Method for production of alloyed titanium welding wire

Abstract

A method for producing a weldable titanium alloy and/or composite wire. The method includes: a) forming a green object by blending particulates of titanium sponge with one or more powdered alloying additions and cold compacting the blended mixture and subjecting the blended mixture including lubricant to pressure; b) forming a work body of alloyed titanium by heating the green object in a protected atmosphere and holding the temperature for a period of at least 4 hours, and then hot working the green object at a temperature of less than 200 C. apart from the beta transition temperature of the titanium alloy and shaping the green object to obtain an elongated profile; and c) forming the welding wire by placing the elongated profile of the work body in a rolling mill having one or more rolls disposed in series.

Claims

1. A method for producing a weldable wire of alloyed titanium, wherein the method comprises the following successive process steps: a) forming a green object by: blending particulates of titanium sponge with a particle diameter in the range from 0.5 to 10 mm with one or more powdered alloying additions with particle size in the range from 50-250 m; and cold compacting the blended mixture and subjecting the blended mixture including lubricant to a pressure in the range from 750 to 1250 MPa; b) forming an elongated profile of alloyed titanium by: heating the green object in a protected atmosphere up to a temperature in the range from 1000 to 1250 C. and holding the temperature for a period of at least 4 hours; and then hot working the green object at a temperature of less than 200 C. apart from the beta transition temperature of the titanium alloy and shaping the green object to obtain an elongated profile of alloyed titanium; c) forming the welding wire of alloyed titanium by: rolling the elongated profile of alloyed titanium in a rolling mill with one or more rolls placed in series to form the weldable wire with the desired diameter.

2. A method according to claim 1, wherein the particles of titanium sponge are crushed and sheared titanium sponge of magnesium reduced, vacuum distilled titanium sponge satisfying the ASTM standard B299-07.

3. A method according to claim 2, wherein the crushed and sheared titanium sponge has a particle size fraction in one of the following ranges: from 0.5 to 8 mm, from 1 to 6 mm, or from 1 to 4 mm.

4. A method according to claim 1, wherein the compacting of the blended mixture is performed at room temperature with a compacting pressure in the range from 1100 to 1200 MPa.

5. A method according to claim 1, wherein compaction is performed in an uniaxial press which comprises a floating stress ring and a floating press ram, wherein walls of the press ring is coated with a lubricant selected from a metal stearates or an amide wax.

6. A method according to claim 5, wherein the lubricant is also blended into the mixture and the green object is subsequent to compaction heated to a temperature in the range from 200-400 C. and held at this temperature for a period of 0.5 to 10 hours.

7. A method according to claim 5, wherein the lubricant is zinc stearate or N,N ethylene bisstearamide.

8. A method according to claim 1, wherein step b) of forming the elongated profile of alloyed titanium is obtained by: heating the green object in a protected atmosphere up to a temperature of approximately 1100 C. and holding the temperature for a period of 6-8 hours; and then hot extruding the green object at a temperature of less than 200 C. from the beta transition temperature of the titanium alloy.

9. A method according to claim 1, wherein step b) of forming the elongated profile of alloyed titanium is obtained by: heating the green object in a protected atmosphere up to a temperature of approximately 1100 C. and holding the temperature for a period of 6-8 hours; and then hot extruding the green object at a temperature of less than 200 C. from the beta transition temperature of the titanium alloy; and step c) of forming the welding wire is obtained by: shaping the elongated profile of alloyed titanium to a drawing wire by: i) annealing the elongated profile at about 400-600 C. for a period from 10 to 60 minutes; ii) rolling the elongated profile to reduce its diameter in a rolling mill; and iii) repeating steps i) and ii) until the diameter of the elongated profile becomes in the range from 1 to 4 mm; and then shaping the drawing wire to the welding wire by: j) annealing the drawing wires at about 400-600 C. for about 10-60 minutes; jj) drawing the drawing wire to reduce its diameter in a per se known manner; and jjj) repeating steps j) and jj) until the wire obtains the intended diameter of the welding wire.

10. A method according to claim 9, wherein each pass through the rolls of the rolling mill reduces the diameter of the elongated profile from 5 to 35%.

Description

LIST OF FIGURES

(1) FIGS. 1a) and b), where a) is a graph showing the applied pressing pressures as a function of particulate size fractions, and b) is a graph showing obtained density of the compact as a function of particulate size fractions.

(2) FIG. 2 is a schematic drawing of a cross-section of an extruder for hot working the billet.

(3) FIG. 3 is a photograph of two objects in alloyed titanium made from DMD-construction with a welding wire made according to the invention.

VERIFICATION OF THE INVENTION

(4) A series of 18 cylindrical billets with diameter 80 mm were made as follows: Crushed titanium sponge with particle sizes from 0.5 to 8 mm, with the main fraction of 1 to 4 mm was mixed with 10 weight % (based on weight of titanium sponge) of master-alloy 433-6 with average particle size fraction from 100 to 250 m and 0.8 weight % (based on total amount of the mixture) of a commercial composite lubricant sold under the trademark Metallub from Hganes AB of Sweden. The mixture was blended in a cement mixer until substantially homogeneous composition.

(5) Each billet was then made by compacting an amount of the powder by loading it stepwise into the chamber of a uniaxial press with a floating die and subject the powder to a stepwise pressure increase. Typical pressing procedure was; initially loading about of the mixture into the press chamber and applying a pressure of about 20 MPa. Then add another of the mixture into the press chamber and applying a pressure of about 40 MPa. Add another small fraction of the mixture and increase the pressure to 90 MPa, before loading another 1/4 of the mixture and increase the pressure to 155 MPa, before adding the remaining mixture and increase the pressure to about 770-780 MPa. This resulted in billets with a density in the range from 80 to 90% of maximum theoretical density, as given in Table 2:

(6) 10 of these billets were heated up to 400 C. for one hour and then held at 200 C. for 12 hours to drive out the lubricant. The lubricant was a commercial composite lubricant sold under the trademark Metallub and comprises a zinc soap and an amide component. Then the billets were loaded into a retort furnace and heated to 1100 C. for 8 hours in an argon atmosphere.

(7) The bolts were then hot extruded to form hot forged work bodies. The billets were coated in glass and pressed through die to form extruded rods of titanium. A schematic drawing showing a cross-section of the extruder is shown in FIG. 2. The billet 1 is moved in the direction indicated by the arrow and pressed towards a die. The die comprises a die support 3 made of high strength steel and a ceramic ring 4. Before the die there is a conical support ring 5 of high strength steel creating

(8) TABLE-US-00002 TABLE 2 Results of compacting 1-8 mm particulates to 80 mm billets Amount Maximum Percentage of blended applied Obtained maximum mixture pressure Height billet density theoretical [g] [MPa] [mm] [g/cm.sup.3] density 2875.0 774.0 141.1 4.02 89.2 3350.0 773.8 170.2 3.88 86.1 3375.0 773.2 170.0 3.91 86.8 3580.0 773.2 184.5 3.83 84.8 3495.0 774.2 176.6 3.91 86.6 3295.0 772.8 180.3 3.60 79.9 3520.0 773.2 179.7 3.86 85.6 3780.0 774.2 203.0 3.68 81.5 3355.0 772.8 170.2 3.89 86.2 3580.0 773.0 185.0 3.81 84.6 3405.0 773.0 171.6 3.91 86.7 3480.0 773.0 177.2 3.87 85.9 3225.0 774.4 162.2 3.93 87.1 3525.0 774.0 179.1 3.88 86.1 2515.0 774.7 132.6 3.75 83.1 3300.0 772.2 170.3 3.85 85.4 4205.0 776.1 224.7 3.70 82.1 3015.0 773.4 157.2 3.78 83.9
a funnel resembling entrance into the die ring. A conical ring made of glass 6 is placed into the support ring 5 to provide lubrication during the extruding of the billet. The parameters employed in the extrusion of the billets are given in Table 3.

(9) One extruded rod (work body) with diameter of 20 mm was subject to several rolling steps to form a welding wire of diameter 1.6 mm. Each rolling step was performed as follows; the work body was stress relieved by heating it to 600 C. and kept at that temperature for 15 minutes, and then passed through a rolling step which decreased the diameter a certain degree. Then the procedure was repeated until the intended diameter of 1.6 mm was obtained. The stepwise decrease in the diameter of the work body was; 18, 12, 8, 6, 4, 3, 2, and 1.6 mm.

(10) The welding wire was employed in a TIG welding torch for building a test object by direct metal depositing four welds onto each other and creating two small objects of

(11) TABLE-US-00003 TABLE 3 Parameters employed in hot extrusion of billets Temperature Diameter extrudate Velocity extruder piston [ C.] [mm] [mm/s] 1000 20 12 1000 26 12 1000 10.5 12 900 16 12 900 16 12 850 16 12 880 16 12 880 16 12 890 20 12 890 20 12
approx. 25 g. The welding was a conventional DMD-process in an argon atmosphere where the TIG-torch was supplied with 70 A at 11 V and an argon flushing of 14 liters argon per minute (room temperature and 1 atmosphere). A photograph of the objects is shown in FIG. 3.

(12) The samples were analysed in a scanning electron microscope with X-ray micro-analysis (SEM/EDS) and compared to a Grade 5 reference material 295-335-HV10. It was found that the titanium alloy of the two objects had an aluminium content of 1.1-2.0 weight % and vanadium content of 1.1-2.1 weight %. These values are about a factor 2 lower than standard grade 5 material which has an Al content of 5.1-5.4 weight % and V content of 4.5-5.1 weight %. The discrepancy is believed to be due to incomplete homogenisation or a segregation of titanium sponge particulates and alloy powder addition in the blended mixture.

(13) However, the SEM/EDS analysis did find that there were no pure master-alloy phases in the welded titanium object and that the alloying elements Al and V were homogeneously distributed in the titanium matrix, showing that a complete dissolution and homogenisation has been obtained. The hardness of the titanium alloy was found to be similar to the hardness of the reference material.

REFERENCES

(14) 1. ASTM standard B299-07, Standard Specification for Titanium Sponge, ASTM International, West Conshohocken, Pa., 2007, DOI: 10.1520/B0299-07. 2. AWS standard A5.16/A5.16M:2007, Specification for Titanium and Titanium-Alloy Welding Electrodes and Rods, Americal Welding Society, Miami, Fla., 2007. 3. ASTM standard B381-06a, 2006, Standard Specification for Titanium and Titanium Alloy Forgings, ASTM International, West Conshohocken, Pa., 2006.