Directed energy deposition (DED) additive manufacturing: Physical characteristics, defects, challenges and applications

Al2O3/Al6Ti2O13 composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based (DED-LB) technology. However, the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions. The shaping quality, microstructure, and mechanical properties of Al2O3/Al6Ti2O13 (6 mol% TiO2) composite ceramics were systematically investigated as a function of energy input in an extensive process window. On this basis, the formation mechanism of solidification defects and the evolution process of microstructure were revealed, and the optimized process parameters were determined. Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases, thus, facilitating the elimination of solidification defects, such as pores and strip gaps. In addition, the microstructure size is strongly dependent on the energy input, increasing when the energy input increases. Moreover, the morphology of the α-Al2O3 phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions. Under the comprehensive influence of solidification defects and microstructure size, the fracture toughness and flexural strength of Al2O3/Al6Ti2O13 composite ceramics present a parabolic law behavior as the energy input increases. Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min2 g-1 mm-1. Within this process window, the average microhardness, fracture toughness, and flexural strength of Al2O3/Al6Ti2O13 composite ceramics are up to 1640 Hv, 3.87 MPa m1/2, and 227 MPa, respectively. This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al2O3/Al6Ti2O13 composite ceramics.

Investigation of melt-growth alumina/aluminum titanate composite ceramics prepared by directed energy deposition

Laser directed energy deposition (DED) of high-quality structural Al-based alloys is challenging due to the inherent physical and thermal properties of the Al powder feedstock. Therefore, an in-depth understanding of the influence of the applied processing parameters on the characteristics of the deposited material is paramount if one is to attain optimal performance. The objective of this study is to investigate the influence of the dominant processing parameters (laser power, scan speed, powder mass flow rate (PMFR), and hatch spacing) on the geometrical characteristics (track's height and dilution) of Al5083 double tracks fabricated using Laser Engineered Net Shaping (LENS®). Central composite design (CCD) response surface methodology (RSM) was utilized to study the influence of the varied processing parameters and their interactions and to develop an empirical statistical prediction model for the studied responses. The results reveal that the applied PMFR has a strong influence on the deposited track's height (positive) and dilution (negative). The laser power at the first-order factor shows a weak influence for both studied responses. However, the interaction between the laser power and the hatch spacing shows significant effects on the track's height and dilution. The microstructure and microhardness of the as-deposited Al5083 double tracks are also discussed, as proxies to the anticipated performance of the deposited material. 

https://doi.org/10.1016/j.jmrt.2022.02.042

The Influence of Laser Directed Energy Deposition (DED) Processing Parameters for Al5083 Studied by Central Composite Design

https://doi.org/10.1016/j.matdes.2022.110461

Additive manufacturing of Ti-Ni bimetallic structures

A thermal finite element model with efficient computation of surface heat fluxes for directed-energy deposition process and application to laser metal deposition of IN718

Process optimization for directed-energy-deposition, an industrial laser-based additive manufacturing technique, is a time-intensive endeavor for manufacturers Herein we investigate the use of a modified analytical process-model based on powder-bed-fusion techniques, to predict quality build parameters by incorporating the effects of three key parameters: laser-power, scanning-speed, and powder flowrate Titanium alloy (Ti6Al4V) tracks of varying parameters were built, studied, and used to predict parameters for quality builds used at different parameters The model agreed well with experimental build quality at powder flowrates less than 65 g/min, whereas, higher flowrates created significant unmelted-particle regions, despite optimal parameter predictions Processing of multi-layer bulk samples revealed that parameters in the optimal range account for relative densities >99%, indicating quality bulk processing parameters Our results indicate that process modeling with the incorporation of powder feedrate as a key parameter is possible using a commercial laser-based additive manufacturing system

Kyler Starkey

Papers

Model-driven directed-energy-deposition process workflow incorporating powder flowrate as key parameter