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.
Tribological property of in situ directly nitrided and sintered Al/AlN composite
Abstract An in situ directly nitrided and sintered Al/AlN composite was developed using a chemical reaction between aluminium and nitrogen gas at temperatures below 823 K. It is clear from SEM and TEM observation that the composite has good bonding of the in situ formed AlN to the aluminium matrix. The composite shows an unusually low friction coefficient (0·004–0·008) under oil lubrication, and also has excellent wear resistance and antiseizure properties when compared with hard anodised aluminium alloys. AlN particles protruding from the matrix create oil microgrooves and which work as oil pits to enhance the formability of oil films. Therefore, it is easy to form hydrodynamic lubrication with continuous oil films on a sliding surface.
The Low-Pressure Rf Plasma as a Medium for Nitriding Iron and Steel
This study compares the nitriding efficiency of a low-pressure pure-nitrogen rf plasma for the materials AISI-316 stainless steel, 99.8% iron and the low-alloy steels AISI 4140 and En41B. The process temperature was 400° C; a range of gas pressures and biasing conditions was explored. The treated samples were examined using instrumented microhardness measurements, proton backscattering, X-ray diffraction and other diagnostics. The degree of nitriding is enhanced by increased bombardment by excited neutral molecules. Ion bombardment assists in the nitriding of iron and the low-alloy steels studied, apparently by aiding the production of Fe2-3N. This phase does not form in the nitriding of 316 stainless steel, and therefore treatment of this material is not assisted by ion bombardment. In comparing low-pressure rf plasmas to procedures involving higher pressures and temperatures, the process described here is more appropriate for hardening austenitic stainless steel, but perhaps less appropriate for the other materials.