METHOD FOR ADDITIVELY MANUFACTURING AN ARTICLE MADE OF A DIFFICULT-TO-WELD MATERIAL
The invention relates to a method for additively manufacturing an article made of a difficult-to-weld highly-precipitation-strengthened Ni-base super alloy that comprises Al and Ti in the sum of more than 5 wt.-% or a difficult-to weld carbide/solution-strengthened cobalt (Co)-base super alloy, whereby a metal particle mixture of at least a first phase and a second phase is provided as a starting material, said first phase of the mixture being a base material and said second phase of the mixture being a material which is a derivative of the first material and has relative to said material of said first phase an improved weldability, and whereby the metal particle mixture is processed by means of an additive manufacturing process which is one of selective laser melting (SLM), selective laser sintering (SLS), electron beam melting (EBM), laser metal forming (LMF), laser engineered net shape (LENS), or direct metal deposition (DMD).
1 . Method for additively manufacturing an article made of a difficult-to-weld highly-precipitation-strengthened Ni-base super alloy comprising more than 6 wt.-% [2 Al (wt.-%)+Ti (wt.-%)] or made of a difficult-to weld carbide/solution-strengthened Co-base super alloy, whereby a metal particle mixture of at least a first phase and a second phase is provided as a starting material, said first phase of the mixture being a base material and said second phase of the mixture being a material which is a derivative of the first material and has relative to said material of said first phase an improved weldability, and whereby said metal particle mixture is processed by means of an additive manufacturing process which is one of selective laser melting (SLM), electron beam melting (EBM), laser metal forming (LMF), laser engineered net shape (LENS), or direct metal deposition (DMD).
2 . The method according to claim 1 , wherein said metal particle mixture is a metal powder.
3 . The method according to claim 1 , wherein said metal particle mixture comprises a suspension.
4 . The method according to one of the claim 1 , wherein said first phase or base metal is a difficult-to-weld metal material that tends to crack formation.
5 . The method according to claim 4 , wherein said first phase or base metal is one of a gamma-prime precipitation-hardened super alloy, such as a nickel (Ni)-base super alloy, or a carbide/solution-strengthened cobalt (Co)-base super alloy.
6 . The method according to one of the claim 1 , wherein said second phase, which is a derivative of said first phase, has a lower melting point than said first phase, and the percentage by weight of the second phase is between 1% and 70%.
7 . The method according to claim 6 , wherein the percentage by weight of the second phase is between 5% and 30%.
8 . The method according to claim 6 , wherein said second phase comprises at least one melting-point-depressing constituent to lower its melting point.
9 . The method according to claim 8 , wherein said at least one melting-point-depressing constituent is one of Boron (B), Hafnium (Hf) or Zirconium (Zr).
10 . The method according to claim 6 , wherein said second phase comprises nanometer-sized powder particles to lower its melting point.
11 . The method according to claim 10 , wherein a percentage of micro particles of the second phase are pre-alloyed with said nanometer-sized powder particles.
12 . The method according to claim 10 , wherein said second phase consists of a percentage of mechanically mixed micro particles and nanometer-sized powder particles.
13 . The method according to claim 1 , wherein said additive manufacturing process is conducted without pre-heating or pre-heating below 400° C. said metal particle mixture.
14 . The method according to claim 1 , wherein said second phase has a higher ductility than said first phase, allowing to absorb stresses resulting from the welding process, which leads to a lower crack formation.
15 . The method according to claim 1 , wherein selective laser melting (SLM) is used as the additive manufacturing process, and the SLM parameters are set-up to melt said second phase only, thereby significantly reducing the heat input during build-up of the article and consequently reducing inherent stresses in the article body which could otherwise lead to crack formation and distortion during manufacturing.
16 . The method according to one of the claim 1 , wherein the high-density of the article is further increased by means of a post heat treatment (T HT ).
17 . The method according to claim 16 , wherein said post heat treatment is applied, such that remaining, non-molten second metal phase particles, encapsulated in the mostly high-density article, fully melt during the post heat treatment, thereby filling the inner (closed) porosity.
18 . The method according to claim 1 , wherein a final hot isostatic pressing (HIP) is carried out at a lower temperature compared to the heat treatment temperature of the material of the first phase.
19 . The method according to claim 1 , wherein the article to be manufactured is a gas turbine component, or a part of a gas turbine component, which is to be joined with other parts by welding or brazing.