چكيده به لاتين
In this research, AISI430 steel samples were duplex treated via niobizing followed by plasma nitriding and plasma nitriding followed by niobizing. The first group of specimens were niobized at 850 ºC, 900 ºC, 950 ºC, 1000 ºC for 2h using a pack cementaion method in a mixture of 80 wt% alumina, 5wt% NH4Cl and 15wt% FeNb. Then the specimens were plasma nitirided for 6h at 450 ºC in a gas mixture of 75% N2 and 25% H2. X-ray diffraction pattern shows that FeNb and Fe2Nb phases were formed on the surface of the specimens after niobizing and NbN after duplex treatment. The second group of the specimens were first plasma nitride, using similar condition for treatment, and then niobized at 950 ºC for 2h.duplex treatment caused the formation of NbN,Fe2Nb and NbCr2 phases on the surface of this group samples. Increasing the niobizing temperature from 850 ºC to 950 ºC in first group samples result in decreasing the surface porosity, therefore; 950 ºC was selected as niobizing temperature for second group samples. The properties of coated layer were studied by means of Atomic Force Microscopy (AFM), micro hardness measurement, polarization test and contact angle. Results show that by niobium nitride formation, surface hardness obtained 3.5 times of that of the AISI430 steel in the first group samples, and 674.2 HV in second group samples. Moreover 950 ºC niobized- plasma nitrided samples exhibit corrosion current density values up to 10 times lower than that of the uncoated steel. In addition to contact angle of water increase from 74º on untreated steel to 105º on the fisrt group samples, which demonstrates good hydrophobicity of these samples surface. But it seems that reverse coating has no significant effect on the water contact angle.
