Advanced Plasma Nitriding for Aluminum and Aluminum Alloys
Low hardness and wear resistance of aluminum alloys limit their use in practical application to automotive parts. Formation of hard aluminum nitride (AlN) layer on the surface can prolong the life time of aluminum automotive parts. Plasma nitriding was selected in the present study to form AlN layer on aluminum alloys. This processing is an environmental friendly method because of its low gas and energy consumption. Normal plasma nitriding requires long processing time to successfully form AlN layer. For advancing this surface treatment, refining microstructure and micro-alloying processes are proposed to activate the formation of AlN by plasma nitriding. Bulk Mechanical Alloying is used not only to make grain-size refinement but also to carry out micro alloying with addition of 1 mass%Ti. The formation rate of AlN layer is improved from 4:2 � 10 � 5 mm/s to 20:8 � 10 � 5 mm/s by microstructure refining. In particular, since the co-formed TiN with AlN works as a template in the initial state nitriding, the micro-alloyed aluminum can be nitrided even without pre-sputtering.
Low-temperature plasma-assisted nitriding
Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For this purpose, ion nitriding by a d.c. glow discharge is generally efficient for numerous materials. However, for some metals and alloys, the processing temperature, dominated by the discharge parameters, is too high and cannot be controlled independently from the plasma reactivity. This paper reviews the following solutions for low-temperature plasma-assisted nitriding: pulsed d.c. discharge, thermionically assisted d.c. triode arrangements, plasma implantation, electron cyclotron resonance systems and thermionic arc discharges. We focus on metallurgical results obtained by these techniques on austenitic stainless steel and aluminium.
New trends on nitriding in low pressure arc discharges studied by optical emission spectroscopy
Abstract The purpose of this work is to present the first results obtained by optical emission spectroscopy (OES) in a high current, low voltage and low pressure arc discharge used for steel nitriding. The apparatus is mainly constituted of an ionisation chamber mounted on the top of the nitriding reactor itself. In this process, workpieces are nitrided at floating potential in ArN 2 gas mixtures. OES measurements are done in pure argon for different arc currents and different gas pressures in the reactor. This plasma diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species. In the case of ArN 2 gas mixtures a strong quenching effect of nitrogen on the electron energy distribution function is observed. OES measurements obtained for various nitrogen percentages in ArN 2 gas mixtures are compared to the results obtained by metallurgical analysis of nitrided Armco iron substrates in the same conditions.