Microstructural control of additively manufactured Ti-6Al-4V

In-situ selective heat treatment of an additive manufactured Ti-6Al-4V alloy effectively induces local microstructural changes and activates the solid-state phase transformation of the β phase within a short time frame. This opens doors for creating intricate 3D architected or composite-like microstructures.

Result
Operando X-ray diffraction of SLHT on thin wall geometry. The burst mode acquisitions were taken at a) 50 µm, b) 150 µm, and c) 250 µm below the top surface. d-f) single XRD patterns taken at the end of the SLHT cycles by summing 10 individual patterns and g-i) Temperature evolution extracted by peak tracing of the (10-10) peak of the plane corresponding to the acquisition position of 50 µm, 150 µm, and 250 µm respectively. The grey scheme on the left represents the positioning of the X-ray beam with respect to the specimen.

The game-changing design freedom offered by Additive Manufacturing (AM) has opened new doors for producing customized products previously unattainable through conventional manufacturing techniques. LPBF, among various AM methods, stands out as the most well-known technique for the production of metallic parts, with a primary objective of producing fully dense parts with minimal porosity. However, the unique properties of the Ti-6Al-4V alloy, such as its martensitic microstructure, pose challenges in achieving the desired balance of strength and ductility.

Researchers from EPFL and PSI  have unveiled an effective strategy for controlling the microstructure of additively manufactured Ti-6Al-4V. The implementation of in-situ Selective Laser Heat Treatment (SLHT) has been designed and tested on various geometries, using a combination of numerical simulations and operando X-ray diffraction measurements. This innovative approach allows for precise control of local microstructural changes within a short time scale, opening avenues for tailored microstructures in additively manufactured parts.

The implications of this research are profound for the field of additive manufacturing. The ability to control microstructure at a local scale opens doors for creating intricate 3D architected (or composite-like) microstructures in the as-built state. This not only addresses challenges associated with the Ti-6Al-4V alloy but also contributes to a deeper understanding of martensite decomposition in LPBF processes.

The X-ray diffraction experiments were performed at the MicroXAS and MS beam line of the Swiss Light Source. This work was supported by the Swiss National Science Foundation.

Dr. Steven Van Petegem
Structure and Mechanics of Advanced Materials
Photon Science Division 
Paul Scherrer Institute
Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
Telephone: +41 56 310 2537 
E-mail: steven.vanpetegem@psi.ch

In-situ Selective Laser Heat Treatment for microstructural control of additively manufactured Ti-6Al-4V
Reza Esmaaeilzadeh, Milad Hamidi-Nasab, Charlotte de Formanoir, Lucas Schlenger, Steven Van Petegem, Claire Navarre, Cyril Cayron, Nicola Casati, Daniel Grolimund, Roland E. Logé
Additive Manufacturing 78 (2023) 103882
DOI: 10.1016/j.addma.2023.103882