Vacuum brazing tantalum alloys

Claim 2

IN A PROCESS FOR VACUUM BRAZING TANTALUM ALLOY STRUCTURAL ELEMENTS, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF: A. POSITIONING BRAZE FOIL OF A COLUMBIUM-VANADIUM ALLOY BETWEEN SURFACES OF THE ELEMENTS TO BE JOINED: B. COATING SURFACES OF THE ELEMENTS THAT ARE TO BE IN CONTACT WITH A TUNGSTEN HEARTH PLATE AND TUNGSTEN PELLETS WITH YTTRIA POWDER; C. POSITIONING THE ELEMENTS ON THE TUNGSTEN HEARTH PLATE DISPOSED IN A VACUUM HEATING ZERO SO THAT THE YTTRIA COATED LOWERMOST SURFACE OF THE ELEMENTS RESTS ON THE HEARTH PLATE; D. PLACING TUNGSTEN PELLETS ON THE YTTRIA COATED UPPERMOST SURFACE OF THE ELEMENTS, THEREBY APPLYING A DOWNWARD PRESSURE THEREON AND CONTROLLING THE GAP BETWEEN THE SURFACES TO BE JOINED; E. HEATING THE ELEMENTS IN THE HEATING ZONE UNDER A VACUUM TO A TEMPERATURE SUFFICIENT TO MELT THE FOIL; AND F. AFTER SOAKING AT THAT TEMPERATURE FOR FROM 3 TO 8 MINUTES ALLOWING THE ELEMENTS TO COOL GRADUALLY TO ROOM TEMPERATURE.

Claim 3

The process according to claim 1 in which the alloy consists of 35 weight percent columbium and 65 weight percent vanadium.

Claim 4

The process according to claim 2 in which the structural elements to be joined comprise a honeycomb core and plate members disposed on its upper and lower surfaces with a braze foil having a thickness ranging from 0.003 to 0.005 inch interposed therebetween; the exposed surfaces of the plate members are coated with the yttria powder; and sufficient pellets are positioned on the plate member disposed on the upper surface of the honeycomb core to exert a downward pressure of at least 0.75 pounds per square inch.

Claim 5

The process according to claim 3 in which the structural elements are heated under a vacuum of about 10 5 torr to a temperature in the range of 3,400* to 3,600* F, the temperature being controlled so that the temperature difference across the plate members does not exceed 150* F.

Claim 6

The process according to claim 4 in which the heating zone is initially vacuum purged at room temperature for a period of at least 6 hours at a 10 5 torr vacuum; at the end of this period the temperature of the heating zone is increased to a temperature ranging from 2,000* to 2,200* F over a period of from 2.5 to 4.5 hours; after a thermal arrest of from about 0.5 to 1.0 hour at a temperature in the aforementioned range the temperature of the heating zone is increased to a temperature ranging from about 3, 100* to 3,150* F in a period of about 10 to 20 minutes; after a thermal arrest of from about 10 to 20 minutes at a temperature in the last mentioned range the temperature of the heating zone is raised to a temperature ranging from 3,400* to 3,600* F in a period of from 6 to 12 minutes; and after soaking at a temperature in the last mentioned range the heating zone is allowed to cool to room temperature.

Claim 7

The process according to claim 5 in which the heating zone is cooled to about 2,900* F within 7 minutes; thereafter the heating zone is cooled to about 1,300* F in increments of 100* F every 5 minutes; and finally the heating zone is allowed to cool to room temperature.

Claim 8

An assembly for fabricating a structure from elements formed from a tantalum alloy comprising a tungsten hearth plate; a first structural element having a Top surface adapted to coincide with a bottom surface of a second structural element, the bottom surface of the first element being coated with yttria powder and the first element being positioned on the hearth plate with its coated bottom surface in contact therewith; a layer of a columbiumvanadium alloy brazing foil covering the top surface of the first element, the bottom surface of the second element being positioned on the brazing foil; a coating of yttria powder covering the top surface of the second element; and tungsten pellets disposed on the coating of yttria powder covering the top surface of the second element.

Claim 9

An assembly for fabricating a structure from elements formed from a tantalum alloy comprising a tungsten hearth plate; a first structural element having a Top surface adapted to coincide with a bottom surface of a second structural element, the bottom surface of the first element being coated with yttria powder and the first element being positioned on the hearth plate with its coated bottom surface in contact therewith; a layer of a columbiumvanadium alloy brazing foil covering the top surface of the first element, the bottom surface of the second element being positioned on the brazing foil; a coating of yttria powder covering the top surface of the second element; and tungsten pellets disposed on the coating of yttria powder covering the top surface of the second element.

Claim 10

An assembly for fabricating a honeycomb panel from a tantalum alloy comprising a tungsten hearth plate; a first tantalum alloy plate having one of its surfaces coated with yttria powder, the plate being positioned on the hearth plate with its coated surface in contact therewith; a first layer of a columbium-vanadium alloy brazing foil positioned on the uncoated surface of the first tantalum alloy plate; a flat tantalum alloy frame positioned on the brazing foil, the outer perimeter of the frame substantially coinciding with the perimeter of the first tantalum alloy plate; a second layer of the brazing foil covering the upper surface and inner edge of the frame; a tantalum alloy honeycomb core having an upper and a lower face and a perimeter greater than the inner and smaller than the outer perimeter of the flat frame, the core being positioned with its lower face in contact with the first layer of brazing foil and the lower face having a recess formed therein around its outer edge in which a portion of the flat frame and the second layer of brazing foil is disposed; a third layer of the brazing foil covering the upper face of the honeycomb core; a second tantalum alloy plate positioned on the third layer of the brazing foil; a fourth layer of the brazing foil outlining the outer edge of the upper surface of the second plate and extending downwardly around the sides of the honeycomb core so as to meet the second layer of brazing foil; a second tantalum alloy frame having a first horizontal member positioned on the portion of the fourth layer of brazing foil outlining the outer edge of the upper surface of the second plate, a vertical leg positioned against the portion of fourth layer of brazing foil extending downwardly around the sides of the honeycomb core, and a second horizontal member positioned on the second layer of the brazing foil with its outer edge substantially coinciding with the outer edge of the flat frame; a coating of yttria powder covering the outer surfaces of the second plate and the second frame; and tungsten pellets disposed on the coating of yttria powder covering the outer surfaces of the second plate and the second frame.

Claim 11

An assembly for fabricating a honeycomb panel from a tantalum alloy comprising a tungsten hearth plate; a first tantalum alloy plate having one of its surfaces coated with yttria powder, the plate being positioned on the hearth plate with its coated surface in contact therewith; a first layer of a columbium-vanadium alloy brazing foil positioned on the uncoated surface of the first tantalum alloy plate; a flat tantalum alloy frame positioned on the brazing foil, the outer perimeter of the frame substantially coinciding with the perimeter of the first tantalum alloy plate; a second layer of the brazing foil covering the upper surface and inner edge of the frame; a tantalum alloy honeycomb core having an upper and a lower face and a perimeter greater than the inner and smaller than the outer perimeter of the flat frame, the core being positioned with its lower face in contact with the first layer of brazing foil and the lower face having a recess formed therein around its outer edge in which a portion of the flat frame and the second layer of brazing foil is disposed; a third layer of the brazing foil covering the upper face of the honeycomb core; a second tantalum alloy plate positioned on the third layer of the brazing foil; a fourth layer of the brazing foil outlining the outer edge of the upper surface of the second plate and extending downwardly around the sides of the honeycomb core so as to meet the second layer of brazing foil; a second tantalum alloy frame having a first horizontal member positioned on the portion of the fourth layer of brazing foil outlining the outer edge of the upper surface of the second plate, a vertical leg positioned against the portion of fourth layer of brazing foil extending downwardly around the sides of the honeycomb core, and a second horizontal member positioned on the second layer of the brazing foil with its outer edge substantially coinciding with the outer edge of the flat frame; a coating of yttria powder covering the outer surfaces of the second plate and the second frame; and tungsten pellets disposed on the coating of yttria powder covering the outer surfaces of the second plate and the second frame.