Development and Design of Binder Systems for Titanium Metal Injection Molding: An Overview
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INTRODUCTION
TITANIUM and its alloys are considered as materials of great interest because of their unique combination of low density, high specific strength, biocompatibility, and excellent corrosion resistance.[1,2] However, the high production cost of titanium components limits their applications.[3,4] Powder metallurgy, especially near-netshaping technologies, offers a promise to reduce the manufacturing cost of titanium products. In the powder metallurgy regime, powder or metal injection molding (PIM/MIM) is recognized as a premier forming method ideal for mass production of parts with medium-to-small size and complex shapes.[5] Not until the late 1980s was the MIM process trialed in titanium powder.[6] Two decades of development have seen significant progress in titanium metal injection molding (Ti-MIM) and some products have been commercially available for many years, for example, a Hitachi Ti alloy watch case.[7] Some other products have been showcased for dental implants, medical devices, and golf clubs.[8] Figure 1 presents some examples of Ti-MIM products. Nevertheless, the Ti-MIM technology has not seen significant breakthroughs, especially in advanced engineering components for aerospace applications. It has been claimed that GUIAN WEN, Post Doctoral Fellow, and PENG CAO, Senior Lecturer, are with the Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Contact e-mail: [email protected] BRIAN GABBITAS, Associate Professor, and DELIANG ZHANG, Professor, are with the School of Engineering, The University of Waikato, Hamilton, New Zealand. NEIL EDMONDS, Senior Lecturer, is with the School of Chemical Science, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Manuscript submitted January 30, 2012. Article published online October 23, 2012 1530—VOLUME 44A, MARCH 2013
technically the Ti-MIM process is ready for industry to take up, particularly for applications where the use of titanium is fully justified by its unique properties.[8] These include, for example, dental and biomedical implants, aerospace components, medical and surgical tools, and chemical devices.[8] Although Ti-MIM is a favorite research topic today,[8] the issue of convincing the designers to use titanium parts made using Ti-MIM still has not been satisfactorily addressed. Much information on how to make titanium parts using Ti-MIM is available, and there are several powder vendors and feedstock suppliers. However, most of the binders in the feedstock are proprietarily protected. Contaminants, either in the original titanium powder, from the sintering atmosphere, or most likely from the binder, are usually a big concern for the component designers because these impurities deleteriously affect the mechanical properties of the final products.[9,10] In this sense, a comprehensive understanding of the binder system and the debinding processes helps us to provide a guideline for choosing a suitable powder feedstock and to validate the MIM approach.
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