Method for joining, by direct brazing, a first part and a second part, including steps of preparing the surface of at least one of the parts
A method for joining, by brazing, a first part and a second part, the steps of preparing at least one of the parts including the following: a) providing a part intended to be brazed, the part being made of carbon or based on titanium, nickel or a CoCr alloy, b) performing inert gas plasma treatment on the part whereby the part is cleaned and an active surface is formed on the part, c) depositing a first layer comprising an active element on the active surface of the part, the active element being a carbide-forming element, d) depositing a second layer of gold on the first layer, whereby the first layer is protected from oxidation and good wetting is ensured.
1 . A method for assembling a first part and a second part by brazing, comprising the following steps:
i) preparing a first part made of carbon, a titanium-based material, a nickel- based material or a CoCr alloy according to the following sub-steps a) to d):
a) providing the first part made of carbon, titanium-based, nickel-based or made of a CoCr alloy,
b) carrying out a plasma treatment with a neutral gas, on the first part whereby the part is cleaned and an active surface is formed on the part,
c) depositing a first layer comprising an active element over the active surface of the first part, the active element being a carbide-forming element,
d) depositing a second layer made of gold over the first layer, whereby the first layer is protected from oxidation and wetting of a filler material is improved during heating;
ii) preparing a second part made of carbon, a titanium-based material, a nickel-based material or a CoCr alloy, the second part being, advantageously, prepared according to sub-steps a) to d) as defined in step i);
iii) bringing the filler material into contact with the first part and with the second part whereby an assembly is obtained;
iv) heating the assembly obtained at the step iii) up to an assembly temperature higher than the melting temperature of the filler material, so as to melt the filler material, and maintaining the assembly temperature for a hold time period, the assembly temperature being lower than 450° C.;
v) cooling the assembly so as to form a solder joint between the first part and the second part, whereby the parts are assembled.
2 . The method according to claim 1 , wherein the active element is Ti, Cr or Zr.
3 . The method according to claim 1 , wherein the first layer has a thickness of 300 μm to 500 μm.
4 . The method according to claim 1 , wherein the method comprises a step e), between step c) and step d), during which a third layer of a non-active element is deposited.
5 . The method according to claim 4 , wherein the first layer has a thickness of 30 to 50 nm and in that the third layer has a thickness of 100 to 500 nm.
6 . The method according to claim 1 , wherein the first layer also comprises a non-active element deposited simultaneously with the active element during step c).
7 . The method according to claim 4 , wherein the third layer has a thickness of 50 to 100 nm.
8 . The method according to claim 1 , wherein the filler material is tin or a tin-based alloy.
9 . The method according to claim 8 , wherein the assembly temperature is between 250° C. and 320° C.
10 . The method according to claim 1 , wherein the first part is a graphite substrate covered with pyrolytic carbon and in that the second part is made of a CoCr alloy.
11 . The method according to claim 4 , wherein the non-active element is W or Nb.
12 . The method according to claim 6 , wherein the non-active element is W or Nb.
13 . The method according to claim 8 , wherein the tin-based alloy is SnAg, SnCu or SnIn.