One of the main fields of investigation of the Thermal Spray Manifacturing group is the charcteristics of rapidly solidified alloys through the UDS process.

Rapid solidification of materials gives a precise control on microstructures, on which the physical properties of a given material depends. The undercooling and rapid solidification of metals are the subject of many fundamental researches. The investigation of the effects of rapid solidification on metallic microstructures has been promising with regular gas atomization (6) consequently, the characteristics of the UDS process are ideally suited to investigate the rapid quenching of metals and the formation of amorphous structures.

An example of microstructural control by rapid solidification processes is the formation of alloys with equiaxed microstructures, which is in conventional sprays needed in many industrial applications. Spray forming is a technique presenting the advantages of a rapid solidification process but the non-uniform thermal history and sizes of the produced droplets lead to deposit microstructures with defects such as porosity. Upon previous experiments with Sn-5 wt % Pb Alloy, it has been shown that:

- a fine equiaxed microstructure is obtained with mushy dropleys (70% liquid phase). [figure 1]

- an epitaxial columnar microstructure is obtained with molten droplets (85 K superheat). [figure 2] (3)

figure1

figure 2