| Project Team | Institution | Role | ||
| Mr Shouqie Al-Goussous | The University of Melbourne | Postgraduate Student | ||
| Dr Colleen Bettles | Monash University | Senior Research Fellow | ||
| Dr Sammy Chan | The University of New South Wales | Senior Research Associate | ||
| Ms Nur Farhana Hayazi | The University of New South Wales | Postgraduate Student | ||
| Mr Daniel Curtis | Monash University | Research Assistant | ||
| Mr Gregory Guo | The University of New South Wales | Postgraduate Student | ||
| Dr Rimma Lapovok | Monash University | Senior Research Fellow | ||
| Mr Ray Low | The University of Queensland | Postgraduate Student | ||
| Dr Shudong Luo | The University of Queensland | Research Fellow | ||
| Dr Ross Marceau | The University of Sydney | Research Fellow | ||
| Assoc Prof Ma Qian | The University of Queensland | Chief Investigator | ||
| Professor Graham Schaffer | The University of Queensland | Chief Investigator | ||
| Dr Gang Sha | The University of Sydney | Senior Research Fellow | ||
| Dr Xiaolin Wu | The University of Melbourne | Research Fellow | ||
| Mr Yi Sun Wu | The University of Melbourne | Postgraduate Student | ||
| Assoc Professor Kenong Xia | The University of Melbourne | Chief Investigator | ||
| Dr Wei Xu | The University of Melbourne | Research Fellow | ||
| Dr Ya-Feng Yang | The University of Queensland | Research Fellow | ||
| Mr Yin Yao | The University of New South Wales | Postgraduate Student | ||
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Executive Summary
The focus has been on the sintering behavior of the titanium powder metallurgy compacts. Two potential sintering aids have been identified, and the mechanisms behind the improved behaviour have been determined. These sintering aids may not be universally applicable, but it is now possible to predict in which systems they are likely to have an effect. Forging dies have been designed and are being manufactured to allow the thermomechanical processing studies to begin. Alternative sintering routes have been investigated, and microwave radiation has been demonstrated to be a viable option for faster throughput, low cost component manufacture.
The focus has been on the sintering behavior of the titanium powder metallurgy compacts. Two potential sintering aids have been identified, and the mechanisms behind the improved behaviour have been determined. These sintering aids may not be universally applicable, but it is now possible to predict in which systems they are likely to have an effect. Forging dies have been designed and are being manufactured to allow the thermomechanical processing studies to begin. Alternative sintering routes have been investigated, and microwave radiation has been demonstrated to be a viable option for faster throughput, low cost component manufacture.
This project is based on the premise that at some time in the foreseeable future there will be a commercial source of inexpensive titanium powder (either commercially pure or as alloy). Its aim, therefore, is to develop new titanium alloys and/or processing strategies based on a powder metallurgical approach, whilst at the same time addressing some of the fundamental issues associated with the various processing steps. The project will have two options for the first processing step (ECAP and Conventional Powder Metallurgy). The post-consolidation stages are selected from a suite of thermo-mechanical processes at our disposal, with the overall aim being to produce material which meets all the target properties. Alloy compositions will be selected by the researchers, based on what is most appropriate for the primary consolidation process. This can be an existing alloy or an entirely novel composition achieved through blended elemental powder metallurgy techniques.
These are based on the requirements for a P/M connecting rod (AISI 1141):
UTS
Proof Strength
Young's Modulus
Fatigue Limit
Ductility
660MPa
370MPa
100GPa
240MPa (R=-1, 107 cycles)
5% (tensile elongation)
Project Progress: Technical Details and Research Outcomes
Chlorides are common impurities in both titanium sponge powder and hydride-dehydride (HDH) titanium powder processed from titanium sponge raw materials. They cause residual porosity in sintered and hot isostatically pressed components due to their volatile nature. Currently, in applications where porosity must be minimised, expensive high purity powders must be used. A chlorine scavenger, introduced at the trace addition level, has been identified which can remarkably mitigate the detrimental effects of the chlorine on the liquid phase sintering of titanium alloys. The effects of the addition are shown in Figure A15. The scavenger aids the sintering process by absorbing the chlorine from the powder. The addition has been found to be also scavenging sulphur but it is uncertain if the scavenging of sulphur is contributing to the enhanced densification or not. There are indications also that the addition may have an additional sintering effect outside of the scavenging effect. This discovery is timely, given the increased interest worldwide in low-cost titanium powder metallurgy processing. The scavenging of chloride and sulphide impurities may also have implications in other fields of materials processing.
Chlorides are common impurities in both titanium sponge powder and hydride-dehydride (HDH) titanium powder processed from titanium sponge raw materials. They cause residual porosity in sintered and hot isostatically pressed components due to their volatile nature. Currently, in applications where porosity must be minimised, expensive high purity powders must be used. A chlorine scavenger, introduced at the trace addition level, has been identified which can remarkably mitigate the detrimental effects of the chlorine on the liquid phase sintering of titanium alloys. The effects of the addition are shown in Figure A15. The scavenger aids the sintering process by absorbing the chlorine from the powder. The addition has been found to be also scavenging sulphur but it is uncertain if the scavenging of sulphur is contributing to the enhanced densification or not. There are indications also that the addition may have an additional sintering effect outside of the scavenging effect. This discovery is timely, given the increased interest worldwide in low-cost titanium powder metallurgy processing. The scavenging of chloride and sulphide impurities may also have implications in other fields of materials processing.
A systematic study on the sintering of Ti-7Ni alloys has led to the finding of an effective sintering aid for the densification of these alloys. Small additions of the sintering aid allow for rapid (15 min) and full densification at 1200°C (see Figure A16). In addition, it significantly refines the sintered grain structures. Mechanical properties of the sintered Ti-7Ni-(0.3-0.9)%X alloys have been tested. Unfortunately, despite full densification, the ductility is poor (UTS: 700 MPa; Yield stress (0.2%): 559 MPa; Modulus: 120 GPa; Plastic strain at break: 0.5%). Work is underway to modify the microstructure by thermomechanical processing in an attempt to improve the properties of Ti-Ni alloys and to apply this discovery to the sintering of commercially important titanium alloys. As a result of this project, several basic principles have been developed for the identification of new sintering aids for other titanium alloy systems.
Back pressure ECAP has been used to consolidate powder mixtures of Ti-7Ni based alloys. The results show that the powder mixtures can be consolidated into fully dense materials at temperatures between 350 and 500°C and back pressures between 100 and 200 MPa. Samples consolidated by ECAP and conventional sintering will undergo forging operations to compare properties and microstructures. Dies to be used for the assessment of their forgeability have been designed.
Titanium hydride powder has several advantages over titanium sponge powder and HDH titanium powder for the fabrication of titanium and titanium composite parts. However, sufficient dehydrogenation after forming has to be achieved to avoid distortion and cracking in the later stages of fabrication. Work to date has shown that the optimum dehydrogenation parameters are 650°C for 1 hour at a heating rate of 10°C/min. The microstructural and phase changes of the powder during dehydrogenation have been studied in detail.
Progress has been made towards making miniaturised con-rod samples. The literature on con-rod production from different materials has been analysed and the simulation of the con-rod forging operation from solid and powder preforms has been analysed. The dimensions of miniature con-rod geometry to be used in a case study have been chosen. A two-step forging process is planned: blocking forging followed by finishing forging. The dies to be used for each step have been designed and manufactured (see Figure A17). Preliminary trials have been carried out using compacted CP-Ti samples. The adapters for a forging press are now in preparation and trials have been scheduled.
Titanium hydride powder has several advantages over titanium sponge powder and HDH titanium powder for the fabrication of titanium and titanium composite parts. However, sufficient dehydrogenation after forming has to be achieved to avoid distortion and cracking in the later stages of fabrication. Work to date has shown that the optimum dehydrogenation parameters are 650°C for 1 hour at a heating rate of 10°C/min. The microstructural and phase changes of the powder during dehydrogenation have been studied in detail.
Progress has been made towards making miniaturised con-rod samples. The literature on con-rod production from different materials has been analysed and the simulation of the con-rod forging operation from solid and powder preforms has been analysed. The dimensions of miniature con-rod geometry to be used in a case study have been chosen. A two-step forging process is planned: blocking forging followed by finishing forging. The dies to be used for each step have been designed and manufactured (see Figure A17). Preliminary trials have been carried out using compacted CP-Ti samples. The adapters for a forging press are now in preparation and trials have been scheduled.
Work to date has shown that microwave (MW) radiation is an effective means of densification for the sintering of titanium. A relative density as high as 96.3% was obtained for samples made from fine Ti powder (particle size: 20 µm) by MW radiation. The heating time by MW radiation to the sintering temperature (1200 °C) is substantially shorter than conventional vacuum heating (25 min vs. 212 min from 350 °C to 1200 °C). Detailed microstructural analyses revealed that MW sintering resulted in a coarser grain structure than conventional vacuum sintering under identical isothermal sintering times. Excellent metallurgical bonds between Ti grains were observed in MW-sintered samples by high resolution TEM.
Future Activity Plan
Current research areas of Project A4 will be continued, such as Mg-based BMG discovery and development of alloys with higher glass-forming ability and improved mechanical or functional properties. Several new higher degree research students will join the project, where they will carry out research on the development new Al- and Ti-based amorphous alloys and in-situ composites. The recent commissioning of rapid cooling, semi-solid-state equipment within the Centre will enable researchers to explore new methods for developing BMG composites. Research on direct strip casting of BMGs will be extended to produce continuous strip material based on new glassy alloy systems. Recently developed international collaborations with access to leading edge facilities are also expected to generate fundamental results leading to a greater understanding of these materials.
Current research areas of Project A4 will be continued, such as Mg-based BMG discovery and development of alloys with higher glass-forming ability and improved mechanical or functional properties. Several new higher degree research students will join the project, where they will carry out research on the development new Al- and Ti-based amorphous alloys and in-situ composites. The recent commissioning of rapid cooling, semi-solid-state equipment within the Centre will enable researchers to explore new methods for developing BMG composites. Research on direct strip casting of BMGs will be extended to produce continuous strip material based on new glassy alloy systems. Recently developed international collaborations with access to leading edge facilities are also expected to generate fundamental results leading to a greater understanding of these materials.