Method of manufacturing titanium and titanium alloy products

Abstract

A method of manufacturing titanium or titanium alloy semi-finished or ready-to-use products is disclosed. The method includes forming shaped bodies of titanium oxide particles and positioning the shaped bodies in an electrolytic cell which includes: an anode, a cathode, and a molten electrolyte. The shaped bodies are positioned to form at least a part of the cathode. The electrolyte includes cations of a metal that is capable of chemically reducing titanium oxide. The method further includes reducing the titanium oxide to titanium in a solid state in the electrolytic cell so that the shaped bodies become shaped bodies of titanium sponge. Finally, the method includes processing the shaped bodies of titanium sponge to reduce the volume or at least one of the dimensions of the bodies thereby to form the semi-finished or ready-to-use products.

1 . A method of manufacturing titanium or titanium alloy semi-finished or ready-to-use products which includes the steps of: 
 (a) forming shaped bodies of titanium oxide particles;    (b) positioning the shaped bodies in an electrolytic cell which includes: an anode, a cathode, and a molten electrolyte, with the shaped bodies forming at least a part of the cathode, and with the electrolyte including cations of a metal that is capable of chemically reducing titanium oxide;    (c) reducing the titanium oxide to titanium in a solid state in the electrolytic cell so that the shaped bodies become shaped bodies of titanium sponge; and    (d) processing the shaped bodies of titanium sponge to reduce the volume or at least one of the dimensions of the bodies thereby to form the semi-finished or ready-to-use products.    
     
     
         2 . The method defined in  claim 1  wherein the shaped bodies formed in step (a) are pellets.  
     
     
         3 . The method defined in  claim 2  wherein the pellets have a thickness of 8 mm or less.  
     
     
         4 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies of titanium oxide particles having particle sizes in the range of 1-15 μm.  
     
     
         5 . The method defined in  claim 4  wherein the particle sizes are in the range of 1-10 μm.  
     
     
         6 . The method defined in  claim 5  wherein the particle sizes are in the range of 1-5 μm.  
     
     
         7 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies having a porosity of 30-40%.  
     
     
         8 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies of titanium oxide particles, with the shaped bodies having pores sized in the range of 1-15 μm.  
     
     
         9 . The method defined in  claim 8  wherein the sizes of the pores are in the range of 1-10 μm.  
     
     
         10 . The method defined in  claim 9  wherein the sizes of the pores are the range of 1-5 μm.  
     
     
         11 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies by slip casting or pressing titanium oxide particles into the shaped bodies.  
     
     
         12 . The method defined in  claim 11  wherein step (a) includes sintering the slip cast or pressed shaped bodies to increase the strength of the shaped bodies to withstand subsequent handling of the shaped bodies prior to being positioned in the electrolytic cell in step (b) and to withstand processing in the cell in step (c).  
     
     
         13 . The method defined in  claim 11  wherein step (a) includes sintering the slip cast or pressed shaped bodies at a temperature of at least 850° C.  
     
     
         14 . The method defined in  claim 13  wherein the sintering temperature is at least 1050° C.  
     
     
         15 . The method defined in  claim 13  wherein the sintering temperature is less than 1250° C.  
     
     
         16 . The method defined in  claim 11  wherein step (a) includes sintering the slip cast or pressed shaped bodies for at least 2 hours.  
     
     
         17 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies by (i) sintering sub-micron size particles into millimetre-size particles, (ii) crushing the millimetre-size particles into 30-40 μm size particles, 
 (iii) slip casting the 30-40 μm size particles into shaped bodies, (iv) drying the shaped bodies, and (v) sintering the shaped bodies.    
     
     
         18 . The method defined in  claim 17  wherein step (a)(iii) includes slip casting 30-40 μm size particles and 0.2-0.5 μm size particles into shaped bodies.  
     
     
         19 . The method defined in  claim 18  wherein the 0.2-0.5 μm size particles are up to 20% by weight of the particles that are slip cast in step (a)(iii).  
     
     
         20 . The method defined in  claim 1  wherein step (a) includes forming shaped bodies by (i) cold pressing sub-micron size particles into shaped bodies, and (ii) sintering the shaped bodies.  
     
     
         21 . The method defined in  claim 17  wherein the sub-micron sized particles are smaller than 0.5 μm.  
     
     
         22 . The method defined in  claim 21  wherein the sub-micron sized particles are 0.2-0.5 μm in size.  
     
     
         23 . The method defined in  claim 1  wherein the shaped bodies of titanium sponge produced in step (c) include fine particles of titanium having particle sizes in a range of 5-30 μm.  
     
     
         24 . The method defined in  claim 1  wherein the shaped bodies of titanium sponge produced in step (c) include fine pores having sizes in a range of 5-30 μm.  
     
     
         25 . The method defined in  claim 1  wherein the shaped bodies of titanium sponge produced in step (c) have a porosity of 40-70%.  
     
     
         26 . The method defined in  claim 1  wherein the shaped bodies of titanium sponge produced in step (c) have an oxygen content of less than 0.5 wt. %.  
     
     
         27 . The method defined in  claim 26  wherein the oxygen content is less than 0.3%.  
     
     
         28 . The method defined in  claim 27  wherein the oxygen content is less than 0.1%.  
     
     
         29 . The method defined in  claim 1  wherein step (c) includes reducing the titanium oxide to titanium in the electrolytic cell by operating the cell at a potential that is above a potential at which cations of the metal that is capable of chemically reducing the cathode metal oxide deposit as the metal on the cathode, whereby the metal chemically reduces the cathode metal oxide.  
     
     
         30 . The method defined in  claim 29  wherein the metal deposited on the cathode is soluble in the electrolyte and can dissolve in the electrolyte and thereby migrate to the vicinity of the cathode metal oxide.  
     
     
         31 . The method defined in  claim 29  wherein the electrolyte is a CaCl 2 -based electrolyte that includes CaO as one of the constituents of the electrolyte.  
     
     
         32 . The method defined in  claim 31  wherein the cell potential is above the potential at which Ca metal can deposit on the cathode, i.e. the decomposition potential of CaO.  
     
     
         33 . The method defined in  claim 1 , including removing the shaped bodies of titanium sponge produced in step (c) from the electrolytic cell and cleaning the shaped bodies to remove electrolyte from the shaped bodies.  
     
     
         34 . The method defined in  claim 1  wherein step (d) includes processing the shaped bodies of titanium sponge by cold pressing and/or cold rolling the shaped bodies of titanium sponge.  
     
     
         35 . The method defined in  claim 34  wherein step (d) further includes high temperature sintering of the cold pressed and/or cold rolled shaped bodies of titanium sponge.  
     
     
         36 . The method defined in  claim 35  wherein the high temperature sintering is carried out at a temperature of 1100-1300° C. for 2-4 hours.  
     
     
         37 . The method defined in  claim 35  including cold pressing and/or cold rolling the shaped bodies of titanium sponge to reduce the porosity to 20% or less and thereafter sintering the cold pressed and/or cold rolled shaped bodies to form the semi-finished or ready-to-use product with a porosity of 1% or less.  
     
     
         38 . The method defined in  claim 36  including cold pressing and/or cold rolling the shaped bodies of titanium sponge to reduce the porosity to 10% or less.  
     
     
         39 . The method defined in  claim 1  wherein step (d) includes processing the shaped bodies of titanium sponge by hot pressing the shaped bodies of titanium sponge.  
     
     
         40 . The method defined in  claim 39  wherein hot pressing is carried out at a temperature of 800-1000° C. at a pressure of 10-100 Mpa for up to 60 minutes.  
     
     
         41 . The method defined in  claim 39  including hot pressing the shaped bodies to form the semi-finished or ready-to-use product with a porosity of 1% or less.  
     
     
         42 . The method defined in  claim 1  wherein step (d) includes processing the shaped bodies of titanium sponge by cold pressing and thereafter hot pressing the shaped bodies of titanium sponge.  
     
     
         43 . The method defined in  claim 42  including cold pressing the shaped bodies of titanium sponge to reduce the porosity to 50% or less and thereafter hot pressing the shaped bodies to form the semi-finished or ready-to-use product with a porosity of 1% or less.  
     
     
         44 . The method defined in  claim 1  wherein the semi-finished or ready-to-use products produced in step (d) have a porosity of less than 5%.  
     
     
         45 . The method defined in  claim 44  wherein the porosity is less than 3%.  
     
     
         46 . The method defined in  claim 44  wherein the porosity is less than 1%.  
     
     
         47 . A shaped body of titanium sponge made up of fine particles of titanium and fine pores.  
     
     
         48 . The shaped body defined in  claim 47  wherein the fine particles of titanium have particle sizes in a range of 5-30 μm.  
     
     
         49 . The shaped body defined in  claim 47  wherein the fine pores have sizes in a range of 5-30 μm.  
     
     
         50 . A semi-finished or ready-to-use product formed by electrochemically reducing a shaped body of titanium oxide and thereafter processing the shaped body by cold pressing and/or cold rolling and thereafter high temperature sintering the shaped body so that the semi-finished or ready-to-use product has a porosity of 1% or less.  
     
     
         51 . A semi-finished or ready-to-use product formed by electrochemically reducing a shaped body of titanium oxide and thereafter processing the shaped body by hot pressing the shaped body so that the semi-finished or ready-to-use product has a porosity of 1% or less.