Process for treating a piece of tantalum or of a tantalum alloy

Patent metadata

Field	Value
Publication number	US-2016376692-A1
Application number	US-201615189778-A
Country	US
Kind code	A1
Filing date	Jun 22, 2016
Priority date	Jun 25, 2015
Publication date	Dec 29, 2016
Grant date	—

Abstract

A process for treating a piece of tantalum or of a tantalum alloy, which consists in: placing the piece in a furnace and heating the furnace under vacuum at least at 1 400° C.; forming a carbon multilayer in the peripheral part of the piece, by injecting, in the heated furnace, a gas carbon source at a pressure ≦10 mbar, the multilayer comprising at least one layer C 1 of tantalum carbide, which is located at the surface of the piece, and two layers C 2 and C 3 comprising a carbon content lower than the carbon content of the layer C 1; stopping the formation of the multilayer by cooling the piece; placing around the piece a device capable of trapping carbon, oxygen and nitrogen to protect the piece from carbon and oxygen and nitrogen traces present in the furnace; causing the diffusion of carbon present in the layer C 1 towards the layers C 2 and C 3, by heating the furnace under vacuum, the piece being held in the protecting device; and stopping the diffusion of carbon in the piece by cooling the piece under vacuum before the carbon present in the multilayer reaches the centre part of the piece. Thus, a piece the surface of which is free from TaC, the centre part of which is free from carbon and the part of which located between the surface and the centre part comprises tantalum and carbon is obtained.

First claim

1 . A process for treating a piece of tantalum or of a tantalum alloy, the piece having a peripheral part and a centre part, the process comprising the steps of:
a) placing the piece in a furnace and heating the furnace under vacuum at a temperature at least equal to 1 400° C.; b) forming a carbon multilayer ( 1 ) in the peripheral part of the piece, by injecting, in the heated furnace, a gas carbon source at a pressure at most equal to 10 mbar, the carbon multilayer comprising at least one layer C 1 of tantalum carbide, which is located at a surface of the piece, and two underlying layers C 2 and C 3 each comprising a carbon content which is different and lower than a carbon content of the layer C 1 ; c) stopping the formation of the carbon multilayer ( 1 ) by cooling the piece; d) placing around the piece a protecting device for trapping carbon, oxygen and nitrogen to protect the piece from carbon as well as possible oxygen and nitrogen traces present in the furnace; e) causing a diffusion of all or part of carbon present in the layer C 1 towards the layers C 2 and C 3 , by heating the furnace under vacuum, the piece being held in the protecting device; and f) stopping the diffusion of carbon in the piece by cooling the piece under vacuum before carbon present in the carbon multilayer reaches the centre part of the piece; whereby a piece the surface of which is free from tantalum as TaC, the centre part of which is free from carbon and a part of which is located between the surface and the centre part comprises tantalum and carbon is obtained.

2 . The process of claim 1 , wherein step d) comprises:
placing the piece in a closed cavity having walls made of a material attracting carbon, oxygen and nitrogen, the material being preferably of tantalum; and draining the cavity using an inert gas so as to discharge from the furnace any gas likely to contain at least one of atomic elements chosen from carbon, oxygen and nitrogen.

3 . The process of claim 1 , wherein step a) comprises:
introducing the piece into the furnace; putting the furnace under vacuum; and gradually heating the furnace until a working temperature between 1 500 and 1 700° C. is reached.

4 . The process of claim 1 , wherein step b) comprises injecting the gas carbon source in the furnace at a flow rate between 1 and 100L.h −1 and an injection pressure lower than or equal to 10 mbar.

5 . The process of claim 4 , wherein the injection of the gas carbon source in step b) is made at an injection pressure of 5 mbar for a flow rate of 20L.h −1 and in a furnace heated at a temperature of 1 600° C.

6 . The process of claim 1 , wherein step e) comprises heating the furnace at a temperature of 1 600° C. and at a pressure of 10 −2 mbar.

7 . The process of claim 1 , wherein the gas carbon source used in step b) is ethylene.

Assignees

• Commissariat Energie Atomique

Inventors

• Cotton Dominique
• Faure Sebastien
• Jacquet Philippe
• Vignal Vincent

Classifications

• C22F1/18

  High-melting or refractory metals or alloys based thereon · CPC title

• C23C8/20 Primary

  Carburising · CPC title

• C22F1/02

  in inert or controlled atmosphere or vacuum (adjusting the composition of the atmosphere C21D1/76) · CPC title

• F27D2009/0081

  the cooling medium being a fluid (other than a gas in direct or indirect contact with the charge) · CPC title

• F27D2019/0056

  Regulation involving cooling · CPC title