The Interface of TiB sub(2) and Al sub(3)Ti in Molten Aluminum

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 47; no. 6; pp. 3285 - 3290
• Main Authors: Wang, Xiaoming, Song, Jie, Vian, Wei, Ma, Haibin, Han, Qingyou
• Format: Journal Article
• Language: English
• Published: 01.12.2016
• Subjects: Aluminum; Grain refinement; Grains; Intermetallic compounds; Intermetallics; Master alloys; Nucleation; Titanium aluminides; Titanium diboride
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-015-0570-0

In the grain refinement of aluminum, Al sub(3)Ti and TiB sub(2) particles are introduced to reduce the casting grain size down to 200 micrometer level, which makes cold working possible. The particles are brought in by the addition of Al-Ti-B-type master alloys. It is generally believed that TiB sub(2) particles are stable and nucleate alpha -Al grains in solidification in the presence of titanium in solution from the dissolution of Al sub(3)Ti particles in the master alloys. The titanium in solution either forms Al sub(3)Ti layers on the surface of TiB sub(2) particles to promote the nucleation of alpha -Al grains or remains as solute to restrict the growth of alpha -Al grains in solidification. However, a consensus on a grain refinement mechanism is still to be reached due to the lack of direct observation of the three phases in castings. This paper presents finding of the TiB sub(2)/Al sub(3)Ti interfaces in an Al-Ti-B master alloy. It demonstrates a strong epitaxial growth of Al sub(3)Ti on the surface of TiB sub(2) particles, a sign of the formation of an Al sub(3)Ti layer on the surface of TiB sub(2) particles in grain refinement practice. The Al sub(3)Ti layer has a crystal coherency with alpha -Al and hence offers a substrate for heterogeneous nucleation of alpha -Al grains. However, the layer must be dynamic to avoid the formation of compounded Al sub(3)Ti and TiB sub(2) particles leading to the loss of efficiency in grain refinement.