الفهرس 
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Abstract
TiAlN is a ternary nitride system which is industrially important material for a variety of applications particularly that needs severe conditions such as intensive loads, high speeds and harsh applications. This is ascribed to the higher chemical stability of TiAlN which increases the oxidation resistance at high temperature in comparison to binary nitrides like TiN and AlN coatings. The merger of Al into the face centered cubic (fcc) TiN structure on Ti sites lead to form TiAlN super hard phase with superior mechanical and physical properties i.e.; high hardness, high oxidation temperature, and high wear resistance.
Various approaches have been used to prepare TiAlN coatings, such as plasma-enhanced chemical vapor deposition (PECVD), sputtering cathodic arc plasma evaporation, ion beam deposition and metal plasma immersion ion implantation and deposition (MPIIID). However, the PECVD process usually needs a relatively high substrate temperature, which limits its application in precision component. In addition, the coating synthesize by reactive magnetron sputtering usually shows poor adhesion strength. Meanwhile, large amounts of macro-particles in ion plating degrade the surface quality and mechanical properties of the as-deposited coating. Finally, MPIIID works at low substrate temperature, and can obtain high adhesion strength through ion implantation.
MPIIID is a surface modification method that associates excellent bonding strength between film and substrate with a three-dimensional complex-shape. In the MPIIID process, ions are implanted when the high voltage pulses are applied in the substrate (pulse time on) and the deposition occurs between the applied high voltages pulses (pulse time off).
The aim of the present work was planned to synthesize and characterize of pre-implanted surface TiN and TiAlN super hard phase prepared by duplex treatment NPIII and MPIIID respectively.
Nitrogen plasma immersion ion implantation (NPIII) has been used to pre-implant titanium by plasma nitrogen species (TiN) to improve the load bearing capacity of a coating-substrate system (TiAlN-Ti) and to reduce the miss-match between the hard coating (TiAlN) and base material (Ti). The properties of the processed samples were evaluated using optical microscope (OM), X-ray diffraction (XRD), Auger electron spectroscopy (AES), nano-indentation technique, Tafel polarization technique, ball-on-disk tribometer type, surface profilemeter.
This work includes two groups:
1- The first group
This group reports on the pre-implantation of Ti using nitrogen plasma immersion ion implantation (NPIII). NPIII of titanium was performed in a high vacuum chamber equipped with a radio frequency source operating at a frequency of 40.68 MHz and a power of 700 W. Negative high voltage pulses of 20 kV was applied to the samples with pulse width of 5 µs. The implanted dose of nitrogen was calculated to be 5 × 1018 atoms/cm2 and the nitrogen pulse frequency was 1700 Hz.
The results show that, the hardness increased from nearly 2.5 GPa for the un-implanted titanium to 5 GPa for the implanted titanium by NPIII. Moreover, the elastic modules increased from nearly 100 GPa for the un-implanted titanium to 168 GPa for the pre-implanted titanium.
The wear volume loss decreased from nearly 65.8 x105 µm3 for the untreated titanium to 24.7 x105 µm3 for the pre-implanted titanium demonstrating the enrichment of wear resistance for the pre-implanted titanium. The friction coefficient decreases from approximately 0.8 for the un-implanted titanium to nearly 0.3 for the implanted titanium; that represents a factor of more than 2.5 reductions in friction coefficient.
The corrosion current density decreases from nearly 46 µA/cm2 for the untreated titanium to approximately 18 µA/cm2 for the implanted titanium; nearly 3-fold reductions in the corrosion current density. Furthermore, the corrosion potential increases from -306 mv for the untreated titanium to -205 mv for the implanted titanium using NPIII.
The decrease in the corrosion current density and the increase in corrosion potential reflected the amplification in the corrosion resistance for the pre-implanted titanium. The enhancement in the mechanical and chemical properties of Ti is correlated to the formation TiN layer into titanium surface.
2- The second group
This group reports on synthesis and characterization of TiAlN/ TiN prepared by duplex treatment NPIII and MPIIID. Moreover, the effect of nitrogen gas fraction in the plasma-processing atmosphere on the microstructure and mechanical properties of TiAlN has been studied.
The results clarify that, the microhardness of TiAlN coatings increases with increasing the nitrogen gas fraction in the plasma-processing atmosphere to reach a value of nearly 30 GPa at a nitrogen gas fraction of 100%. That represents approximately 6-folds increment in the microhardness of TiAlN coating in comparison with the pre-implanted TiN and 12-folds with pure Ti. The plasticity index and the resistance to plastic deformation of TiAlN coatings increase with increasing the nitrogen gas fraction in the plasma-processing atmosphere. The higher H/E and H3/E2 for TiAlN coatings, the greater resistance to plastic deformation and accordingly the enrichment in the wear resistance.
The wear volume loss of TiAlN coatings decreases by a factor of approximately 103 in comparison with pure Ti and TiN. Moreover, the friction coefficient decreases from nearly 0.8 for the pure titanium to nearly 0.25 for the TiAlN coatings prepared by MPIIID that represents a factor of more than 3-reductions in friction coefficient.
The superior mechanical properties of TiAlN coatings compared to that of Ti and TiN are ascribed to the more random-oriented microstructure, finer grain size, and residual stress due to substitution of Al ions for the Ti site in the TiN crystal lattice. Moreover, the TiN interface acts as barrier to the motion of dislocation in the layers.
As the layer thickness and crystallite size approach nanometer dimension, the dislocation nucleation becomes energetically unfavorable. Both factors make the TiAlN stronger than expected from the rule of mixtures.
Keywords: Ti, TiN, TiAlN, Plasma Immersion Ion implantation (PIII), Metal Plasma Immersion Ion implantation and Deposition (MPIIID), Plasma nitriding, Microhardness, X-ray diffraction, OM, Grain size, Surface morphology, Gas composition, Wear resistance, Friction coefficient, Surface roughness, Strain, Nanoindentation technique, Elastic modulus, Young’s modulus, Elastic deformation, Plastic deformation, plasticity index, resistance to plastic deformation.