balance being titanium apart from incidental impurities. 
     Alternatively, the alloy may consist of 5.6-6.0% aluminium, 3.5-4.5% tin, 3.0-4.0% zirconium, 0.6-0.8% niobium, 0.3-0.6% molybdenum, 0.03-0.10% carbon, 0.15-0.5% silicon and 0.5-2.5% germanium, the balance being titanium apart from incidental impurities. 
     Alternatively, the alloy may consist of 5.6-6.0% aluminium, 3.5-4.5% tin, 3.0-4.0% zirconium, 0.6-0.8% niobium, 0.3-0.6% molybdenum, 0.03-0.10% carbon and 1.0-3.0% germanium, the balance being titanium apart from incidental impurities. 
     The alloys according to the invention are preferably heat-treated and subsequently cooled. The alloys are then preferably aged by heating to a selected temperature for a predetermined period of time and then cooled. The aging temperature may be in excess of 600° C. and may be as high as 700° C. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Examples of an alloy according to the invention are now provided. 
     The alloys set out in Table 1 below were prepared: 
     
                       TABLE 1______________________________________Analysed Compositions (wt %)ALLOY  Al      Sn     Zr   Nb   Mo   C     Si   Ge______________________________________No. 1  5.78    4.0    3.5  0.7  0.48 0.08  0.2  1.1No. 2  5.79    4.0    3.5  0.7  0.49 0.08  0.2  0.6No. 3  5.88    4.0    3.5  0.7  0.48 0.07  0    2.0______________________________________ 
    
     The prepared alloys were then each heat treated at 1030° C. for 2 hours and then air cooled. Subsequently each alloy was aged by heating at 700° C. for 2 hours. The mechanical properties for each alloy are set out in Table 2 below. The creep exposure was 100 hours at 600° C. at 125 MPa for each sample. 
     
                                           TABLE 2__________________________________________________________________________Mechanical Properties for 700° C. Age        0.1% 0.2%            Red.   TPS  YS   YS   UTS  Elongation                             AreaALLOYTest   Nmm.sup.-2        Nmm.sup.-2             Nmm.sup.-2                  Nmm.sup.-2                       %     %__________________________________________________________________________No 1 A       990  1030 1164 10    18B       286   342  551 66    86C  0.102        1044 1059 1041  1     2No 2 A       972  1002 1125  9    15B       329   355  532 40    71C  0.124        1022 1038 1125  11/2  3No 3 A       1033 1069 1196  8    16B       373   414  583 55    71C  0.104        1093 1107 1111  1    1/2__________________________________________________________________________ TPS = Total Plastic Strain YS = Yield Stress 
    
     Test A was at room temperature; Test B was at an elevated temperature of 700° C.; Test C was at room temperature after the creep exposure referred to above. 
     The increase in yield stress for these alloys aged at 700° C. shows significant improvements over a comparable alloy containing silicon but with no germanium. 
     The alloys in accordance with the invention possess excellent creep resistance particularly at temperatures above 540° C. which makes them particularly valuable in gas turbine engine applications.