Tough stuff - titanium takes on TRIP steel?
Beta titanium alloys that exhibit toughness properties similar to transformation-induced plasticity (TRIP) steels are being investigated by researchers in The Netherlands. They hope to use this material in applications such as aeroplane landing gear, which faces heavy loads and demanding fail-safe applications, but could benefit from a lighter material.
The formation of martensite in titanium alloys to increase its toughness has previously been demonstrated, but the ideal temperature to achieve this had not been fully identified.
The team at the Delft University of Technology spent three years creating a thermodynamics-based model to predict the martensite start temperature of the beta alloys. Using this model, the group says it has transformed the metastable beta phase of a 10-2-3 alloy (Ti-10V-2Fe-3Al) to a martensitic phase. This increases its failure load by 30%, ‘though we are convinced a larger increase should be possible’, says Professor Sybrand van der Zwaag of Delft’s Centre for Materials.
The technology used is similar to the phase transformation that occurs during the straining of TRIP steel. The material usually consists of ferrite, bainite, martensite components and restrained austenite. Straining causes the austenite to transform into martensite. This increases the overall strength of the steel.
‘The concept is based on heat treatment to destabilise the beta phase alloy,’ says van der Zwaag. ‘This involves a redistribution of the solute atoms [to the point where] the destability gets the best effect during straining at room temperature. The effect can be switched on or off by choosing a higher or lower temperature.’
Furthermore, he adds, the stress-strain curve of the resulting alloy shows a double yield point, ‘which results in the materials being more formable, as well as stronger’.
The temperature model developed by the researchers is based on the Ghosh-Olson approach to martensite nucleation, which treats the nucleation as a faulting mechanism resulting from the grouping together of dislocations found in the high-temperature phase.
‘At this stage we have not properly identified the full processing window (temperature and time combinations), but based on what we know now, the temperature window should be wide enough to allow industrial applications.’
Dr Richard Bolingbroke of global titanium producer TIMET says this project shows promise. However, he notes, ‘if the deformation is at a low temperature it may be difficult to transfer it to a large landing gear beam. These are very high strength alloys (around 1,400MPa) and all processing is currently carried out at temperatures above 700ºC’.
The group is collaborating with roller bearing company SKF and Tata Steel to further develop the alloys.
Materials World Magazine, 01 Apr 2009
The formation of martensite in titanium alloys to increase its toughness has previously been demonstrated, but the ideal temperature to achieve this had not been fully identified.
The team at the Delft University of Technology spent three years creating a thermodynamics-based model to predict the martensite start temperature of the beta alloys. Using this model, the group says it has transformed the metastable beta phase of a 10-2-3 alloy (Ti-10V-2Fe-3Al) to a martensitic phase. This increases its failure load by 30%, ‘though we are convinced a larger increase should be possible’, says Professor Sybrand van der Zwaag of Delft’s Centre for Materials.
The technology used is similar to the phase transformation that occurs during the straining of TRIP steel. The material usually consists of ferrite, bainite, martensite components and restrained austenite. Straining causes the austenite to transform into martensite. This increases the overall strength of the steel.
‘The concept is based on heat treatment to destabilise the beta phase alloy,’ says van der Zwaag. ‘This involves a redistribution of the solute atoms [to the point where] the destability gets the best effect during straining at room temperature. The effect can be switched on or off by choosing a higher or lower temperature.’
Furthermore, he adds, the stress-strain curve of the resulting alloy shows a double yield point, ‘which results in the materials being more formable, as well as stronger’.
The temperature model developed by the researchers is based on the Ghosh-Olson approach to martensite nucleation, which treats the nucleation as a faulting mechanism resulting from the grouping together of dislocations found in the high-temperature phase.
‘At this stage we have not properly identified the full processing window (temperature and time combinations), but based on what we know now, the temperature window should be wide enough to allow industrial applications.’
Dr Richard Bolingbroke of global titanium producer TIMET says this project shows promise. However, he notes, ‘if the deformation is at a low temperature it may be difficult to transfer it to a large landing gear beam. These are very high strength alloys (around 1,400MPa) and all processing is currently carried out at temperatures above 700ºC’.
The group is collaborating with roller bearing company SKF and Tata Steel to further develop the alloys.
Materials World Magazine, 01 Apr 2009
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