Future work

4.2.1

Friction stir welding of Ti 15Mo alloys

If experiment could be resumed in the future, then future work on the research of friction stir welding of Ti 15Mo alloys includes:

• Apply thermocouples. The temperature history of weld was not measured dur- ing experiment. So it is very difficult to correlate temperature with various input parameters and weld responses. Thermocouples must be used and tem- perature history must be measured during experiment. The correlations that cannot be found at this point, such as temperature and grain size distribu- tion, temperature and ultimate tensile strength, can be resolved by introducing thermocouples.

• More welds with different parameters. Although trends shown in the conclusion part could be established from currently available weld data files, more experi- ments need to be done in order to validate and confirm the overall correlation between different parameters. First, at least two more experiments with differ- ent RPM are needed to evaluate the correlation between weld energy and RPM. Second, the relationship between ultimate tensile strength and advancing per revolution can be further clarified by completing 3 more welds with different APR. Third, the variation of Vickers hardness for these 5 welds doesn’t change too much. So heat treatment of these welds might be needed.

4.2.2

Friction consolidation on CP Ti and Ti 15Mo chips

Unfortunately, the consolidation die broke during experiment due to torsional crack (Figure 4.6). If a new consolidation die could be available in the future, the followings should be done as future work

Figure 4.6: Torsional crack of the consolidated die

• More runs should be done in order to optimize consolidation parameters. • New approachs and methods are needed to explain the correlation between high

Vickers hardness and ultimate tensile strength.

• More sub-scale tensile tests should be performed to find the stress-strain curve of tensile bars in the ultra high Vickers hardness region.

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