Binder-Based Sintering Technologies for Titanium and Titanium Alloys

Dear Colleagues,

Sintering in combination with feedstock consisting of metal powder and polymeric binder has been gaining more and more interest within industry and research as an alternative to near-net-shape production by SLM (selective laser melting) and EBM (electron beam melting). Rather established technologies, like MIM (Metal Injection Moulding), as well as tool-less techniques, like FFF (Fused Filament Fabrication) and binder jetting, offer a variety of different possibilities to shape complex geometries. The choice of the specific method depends on boundary conditions, such as the complexity and number of parts to be produced. Independent of the shaping process, all techniques share the same post-processing procedure, namely debinding and sintering. FFF with metal powder-filled filaments, for example, supplements MIM in an ideal manner with respect to prototype manufacturing prior to the production of an expensive mold for MIM. A filament printer is of low cost and debinding and sintering facilities already exist.

However, in addition to MIM, the techniques are being applied slowly and, for all methods, titanium still has a niche presence, in spite of the fact that raw material and conventional processing is relatively expensive. In many cases, MIM or other sintering-based techniques could drastically decrease costs if their special possibilities were exploited.

All powder techniques are actually profiting from the current Additive Manufacturing boost; here, this refers to mainly SLM and EBM, as well as Direct Laser Deposition and related technology. The availability of powders has improved, and the price is decreasing. There are many studies on lowering the costs of a titanium component further through the usage of low-cost powders and simpler processing. MIM is still the better choice for high numbers of identical parts, and sintering is quite easy to control. FFF and binder jetting enable the easy production of individual parts. However, no titanium filament can currently be purchased commercially and the optimal binder is under development. The binder has to be adapted to the specific shaping technology and much research has to be done to ensure the mechanical properties of feedstock and green part, the removal of the binder, and acceptable contamination of the metal during sintering.

Furthermore, cost efficiency is a crucial topic, as is the application of binder-based sintering technologies for demanding fields, like aerospace and the medical science. Here, fatigue properties play an important role, and there is still too little fundamental knowledge. Thus, basic scientific studies and technological investigations have to go hand in hand to enable sintering to become a competitive technology for the conventional processing of titanium and titanium alloys.

This Special Issue gives an overview of the current status in both science and technology. Several key topics are discussed in the papers:

• The usage of low-cost powders;
• The reduction of processing costs;
• Binder development;
• Fatigue behavior;
• Basic properties of novel technologies;
• Microstructure and properties;
• Influence of impurities;
• The processing of special alloys;
• Medical applications;
• Applications in automotive and aerospace.

Dr. Thomas Ebel
Guest Editor

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