METHOD FOR MANUFACTURING A THREE-DIMENSIONAL ARTICLE
The disclosure refers to a method for manufacturing a three-dimensional article, the method including successively building up the article from a metallic base material by means of an additive manufacturing process, thereby creating an article with a substantial anisotropy of its properties and heat treating the manufactured article at a sufficiently high temperature to reduce the anisotropy significantly by recrystallization and/or grain coarsening.
1 . A method for manufacturing a three-dimensional article, comprising:
a) successively building up said article from a metallic base material by means of an additive manufacturing process, thereby creating an article with a substantial anisotropy of its properties; and
b) heat treating said manufactured article at sufficient high temperature to reduce said anisotropy significantly by recrystallisation and/or grain coarsening.
2 . The method according to claim 1 , wherein
said additive manufacturing process is selected from the group consisting of laser metal forming, laser engineered net shape and direct metal deposition, and
that a metallic base material of wire form is used.
3 . The method according to claim 1 , wherein
said additive manufacturing process is selected from the group consisting of selective laser melting, selective laser sintering and electron beam melting, and
that a metallic base material of powder form is used.
4 . The method according to claim 3 , said method further comprising:
a) generating a three-dimensional model of said article followed by a slicing process to calculate the cross sections;
b) passing said calculated cross sections to a machine control unit afterwards;
c) providing a powder of said base material, which is needed for the process;
d) preparing a powder layer with a regular and uniform thickness on a substrate plate or on a previously processed powder layer;
e) performing melting by scanning with an energy beam an area corresponding to a cross section of said articles according to the three-dimensional model stored in the control unit;
f) lowering the upper surface of the previously formed cross section by one layer thickness;
g) repeating said steps from c) to f) until reaching the last cross section according to the three-dimensional model; and
h) heat treating said three-dimensional article.
5 . The method according to claim 4 , wherein the grain size distribution of said powder is adjusted to the layer thickness of said powder layer in order to establish a good flowability, which is required for preparing powder layers with regular and uniform thickness.
6 . The method according to claim 3 wherein the powder grains have a spherical shape.
7 . The method according to claim 3 wherein an exact grain size distribution of the powder is obtained by sieving and/or winnowing (air separation).
8 . The method according to claim 4 , wherein said powder is provided by means of a powder metallurgical process, specifically one of gas or water atomization, plasma-rotating-electrode process or mechanical milling.
9 . The method according to claim 3 , wherein said additive manufacturing process uses a suspension instead of powder.
10 . The method according to claim 1 wherein said metallic base material is a high-temperature Ni-based alloy.
11 . The method according to claim 1 wherein said metallic base material is a high-temperature Co-based alloy.
12 . The method according to claim 1 wherein said metallic base material is a high-temperature Fe-based alloy.
13 . The method according to claim 1 wherein said alloy contain finely dispersed oxides, specifically one of Y 2 O 3 , AlO 3 , ThO 2 , HfO 2 , and ZrO 2 .
14 . The method according to claim 1 wherein said heat treatment is used to reduce the anisotropy of Young's modulus.
15 . The method according to claim 1 wherein said heat treatment is a combination of different individual heat treatments.
16 . The method according to claim 1 wherein said heat treatment consists of multiple steps, each representing a specific combination of heating rate, hold temperature, hold time and cooling rate.
17 . The method according to claim 16 , wherein at least one of said heat treatment steps is conducted at a sufficient high temperature and for a hold time long enough to partially or completely dissolve constituents in the microstructure of said manufactured article, specifically intermetallic phases, carbides or nitrides.
18 . The method according to claim 16 wherein at least one of said heat treatment steps is conducted at a sufficient high temperature and for a hold time long enough to precipitate metal-carbides, metal-nitrides or metal-carbonitrides, specifically one of M(C, N), M 6 C, M 7 C 3 and M 23 C 6 .
19 . The method according to claim 16 , wherein at least one of said heat treatment steps is conducted at a sufficient high temperature and for a hold time long enough to precipitate intermetallic phases, specifically one of Ni 3 (Al, Ti), or Ni 3 (Nb, Al, Ti), and Ni 3 Nb.
20 . The method according to claim 16 wherein at least one of said heat treatment steps is conducted at a sufficient high temperature and for a hold time long enough to precipitate metal-borides, specifically M 3 B 2 , to improve grain boundary strength.
21 . The method according to claim 18 wherein at least one of said heat treatment steps is conducted at a sufficient high temperature and for a hold time long enough to modify the volume fraction, size, shape and distribution of said precipitations.
22 . The method according to claim 16 wherein at least one of said heat treatment steps can be conducted additionally under hot isostatic pressing conditions, to further improve the microstructure.
23 . The method according to claim 1 wherein only part of said manufactured article is subjected to said heat treatment.
24 . The method according to claim 1 wherein before and/or after said heat treatment, individual heat treatments or heat treatment steps, respectively, said manufactured articles are subjected to additional processing steps, selected from the group consisting of machining, welding and brazing.