Carbon Plasma Immersion Ion Implantation Research Articles

Study of the Mechanical Properties of NiTi Modified by Carbon Plasma Immersion Ion Implantation Using Nano-Indentation Test and Finite Element Method Simulation

Study of the Mechanical Properties of NiTi Modified by Carbon Plasma Immersion Ion Implantation Using Nano-Indentation Test and Finite Element Method Simulation

Investigation of corrosion mechanism of NiTi modified by carbon plasma immersion ion implantation (C-PIII) by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is conducted to investigate the corrosion behavior and mechanism of NiTi modified by carbon plasma immersion ion implantation (C-PIII) in 3.5% NaCl and simulated body fluids (SBF) solutions. The unstable native oxide formed on the pristine NiTi is easily corroded by aggressive ions leading to delamination of the surface structure. C-PIII enhances the surface stability by forming a smooth and crack-free coating with a thickness of 50 nm. Ni leaching is reduced and EIS reveals significantly improved corrosion resistance. The amounts of nickel ions released to SBF and 3.5% NaCl solution are 1.3724 and 4.1463 mg L−1 cm−2, respectively, and C-PIII decreases the amounts of nickel ions in SBF and 3.5% NaCl solution by 99.13 and 99.31%, respectively, after immersion for 96 h. The corrosion resistance mechanism depends on the inactive protection layer and functional carbon film on the NiTi surface. Formation of a homogeneous and uniform layer on the surface, precipitation of corrosion products from soluble compounds, especially in SBF, and formation of titanium oxide at local defects due to the penetration of corrosive ions such as Cl− and water absorption are the major mechanisms responsible for the improved corrosion resistance of the C-PIII NiTi.

Enhancement of mechanical properties and corrosion resistance of NiTi alloy by carbon plasma immersion ion implantation

NiTi alloys are used in orthodontic and orthopedic applications but the long-term corrosion resistance and related properties need improvement in order to satisfy the demand by more stringent applications. In this study, carbon plasma immersion ion implantation (C-PIII) is performed to improve the corrosion resistance and mechanical properties of the Ni50.8Ti49.2 (at.%) alloy. The structure, morphology, chemical and mechanical properties, and corrosion resistance are investigated systematically. A uniform, smooth, and crack-free surface layer with a thickness of 50 nm is produced after C-PIII for 2 h. C-PIII also changes the roughness, hardness, and elastic modulus from 17.4 nm, 64.31 GPa, and 2.74 GPa for the pristine NiTi alloy to 6.1 nm, 89.27 GPa, and 4.77 GPa of the C-PIII sample, respectively. Electrochemical impedance spectroscopy (EIS) indicates that C-PIII improves the corrosion resistance and hardness of NiTi. No surface defects are observed and the reinforced surface structure improves the corrosion resistance by 85%. Penetration of corrosive ions during immersion in 3.5% NaCl results in failure of the passive layer but subsequent reactions with titanium re-form the passive layer. The passive layer is more stable at the immersion time point of 96 h and C-PIII also increases the pitting or local corrosion resistance.

Effects of Carbon and Nitrogen Plasma Immersion Ion Implantation on In vitro and In vivo Biocompatibility of Titanium Alloy

Growth of bony tissues on titanium biomedical implants can be time-consuming, thereby prolonging recovery and hospitalization after surgery and a method to improve and expedite tissue-implant integration and healing is thus of scientific and clinical interests. In this work, nitrogen and carbon plasma immersion ion implantation (N-PIII and C-PIII) is conducted to modify Ti-6Al-4V to produce a graded surface layer composed of TiN and TiC, respectively. Both PIII processes do not significantly alter the surface hydrophilicity but increase the surface roughness and corrosion resistance. In vitro studies disclose improved cell adhesion and proliferation of MC3T3-E1 preosteoblasts and L929 fibroblasts after PIII. Micro-CT evaluation conducted 1 to 12 weeks after surgery reveals larger average bone volumes and less bone resorption on the N-PIII and C-PIII titanium alloy pins than the unimplanted one at every time point. The enhancements observed from both the in vitro and in vivo studies can be attributed to the good cytocompatibility, roughness, and corrosion resistance of the TiN and TiC structures which stimulate the response of preosteoblasts and fibroblasts and induce early bone formation. Comparing the two PIII processes, N-PIII is more effective and our results suggest a simple and practical means to improve the surface biocompatibility of medical-grade titanium alloy implants.

New plasma surface-treated memory alloys: Towards a new generation of “smart” orthopaedic materials

This paper describes the corrosion resistance, surface mechanical properties, cyto-compatibility, and in-vivo performance of plasma-treated and untreated NiTi samples. Nickel–titanium discs containing 50.8% Ni were treated by nitrogen and carbon plasma immersion ion implantation (PIII). After nitrogen plasma treatment, a layer of stable titanium nitride is formed on the NiTi surface. Titanium carbide is also found at the surface after carbon plasma implantation. Compared to the untreated samples, the corrosion resistances of the plasma PIII samples are better by a factor of five and the surface hardness and elastic modulus are better by a factor of two. The concentration of Ni leached into the simulated body fluids from the untreated samples is 30 ppm, whereas that from the plasma-treated PIII are undetectable. Although there is no significant difference in the ability of cells to grow on either surface, bone formation is found to be better on the nitrogen and carbon PIII sample surfaces at post-operation 2 weeks. All these improvements can be attributed to the formation of titanium nitride and titanium carbide on the surface.

Improvement on corrosion resistance of NiTi orthopedic materials by carbon plasma immersion ion implantation

Nickel–titanium shape memory alloys (NiTi) have potential applications as orthopedic implants because of their unique super-elastic properties and shape memory effects. However, the problem of out-diffusion of harmful Ni ions from the alloys during prolonged use inside a human body must be overcome before they can be widely used in orthopedic implants. In this work, we enhance the corrosion resistance of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Results of atomic force microscopy (AFM) indicate that both C2H2-PIII&D and C2H2-PIII do not roughen the original flat surface to an extent that can lead to degradation in corrosion resistance.

Carbon plasma immersion ion implantation of nickel–titanium shape memory alloys

Nickel–titanium (NiTi) shape memory alloys possess super-elasticity in addition to the well-known shape memory effect and are potentially suitable for orthopedic implants. However, a critical concern is the release of harmful Ni ions from the implants into the living tissues. We propose to enhance the corrosion resistance and other surface and biological properties of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Our tribological tests show that the treated surfaces are mechanically more superior and cytotoxicity tests reveal that both sets of plasma-treated samples favor adhesion and proliferation of osteoblasts.

Effects of mesh-assisted carbon plasma immersion ion implantation on the surface properties of insulating silicon carbide ceramics

Plasma immersion ion implantation (PIII) is an effective materials modification and synthesis technique but has seldom been applied to ceramic materials due to the high electrical resistance that reduces the ion bombardment energy and sometimes causes serious electrical arcing in the instrument. Even in cases where PIII is applicable, the surface properties of the implanted insulating materials can be seriously affected due to the low ion energy and materials damage from electrical arcing. In order to enhance the surface and mechanical properties such as wear resistance of ceramic materials used in many industrial applications, surface modification is needed. In this work, we conduct carbon implantation into sintered α-SiC (silicon carbides that are widely used in vacuum ceramic bearings) using mesh-assisted plasma immersion ion implantation to enhance the surface properties. The use of a conducting grid is necessitated by the high electrical resistance that induces a large voltage drop across the substrate when a negative voltage is applied to the back of the specimen. The rough surfaces make direct assessment of the shallow depth profiles difficult and so we directly measure the hardness and surface friction coefficients, both of which are significantly enhanced after implantation. Our data suggest different wear mechanisms for the unimplanted and implanted samples as inferred from the surface topography and wear tracks.

Nitrogen and carbon expanded austenite produced by PI 3

Expanded austenite can be formed either by nitrogen or carbon plasma immersion ion implantation (PI 3 ™) from a nitrogen or methane plasma at elevated temperatures. The structure and properties of nitrogen and carbon expanded austenite layers produced on austenitic stainless steel X5CrNi189 are compared. A new structural model of expanded austenite based on a defect rich face centred cubic (fcc) lattice is proposed. Although the structure of the two expanded austenite layers is similar, there is a remarkable difference in the uptake of nitrogen or carbon, despite the use of similar treatment conditions. The modified surfaces have different hardness, corrosion and wear properties.

Evolution of microstructure of instrumental AISI M2 steel after plasma immersion nitrogen and carbon implantation

Investigations of the elemental and phase composition, microstructure, microhardness and tribological properties of AISI M2 steel subjected to nitrogen and carbon plasma-immersion ion implantation (PIII) at different regimes are presented. Elemental composition was studied by Auger electron spectroscopy (AES) and X-ray microanalysis. Phase composition was identified by means of conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction (XRD). Using these methods it was established that nitrogen PIII at a target temperature of 380°C resulted in phase transformations: from α′-Fe(C,M)+M 6C+MC (M: Fe,Cr,W,Mo) to ε-(Fe,M) 2+ x (N,C)+M 6(C). With increasing temperature up to 500°C in nitrogen PIII the retained martensite, in addition to ε-(Fe,M) 2+ x (N,C), was observed. Joint nitrogen and carbon PIII leads to the formation of ε-(Fe,M) 2+ x C and (Fe,M) 7C 3 (M:Cr,W,Mo) carbides. Theoretical analysis of the distribution of thermoelastic stresses during PIII demonstrated the essential increase in the mass transport process of implanted atoms into the target volume. On the basis of the estimations conducted, it has been shown that migration processes of nitrogen into steel during PIII have a complicated character and can be described with the help of mechanisms stimulated by the reaction of a crystal lattice under the impulse influence.

Surface modification of 9Cr18 bearing steels by a metal and carbon co-plasma immersion ion implantation

In the aerospace industry, 9Cr18 martensitic stainless steel (AISI 440) is commonly used as a bearing material. Because of its ability to rapidly treat irregular industrial components, plasma immersion ion implantation (PIII) is an effective method to improve the wear resistance of 9Cr18 precision bearings and prolong their working lifetime. Vacuum arc plasma sources provide a good means of introducing metal ions into the bearing steel to create a special surface to enhance its surface properties. In this work, tungsten and titanium PIII was performed on 9Cr18 bearing steel using a vacuum arc plasma source, followed by carbon PIII using acetylene (C 2H 2) plasma, without breaking the vacuum. The surface properties were evaluated by measuring the microhardness, wear properties and friction coefficient, as well as the elemental depth profiles and chemical composition of the modified layer. It was found that the microhardness of the treated samples was much higher. The tribological characteristics were also significantly improved, as demonstrated by the reduced friction coefficient and wear track width. This improvement can be attributed to the diamond-like-carbon (DLC) surface layer, as well as favorable ion mixing caused by the implanted metal ions.