No abstract

Ni-Ti coatings were deposited using APS process. In this regard, mechanically activated Ni-Ti powders with amorphous/nanocrystalline structure were used. Two different sieved powders, one of nominal size range of (263 to z20 mm) and the other of nominal size of (2125 to z63 mm), were employed in the experiments. The phase composition and microstructure of the coatings were examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The results indicated that for coating produced using finer powder, increasing plasma power has caused severe cracking of the coatings whereas using the minimum power a coating with better quality can be deposited. In contrast, for coating produced using coarser powder, by selecting the medium power a coating with better quality can be deposited. Based on results of X-ray diffraction, the phase composition of coatings consists of NiTi, Ni 4 Ti 3 , Ni and some oxides.

NiTi alloys were sprayed on AISI 1045 steel substrate using high velocity oxyfuel process. In this regard, amorphous/nanocrystalline NiTi powders were used as feedstock. The phase composition and microstructure of the coatings were examined by X-ray diffraction and scanning electron microscopy. The results indicated that B2-NiTi (austenite phase), Ni 4 Ti 3 , Ni and NiTiO 3 were present in the coatings. In addition, all sprayed coatings showed high microhardness values (.588 HV0?3). Further investigations showed that with the increase in fuel/oxygen ratio, the oxide content increased and porosity level decreased. Hereon, a dense coating with porosity level of 0?8% and oxide content of 5% was obtained as the optimum coating. Polarisation tests were employed to study the corrosion behaviour of the optimum coating in 3?5%NaCl solution. These tests indicated that the corrosion current density of the optimum coating is comparable to that of NiTi alloys reported in the literature.

No abstract

No abstract

NiTi coatings were sprayed on AISI 1045 steel coupons by air plasma spraying. Two types of amorphous/nanocrystalline NiTi powders, one of nominal size range (263 to z20 mm) and the other of nominal size (2125 to z63 mm), were used. Open circuit potential E OC measurements and Tafel polarisation tests were employed to study corrosion behaviour of the coatings in 3?5% NaCl solution at 23uC. These tests indicated that the corrosion performance of the coating produced by using finer powder was better than that of the coating produced by using coarser powder. After 10 h of immersion, the steel substrate had not been corroded in the former case, while it had been corroded in the latter case. In addition, it was shown that corrosion current densities are six times lower in the coating produced by using finer powder than in that sprayed by using coarser powder.

Ni-3Al and Ni-3Ti alloys were deposited on AISI 1045 steel substrate using air plasma spraying process. In this regard, mechanically alloyed feedstock powders were used. Open circuit potential E OCP measurements and Tafel polarisation tests were carried out to study corrosion behaviour of the coatings in 3?5%NaCl solution. These tests indicated that the corrosion performance of the Ni-3Ti coating is better than that of the Ni-3Al coating. The corrosion current densities were three times lower in the Ni-3Ti coating than in Ni-3Al coating. In addition, Ni-3Ti coating showed better passive behaviour than Ni-3Al coating. After 10 h of immersion, the surface of Ni-3Al coating became pitted, and rust spots appeared on the surface. In contrast, there was no rusting and pitting on the surface of Ni-3Ti coating even after 10 h of immersion.

No abstract