Mechanical Characterization of Additive-Manufactured Ti-6Al-4V Processed via Bound Metal Deposition

Abstract

Background

Additive manufacturing (AM) is rapidly growing, with new AM methods continually in development. Alloys processed with novel methods require systematic characterization to understand and validate the materials, especially for demanding fields.

Objective

This study characterized the mechanical properties and failure mechanisms of a Ti-6Al-4V alloy manufactured with bound metal deposition (BMD), a form of metal extrusion (MEX) AM.

Methods

Specimens made of Ti64 were printed via Desktop Metal’s Studio System 2 through a printing, debinding, and sintering process. The microstructure was analyzed with optical metallography and a newly developed open-source porosity analysis tool. Scanning electron microscopy (SEM), optical microscopy, and compositional analysis of green, brown, and sintered parts were conducted to study the material and its failure modes. Sintered specimens were tensile and hardness tested.

Results

As-sintered specimens exhibited ductility more than 10 times lower than wrought Ti64, partially due to contamination/impurity that formed brittle \(\alpha \)-case titanium. Sources of contamination may have included the sacrificial Al\(_2\)O\(_3\) interlayer, the wax/polymer binder, and/or impurity introduction from the furnace. Fractography imaging found quasi-cleavage fracture initiating at areas of high surface roughness along the ceramic interlayer surface of the parts and transitioning into dimple rupture and intergranular decohesion.

Conclusions

Elevated contamination levels, high surface roughness, and internal porosity led to low elongation and ultimate strength in the Ti64 BMD alloy. With the processing route presented here, BMD for Ti64 may not be suitable for applications that demand high ductility and strength with minimal impurities, although with process refinement, the method may be promising for certain applications