Microstructural control during direct laser deposition of a β-titanium alloy

• Good structural and geometrical integrity could be achieved by process design.
• Build height increases with decreased scanning speed and increased powder flow rate.
• Keeping Z increment close to actual layer thickness is crucial for consistent building.
• The laser deposited Ti5553 are dominated by mixed columnar and equiaxed grains.
• In situ dwelling and annealing promote α precipitation which improves microhardness.

A concern associated with Direct Laser Deposition (DLD) is the difficulty in controlling microstructure due to rapid cooling rates after deposition, particularly in beta-Ti alloys. In these alloys, the beta-phase is likely to exist following DLD, instead of the desirable duplex alpha + beta microstructure that gives a good balance of properties. Thus, in this work, a parametric study was performed to assess the role of DLD parameters on porosity, build geometry, and microstructure in a beta-Ti alloy, Ti–5Al–5Mo–5V–3Cr (Ti5553). The builds were examined using optical microscopy, scanning electron microscopy, and X-ray diffraction. Microhardness measurements were performed to assess the degree of re-precipitation of alpha-phase following an in situ dwelling and laser annealing procedure. The study identified several processing conditions that enable deposition of samples with the desired geometry and low porosity level. The microstructure was dominated by beta-phase, except for the region near the substrate where a limited amount of alpha-precipitates was present due to reheating effect. Although the microstructure was a mixture of equiaxed and columnar beta-grains alongside infrequent fine alpha-precipitates, the builds showed fairly uniform microhardness in different regions. In situ dwelling and annealing did not cause an obvious change in porosity, but did promote the formation of alpha-precipitates.

Microstructural development of Ti5553 during Direct Laser Deposition (DLD).Figure optionsDownload as PowerPoint slide