Numerical and experimental study of molten pool behaviour and defect formation in multi-material and functionally graded materials laser powder bed fusion

2021 ◽  
Author(s):  
Heng Gu ◽  
Chao Wei ◽  
Lin Li ◽  
Michael Ryan ◽  
Rossitza Setchi ◽  
...  
Keyword(s):  
Experimental Study ◽  
Functionally Graded Materials ◽  
Molten Pool ◽  
Defect Formation ◽  
Functionally Graded ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Graded Materials ◽  
Powder Bed

scholarly journals Development of an Empirical Process Model for Adjusted Porosity in Laser-Based Powder Bed Fusion of Ti-6Al-4V

2021 ◽  
Author(s):  
Nicole Emminghaus ◽  
Johanna Paul ◽  
Christian Hoff ◽  
Jörg Hermsdorf ◽  
Stefan Kaierle
Keyword(s):  
Functionally Graded Materials ◽  
Process Model ◽  
Empirical Process ◽  
Defect Formation ◽  
Functionally Graded ◽  
Powder Bed Fusion ◽  
Graded Materials ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Gas Porosity

Abstract A promising approach to address the mismatch of bone and implant stiffness, leading to the stress-shielding phenomenon, is the application of functionally graded materials with adjusted porosity. Although defect formation and porosity in laser-based powder bed fusion of metals (PBF-LB/M) are already widely investigated, so far there is little research on the influences and parameter interactions regarding the pore characteristics. This work therefore aims to provide an empirical process model for the generation of gas porosity in the PBF-LB process of Ti-6Al-4V. For the first time, parts with closed locally adjusted porosity of ~ 6 % achieved through gaseous pores instead of lack-of-fusion defects or lattice structures were built by PBF-LB. Parameter variation and evaluation of relative density, pore size and sphericity was done in accordance with the design of experiments approach. A parameter set for maximum gas porosity (laser power of 189 W, scanning speed of 375 mm/s, hatch spacing of 150 µm) was determined for a constant layer thickness of 30 µm and a spot diameter of 35 µm. Tensile tests were conducted with specimens consisting of a core with maximum gas porosity or lack-of-fusion porosity, respectively, and a dense skin as well as fully dense specimens. Whereas lack of fusion defects can lead to significant reduction of stiffness, the elastic modulus remained unchanged when implementing spherical pores. Nevertheless, the found superior strength and ductility of specimens with gas porous core underline the advantages of adjusted porosity for the application in functionally graded materials and lightweight applications.

scholarly journals Development of an empirical process model for adjusted porosity in laser-based powder bed fusion of Ti-6Al-4V

2021 ◽  
Author(s):  
Nicole Emminghaus ◽  
Johanna Paul ◽  
Christian Hoff ◽  
Jörg Hermsdorf ◽  
Stefan Kaierle
Keyword(s):  
Functionally Graded Materials ◽  
Process Model ◽  
Empirical Process ◽  
Defect Formation ◽  
Functionally Graded ◽  
Powder Bed Fusion ◽  
Graded Materials ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Gas Porosity

AbstractA promising approach to address the mismatch of bone and implant stiffness, leading to the stress-shielding phenomenon, is the application of functionally graded materials with adjusted porosity. Although defect formation and porosity in laser-based powder bed fusion of metals (PBF-LB/M) are already widely investigated, so far there is little research on the influences and parameter interactions regarding the pore characteristics. This work therefore aims to provide an empirical process model for the generation of gas porosity in the PBF-LB process of Ti-6Al-4V. Parts with closed locally adjusted porosity of $\sim $ ∼ 6 % achieved through gaseous pores instead of lack of fusion defects or lattice structures were built by PBF-LB. Parameter variation and evaluation of relative density, pore size and sphericity was done in accordance with the design of experiments approach. A parameter set for maximum gas porosity (laser power of 189 W, scanning speed of 375 mm/s, hatch spacing of 150 μm) was determined for a constant layer thickness of 30 μm and a spot diameter of 35 μm. Tensile tests were conducted with specimens consisting of a core with maximum gas porosity or lack of fusion porosity, respectively, and a dense skin as well as fully dense specimens. Whereas lack of fusion defects can lead to significant reduction of stiffness of 32.2 %, the elastic modulus remained unchanged at 110.0 GPa when implementing spherical pores. Nevertheless, the found superior strength and ductility of specimens with gas porous core (> 1100 MPa and > 0.05 mm/mm, respectively) underline the advantages of adjusted porosity for the application in functionally graded materials and lightweight applications.

scholarly journals Review of Laser Powder Bed Fusion of Gamma-Prime-Strengthened Nickel-Based Superalloys

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 996
Author(s):  
Olutayo Adegoke ◽  
Joel Andersson ◽  
Håkan Brodin ◽  
Robert Pederson
Keyword(s):  
Defect Formation ◽  
State Of The Art ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Cast Material ◽  
Creep Properties ◽  
Powder Bed ◽  
Gamma Prime ◽  
Cracking Mechanisms ◽  
Nonequilibrium Solidification

This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.

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