Corrosion resistance of Al ion implanted AZ31 magnesium alloy at elevated temperature

The Al ion implantation into AZ31 magnesium alloy was carried out in a MEVVA 80-10 ion implantation system at an ion energy of 40-50 keV with an ion implantation dose ranging from 2 × 10¹⁶ to 1 × 10¹⁷ ions/cm² at an elevated temperature of 300 °C induced by an ion current density of 26 μA/cm². The concentration-depth profile of implanted Al in AZ31 alloy measured by Rutherford backscattering spectrometry (RBS) is a Gaussian-type-like distribution in a depth up to about 1200 nm with the maximum Al concentration of about 8 at.%. The X-ray diffraction (XRD) analysis revealed the formation of α-Mg(Al) phase, intermetallic β-Mg₁₇Al₁₂, and MgO phase on the Al ion implanted samples. The potentiodynamic anodic polarization curves of the Al ion implanted samples in the 0.01 mol/l NaCl solution with a pH value of 12 showed increases of the corrosion potential and the pitting breakdown potential, and a decrease of the passive current density, respectively. The Al ion implanted samples with 6 × 10¹⁶ ions/cm² achieved the high pitting breakdown potential to about − 480 mV (SCE). In the 0.08 mol/l NaCl solution with pH = 12, the Al ion implanted samples with 1 × 10¹⁷ ions/cm² showed an increased pitting breakdown potential to about − 1290 mV (SCE), from around − 1540 mV (SCE) of unimplanted samples. It is indicated that different corrosion mechanisms are responsible for improvement in corrosion resistance of the AZ31 magnesium alloy in the NaCl solutions with the varied concentrations.     

Composition and structure of Al ions implanted Fe at elevated temperatures

Al ions with ion energy of 120 keV are implanted into Fe under ion current density of 3.18 μA/cm² to implantation doses of 5 × 10¹⁶ and 1 × 10¹⁷ ions/cm² at room temperature and elevated temperatures of 250 and 500 °C, respectively. At 250 °C, the distribution depth of implanted Al reaches 160 nm with a peak concentration of 6 at.% at the dose of 5 × 10¹⁶ ions/cm², and 180 nm with 10 at.% at 1 × 10¹⁷ ions/cm², analyzed by Rutherford backscattering spectroscopy, respectively. At 500 °C, the implantation depth is 200 nm and the maximum concentration of Al is 10 at.% at the dose of 1 × 10¹⁷ ions/cm². With 5 × 10¹⁶ ions/cm², the intermetallics Al₁₃Fe₄ is formed in the Fe samples at 500 °C, revealed by X-ray diffraction. With 1 × 10¹⁷ ions/cm², the phase is also detected at 250 °C. The concentration-depth profiles of implanted Al in Fe samples at the room temperature, 250 °C and 500 °C are calculated by a mass transfer model that is built based on the transport of ions in matter and the irradiation enhanced diffusion. The calculated concentration-depth profiles are in reasonable agreement with those obtained from the experiments.     

Microstructure control of CrNx films during high power impulse magnetron sputtering

The microstructure and composition of CrN_x (0 ≤ x≤ 1) films grown by reactive high power pulsed magnetron sputtering (HIPIMS or HPPMS) have been studied as a function of the process parameters: N₂-to-Ar discharge gas ratio, (f_N2/Ar), negative substrate bias (V_s), pulsing frequency, and energy per pulse. The film stoichiometry is found to be determined by the composition of the material flux incident upon the substrate during the active phase of the discharge with no nitrogen uptake between the high power pulses. Scanning electron microscopy investigations reveal that for 0 < f_N2/Ar < 0.15 and 150 V bias, a columnar film growth is suppressed in favor of nano-sized grain structure. The phenomenon is ascribed to the high flux of doubly charged Cr ions and appears to be a unique feature of HIPIMS. The microstructure of column-less films for 100 V ≤ V_s ≤ 150 V is dominated by the CrN and hexagonal β-Cr₂N phases and shows a high sensitivity to V_s. As the amplitude of V_s decreases to 40 V and self-biased condition, the film morphology evolves to a dense columnar structure. This is accompanied by an increase in the average surface roughness from 0.25 nm to 2.4 nm. CrN_x samples grown at f_N2/Ar ≥ 0.3 are columnar and show high compressive stress levels ranging from −7.1 GPa at f_N2/Ar = 0.3 to −9.6 GPa at f_N2/Ar = 1. The power-normalized deposition rate decreases with increasing pulse energy, independent of f_N2/Ar. This effect is found to be closely related to the increased ion content in the plasma as determined by optical emission spectroscopy. The HIPIMS deposition rate normalized to DC rate decreases linearly with increasing relative ion content in the plasma, independent of f_N2/Ar and pulsing frequency, in agreement with the so-called target-pathways model. Increasing frequency leads to a finer grain structure and a partial suppression of the columnar growth, which is attributed to the corresponding increase of the time-averaged mean energy of film-forming ions arriving at the substrate.     

High frequency and low voltage plasma immersion ion implantation of nitrogen on industrial pure iron at different Rf power

Traditional plasma ion immersion implantation (PIII) can effectively improve material mechanical property and corrosion resistance. But the modified layer by PIII is too thin for many industrial applications. High frequency and low voltage plasma immersion ion implantation (HLPIII) has advantages of PIII and nitriding. Comparing with traditional ion nitriding, HLPIII can obtain higher implantation energy and create a thick modified surface layer. In the present paper nitriding layers were synthesized on industrial pure iron using high frequency and low voltage plasma immersion ion implantation with different RF power (400 W, 600 W, and 800 W). The microstructure of the nitriding layers was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanical properties such as microhardness and wear resistance were analyzed using HXD1000 microhardness and CSEM pin-on-disk wear testing machine. The anodic polarization characteristics were measured in a 0.9% NaCl solution at room temperature to examine the corrosion resistance of the nitriding layer. The results reveal that Fe₂N, Fe₃N and Fe₄N coexist in the nitriding layer. The nitriding layer is a corrosion protective coating on industrial pure iron in 0.9% NaCl solution. The hardness, wear resistance and corrosion resistance of the nitrided layers on industrial pure iron increase with RF power.     

Wear and corrosion properties of plasma-based low-energy nitrogen ion implanted titanium

Plasma-based low-energy nitrogen ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition, has emerged as a low-temperature surface engineering technique for metal and alloy. In this paper, the pure metal Ti samples have been modified by the plasma source ion nitriding process at a process temperature of 700 °C for a processing time of 4 h. The nitrided Ti surfaces were constructed of a continuous and dense Ti₂N compound layer about 2 μm thick and a 7-8 μm diffused layer. During tribological test on a ball on disk tribometer against the Si₃N₄ ceramic counterface, a low friction coefficient of about 0.3 and the faint wear volume were obtained for the nitrided Ti samples. The cyclic polarization curves of the nitrided Ti samples in 3.5% and 6.0% NaCl solutions showed that the improved pitting corrosion resistance with an increase of corrosion potential and a decrease of passive current, compared with that of the unnitrided Ti sample. The plasma source ion nitriding of the Ti samples provided the engineering surfaces for the functional applications with the combined improvement in wear and corrosion resistance.     

High-energy heavy ion beam annealing effect on ion beam synthesis of silicon carbide

Silicon carbide (SiC) is a superior material potentially replacing conventional silicon for high-power and high-frequency microelectronic applications. Ion beam synthesis (IBS) is a novel technique to produce large-area, high-quality and ready-to-use SiC crystals. The technique uses high-fluence carbon ion implantation in silicon wafers at elevated temperatures, followed by high-energy heavy ion beam annealing. This work focuses on studying effects from the ion beam annealing on crystallization of SiC from implanted carbon and matrix silicon. In the ion beam annealing experiments, heavy ion beams of iodine and xenon, the neighbors in the periodic table, with different energies to different fluences, I ions at 10, 20, and 30 MeV with 1-5 × 10¹² ions/cm², while Xe ions at 4 MeV with 5 × 10¹³ and 1 × 10¹⁴ ions/cm², bombarded C-ion in implanted Si at elevated temperatures. X-ray diffraction, Raman scattering, infrared spectroscopy were used to characterize the formation of SiC. Non-Rutherford backscattering and Rutherford backscattering spectrometry were used to analyze changes in the carbon depth profiles. The results from this study were compared with those previously reported in similar studies. The comparison showed that ion beam annealing could indeed induce crystallization of SiC, mainly depending on the single ion energy but not on the deposited areal density of the ion beam energy (the product of the ion energy and the fluence). The results demonstrate from an aspect that the electronic stopping plays the key role in the annealing.     

Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation

Superhard nanostructured coatings, prepared by plasma-assisted chemical vapour deposition (PACVD) and physical vapour deposition (PAPVD) techniques, such as vacuum arc evaporation and magnetron sputtering, are receiving increasing attention due to their potential applications for wear protection. In this study nanocomposite (TiAl)B_xN_y (0.09 ≤ x ≤ 1.35; 1.07 ≤ y ≤ 2.30) coatings, consisting of nanocrystalline (Ti,Al)N and amorphous BN, were deposited onto Si (100), AISI 316 stainless steel and AISI M2 tool steel substrates by co-evaporation of Ti and hot isostatically pressed (HIPped) Ti-Al-B-N material from a thermionically enhanced twin crucible electron-beam (EB) evaporation source in an Ar plasma at 450 °C. The coating stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), in combination with nanoindentation measurements. Aluminium (∼ 10 at.% in coatings) was found to substitute for titanium in the cubic TiN based structure. (Ti,Al)B_0.14N_1.12 and (Ti,Al)B_0.45N_1.37 coatings with average (Ti,Al)N grain sizes of 5-6 nm and either ∼ 70, or ∼ 90, mol% (Ti,Al)N showed hardness and elastic modulus values of ∼ 40 and ∼ 340 GPa, respectively. (Ti,Al)B_0.14N_1.12 coatings retained their ‘as-deposited’ mechanical properties for more than 90 months at room temperature in air, comparing results gathered from eight different nanoindentation systems. During vacuum annealing, all coatings examined exhibited structural stability to temperatures in excess of 900 °C, and revealed a moderate, but significant, increase in hardness. For (Ti,Al)B_0.14N_1.12 coatings the hardness increased from ∼ 40 to ∼ 45 GPa.     

Electrochemical corrosion behaviour of microcrystalline aluminium in acidic solutions

The electrochemical corrosion behaviour of microcrystalline pure aluminium coating, fabricated by a magnetron sputtering technique, has been investigated in both 0.5 mol/l NaCl and 0.5 mol/l Na₂SO₄ acidic (pH = 2) aqueous solutions. The corrosion resistance of the microcrystalline Al coating has deteriorated more compared with that of the cast pure Al in Na₂SO₄ acidic solution. However, its oxide film has a higher pitting resistance in the NaCl acidic solution. Chloride ions play a big role in the formation of the oxide film on the microcrystalline Al coating. The higher pitting resistance was attributed to the more acidic isoelectric point which the oxide film achieved.     

Characterization of nanocrystalline AlTiN coatings synthesized by a cathodic-arc deposition process

Graded and multilayered Al_xTi_1−xN nanocrystalline coatings were synthesized by using cathodic-arc evaporation (CAE) process. Ti₃₃Al₆₇ and Ti₅₀Al₅₀ alloy cathodes were used for the deposition of Al_xTi_1−xN nanocrystalline coatings with different Al/(Ti+Al) ratios. Optical emission spectra of the plasma species including atomic and ionized Ti, atomic Al, excited and ionized nitrogen (N₂ and N₂⁺) revealed that the excitation, ionization and charge transfer reactions of the Al-Ti-N plasma occurred during the Al_xTi_1−xN coating process. A preferred (111) orientation was shown in the Al_0.67Ti_0.33N with high Al/(Ti+Al) atomic content ratio (0.63) and small grain size (29 nm). The graded Al_0.67Ti_0.33N/TiN possessed the highest hardness of Hv_25 g 3850 ± 180. However, the multilayered Al_0.67Ti_0.33N/TiN coating supported a longer tool life with lower residual stress. It has been found that the wear performance and mechanical properties of the films were correlated with the Al/(Ti+Al) content ratio and multilayered structure.     

CrN/NbN coatings deposited by HIPIMS: A preliminary study of erosion-corrosion performance

Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion-corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion-corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS-HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr²⁺ and 1% Cr³⁺ ions and J_s of 155 mAcm^− 2. For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L_C 80 N, high hardness of 34 GPa and Young's modulus of 381 GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K_C (1.22 × 10^− 15 m³Nm^− 1) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion-corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na₂CO₃ + NaHCO₃ buffer solution with Al₂O₃ particles of size 500-700 µm) at 90° impact angle with a velocity of 4 ms^− 1. Experiments have been carried at − 1000 mV, + 300 mV and + 700 mV representing 3 different corrosion conditions.     

Development and irradiation performance of stencil masks for heavy-ion patterned implantation

Heavy-ion implantation is a powerful tool to conduct atomic injection and to create buried nanoparticles with good depth-controllability in dielectric material. Metal nanoparticle composites, especially, the metal ion implanted insulators (e.g. SiO₂) with patterned nanoparticles are promising for plasmonic applications, possessing an enhanced surface plasmon resonance and nonlinear optical property as compared with randomly implanted specimens [1]. Contact masked implantation is one practical method for patterned implantation, which has advantage of reliable 2D nanoparticle spatial controllability without any abreactions. In this experiment, the Si stencil mask was made from top Si layer of SOI wafer by using e-beam lithography and plasma deep etching. The mask can be fabricated with required aspect ratio (from 3 up to 100), fine pore shape, surface flatness, and mechanical hardness. 60 keV Cu ion irradiation damage test shows that, below the fluence of 1 × 10¹⁷ ions/cm², Si stencil mask can keep dimensional stability.     

Applications of combined ion implantation for improved tribological performance

Ion implantation set-up on the base of ion gun with target sputtering by Penning discharge plasma was created. The set-up allows to conduct implantation of ions of various materials with an implantation current of 100 μA/cm² at acceleration voltage of up to 30 kV. Combined implantation of TiB₂ compound and Argon or Nitrogen were applied for surface properties modification of WC-Co hard alloy and SKD11 steel. The effect of implantation on mechanical and tribological properties has been studied and discussed with respect to implantation fluence. It was shown that the main effect of implantation is the modification of thin surface layer with formation of Ti, B, N₂ — base compounds, which leads to modification of surface adhesion interaction and wear resistance improvement. Examples of application to real products are presented.     

Ta-doped multifunctional bioactive nanostructured films

Ta-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering or ion implantation assisted magnetron sputtering of composite (Ti,Ta)C + Ca₃(PO₄)₂ and (Ti,Ta)C + CaO targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, transmission electron microscopy, X-ray photoelectron, Raman, and IR spectroscopy. The films deposited in an Ar atmosphere consisted of (Ti,Ta)C, Ti_xO_y, and CaO phases in an amorphous matrix with P-O, C-O, and O-H bonding. In the films deposited in a gaseous mixture of Ar + 14%N₂, apart from the (Ti,Ta)(C,N), Ti_xO_y, and CaO phases, the indication of diamond-like carbon, bcc Ta and traces of P-O bonding were observed. The MuBiNaFs demonstrated high hardness in the range of 38-44  GPa, Young's modulus 310-350  GPa, high percentage of elastic recovery 70-75%, low friction coefficient down to 0.17-0.25 (both in air and under physiological solution) and two orders of magnitude lower wear rate compared with Ti substrate. Ti ion implantation of growing films was shown to be an effective instrument to decrease their high internal stress. Static water contact angle measurements indicated hydrophilic nature of film surfaces. The electrochemical tests demonstrated that the Ta-doped films had positive values of corrosion potential with low current density. In vitro studies showed that cultured IAR-2 epitheliocytes and MC3T3-E1 osteoblastic cells were well spread on the surface of films and their actin cytoskeleton was well organized. Osteoblastic cells had a high rate of proliferation on all examined films and expressed alkaline phosphatase activity, an early-stage differentiation marker. The MuBiNaF revealed a high level of biocompatibility and biostability at experiments in vivo.     

Secondary electron suppression in nitrogen plasma ion implantation using a low DC magnetic field

Experiments aiming at the reduction or even total suppression of secondary electrons during the plasma immersion ion implantation were carried out using a plasma device with low DC magnetic field. Comparison of ion implantations in B = 0 and another case with B = 43 G, indicated that the magnetic field was effective to suppress SE flow in the direction transversal to B but only partial suppression was attained in the longitudinal direction. However, these results are already significant since the efficiency of implantation was increased and the flow of SE to the walls became localized to the regions with B crossing the walls.     

N / Ti / Al 离子注入 304 不锈钢的耐磨性

目的研究N,Ti,Al离子注入对304不锈钢耐磨性的影响规律,为304不锈钢材料的改良提供参考。方法采用等离子注入技术,在不同剂量下对304不锈钢分别进行N,Ti,Al离子注入,对离子注入后的试样进行表面微观形貌观测、表面硬度测试、摩擦磨损性能测试,并与304不锈钢基材进行对比。结果 304不锈钢经3种离子注入后,均能获得平整、致密,没有裂纹,具有一定光洁度的表面组织,但是注入剂量增大会引起表面起泡现象,形成多孔形貌,光洁度降低。此外,3种离子注入均能提高304不锈钢的表面硬度,且高剂量注入试样的硬度比低剂量注入试样更高,相较而言,N离子注入使表面硬度的提高更明显。相比未注入基材,注N与注Ti表面层的摩擦系数均变小,注Al表面层的摩擦系数反而变大,但磨损量都明显降低。高剂量注N、注Al试样的耐磨性均高于低剂量注入试样,而高剂量注Ti试样的耐磨性低于低剂量注入试样,但仍好于注N、注Al试样。结论在相同实验条件与注入工艺下,N离子注入对表面硬度提高最显著(剂量为5.0×1017ions/cm2),约提高41%;Ti离子注入对耐磨性提高最显著(剂量为3.0×1017ions/cm2),约提高6倍。     

Microstructure and mechanical properties of CrN coating deposited by arc ion plating on Ti6Al4V substrate

CrN coatings have been grown by arc ion plating (AIP) onto Ti6Al4V alloy substrate at various nitrogen pressures (PN₂). The goals of this investigation are to study the influence of nitrogen pressure content on the composition, structure and mechanical properties of AIP CrN coatings, as well as their tribological properties. With an increase of PN₂, the main phases in the coatings changed from CrN + Cr₂N + Cr to CrN, and the texture of CrN was transformed from CrN (111)-oriented to (220)-oriented. Furthermore, the multi-layers including a metal Cr layer, a Cr₂N layer and a CrN layer were observed by cross-sectional TEM (XTEM), besides an “unbalanced” state transition layer at the interface of CrN/substrate which was analyzed by nucleation thermodynamics subsequently. An increase in nitrogen pressure also resulted in a change of micro-hardness due to the variation in composition and structure. Finally, the tribological properties of the Ti6Al4V substrate and the CrN/Ti6Al4V coating system have also been explored, which shows that CrN coatings can act as good wear resistance layer for Ti6Al4V substrate.     

Structure, mechanical properties and oxidation behaviour of arc-evaporated NbAlN hard coatings

Nb_1 − xAl_xN hard coatings were synthesised by cathodic arc-evaporation in order to study the influence of the Al concentration on crystal structure, mechanical properties and oxidation resistance. Structural investigations by X-ray diffraction revealed a transition from the face-centered cubic structure of δ-NbN to the wurtzite structure of AlN at x = 0.45… 0.56 depending on the deposition parameters. The maximum values of the mechanical properties like hardness and residual stress obtained by nanoindentation and biaxial stress temperature measurements, respectively, were found for the coatings with cubic structure and generally decrease with increasing Al content. On the other hand, higher Al concentrations are beneficial in terms of oxidation resistance as shown by annealing experiments in ambient air. The onset temperature for oxidation rises from 600 to 700 °C for Nb_0.73Al_0.27N to above 800 °C for Nb_0.29Al_0.71N regardless of changes in the crystal structure.     

Nano-wear, nano-hardness and corrosion-resistance of electroplated nickel surfaces after co-implantation of Cr and N2 ions

In this work, a successful sequential co-implantation treatment of Cr⁺ and N₂⁺ ions into electrodeposited nickel plates is presented. The goal of this treatment is the simultaneous enhancement of the wear resistance, mechanical stability and corrosion-protection properties of the Ni surfaces. The ion-implanted surfaces have been characterized by glow-discharge optical-emission spectroscopy, X-ray diffraction, nano-hardness, roughness, nano-wear and potentio-dynamic corrosion tests. It has been observed that the implantation of Cr⁺ or N₂⁺ alone is not sufficient to achieve simultaneously the enhancement of both the wear-resistance and the corrosion-protection properties. Conversely, the sequential implantation of Cr⁺ and N₂⁺ at 140 keV and fluencies of 3 × 10¹⁷ and 1.5 × 10¹⁷ ions/cm² respectively, permits the formation of a functional surface capable of reducing both the corrosion rate and the wear rates, with respect to those exhibited by the un-implanted Ni surfaces.This treatment can be used to protect the surfaces of micro-embossing/stamping dies based on electroformed Nickel, as an alternative to other coating strategies. Furthermore, the ion implantation assures the non-modification of the net-shape and surface finish of these types of dies, which is of crucial importance when they are used for high-precision micro-texturing/imprinting applications.     

Corrosion behavior and surface characterization of tantalum implanted TiNi alloy

TiNi shape memory alloy has been modified by Ta plasma immersion ion implantation technology to improve corrosion resistance. The results of the polarization tests show that the corrosion resistance of TiNi alloy in Ringer's solution at 310 K has been improved by the Ta ion implantation and the Ta/TiNi sample with a moderate incident dose of 1.5 × 10¹⁷ ions/cm² exhibits the best corrosion resistance ability. The surface characterization and chemical composition of the Ta/TiNi samples were determined by Auger electron spectroscopy (AES), Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) methods. AFM images reveal that compact aggregates of nano-grains uniformly disperse on the surface of the Ta/TiNi samples. AES and XPS analyses on the Ta/TiNi sample show that the component of the surface layer is mainly composed of TiO₂ and Ta₂O₅, which is benefit to the corrosion resistance ability and biocompatibility.