| Summary: |
On the last decades, titanium and titanium alloys have been under intensive research and development, both for critical applications (aerospace, aeronautic, automotive, chemical and biomedical industries) and for non-critical ones (sports equipment, photography, arquitecture). As a result of such effort, a large number of titanium alloys with combination of excellent tensile properties, creep strength and corrosion resistance, associated to a superior strength-to-weight ratio, are now available. Nevertheless, the use of titanium alloys is still reduced, mainly due to the extremely high price of ready to use parts. The actual production for consumer products is expected to increase on the next years, but that will surely depend on an effective cost reduction, either by the development of technological factors (new alloys and production techniques) or by a decrease in the prices of raw materials and production costs.
The major part of titanium and titanium alloys components is produced by plastic formation (forging, rolling, extrusion) and machining, and just a small quantity is produced by casting. However, the increase in the use of casting processes to produce near net shape titanium parts, is believed to be one of the most effective ways to decrease the actual production costs. The production of high quality titanium castings is a difficult and expensive task. The main reasons for that are: the high melting point; the extremely high reactivity of titanium alloys against a large amount of elements at high temperatures, with particular emphasis to oxygen. For this reason, traditional casting techniques and materials cannot be used, both for the melting and the moulding operations, and melting and pouring have to be performed under vacuum or inert gas.
Elements of the research team developed a multi-layered ceramic crucible, which is actually under a patenting process in Portugal and Germany, suitable for the production of titanium alloys without contaminati  |
Summary
On the last decades, titanium and titanium alloys have been under intensive research and development, both for critical applications (aerospace, aeronautic, automotive, chemical and biomedical industries) and for non-critical ones (sports equipment, photography, arquitecture). As a result of such effort, a large number of titanium alloys with combination of excellent tensile properties, creep strength and corrosion resistance, associated to a superior strength-to-weight ratio, are now available. Nevertheless, the use of titanium alloys is still reduced, mainly due to the extremely high price of ready to use parts. The actual production for consumer products is expected to increase on the next years, but that will surely depend on an effective cost reduction, either by the development of technological factors (new alloys and production techniques) or by a decrease in the prices of raw materials and production costs.
The major part of titanium and titanium alloys components is produced by plastic formation (forging, rolling, extrusion) and machining, and just a small quantity is produced by casting. However, the increase in the use of casting processes to produce near net shape titanium parts, is believed to be one of the most effective ways to decrease the actual production costs. The production of high quality titanium castings is a difficult and expensive task. The main reasons for that are: the high melting point; the extremely high reactivity of titanium alloys against a large amount of elements at high temperatures, with particular emphasis to oxygen. For this reason, traditional casting techniques and materials cannot be used, both for the melting and the moulding operations, and melting and pouring have to be performed under vacuum or inert gas.
Elements of the research team developed a multi-layered ceramic crucible, which is actually under a patenting process in Portugal and Germany, suitable for the production of titanium alloys without contamination, or with a maximum oxygen content of 0,5 at%. Although, the problem concerning the mould material and moulding technique still persists, and until now no titanium casting was produced without surface contamination, reason why surface chemical milling to eliminate the alpha-case (hard layer at the casting surface) still remains an expensive stage of the production process.
This project aims the development of a multi-layer moulding technique (interior layers made of a chemically inert material facing the titanium alloy, and exterior layers made of a low cost refractory material with suitable mechanical and thermal-shock resistance), based on the investment casting process, with which accurate and sound titanium castings might be produced at competitive costs. |