The Ti–6Al–4V alloy was treated by inductively coupled rf plasma nitriding. The
effects of plasma-processing time in the range of 5–35 min on the microstructure
and the mechanical properties of the plasma-nitrided Ti–6Al–4V samples
were studied. The plasma power input was adjusted at 450 W and pure
N2
gas was introduced to establish a treatment pressure of
8.0–8.4 × 10−2 mbar. The characteristics of the nitrided layers have been investigated by microhardness
testing, surface roughness measurements, optical microscopy, and x-ray diffraction. The results
show that the surface microhardness increases as the plasma-processing time increases to
reach 2000 HV0.1 at a plasma-processing time of 35 min. A high nitriding rate of
2.81 µm2 s−1
at a plasma-processing time of 25 min was achieved. The formation of the hard phases TiN,
Ti2N, and Ti(N) in the Ti–6Al–4V surfaces are found to be the reason for the increased
microhardness. Surface energy, yield strength and Young’s modulus for the nitrided
Ti–6Al–4V alloy were calculated from the Vickers microhardness data.
Samples of pure titanium were laser nitrided by continuous wave CO2 laser irradiation in mixtures of nitrogen and argon gas with different ratios. In all cases, TiN formed in the surface. The properties and the characteristics of the processed samples were evaluated using a nanoindentation technique, optical microscopy, surface roughness measurements, x-ray diffraction and wear resistance measurements. It was found that the nitrogen content in the gas atmosphere has a massive effect on the microstructure and the mechanical properties of the laser nitrided samples. For all treated samples, the mechanical properties improve with the nitrogen content in the gas atmosphere. Moreover, the thickest TiN layers with high values of the microhardness and good wear resistance were obtained for the titanium sample that was treated in 80% N2 and 20% Ar. In addition, the strain and the grain size of the coatings formed at the surface of the laser nitrided titanium samples were determined from x-ray data.
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