Papers by Author: Petru Nita

Abstract: Pack cementation procedure implies the use of a powder mixture containing the diffusive elements, which in our case are either Ti or Ti+Al, Al2O3 and NHCl as activator. In the case of titanizing the powder mixture contained 77% in weight Ti, while for alumino-titanizing Al/Ti = 1/5 ratio was employed. NH4Cl content was 3% in weight in all cases. Aluminium additions to the powder mixtures led to a decrease of the process temperature. Activation energy for the aluminizing of austenitic 316L steel is 73.87 KJ/mol, much smaller than for the titanizing, 257.86 KJ/mol. Activation energy for alumino-titanizing, in the same conditions, is 146.01 KJ/mol. All diffusion coatings, in the Ti – 316L and Ti+Al – 316L couples are formed of two layers having different structures and compositions. All couples were investigated by optical microscopy, electron microscopy (SEM and EDX), X-ray diffraction and microhardness trials.

Abstract: Samples of 316L austenitic steel were submitted to a thermochemical treatment which implies surface diffusion of Al and Ti. The technique of pack cementation with NH4Cl as activator was employed. The powder mixture was made of aluminium, titanium, aluminium oxide and ammonium chloride. The same ratio of Al : Ti = 1 : 5 was used in all experiments. The variables were temperature and time. As a function of these parameters, diffusion layers of different thicknesses were obtained. The samples were analyzed by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX), X-ray diffraction and Vickers microhardness trials. All layers were formed by diffusion with reaction and present two zones with different structures and compositions and therefore different properties. The Ti3NiAl2N compound was identified by X-ray diffraction. The presence of this compound in the diffusion coatings increases the superficial hardness of the samples.