Effect of nano-CeO2 on microstructure properties of TiC/TiN+TiCN-reinforced composite coating

TiC/TiN+TiCN-reinforced composite coatings were fabricated on Ti–6Al–4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings have been studied by means of X-ray diffraction and scanning electron microscope. X-ray diffraction results indicated that Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial in increasing microhardness and wear resistance of Ti–6Al–6V alloy.     

The effect of nanolayer thickness on the structure and properties of multilayer TiN/MoN coatings

The effect of nanolayer thickness on the structure and properties of nanocomposite multilayer TiN/MoN coatings is revealed. The multilayer (alternating) TiN/MoN coatings are prepared by the Arc-PVD method. The selected thickness of the nanolayers is 2, 10, 20, and 40 nm. The formation of two phases—TiN (fcc) and γ-Mo₂N—is found. The ratio of Ti and Mo concentrations varies with varying layer thickness. The maximum hardness value obtained for different thicknesses of the layers does not exceed 28–31 GPa. The stability of TiN/MoN during cutting and tribological tests is significantly higher than that of products with TiN coatings. The nanostructured multilayer coatings with layer thicknesses of 10 and 20 nm exhibit the lowest friction coefficient of 0.09–0.12.     

Structure,hardness and tribological properties of nanolayered TiN/TaN multilayer coatings

TiN/TaN coatings, consisting of alternating nanoscaled TiN and TaN layers, were deposited using magnetron sputtering technology. The structure, hardness, tribological properties and wear mechanism were assessed using X-ray diffraction, microhardness, ball-on-disc testing and a 3-D surface profiler, respectively. The results showed that the TiN/TaN coatings exhibited a good modulation period and a sharp interface between TiN and TaN layers. In mutilayered TiN/TaN coatings, the TiN layers had a cubic structure, but a hexagonal structure emerged among the TaN layers besides the cubic structure as the modulation period went beyond 8.5 nm. The microhardness was affected by the modulation period and a maximum hardness value of 31.5 GPa appeared at a modulation period of 8.5 nm. The coefficient of friction was high and the wear resistance was improved for TiN/TaN coatings compared with a homogenous TiN coating, the wear mechanism exhibited predominantly ploughing, material transfer and local spallation.     

Effect of nano-CeO2 on microstructure properties of TiC/TiN+nTi(CN) reinforced composite coating

TiC/TiN+TiCN reinforced composite coatings were fabricated on Ti?C6Al?C4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of the crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings were studied by means of X-ray diffraction and scanning electron microscope. The X-ray diffraction results indicated that the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial to increase the microhardness and wear resistance of Ti?C6Al?C6V alloy.     

Ion beam nitriding of high purity iron surfaces

Ion beam nitriding of iron by N₂⁺ ions of medium energy (1–10 keV) was investigated. This nitriding technique leads to the formation of layer structures quite similar to those obtained by other methods but compared with these the nitride layers obtained are pore free. Results consisting of the surface topography of the samples, the stages of nitride coverage, the formation of different nitrides and their precipitation depth as well as microhardness and electrochemical corrosive behaviour are presented and discussed.     

In situ synthesis of TiN/Ti3Al intermetallic matrix composite coatings on Ti6Al4V alloy

The aim of this paper was to develop an in situ method to synthesize the TiN reinforced Ti₃Al intermetallic matrix composite (IMC) coatings on Ti6Al4V alloy. The method was divided into two steps, namely depositing pure Al coating on Ti6Al4V substrate by using plasma spraying, and laser nitriding of Al coating in nitrogen atmosphere. The microstructure and mechanical properties of TiN/Ti₃Al IMC coatings synthesized at different laser scanning speeds (LSSs) in laser nitriding were investigated. Results showed that the crack- and pore-free IMC coatings can be made through the proposed method. However, the morphologies of TiN dendrites and mechanical properties of coatings were strongly dependent on LSS used in nitriding. With decreasing the LSS, the amount and density of TiN phase in the coating increased, leading to the increment of microhardness and elastic modulus and the decrement of fracture toughness of coating. When the LSS was extremely high (i.e., 600 mm/min), only a thin TiN/Ti₃Al layer with thickness around of 100 μm was formed near the coating surface.     

Influence of the high-temperature annealing on the structure and mechanical properties of vacuum–arc coatings from Mo/(Ti + 6 wt % Si)N

Scanning electron microscopy with energy dispersive element microanalysis, X-ray structural analysis, and microindentation were used to study the effect of the deposition conditions in a reactive nitrogen atmosphere on the growth morphology, phase composition, structure, and microhardness of vacuum–arc multilayer coatings produced by the evaporation of cathodes from Mo and (Ti + 6 wt % Si) both after their deposition and after high-temperature annealing. It has been established that the use of the composite cathode of Ti and Si allows the formation of the structure state inclined to ordering to form a two-phase compound from TiN and Ti₅Si₃ at high-temperature annealing. In this case the coating hardness increases to a value higher than 45 GPa.     

Saddle field fast atom beam source: A new low pressure plasma nitriding method for a alloy Ti-6Al-4V

Ti and its alloys (Ti-6Al-4V) have been used in different engineering applications due to their several outstanding properties. Nevertheless, their use in practical applications is limited in many cases due to their poor tribological property. Researches are ongoing on surface modification of Ti based materials by different plasma and ion based techniques to overcome this problem. However, the conventional plasma nitriding techniques have several problems such as formation of an arc, increased possibility of surface contamination due to a comparatively higher operating pressure, production of a very thin nitrided layer after a long processing time, etc. In this present work, the possibility of a new low-pressure plasma nitriding process using a Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source on a Ti-6Al-4V alloy sample is investigated. Plasma nitriding was carried out at 900 °C and at a pressure 0.1 Pa for 8 h by using a beam current 0.5 A. Optical Microscopy investigation of the cross-section of the nitrided sample revealed a compound nitrided layer (thickness approximately 16 μm) followed by a diffusion layer. X-Ray Diffraction (XRD) analysis confirmed the presence of a TiN phase in the nitrided layers. A roughly three fold higher hardness value (1578 HV_0.015) in the top nitriding layer was observed by Vickers microhardness testing compared to hardness value of untreated sample (568 HV_0.015),with a gradually decreasing hardness in the core material. The results show that this is a promising method for low pressure plasma nitriding of Ti alloy within a short processing time compared to the conventional nitriding process.     

Corrosion resistance of composite TiN-TiC layers deposited on tool steels by different techniques

TiC layers were formed by the low-pressure chemical vapour deposition (LPCVD) technique on tool carbon steel (0.9 wt% C;0.4 wt%Si;0.5 wt% Mn), bare or nitrided by glow discharge with formation of zones consisting of ( + ) and () phases. The composite TiN-TiC layers were formed by the deposition of TiN on the coated TiC layers, by a pressure-assisted chemical vapour deposition (PACVD) technique or by TiC sputtering in nitrogen under glow discharge conditions. The electrochemical behaviour of the metal/coating has been established by potentiodynamic tests done in acid (20% H₃PO₄) and alkaline (0.1 n NaOH) solutions. The deposited layers protect the steel by decreasing the steel area exposed to the aggressive solution and by promoting steel passivation. The protective ability of composite TiN/TiC layers is higher than that of corresponding single layers. Improvement of the protective ability of LPCVD TiC layers is achieved by the deposition conditions, providing the formation of fine grains 111 texture. The electrochemical behaviour of steel coated with complex TiN/TiC layers approaches the intrinsic electrochemical behaviour of TiN.     

Limitation of Ti/TiN diffusion barrier layers in silicon technology

The usefulness of Ti/TiN and TiSi₂/TiN bilayers as low resistive contacts and diffusion barriers between doped silicon and aluminium has been examined. The Ti layer was magnetron sputtered and the TiN layers were deposited by reactive magnetron sputtering in an argon/nitrogen mixture. After Ti/TiN deposition part of the samples were annealed in a vacuum furnace to form a TiSi₂/TiN structure. The films were characterized by Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD) and resistivity measurements. The integrity of the final metallization systems, with aluminium as top level, for annealing temperatures in the range 400–600°C was evaluated by RBS and electrical measurements on fully processed test vehicles containing structures for contact resistivity measurements and shallow implanted gated diodes. A significant discrepancy has been observed between recorded RBS data and electrical measurements. No reaction was detected by RBS at temperatures below 525°C although a significant degradation of the electrical performance was readily observed at lower annealing temperatures, e.g. an increase in contact resistance and large reverse leakage currents. It is concluded that RBS, commonly used in the study of diffusion barrier properties, gives optimistic information on the upper limit of the metallurgical stability of the barrier layers, whereas other factors such as step coverage, compositional variation and mechanical stress are of predominant significance when actual device metallization is concerned.     

The effect of different methods to add nitrogen to titanium alloys on the properties of titanium nitride clad layers

In this investigation, titanium nitride (TiN) reinforcements are synthesized in situ on the surface of Ti–6Al–4V substrates with gas tungsten arc welding (GTAW) process by different methods to add nitrogen, nitrogen gas or TiN powder, to titanium alloys. The results showed that if nitrogen gas was added to titanium alloys, the TiN phase would be formed. But if TiN powder was added to titanium alloys, TiN + TiN_x dual phases would be presented. The results of the dry sliding wear test revealed that the wear performance of the Ti–6Al–4V alloy specimen coated with TiN or TiN + TiN_x clad layers were much better than that of the pure Ti–6Al–4V alloy specimen. Furthermore, the evolution of the microstructure during cooling was elucidated and the relationship among the wear behavior of the clad layer, microstructures, and microhardness was determined.     

The microstructure and mechanical properties of TaN/TiN and TaWN/TiN superlattice films

The microstructure and the microhardness of the TaN/TiN and TaWN/TiN superlattice films have been studied with X-ray diffraction, transmission electron microscopy and microhardness tester. The results showed that both TaN/TiN and TaWN/TiN superlattice films have a cubic crystal structure with an epitaxially grown mode of polycrystallinity. Lattice constants of superlattice films are between those of the constituent materials. The superhardness effect was found in TaN/TiN and TaWN/TiN superlattice films and the maximum hardness value was 40.0 GPa at a modulation period of 9.0 nm for TaN/TiN, and 50.0 GPa at a modulation period of 5.6 nm for TaWN/TiN. It is proposed that the lattice mismatch affects the microhardness value and the peak position of maximum hardness. The inhibition of dislocation motion by alternating stress fields of interfacial coherent strains is believed responsible for hardness anomalies.     

Increasing the wear resistance of the T15K6 hard alloy by boriding and complex saturation with boron and copper

The formation of complex diffusion boride layers on the T15K6 hard alloy using the powder method has been studied. The phase and chemical compositions, thickness, and microhardness of the layers produced on the hard alloy have been defined. It has been found that the diffusion layers, produced in a borating medium with an addition of copper-containing compounds, which act as the copper source, consist of the TiB, CoB, WC, and Cu phases. The boriding makes it possible to form boride phases in a surface zone of the hard alloy with a microhardness up to 33 GPa, and complex saturation with boron and copper to 25 GPa as compared with the basic material (13.5 GPa) and thus, the wear resistance of the T15K6 hard alloy is increased by a factor of 2.0–2.2.     

Cathodic cage plasma nitriding (CCPN) of austenitic stainless steel (AISI 316): Influence of the different ratios of the (N2/H2) on the nitrided layers properties

In this study, we assess how the ratio (N₂/H₂) - working atmosphere gas mixture - influences the properties of the layers produced on austenitic stainless steel surface by Cathodic Cage Plasma Nitriding (CCPN). The nitriding atmospheres contained nitrogen and hydrogen in three proportions: 20% N₂ + 80% H₂, 50% N₂ + 50% H₂, and 80% N₂ + 20% H₂ delivered at a flow rate of 20 sccm. The effect of 100% N₂ was also examined. The morphology, microstructure and electrochemical properties of the layer produced were studied. The samples characteristics were determined by optical microscopy, x-ray diffraction, microhardness test and electrochemical potential curves.     

Nanocrystalline matrix TiC–Al3Ti and TiC–Al3Ti–Al composites produced by reactive hot-pressing of milled powders

Mechanically alloyed nanocrystalline TiC powder was short-term milled with 40 vol.% of Al powder. The powders mixture was consolidated at 1200 °C under the pressure of 4.8 GPa for 15 s and at 1000 °C under the pressure of 7.7 GPa for 180 s. The bulk materials were characterised by X-ray diffraction, light and scanning electron microscopy, energy dispersive spectroscopy, hardness, density and open porosity measurements. During the consolidation a reaction between TiC and Al occurred, yielding an Al₃Ti intermetallic. The microstructure of the produced composites consists of TiC areas surrounded by lamellae-like regions of Al₃Ti intermetallic (after consolidation at 1200 °C) or Al₃Ti and Al (after consolidation at 1000 °C). The mean crystallite size of TiC is 38 nm. The hardness of the TiC–Al₃Ti and TiC–Al₃Ti–Al composites is 13.28 GPa (1354 HV1) and 10.22 GPa (1041 HV1) respectively. The produced composites possess relatively high hardness and low density. The results obtained confirmed satisfactory quality of the consolidation with keeping a nanocrystalline structure of TiC.     

Author index

Films of TiC, TiN and their composite were prepared on molybdenum by a reactive sputtering method with CH₄ and N₂ as the reactive gases and argon as the sputtering gas and applying bias potentials to the substrate material.The films were characterized by X-ray photoelectron spectroscopy and Auger electron spectroscopy. The quantitative chemical composition of the TiC and TiN coatings was determined as a function of the partial pressures of CH₄ (P_CH4) and N₂ (P_N2) during the reactive sputtering. For the TiC coating the most suitable P_CH4 range which gives the stoichiometric composition (carbon-to-titanium ratio, 0.8–1.0) without impurities was found to be (2–5) × 10^?4 Torr (substrate temperature, 300 °C; bias potential, ? 300 V). For the TiN coating the structure and composition of the films prepared by reactive sputtering were observed to depend greatly on the condition of applying the bias potential. The suitable P_N2 range which gives golden films of the stoichiometric composition was higher than 1 × 10^?4 Torr (substrate temperature, 200–300 °C; bias potential from ?75 to ?200 V).On the basis of these experimental studies of TiC and TiN coatings successive coatings of TiC and TiN were deposited onto a molybdenum substrate to achieve higher thermal stability and better adhesion to the substrate. The successive coating method is a promising technique for use in fusion reactors.     

TiN/TiC multilayer films deposited by pulse biased arc ion plating

TiN/TiC multilayer films were deposited on high-speed-steel (HSS) substrates using pulse biased arc ion plating. For comparison, TiN and TiC films were also deposited. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Auger electron spectroscopy (AES) were applied to investigate the modulation period thickness, microstructure and content depth distribution of the films, respectively. And microhardness and film/substrate adhesion were also analyzed using knoop tester and scratching method. The results showed that the multilayer films with different modulation period of 40-240 nm exhibit a modulation structure and the interface width is about 20∼30 nm. Microhardness of the multilayer films were not obviously improved compared to that of TiN and TiC film, and the reason was analyzed. In comparison to TiN film, film/substrate adhesion values of the multilayer films were deteriorated with the increasing of modulation period due to the brittle characteristics of TiC film.     

Characterization of Plasma Nitrided and PVD-TiN Duplex Treated Armco Iron and En40B Steel by Nanoindentation

The nanoindentation test has been applied to evaluate the mechanical properties such as hardness, elastic moduli and deformation behaviors of Fe₄N iron nitride layers produced on Armco iron and En40B steel by plasma nitriding, and PVD-TiN coatings deposited on En40B with or without prior plasma nitriding treatment. Results showed that the Fe₄N layer produced on En40B exhibits higher hardness than that on Armco iron. This is attributed to the effect of the alloy compositions, especially Cr element. However, similar elastic modulus values to that of bulk ferrous alloys have been found for Fe₄N layers produced on both Armco iron and En40B. Under lower loads, TiN coatings on nitrided substrate behave quite the same in hardness and elastic modulus as TiN coatings on untreated En40B. Whilst with increasing indentation load and depth, duplex treated (i.e., combined plasma nitriding and PVD-TiN coating) En40B possesses higher composite hardness, elastic modulus and load bearing capacity than TiN coated base material.     

Influence of substrate temperature on the materials properties of reactive DC magnetron sputtered Ti/TiN multilayered thin films

Ti/TiN multilayers were deposited by DC reactive magnetron sputtering method using a titanium target and an Ar-N₂ mixture discharge gas. XRD technique was employed to study the structure of the coatings and to observe the variations of structural parameters with substrate temperatures. An increase in grain size with increase of substrate temperature was observed. The components of Ti 2p doublet, related to TiN, TiON and TiO₂, were observed in the core-level spectra of the deposited multilayer films from XPS analysis. A microhardness value of 25.5 GPa was observed for Ti/TiN multilayers prepared at 400 °C. Electrical properties were found to depend on substrate temperature.     

金属钛激光气体氮化层组织及表面特征

采用连续波Nd-YAG激光在氮气环境中对金属钛进行激光气体氮化处理.利用SEM,XRD,XPS研究氮化层的显微组织、表面成分、结构.结果表明:通过激光气体氮化可以在金属钛表面得到表面相对平滑、无裂纹的氮化层;氮化层与基体材料之间为冶金结合.氮化层主要由枝晶状TiN组成,同时有TiNxOy,TiO2及TiC存在,外表面有C,O污染或吸附;TiN枝晶密度由表面沿深度方向下降.