Metal injection moulding of non-spherical titanium powders

Traditional techniques to manufacture Titanium such as machining from forged blanks are costly and produce up to 90% waste. Metal injection moulding is a simple and low cost technique that integrates powder metallurgy with a plastic injection moulding technique (for its ability to perform fast production of complex parts). Inexpensive non-spherical hydride-dehydride powders are readily available for a fraction of cost of spherical Titanium powders. The combination of these two (i.e. metal injection molding and hydride-dehydride powders) could be considered to be an effective approach for the economic manufacture of many small industrial parts.

A study conducted at the Queensland Center for Advanced Materials Processing and Manufacturing (AMPAM), in the School of Mechanical and Mining Engineering, at The University of Queensland in Australia by a group of researchers led by Professor Ma Qian, identified the appropriate process parameters to perform the metal injection  moulding of non-spherical hydride-dehydride powders of titanium to achieve minimal distortion and maximum dimensional precision. One of the important parameters to identify and obtain consistent mechanical properties were the sintering parameters, for allowing the production of samples with less distortion, less porosity and less oxygen absorption. The research work is now published in Journal of Manufacturing Processes.

To enable the metal injection moulding of non-spherical hydride-dehydride titanium powders, a simple binder system was selected to make the feedstock material using the non-spherical hydride-dehydride titanium powder. Then the feedstock material was used in an injection molder to produce green components. The samples were then immersed in a hexane bath followed by thermal debinding to extract all the binder from parts. As a next step, sintering was carried out in a vacuum in various temperature-time combinations to obtain optimum properties.

From the aforementioned process, the research team was able to perform injection moulding with a good solid loading (volume fraction of Titanium powder to binder) of approximately 61%. Based on the results presented, the authors suggested that, in order to avoid excessive distortion or disintegration of the samples, the thermal de-binding should be carried out slowly at a heating rate of approximately 1.0 k/min. In addition to this, it is confirmed that, the combination of temperature and time (1250 ºC for 120 min) in the sintering process is adequate to manufacture samples with a tensile strength of 395 MPa and elongation of 12,5%. These results indicate that the metal injection moulding of non-spherical hydride-dehydride powders of titanium possesses the necessary conditions to be considered as an economic method for the manufacture of small industrial parts.