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.
Active screen plasma nitriding of Al using an iron cage: Characterization and evaluation
Abstract In this research iron nitride coating was deposited on Al substrate using active screen plasma nitriding technique. Samples were plasma nitrided in an iron cage, at 550 °C, gas mixture of N 2 :H 2 % = 3:1 for 2.5, 5 and 7.5 h. The coatings were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Corrosion resistance of samples was investigated using polarization technique. Mechanical properties including nano hardness, wear performance and adhesion strength were also studied. Results showed that the coatings were mainly consist of Fe 2-3 N particles whose size increased by nitriding at longer time periods. Moreover, it was found that at longer coating times such as 7.5 h, the nitrogen atoms diffused into the Al substrate and formed a thin layer of AlN under the Fe 2-3 N coating. Formation of the AlN coating increased the corrosion resistance of the coated sample, but it was still poor compared to uncoated Al. On the contrary, mechanical features of coated Al improved by increasing the nitriding time. Finally, the mechanical characteristics of the deposited coatings were compared to those of conventionally plasma nitrided Al. Despite the higher hardness of the AlN coating, Fe 2-3 N showed superior scratch hardness and wear resistance.
Study of Nitrogen Implanted in Aluminum at Various Doses
Abstract Experimental and theoretical studies are carried out to understand transport of nitrogen in aluminum during implantation process. 60 keV and 120 keV N2 + ion are implanted in pure Al substrates at doses ranging from l×l017 to 9×l017 N-atoms per cm2. RBS and Glancing angle XRD studies are carried out. RBS studies show that the depth profiles are gaussian in nature at low doses and gradually become rectangular in shape as the dose increases. XRD analysis reveals that AlN is formed even at low doses. Theoretical simulations of depth profiles at low dose, include displacement mixing and radiation enhanced diffusion, which are modelled to be described by a diffusion like process. Effective diffusion coefficient in radiation environment is found to be equal to 8×l0−16 cm2.sec−1. At high doses, when new N-atoms are added during implantation their transport gets linked with the already formed AlN. This leads to a rectangular shape of depth profiles observed at high doses.