Fabrication of titanium/titanium alloy components by powder injection moulding
Ong, Amanda Ziyan
Date of Issue2014
School of Mechanical and Aerospace Engineering
A*STAR Singapore Institute of Manufacturing Technology
Titanium (Ti) excellent mechanical and physical properties made it an attractive metal for engineering applications. However, its high material cost and difficulty to machine and bulk form limit its expansion to a vast number of applications. Powder injection moulding (PIM) for titanium material was proposed as it is a near net or net shape forming process, hence, reduces material wastages and manufacturing cost. However, Ti components produced by PIM usually have less superior mechanical properties than their cast or wrought counterparts due to interstitial contamination. Therefore, in this research work, the fabrication of high strength Ti components by PIM is studied. ASTM B265 Grade 3 CP-Ti and Grade 5 Ti-6Al-4V are the targeted standard for this research work. The first phase of the research focused on PIM of CP-Ti tensile components. Tensile tests showed components sintered at 1240 oC, 1260 oC and 1280 oC in argon have met the ultimate tensile strength (UTS) for Grade 3 CP-Ti (> 450 MPa) but still lacked in elongation. The sintered components have elongations less than 10 %, which were lower than the targeted value of 18 %. Their microstructures revealed high level of porosities and relative densities were measured to be only 95 %. This was attributed by argon gas entrapment and also non-uniform shrinkage of the components during sintering. XRD spectra of the sintered components showed oxides peaks, indicating contamination. The second phase of the research involved the fabrication of Ti-6Al-4V tensile components. The processing parameters used in the fabrication of CP-Ti were improvised and implemented to the Ti-6Al-4V fabrication process. 24-1 fractional DOE study was also conducted to study the effects of the sintering parameters on the UTS and elongation of Ti-6Al-4V. The sintering parameters examined were sintering temperature (1200 oC, 1300 oC), dwell time (1 h, 3 h), ramp rate (1 oC/minute, 10 oC/minute) and cooling rate (1 oC/minute, 10 oC/minute). Results showed all four sintering parameters have significant influence on the UTS while, only dwell time and ramp rate have significant influence on the elongation. In the DOE study, some of the sintered Ti-6Al-4V components with certain parameters have met the Grade 5 Ti-6Al-4V standard for UTS (> 895 MPa) and elongation (> 10%). The relative densities for most of the sintered components obtained from the DOE study were above 96 %. Only one had relative density of 94 % due to incomplete sintering. Lower cooling rate favored thicker α plate thickness and larger α colony size. β prior grains were also identified in some of the components, mainly in those sintered at higher temperature and longer dwell time. The microstructures and the relatively density of the sintered components were also found to have influence on the UTS and elongation. In general, sintered components with smaller α plate thickness or α colony size has better UTS and elongation. UTS and elongation were also observed to increase with increasing relative density.
DRNTU::Engineering::Materials::Material testing and characterization