Identification of Contamination Levels and the Microstructure of Metal Injection Moulded Titanium

The chemical elements used in the binder system for the injection moulding of titanium metal powders will change the final composition when not adequately controlled. Excess levels of carbon, hydrogen, nitrogen and oxygen adversly effect the mechanical properties by embrittlement. Before sintering debinding is done to remove the maximum possible amount binder thereby ensuring residual carbon levels are minimal. Testing the mechanical properties of samples can acknowledge deficiencies in the final part however, identification of the nature of the deficiencies is not so simple.In this work titanium-based metal parts were made using the metal injection moulding process and the microstructure was inspected. The investigation used scanning electron microscopy imaging, electron dispersion spectroscopy point and area mapping, LECO trace analysis and X-ray diffraction elemental mapping. Following this samples were ground and polished before immersing their surfaces in an etching solution to further expose the microstructure. Although the data collected from debinding indicated the binder had been removed prior to sintering contamination was still evident. This result showed that the traditional means of reporting binder levels in proportion to part mass after debinding is inaccurate. Subsequently laser induced breakdown spectroscopy was trialed as a method by which to determine the binder levels for parts in the green, grey, brown and sintered form.Interstitial carbon is a known alpha stabiliser however excess carbon on particle surfaces may impinge on particle coalesence limiting density levels. Comparison of the part mass method of binder determination with the laser induced breakdown spectroscopy results showed that the mass determination method was more accurate for the green and grey parts but the laser induced breakdown spectroscopy results were able to detect the residual binder more accurately for brown and sintered parts.