The effect of grain size on the surface properties of titanium grade 2 after different treatments

This paper presents findings concerning the influence of the grain size of titanium on its surface properties and on the efficiency of surface treatments. The investigations were performed on titanium grade 2 of two grain sizes. The chemical composition and chemical state of the surface were analyzed by X-ray photoelectron spectroscopy. Different types of surface treatment were applied: plasma nitriding, and a combination of chemical and mechanical modifications using etching with hydrofluoric acid and shot peening. The effect of the grain size on surface treatments was evaluated through roughness quantification, hardness measurements, and observations of the surface and microstructure. The investigations showed that grain size influences the wettability and surface free energy of titanium grade 2. A reduction in grain size is beneficial for the effectiveness of plasma nitriding. The results also indicate that the grain size of titanium grade 2 affects the surface morphology after shot peening and chemical etching with HF acid; these various methods make it possible to modify the surface roughness of titanium over a wide range. The present paper demonstrates that grain size affects the surface properties of titanium grade 2 and can be used as an additional parameter in optimizing the microstructure and properties of surface layers and coatings. •Grain size influences the wettability and SFE of titanium grade 2.•Nanostructure of titanium is stable up to 400°C.•Nanostructure has positive effect on nitride layer formation during plasma nitriding.•Difference in grain size allows to produce the surface with roughness in wide range.