Microstructure and property of Fe-Co-B-Si-C-Nb amorphous composite coating fabricated by laser cladding process

Laser cladding of Fe34Co34B20Si5C3Nb4 on a low carbon steel substrate was conducted using coaxial powder feeding method. Microstructure, phase and microhardness were investigated by scanning electronic microscopy, transmission electron microscopy, X-ray diffraction, electron probe micro-analysis and microhardness tester. Amorphous coating with NbC particles embedded in the matrix was formed. Differential scanning calorimetry curve showed that the glass transition temperature (Tg) and the onset crystallization temperature (Tx) were 799 K and 850 K, respectively. The supercooled liquid region (ΔTx = Tx − Tg) was as large as 51 K, which implied the high thermal stability of the supercooled liquid against crystallization. Due to the NbC particles embedded in the amorphous matrix, the mean value of the microhardness of the coating prepared by laser cladding was higher than that of the bulk metallic glass formed by the copper mold casting method. The contribution of NbC particles to the total microhardness was theoretically estimated. The estimated hardness of the composite coating agreed well with the tested value.