International Journal of Metalcasting, Oct 1, 2013
Practical measurements, in conjunction with computer simulation modelling, were carried out to st... more Practical measurements, in conjunction with computer simulation modelling, were carried out to study the effects of cooling rate and temperature gradient on shrinkage porosity in a Ti-46Al-8Nb investment casting, by investigating the influence of casting geometry and preheat mould temperature on shrinkage porosity. A tilt-fill solidification model (ProCast) Ti-46Al-8Nb investment casting was developed and used to compute Niyama criterion function in different test bars with different taper angles, at 500C (932F) and 1000C (1832F) mould temperatures. Analyzing the model results and matching them with the experimentally measured area percentage of porosity revealed that enhancing directional solidification by increasing the taper coefficient significantly reduced the amount of porosity, due to the influence of improved temperature gradient on the formation of the shrinkage porosity. The Niyama criterion function was validated to predict shrinkage-related porosity in Ti-46Al-8Nb castings. Positions in a casting with Niyama values above 4 (°C.min) 0.5 cm-1 could be considered completely sound, with the critical value of the Niyama function being 2 (°C.min) 0.5 cm,-1 below which the local area would be susceptible to macroshrinkage porosity.
Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic ... more Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic layer porosity. This research aims to develop a better understanding of shrinkage porosity in Ti-46Al-8Nb alloy and how to minimize it. Practical measurements in conjunction with computer simulations were carried out in order to study the effects of cooling rate and temperature gradient on shrinkage porosity in Ti-46Al-8Nb investment castings, through investigating the influence of casting geometry, specifically mould taper on cylindrical bars, and preheating mould temperature on the macrostructure and the formation of shrinkage porosity. The interface heat-transfer coefficient of the ceramic shell/surroundings was determined using measured cooling curves obtained in 200 mbar of Argon and in vacuum. Furthermore, the alloy/mould interfacial heat transfer coefficient was estimated and was verified by comparing measured and predicted cooling curves of Ti-46Al-8Nb. The Niyama criterion funct...
International Journal of Metalcasting, Oct 1, 2013
Practical measurements, in conjunction with computer simulation modelling, were carried out to st... more Practical measurements, in conjunction with computer simulation modelling, were carried out to study the effects of cooling rate and temperature gradient on shrinkage porosity in a Ti-46Al-8Nb investment casting, by investigating the influence of casting geometry and preheat mould temperature on shrinkage porosity. A tilt-fill solidification model (ProCast) Ti-46Al-8Nb investment casting was developed and used to compute Niyama criterion function in different test bars with different taper angles, at 500C (932F) and 1000C (1832F) mould temperatures. Analyzing the model results and matching them with the experimentally measured area percentage of porosity revealed that enhancing directional solidification by increasing the taper coefficient significantly reduced the amount of porosity, due to the influence of improved temperature gradient on the formation of the shrinkage porosity. The Niyama criterion function was validated to predict shrinkage-related porosity in Ti-46Al-8Nb castings. Positions in a casting with Niyama values above 4 (°C.min) 0.5 cm-1 could be considered completely sound, with the critical value of the Niyama function being 2 (°C.min) 0.5 cm,-1 below which the local area would be susceptible to macroshrinkage porosity.
Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic ... more Titanium aluminide alloys are prone to extensive shrinkage porosity, particularly interdendritic layer porosity. This research aims to develop a better understanding of shrinkage porosity in Ti-46Al-8Nb alloy and how to minimize it. Practical measurements in conjunction with computer simulations were carried out in order to study the effects of cooling rate and temperature gradient on shrinkage porosity in Ti-46Al-8Nb investment castings, through investigating the influence of casting geometry, specifically mould taper on cylindrical bars, and preheating mould temperature on the macrostructure and the formation of shrinkage porosity. The interface heat-transfer coefficient of the ceramic shell/surroundings was determined using measured cooling curves obtained in 200 mbar of Argon and in vacuum. Furthermore, the alloy/mould interfacial heat transfer coefficient was estimated and was verified by comparing measured and predicted cooling curves of Ti-46Al-8Nb. The Niyama criterion funct...
Uploads
Papers by Iman Khaled