Microstructure and properties of TiC–Fe cermet coatings by reactive flame spraying using asphalt as carbonaceous precursor

Abstract

A kind of agglomerated Ti–Fe–C compound spraying powder was prepared by heating a mixture of ferrotitanium and asphalt to pyrolyze the asphalt as carbonaceous precursor. The carbon by the pyrolysis of the asphalt acts as a reactive constituent as well as a binder in the compound powders. TiC–Fe cermet coatings were prepared by RFS of the compound powder. XRD, SEM, EDS and TEM were employed to analyze the microstructure of the cermet coating. In order to investigate the forming mechanism of the cermet coating, a quenching test was performed. The results show that the Ti–Fe–C compound powder has a very tight structure, which can avoid the problem that reactive constituent particles are separated during spraying. The TiC–Fe cermet coatings presents a typical morphology of thermal spraying coatings with two different laminated layers: the one is the composite layers in which the round fine TiC particles (<500 nm) are dispersed within a Fe matrix, the other is the paragentic layers of TiC and Ti 2O 3. The nucleation mechanism of the TiC in the two layers is homogeneous nucleation and heterogeneous nucleation, respectively. The TiC in the composite layers grows in the dissolution-precipitation mode that the smaller particulates dissolve and larger ones grow. The TiC–Fe cermet coating by RFS shows high hardness and wear resistance property: The surface hardness of the TiC–Fe cermet coating is 65 ± 6(HR30N). In the same fretting conditions, the wear area of Ni60 coating is much more than that of the TiC–Fe cermet coating.