Wettability and spreading behavior of Sn–Cr alloys on SiC.

Knowing of the wetting of filler alloy on substrate is significant for brazing. Here, the isothermal wetting behavior of Sn- x Cr alloys (x = 1, 2, 3, 4 and 5 wt%) on SiC substrates was studied by a modified sessile drop method in the temperature range of 1173 K–1323 K. The interfacial microstructures were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) and its evolution was analyzed thermodynamically. Also, the spreading kinetics is calculated and the formation of precursor film is discussed. The spreading of Sn melt on SiC consists of rapid-spreading and sluggish-spreading stages. A better wettability is obtained at higher Cr concentration and isothermal temperature. The direct reaction between Cr and SiC forming metallics Cr–C compounds (Cr 3 C 2 , Cr 7 C 3 and Cr 23 C 6) at the interface accounts for the improving wettability of Sn melt on SiC. More metallic Cr–C compound occupies a higher proportion of interfacial layer inducing a lower final contact angle. Temperature has a violent influence on the spreading kinetic constant K r. The spreading activity energy is calculated to be 312 kJ/mol. • Cr addition induces a good wetting of Sn–Cr alloy on SiC substrate. • Formation of Cr–C compounds at the interface improves the wettability of Sn–Cr alloys on SiC. • Spreading behavior of Sn–Cr alloy on SiC is controlled by the interface chemical reaction during isothermal wetting. [ABSTRACT FROM AUTHOR]