I believe you can also find interesting the comparison of grain structures between Al-Ti-C and Al-Ti-B, presented in the following interesting paper:
- The Impact of TiCAl ™ and TiBAl ™ Grain Refiners on Casthouse Processing A. M. Detomi, A. J. Messias, S. Majer and P. S. Cooper TMS 2001 Congress NEW ORLEANS, LOUISIANA FEBRUARY 11-15, 2001
Available at: https://amg-al.com/wp-content/uploads/2019/07/3.-impact-of-grainrefiners.pdf
your question is very interesting (… and not easy !!!) because grain refinement plays a pivot role in improving characteristics and properties of Al alloys. Generally Al-Ti and Al-Ti-B master alloys are added to the Al alloys to grain refine the solidified product but, the mechanism of grain refinement is of considerable controversy in the scientific literature and subject of intensive research as said in the paper:
-Effects and mechanisms of grain refinement in aluminium alloys
K.T. Kashyap, T. Chandrashekar
Bulletin of Materials Science 24(4):345-353 (2001)
Available on ResearchGate at: https://www.researchgate.net/publication/225412167_Effects_and_mechanisms_of_grain_refinement_in_aluminium_alloys
I suggest you some other papers, hoping that they will be useful in your research:
-Fading mechanism of grain refinement of aluminum-silicon alloy with Al-Ti-B grain refiners
Chaowalit Limmaneevichitr, W. Eidhed
Materials Science and Engineering A 349:197-206 (2003)
Available on ResearchGate at: https://www.researchgate.net/publication/235889819_Fading_mechanism_of_grain_refinement_of_aluminum-silicon_alloy_with_Al-Ti-B_grain_refiners
-Influence of Titanium Diboride Particle Size on Structure and Mechanical Properties of an Al-Mg Alloy
Anton P. Khrustalyov, Alexander A. Kozulin, Ilya A. Zhukov, Marina G. Khmeleva, Alexander B. Vorozhtsov, Dmitry Eskin, Suwaree Chankitmunkong, Vladimir V. Platov and Sergey V. Vasilyev