Surface nitriding and alloying of steels with Ti and Nb atoms by compression plasma flows treatment

• Surface alloying and nitriding of steels was carried out by compression plasma impact.
• Alloying element concentration depended on the pulses number.
• Ti(C,N) and Nb(C,N) were formed at steel surface due to nitriding and alloying.
• Alloyed layer consisted of intermetallides and α-Fe supersaturated solid solution.
• Compression plasma impact resulted in steels microhardness substantially increase.

Phase and element composition, microhardness of Ti/steel and Nb/steel systems treated by compression plasma flows have been investigated in this work. Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersion X-ray microanalysis and Vickers microhardness measurements were used for sample characterization. The findings showed that treatment of a “coating/steel” system by compression plasma flows generated in nitrogen atmosphere allowed alloying of the surface layer of steel by the coating element and nitriding it simultaneously. The variation of the pulses number (1–6) resulted in change of the alloying element concentration and formation of a number of phases in the alloyed layer: Fe2Ti, a supersaturated solid solution α-Fe(Ti,C) in the Ti alloyed layer and a supersaturated solid solution α-Fe(Nb,C) in the Nb alloyed layer. The formation of Ti(C,N) and Nb(C,N) carbonitrides with fcc crystal structure at the surface was also found. The change of phase composition and quenching effects resulted in substantial increase of microhardness.