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-xCr 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 (Cr₃C₂, Cr₇C₃ and Cr₂₃C₆) 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.