Wear-resistant Ti-Al-Si-C-N coatings produced by magnetron sputtering of SHS targets

The results of an investigation into hard wear-resistant nanostructured coatings in the Ti-Al-Si-C-N system produced by the magnetron sputtering of multicomponent composite targets with various ratios of metallic and nonmetallic elements are presented. Coatings are deposited in the reaction gas mixture with constant values of the substrate temperature and bias voltage. The structure of coatings is investigated using X-ray diffraction, glow-discharge optical emission spectroscopy, scanning and transmission electron microscopy. The mechanical and tribological properties are determined using the nanoindentation and scratch-testing methods, as well as using tribological tests according to the “pin-on-disc” scheme. The results of investigations show that the coatings are based on the fcc phase consisted of titanium carbonitride with an average crystallite size of 2–20 nm; the crystallites are arranged in an amorphous matrix. The coatings of optimal composition possess hardness of 40–50 GPa, a stable friction coefficient of <0.55, an adhesion strength of ≥50 N, and a wear rate of <1 × 10^?5 mm³/(N m).     

Formation of ZrO<Subscript>2</Subscript>–SiC Composite Coating on Zirconium by Plasma Electrolytic Oxidation in Different Electrolyte Systems Comprising of SiC Nanoparticles

Plasma electrolytic oxidation (PEO) coupled with electrophoretic deposition (EPD) was used to fabricate ZrO₂/SiC composite coating on the zirconium metal. The PEO–EPD process was carried out in three different electrolyte systems consisting of 5 g/l sodium aluminate or trisodium orthophosphate or sodium metasilicate with 4 g/l SiC nanoparticles. The X-ray diffraction results indicate monoclinic zirconia is the major phase in phosphate and silicate electrolyte while the coating produced in aluminate electrolyte is composed of tetragonal zirconia. The potentiodynamic polarization studies (PDP) indicate that composite coating produced in phosphate?+?SiC nanoparticle containing electrolyte exhibit superior resistance to corrosion, which can be attributed to the pore-free morphology of the coating. All the PEO–EPD coatings show exceptionally good adhesion strength (L_c ?> 40 N). The coating fabricated in phosphate?+?SiC nanoparticles is found to be the best coating because of its superior resistance to corrosion and reasonably good adhesion strength.     

Preparation and Characterization of Plasma Electrolytic Oxidation Coating on 5005 Aluminum Alloy with Red Mud as an Electrolyte Additive

A coating with red mud as an electrolyte additive was applied to 5005 aluminum alloy using plasma electrolytic oxidation (PEO). The phase composition of the coating was investigated using X-ray diffraction. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS) was used to determine the microstructure and composition profiles of the coating. The coating/substrate adhesion was determined by scratch testing. The corrosion behaviors of the substrate and coating were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results indicated that the PEO coating with red mud consisted mainly of α-Al₂O₃ and γ-Al₂O₃, with small amounts of Fe₂O₃, CaCO₃, and CaTiO₃. The surface of the coating was the color of the red mud. The coating had a uniform thickness of about 80 μm and consisted of two main layers: a 6-μm porous outer layer and a 74-μm dense inner layer, which showed typical metallurgical adhesion (coating/substrate adhesion strength of 59 N). The coating hardness was about 1142 HV, much higher than that of the substrate (60 HV). The corrosion potential E _corr and corrosion current density i _corr of the coating were estimated to be ?0.743 V and 3.85 × 10^?6 A cm^?2 from the PDP curve in 3.5 wt pct NaCl solution, and the maximum impedance and phase angle of the coating were 11 000 Ω and ?67 deg, respectively, based on EIS. PEO coating with red mud improved the surface properties and corrosion resistance of 5005 aluminum alloy. This study also shows a potential method for reusing red mud.     

Thick Low-Friction nc-MeC/a-C Nanocomposite Coatings on Ti-6Al-4V Alloy: Microstructure and Tribological Properties in Sliding Contact with a Ball

In this paper, we show that duplex surface treatment, combining oxygen diffusion hardening with the subsequent deposition of thick, low-friction nanocomposite nc-MeC/a-C coatings to improve the tribological properties of the Ti-6Al-4V alloy. We have synthesized, in a magnetron sputtering process, the nanocomposite nc-MeC/a-C coatings (where Me denotes W or Ti transition metal) consisting of two dissimilar materials (nanocrystallites of transition metal carbides MeC and an amorphous carbon matrix a-C). The nano and microstructure of the substrate material and coatings were examined with the use of scanning and transmission electron microscopy as well as by X-ray diffractometry. It was found that different carbide nanocrystals of the same transition metal were embedded in an amorphous carbon matrix of both coatings. The HRTEM analysis indicated that the volume fraction of tungsten carbides in the nc-WC/a-C coating was equal to 13 pct, whereas in the nc-TiC/a-C one the volume fraction of the titanium carbides was equal to just 3 pct. The tribological properties, hardness, and scratch resistance of the coatings were investigated as well. The coefficient of friction (COF) of the coatings during dry sliding against 6 mm diameter alumina ball reached very low value, 0.05, in comparison with an oxygen-hardened alloy, whose COF was equal to 0.8. This low-friction effect of the coatings has been attributed to the formation of a self-lubricating film in sliding contact. The coatings exhibited similar failure morphology in the scratch tests. Even though the hardness was rather low, the coatings exhibited a very good wear resistance during sliding friction. The wear rate of the nc-WC/a-C coating was equal to 0.08 × 10^?6 mm³ N^?1 m^?1 and for the nc-TiC/a-C one it was 0.28 × 10^?6 mm³ N^?1 m^?1.     

The Effect of Substrate Position during Cylindrical DC Magnetron Sputtering on Physical Properties of Fe7Co3 Thin Film

The high saturation induction makes Fe_1?x Co _x thin films desirable for use as recording head materials. In this experiment, Fe₇Co₃ thin films were deposited by DC cylindrical magnetron sputtering using the different position of glass substrate in argon pressure of 2 × 10^?2 Torr under sputtering power of 120 W. The magnetic properties were determined by scanning probe microscopy. The surface morphology and r.m.s roughness of thin films were analyzed using atomic force microscopy and the optical properties have been analyzed by spectrophotometer. The thin film thickness, grain size and optical properties were affected by changing substrate position and we found the deposition influenced magnetic properties and surface morphology.     

Properties of nanostructured TiN-Ni ceramic-metal coatings obtained by ion-plasma vacuum-arc method

Physicomechanical and tribological properties of TiN-Ni ceramic-metal coatings prepared by ion-plasma vacuum-arc deposition are investigated. It is established that the hardness (H) increases from 23 to 54 GPa with the Ni content from 0 to 12 at %, which is determined by the influence of the nanostructured nitride component of coatings. Coefficients HE ^?1 and H ³ E ^?2, which characterize the material resistance against the elastic and plastic failure deformation, reach 0.104 and 0.567 GPa, respectively. The further increase in the nickel concentration in coatings to 26 at % leads to a decrease in H to 23–25 GPa, which is associated with the influence of the increasing amount of soft plastic metal and the formation of noticeable porosity in the bulk of coatings. The friction coefficient of studied coatings is 0.45, against 0.58 (for the TiN coating) and 0.72 (for the hard-alloy base). The cohesion failure mechanism of TiN-Ni nanostructured coatings (C _Ni = 2.8–12 at %) is established, and critical loads which characterize the appearance of the first crack (13.5–14.2 N) and the local coating attrition up to the substrate (61.9–64.4 N) are determined. The complete attrition of coatings does not occur up to a load of 90 N, which points to their high adhesion strength. The developed nanostructured ceramic-metal coatings are characterized by high heat resistance up to 800°C.     

Tensile Mechanical Behaviors of In Situ Metallic Glass Matrix Composites at Ambient Temperature and in Supercooled Liquid Region

In this study, new Ti-based metallic glass matrix composites (MGMCs) are fabricated, which contains ~41 vol pct of large dendrites with a size of ~0.8 to 1.2 μm, The newly developed Ti-based MGMCs exhibit excellent tensile strength of ~1650 MPa and a tensile strain of ~2.5 pct at room temperature. During tensile deformation, the work hardening is scarcely found in this alloy. Thus, the deformation of the in situ MGMC is simply described with two stages: (1) elastic and (2) softening deformation stages. Two simple models are adapted to simulate each stage. In the supercooled liquid region [at 613 K (340 °C)], superplastic homogeneous deformation, which is the feature of monolithic bulk metallic glasses, is not observed. The mechanical properties at 613 K (340 °C) are sensitive to the strain rates, the yield strength drops from 1390 to 960 MPa, when the strain rate decreases from 1 × 10^?2 to 1 × 10^?3/s, while the displacement is almost increased by twofold.     

In-Situ Time-of-Flight Neutron Diffraction Study of High-Temperature α-to-β Phase Transition in Elemental Scandium

Lattice parameters for both hcp α-Sc and bcc β-Sc were determined between 1200 °C and 1400 °C from time-of-flight (TOF) neutron diffraction data collected from an elemental Sc sample vacuum sealed inside a niobium crucible. On heating, the high-temperature β-Sc phase first appeared between 1340 °C and 1350 °C, close to the reported transition temperature of 1337 °C. The lattice constants of hcp α-Sc were found to vary between a = 3.3522(4) Å, c = 5.3807(7) Å at 1200 °C and a = 3.3579(6) Å, c = 5.398(1) Å at 1340 °C. The lattice constants of bcc β-Sc were found to vary between a = 3.752(2) Å at 1350 °C and a = 3.7572(8) Å at 1400 °C. The average thermal expansion coefficient for the bcc β-Sc phase was 1.61 × 10^?5 °C^?1 over the temperature range 1360 °C to 1400 °C. The average thermal expansion coefficient along the a-axis of hcp α-Sc between 1200 °C and 1340 °C was 1.46 × 10^?5 °C^?1. The average thermal expansion coefficient along the c-axis of hcp α-Sc between 1200 °C and 1340 °C was 2.22 × 10^?5 °C^?1.     

Voltammetric determination of venlafaxine as an antidepressant drug employing Gd2O3 nanoparticles graphite screen printed electrode

Graphite screen printed electrode modified with Gd_2 O_3 nanoparticles(Gd_2 O_3/SPE) was developed for the determination of venlafaxine(VF). The Gd_2 O_3 nanoparticles were thoroughly characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analyses. To study the electrochemical behaviour of venlafaxine cyclic voltammetry(CV), chronoamperometry(CHA)and differential pulse voltammetry(DPV) were employed. These studies reveal that the oxidation of venlafaxine is facilitated at Gd_2 O_3/SPE. After optimization of analytical conditions, analysis of venlafaxine using the modified electrode in 0.1 mol/L PBS(pH 7.0) demonstrates that the peak currents corresponding to venlafaxine vary linearly with its concentration in the range of 5.0 ×10~(-6)-9.0 × 10~(-4) mol/L. The detection limit(S/N = 3) of 2.1 × 10~(-7) mol/L is obtained for venlafaxine using DPV. The prepared modified electrode benefits from advantages such as simple preparation method, high sensitivity and low detection limit.Moreover, the evaluation of practical applicability of this proposed method is successful in the identification of venlafaxine in pharmaceutical formulations, urine and water samples.     

Study on the Formation and Characterization of the Intermetallics in Friction Stir Welding of Aluminum Alloy to Coated Steel Sheet Lap Joint

Multimaterial fabrication such as joining of steel and aluminum is currently prominent in a variety of industries. Friction stir welding is a novel solid-state welding process that causes good joint strength between steel and aluminum. However, the phenomenon contributing significant strength at the interface is not yet clear. In the present study, the interface of the friction stir lap-welded aluminum and coated steel sheet having joint strength maximum (71.4 pct of steel base metal) and minimum, respectively, under two parameter combinations, i.e., 1000 rpm 50 mm min^?1 and 500 rpm 100 mm min^?1, was exclusively characterized by X-ray diffraction, transmission electron microscopy (TEM), concentration profile, and elemental mapping by electron-probe microanalysis. A TEM-assisted EDS study identifies the morphologies of large size Al₁₃Fe₄ and small size Fe₃Al-type intermetallic compounds at the interface. The diffusion-induced intermetallic growth (thickness) measured from a backscattered image and concentration profile agreed well with the numerically calculated one. The growth of these two phases at 1000 rpm 50 mm min^?1 is attributed to the slower cooling rate (~3.5 K/s) with higher diffusion time (44 seconds) along the interface in comparison to the same for 500 rpm 100 mm min^?1 with faster cooling rate (~10 K/s) and less diffusion time (13.6 seconds). The formation of thermodynamically stable and hard intermetallic phase Al₁₃Fe₄ at 1000 rpm and travel speed 50 mm min^?1 in amounts higher than 500 rpm and a travel speed of 100 mm min^?1 results in better joint strength, i.e., 71.4 pct, of the steel base metal.     

Effect of Internal Interfaces on Hardness and Thermal Stability of Nanocrystalline Ti<Subscript>0.5</Subscript>Al<Subscript>0.5</Subscript>N Coatings

The effect of microstructure on the thermal stability and hardness of the cathodic arc evaporated Ti_0.5Al_0.5N coatings was investigated with the aid of the in-situ high-temperature X-ray diffraction experiments, which were accompanied by high-resolution transmission electron microscopy (HRTEM) and nanoindentation measurements. The microstructure of the coatings was modified through the choice of the bias voltage in the deposition process. It was found that the bias voltage affects strongly the uniformity of the local distribution of titanium and aluminum in the coatings. The nonuniform distribution of the elements contributes to the formation of lattice strains at the crystallite and phase boundaries. The lattice strains at the crystallite boundaries increase the hardness of the coatings; the lattice strains at the phase boundaries improve their thermal stability. A certain nonuniformity of the distribution of the metallic species in the coatings is regarded as advantageous. However, a great nonuniformity in the distribution of the metallic species accelerates the degradation of the coatings at high temperatures. As a measure for the nonuniformity of the distribution of the atomic species in the as-deposited (Ti, Al) N samples, the stress-free lattice parameter of fcc-(Ti, Al) N is suggested.     

Microstructural Characterization and Properties Evaluation of Ni-Based Hardfaced Coating on AISI 304 Stainless Steel by High Velocity Oxyfuel Coating Technique

The present study concerns a detailed investigation of microstructural evolution of nickel based hardfaced coating on AISI 304 stainless steel by high velocity oxy-fuel (HVOF) deposition technique. The work has also been extended to study the effect of coating on microhardness, wear resistance and corrosion resistance of the surface. Deposition has been conducted on sand blasted AISI 304 stainless steel by HVOF spraying technique using nickel (Ni)-based alloy [Ni: 68.4 wt pct, chromium (Cr): 17 wt pct, boron (B): 3.9 wt pct, silicon (Si): 4.9 wt pct and iron (Fe): 5.8 wt pct] of particle size 45 to 60 ??m as precursor powder. Under the optimum process parameters, deposition leads to development of nano-borides (of chromium, Cr₂B and nickel, Ni₃B) dispersion in metastable and partly amorphous gamma nickel (??-Ni) matrix. The microhardness of the coating was significantly enhanced to 935 VHN as compared to 215 VHN of as-received substrate due to dispersion of nano-borides in grain refined and partly amorphous nickel matrix. Wear resistance property under fretting wear condition against WC indenter was improved in as-deposited layer (wear rate of 4.65 × 10^?7 mm³/mm) as compared to as-received substrate (wear rate of 20.81 × 10^?7 mm³/mm). The corrosion resistance property in a 3.56 wt pct NaCl solution was also improved.     

Alkaline Electrodeposition of Ni–ZnO Nanocomposite Coatings: Effects of Pulse Electroplating Parameters

The effects of applied current density (1–10 A/dm²), pulse frequency (1–100 Hz) and duty cycle (10–75 %) on the morphology and microhardness of Ni and Ni–ZnO coatings, incorporation rate of ZnO nanoparticles, current efficiency and deposition rate were investigated. Ni–ZnO composites exhibited a nodular morphology. At low current densities, smooth and compact Ni–ZnO coatings were obtained. As the current density increased more gaps and defects appeared on the coatings surface. Maximum incorporation rate of 4.04 vol% was achieved at the current density of 10 A/dm². Presence of ZnO nanoparticles in the electrolyte improved the current efficiency of the process and deposition rate of the matrix. The microhardness values of the composites were considerably higher than those of the nickel coatings.     

Development of a hybrid process of obtaining wear-resistant coatings based on ion-plasma arc sputtering and magnetron sputtering

This work is devoted to the development of a new hybrid method of deposition of coatings based on ion-plasma arc sputtering and magnetron sputtering. The objects of investigation were samples of coatings of the Ti-Al-N system on the VK-6 hard-alloy plates obtained by three different methods, namely, ion-plasma sputtering, magnetron sputtering, and hybrid sputtering. Deposition processes were performed under the rarefaction of 1.3 × 10^?3 Pa at a substrate temperature of 550–600°C. A VT-5 alloy of the composition Ti-Al (6 at %) was used as the sputtered material. The phase and elemental compositions of the coatings, their mechanical properties (microhardness and the Young modulus), and adhesion strength were studied. All samples were tested under the conditions of continuous cutting. The results of investigations showed that the coating obtained by the hybrid method possesses a complex of positive properties of the ion-plasma and magnetron coatings, specifically, a high adhesion strength along with the uniformity of the composition and structure, which explains its increased durability.     

Analysis of Tensile Stress-Strain and Work-Hardening Behavior in 9Cr-1Mo Ferritic Steel

Detailed analysis on tensile true stress (??)-true plastic strain (??) and work-hardening behavior of 9Cr-1Mo steel have been performed in the framework of the Voce relationship and Kocks-Mecking approach for wide range of temperatures, 300 K to 873 K (27 °C to 600 °C) and strain rates (6.33 × 10^?5 to 6.33 × 10^?3 s^?1). At all test conditions, ??-?? data were adequately described by the Voce equation. 9Cr-1Mo steel exhibited two-stage work-hardening behavior characterized by a rapid decrease in instantaneous work-hardening rate (?? = d??/d??) with stress at low stresses (transient stage) followed by a gradual decrease in ?? at high stresses (stage III). The variations of work-hardening parameters and ??-?? as a function of temperature and strain rate exhibited three distinct temperature regimes. Both work-hardening parameters and ??-?? displayed signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. Excellent correlations have been obtained between work-hardening parameters evaluated using the Voce relationship and the respective tensile properties. A comparison of work-hardening parameters obtained using the Voce equation and Kocks-Mecking approach suggested an analogy between the two for the steel.     

An Electrochemical Investigation of Fe(II) Dissolved in a Cryolite Melt

Chronopotentiometric studies were made on a cryolite melt containing 3.0 wt pct Al₂O₃ and 0.466 wt pct Fe(II) at 1293 K (1020 °C). The diffusion coefficient calculated from the time of the principal chronopotentiometric transition decreased as the current density was increased, and at the same time, a second subsequent transition appeared. The diffusion coefficient calculated from this second transition was constant at 5.44 × 10^?5 cm² s^?1. The results were interpreted to show that Fe(II) in the solution exists in two forms. Fe is deposited reversibly from an active form; its exchange current density must be >1 A cm^?2. Deposition from the other form is irreversible, and it occurs directly only at high overpotentials, leading to the second transition. The equilibrium constant [active]/[inactive] = 5.4. When the equilibrium is displaced by electrolysis of the active form, the inactive form decomposes to replenish it with a rate constant of 0.9 s^?1. The Tafel curve for the direct deposition of the inactive form shows a slope of 113 mV/decade, which is interpreted as n = 2 and a symmetry factor ≈1. The exchange current density is approximately 0.3 μA cm^?2. The active and inactive forms are identified tentatively as FeF ₃ ^? and FeF ₅ ^3? , respectively.     

Production and Characterization of PANI/TiO2 Nanocomposites: Anticorrosive Application on 316LN SS

Conductive polyaniline/titanium dioxide (PANI/TiO₂) nanocomposites with different weight ratios were synthesized using in situ chemical oxidative polymerization. PANI/TiO₂ was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis and electrical conductivity. Room temperature conductivities of PANI, PANI/TiO₂ (I), PANI/TiO₂ (II), and PANI/TiO₂ (III) are 9.77 × 10^?4, 1.89 × 10^?5, 2.01 × 10^?5 and 2.87 × 10^?5 S/cm respectively, show decrease of conductivity with increase of TiO₂ content in the nanocomposite due to the hindrance of carrier transport between different conjugated chains of PANI in composite. The IR measurement indicates that there is strong interaction between the PANI and TiO₂ nanoparticles showing beneficial effect on the thermal stability of PANI/TiO₂ nanocomposite. Corrosion inhibition study shows that 316LN stainless steel coated with PANI/TiO₂ nanocomposite with weight ratio 0.05 shows better corrosion inhibition effect than pure PANI and nano-TiO₂ coating.     

Influence of Strain Rate and Temperature on Tensile Deformation and Fracture Behavior of Type 316L(N) Austenitic Stainless Steel

Tensile tests were performed at strain rates ranging from 3.16 × 10^?5 to 3.16 × 10^?3 s^?1 over the temperatures ranging from 300 K to 1123 K (27 °C to 850 °C) to examine the effects of temperature and strain rate on tensile deformation and fracture behavior of nitrogen-alloyed low carbon grade type 316L(N) austenitic stainless steel. The variations of flow stress/strength values, work hardening rate, and tensile ductility with respect to temperature exhibited distinct three temperature regimes. The steel exhibited distinct low- and high-temperature serrated flow regimes and anomalous variations in terms of plateaus/peaks in flow stress/strength values and work hardening rate, negative strain rate sensitivity, and ductility minima at intermediate temperatures. The fracture mode remained transgranular. At high temperatures, the dominance of dynamic recovery is reflected in the rapid decrease in flow stress/strength values, work hardening rate, and increase in ductility with the increasing temperature and the decreasing strain rate.     

Effect of Cyclic Predeformation on the Uniaxial Tensile Deformation Behavior of [017] Cu Single Crystals Oriented for Critical Double Slip

The effect of cyclic predeformation at different plastic strain amplitudes γ _pl on the uniaxial tensile behavior of the [017] critical double-slip-oriented copper single crystal was investigated. A cyclic predeformation at a low γ _pl of 7.0 × 10^?4 was found able to enhance the tensile strength of the [017] crystal at nearly no expense of the decrease in plasticity. However, as the γ _pl for the prefatigue increases to a higher value of 3.0 × 10^?3, the tensile strength of the prefatigued [017] crystal decreases to be slightly less than that of the unfatigued crystal, and simultaneously its tensile plasticity decreases markedly. Therefore, a cyclic predeformation at an appropriate plastic strain amplitude might bring about an obvious strengthening effect for metallic single crystals.     

Genesis of nanocrystalline Ho2O3 via thermal decomposition of holmium acetate: Structure evolution and electrical conductivity properties

This study focuses on the preparation of nanostructured holmium oxide via the decomposition of holmium acetate precursor utilizing the non-isothermal strategy. Thermogravimetric analysis(TGA) was used to follow up the various thermal events involved in the decomposition process. Dehydration completes approximately at 150℃, which is followed by the decomposition of the anhydrous acetate leading to the formation of holmium oxide. Based on the TGA results the acetate precursor was heated non-isothermally at the temperature range of 150 e700℃. The obtained solids were characterized using powder X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR), field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). It is found that nanocrystalline Ho_2 O_3 starts to form at 500℃ and presents the only phase detected at the 500 e700℃ range. The electrical conductivity of the solids that form at the temperature range of 300 e700℃ was investigated. The obtained values were correlated with the observed structural modifications accompanying the heat treatment. The electrical conductivity of the Ho_2 O_3 samples prepared at 500, 600 and 700℃ reaches the values of 1.92 × 10~(-7), 1.61 × 10~(-7) and 8.33 × 10~(-8) Ω~(-1)cm~(-1) at a measuring temperature of 500℃, respectively. These values are potentially advantageous for high-resistivity devices.