Active Control of Microstructure in Powder‐Bed Fusion Additive Manufacturing of Ti6Al4V

Abstract

Because of the complex interactions among the energy beam, the powder bed, and the material phase transformations, powder-bed fusion additive manufacturing is very sensitive to process parameters, such as beam power and scan speed. As a result, the process window to produce fully-dense, ASTM-grade components is narrow. In such scenario, envisioning further control of mechanical properties is very challenging. As a departure from traditional attempts to control microstructure by changing the process parameters, the authors propose the introduction of a thermoelectric module (TEM) as an active device inside the build chamber. Using process modeling, the authors show that by altering the heat flow into the material through the TEM device, the volume fraction of martensite can be controlled in its entire range. In particular, the authors show that modern TEM modules can deliver sufficient thermal power to block the formation of martensite. As a result, microstructure can be controlled locally while retaining the beam power and scan speed optimal for part density and surface finish. While the results are demonstrated for Ti6Al4V and the electron beam melting process, the concept is general and, in principle, applicable to other materials and machines systems such as IN781 and selective laser melting.

Superior Wear Resistance in EBM-Processed TC4 Alloy Compared with SLM and Forged Samples

“…The matensitic α′ phase in the SLM sample and α phase in the EBM sample are confirmed by the SEM micrograph, where the EBM sample shows a singular shape phase and the SLM sample shows a finer acicular shape phase, which are identified as the α phase and α′ martensitic phase, respectively. These findings are in accordance with the reported work [ 5 , 21 , 25 , 30 , 31 ], revealing that the α′ martensitic phase is typical for SLM-processed Ti-6Al-4V samples. The SLM process is said to offer a very high cooling rate in the order of 10 5 –10 6 °C/sec [ 32 , 33 , 34 ].…”

“…With the development of AM, Ti-6Al-4V alloy has been fabricated using both EBM and SLM techniques and has been extensively studied. Compared to the Ti-6Al-4V alloy produced by traditional forging, the SLM/EBM-fabricated materials show a unique microstructure and properties [ 17 , 18 , 19 , 20 , 21 ]. The wear property of Ti-based alloys is one of the most important properties to be considered for particular applications [ 22 , 23 , 24 , 25 , 26 ].…”

Residual Stress in Engineering Materials: A Review

“…In this case, control of residual stresses emerging in metals and alloys during different manufacturing processes is another critical area covered in this section. Current approaches to reducing undesired residual stresses in AM processes include 1) altering the scanning strategy [ 330 ] or 2) heating the build plate. [ 331 ] Vastola and teammates presented an experimentally validated FEM model to assess the impact of different parameters on the control of residual stresses during the AM process of Ti6Al4V.…”

Effect of Heat Treatment on Fracture Behavior of AISI 630 Alloy Manufactured by Directed Energy Deposition

“…It can obtain high surface quality, but its molding size is limited by the powder bed. [11][12][13][14][15] Directed energy deposition (DED) utilizes a high-energy laser beam to melt synchronously conveyed powders to manufacture parts. It has the advantages of high flexibility, no space limit, and high forming efficiency.…”