LIE HomeIssue Contents

Alloy Formation in Laser Surface Alloying of Al with Transition Metals
Amelia Almeida and Rui Vilar

The production of coatings with uniform composition and structure by laser surface alloying requires control over the melting and dissolution of the alloying elements in order to create a homogeneous liquid prior to solidification. This requirement is particularly difficult to achieve when Al is alloyed with transition metals (TMs) because Al tends to combine with the TM to produce intermetallic compounds, which surround the powder particles, drastically slowing down their dissolution. In this paper the conditions for alloy formation in laser surface alloying of Al with various transition metals were investigated. The laser alloying experiments were performed using Cr, Mo and Nb as alloying elements. A detailed study of the microstructure and composition of the alloys was carried out. Coupling the experimental observations with calculations of the temperature of the melt pool showed that uniform coatings can only be obtained when the temperature of the melt exceeds the melting temperature of the intermetallic compounds which may form as a result of the reactions between the TM and liquid Al. For typical values of the laser alloying parameters, this requirement is only satisfied in the upper regions of the melt pool. In its deeper regions the temperature is lower than this melting temperature and an intermetallic compound layer forms around the TM particles, slowing their dissolution and impeding homogenisation of the liquid.

Full Text (IP)