Lower Corrosion Rate Research Articles

Fluoride-treated rare earth-free magnesium alloy ZK30: An inert and bioresorbable material for bone fracture treatment devices.

Bone fractures represent a common health problem, particularly in an increasingly aging population. Bioresorbable magnesium (Mg) alloy-based implants offer promising alternatives to traditional metallic implants for the treatment of bone fractures because they eliminate the need for implant removal after healing. The Mg-Y-rare-earth (RE)-Zr alloy WE43, designed for orthopedic implants, has received European Conformity mark approval. However, currently, WE43 is not clinically used in certain countries possibly because of concerns related to RE metals. In this study, we investigated the use of a RE-free alloy, namely, Mg-Zn-Zr alloy (ZK30), as an implant for bone fractures. Hydrofluoric acid (HF) treatment was performed to improve the corrosion resistance of ZK30. HF-treated ZK30 (HF-ZK30) exhibited lower corrosion rate and higher biocompatibility than those of WE43 in in vitro experiments. After implanting a rod of HF-ZK30 into the fractured femoral bones of mice, HF-ZK30 held the bones and healed the fracture without deformation. Treatment results of HF-ZK30 were comparable to those of WE43, indicating the potential of HF-ZK30 as a bioresorbable and safe implant for bone repair.

A comparative study of the corrosion of Q235 carbon steel in six different strains of marine-isolated sulfate reducing prokaryote

Biocorrosion in marine environments is often associated with biofilms of sulfate reducing prokaryotes. However, the corrosion behaviors of steel differed greatly between the bacterial species. In this study, six strains of sulfate reducing prokaryote including 3 strains of strictly anaerobic bacteria and 3 strains of facultative anaerobic bacteria were isolated from the steel rust immersed in Sanya, China. The corrosion behavior of Q235 carbon steels by isolated six strains was studied by weight loss analysis, electrochemistry measurements, and surface morphology observation. In addition, the relationship between bacterial corrosivity and strain type was investigated. The results indicated that there is no direct relationship between the corrosivity of bacteria and strain type, whether the bacteria were strictly anaerobic or not. The corrosion rates of steel coupons fluctuated with the strain properties and soaking time. Among the strains tested, the strains belonging to Proteobacteria had relatively high corrosion rates on steel coupons, whereas, strain Virgibacillus Dokdonensis of Firmicutes has the lowest corrosion rate. The results provide a guiding basis for exploring the mechanism of microbial corrosion and controlling marine microbial corrosion.

Microstructure characteristics and degradation behaviors of Se/phosphate conversion coatings on Mg-Gd-Ag-Y-Zn alloys in the Hank's electrolyte

In the present study, a selenium-phosphate based conversion coating (SPCC) was successfully developed on the dual rare-earth Mg-Gd-Ag-Y-Zn by immersion in specific acid phosphate bath. The compositions, morphologies, degradation behaviors as well as the formation/deposition mechanism of the SPCC were deeply analyzed. The results declared that the compositions of conversion coatings were the mixture of Mg3(PO4)2/η-Se, with the shallow hill-like structure and dispersive distribution, which was beneficial to enhance the adhesion and corrosion resistance. The electrochemical and static-immersion tests both revealed that the lowest corrosion dissolution rates of the SPCC coatings were realized through pretreatment at 70 °C, with higher Rct value (507.4 Ω·cm2) and lower corrosion rate of 0.603 mm/y. On the one hand, the appropriate temperature was conducive to increasing the concentrations of H2PO4−/SeO32− and accelerating the exchange rates of molecule active-movement in the conversion solution; On the other hand, the dense/stable selenium-phosphate conversion layers formed by redox reaction and hydrolysis reaction retarded the adsorption sites and penetration channels for corrosive ions.

Synthesis of hybrid organosilicon materials of various chemistries as efficient protective coatings for mild steels in NaCl media

This study focuses on optimizing the thermal, morphological, scratch resistance, and anti-barrier characteristics of newly developed hybrid sol-gel coatings. The coatings were formulated by varying the synthetic precursors and incorporating a clay additive. The hybrid coatings were prepared using a mixture of organosilane and zirconium propoxide precursors, and further modified with polydimethylsiloxane (PDMS) and Cloisite 20 A (C20A) clay additives. The coatings were applied onto mild steel substrates and their corrosion protection in 3.5 wt% NaCl solutions were evaluated through electrochemical and visual observation testing. Contact angle measurements revealed a hydrophobic nature of the developed coatings on the steel surfaces, primarily attributed to the presence of an organosilane precursor with a long C18-alkyl chain functionality in all formulations. Electrochemical testing data demonstrated that the coating formulation containing the polydimethylsiloxane precursor exhibited good corrosion protection. After 14 days of immersion in a saline medium, this sample exhibited impedance values higher than 106 Ω.cm2 and a low corrosion rate of 3.5 × 10−3 mpy, as determined by electrochemical impedance spectroscopy (EIS) and polarization testing, respectively. Morphological analyzes confirmed the homogeneous and integrated coating layer of this sample, which contributed to its enhanced corrosion protection. Furthermore, the inclusion of the Zr-propoxide precursor in a formulation containing only silane precursors demonstrated favorable effects on the desired coating properties. The hybrid sol-gel coatings exhibited excellent anti-barrier characteristics, which can be attributed to the formation of highly cross-linked Si-O-Si networks. Overall, the reported hybrid coating formulations offer promising alternatives to commercially available toxic conversion coatings, as they exhibit excellent anti-barrier properties and can be considered environmentally friendly.

Uticaj varijacija u sadržaju Mn na mehaničke i korozione karakteristike Cu-Al-Mn legura sa memorijom oblika

In this work, the role of Mn on the shape memory effect and mechanical and corrosion behavior of Cu-Al-Mn shape memory alloys was studied. The composition of Al was fixed to 10 wt% while that of Mn was varied from 2 to 10 wt%. The strain recovery by SME was evaluated using the bend test, while the yield and ultimate tensile strength were obtained using the tension test. The corrosion behavior was studied using three different solutions: freshwater, substitute ocean water, and Hank's solution. The yield and ultimate tensile strength of Cu-Al-Mn alloys increased with Mn content up to 6%, which was attributed to grain refinement and precipitation hardening, while the fracture analysis showed mixed mode failure for all alloys. The corrosion behavior of Cu-Al-Mn alloys was modified due to the addition of Mn. With the increase in Mn content, the alloys displayed better corrosion resistance and lower corrosion rates. The corroded surface analysis tested in freshwater showed pitting corrosion, while Cu-Al-Mn alloy with low Mn content was tested in substitute ocean water. Hank's solution showed surface damage with an unstable surface layer.

Effects of orientation on fatigue behaviors of ZK60 magnesium alloy pre-corroded in PBS

The strong anisotropy of magnesium alloy affects both its corrosion and fatigue performance by orientation, and it is important to investigate the effect of orientations on the two properties for the development of magnesium alloy in the biomedical field. In this paper, through the corrosion experiments and fatigue experiments of corroded specimens, the differences in corrosion resistance and fatigue failure performance of ZK60 magnesium alloy with different orientations were investigated, and the mechanism of these differences was analyzed. In terms of corrosion performance, compared with the RN surface, the RT surface with higher atomic arrangement density has a lower corrosion rate and higher corrosion resistance. In addition, regarding the fatigue performance, the corroded RT-R specimens had the longest fatigue life, followed by the RN-R and RN-N.

BLUE CRAB SHELL WASTE VALORIZATION AS A SOURCE OF HYDROXYAPATITE FOR BIOCOMPATIBLE DENTAL IMPLANT COATING FABRICATION

In the presented work, the effect of hydroxyapatite/polycaprolactone (HAp/PCL) ratio and the immersion/withdrawal speed on the corrosion rate and antibacterial properties of Ti-6Al-4V ELI dental implant coating was investigated. Ti6Al-4V ELI implants are coated with different HAp-PCL ratios and immersion speeds. The functional groups of product hydroxyapatite were confirmed using the HAp standard JCPDS no. 09-0432, with crystallinity of 88.32% and ratio Ca/P at 2.12. The result shows that the higher concentrations of hydroxyapatite result in the decrease of corrosion rate and increased antibacterial activity reflected in larger inhibition zones. Additionally, the higher immersion and withdrawal speeds during dip-coating lead to lower corrosion rates. Furthermore, decreased corrosion rates may enhance the antibacterial properties of HAp-PCL coatings. These results demonstrate that the HAp/PCL composite can be considered as a prospective candidate for dental implant Ti-6Al-4V ELI coating.

КОРРЕЛЯЦИОННЫЙ АНАЛИЗ ЗАВИСИМОСТИ УСТАНОВЛЕННОГО КОЛИЧЕСТВА ТОНА В ОТРАЖЕННОЙ СПЕКТРАЛЬНОЙ (ЦВЕТОВОЙ) ГРУППЕ И КОРРОЗИОННОЙ СТОЙКОСТИ ОДНОФАЗНЫХ СПЛАВОВ СИСТЕМ NI-CR-MO: Х30Н60М9, HASTELLOY G-35 С ГЦК РЕШЕТКОЙ МАТРИЦЫ

This article discusses the results of a correlation analysis between the indicators (parameters) of the established amount of tone in the spectral group of reflected visible light and corrosion resistance for single-phase nickel alloys of the Ni-Cr-Mo: Kh30N60M9, Hastelloy G-35 systems with a solid solution structure. The initial data for the analysis were the data obtained as a result of the analysis of the tone components of the reflected visible light by calculating the wavelength of the reflected light. The developed software estimated the amount of tone in the participating color groups, reflected visible light, where the tone is estimated by wavelength, determining the participating color groups. Further, the amount of tone determined in the color group is recalculated by the number of image elements - pixels, already offering the tone density in the color group. Corrosion rates were determined by a standard gravimetric method according to ASTM G-28 "A". Correspondence of the parameters: tone and corrosion rates for the alloys under consideration after various heat treatments indicated their high negative connection. The established fact allows us to state that a larger tone value determined for the pixel fragment characterizes a lower corrosion rate and better corrosion resistance in identical test conditions. The indicator correlation coefficient is determined at the level of - 0.93

Pulse electrodeposition of a duplex-layer structured composite nickel-based coating with improved corrosion and abrasion resistance

In this study, a dual amorphous/crystalline nanocomposite coating of Ni–P/Ni–Mo–ZrO2 was designed and successfully deposited on pure copper substrates by pulse electrodeposition. The design of the Ni–P/Ni–Mo–ZrO2 dual coating takes advantage of the properties of the different structures and incorporates second phase reinforcing particles resulting in more comprehensive protective coatings. The surface morphology and microstructure were evaluated by SEM, EDS, WLI, XRD and TEM. The mechanical properties and electrochemical behaviors of the coating in a 3.5 wt% NaCl solution were investigated by wear tests, Tafel and EIS. The results show that the Ni–P/Ni–Mo and Ni–P/Ni–Mo–ZrO2 dual coatings are uniform, dense and crack-free, and the duplex interface is homogeneous. Compared with the Ni–Mo coating, the average friction coefficient and wear rate of the Ni–P/Ni–Mo duplex coating decreased to 0.18 and 5.433 × 10−4 mm3/N·m, respectively. The corrosion potential is positively shifted to −0.43 with a maximum impedance of 308 kΩ cm2. The mismatch of the interlayer defects causes a deviation in the corrosion path, resulting in a transformation from longitudinal pinhole corrosion into extended transverse corrosion, which effectively strengthens the capacity of the coating for corrosion resistance while maintaining the high hardness of its outer coating. Furthermore, the hardness of the dual Ni–P/Ni–Mo coating can be obviously reinforced by nanoparticles from 730 HV to 810 HV, the corrosion potential is shifted to −0.41 V, and the corrosion current density decrease to 7.7803 × 10−7 A/cm2. The improvement in the mechanical properties can be attributed to the ZrO2 nanoparticles, which could carry stress and transfer loads during the wear process. Meanwhile, the ZrO2 nanoparticles can reduce the nodule size by filling the binding boundary which is the main corrosion path, and reduce the number of surface defects, such as pinholes, which leads to a lower corrosion rate. In addition, the corrosion inhibition and nanoparticle codeposition mechanisms of the duplex coatings were further discussed.

Corrosion behaviour of electropolished magnesium materials

Although magnesium and its alloys are promising candidates as biodegradable implant materials, the tendency for localised corrosion mechanism in physiological environment limit their biomedical application. Electropolishing is an attractive strategy for improving the corrosion behaviour of metals, but it is still largely unexplored in magnesium materials. In this study, the characterisation of electropolished surfaces of AM50 and pure magnesium was performed, focussing on their in vitro degradation behaviour in cell medium. Corrosion rates were evaluated using potentiodynamic polarisation. The surface morphology before and after the onset of corrosion was investigated by scanning electron microscopy and confocal laser scanning microscopy. The presented electropolishing process led to improved surface performances, observable by significantly lower corrosion rates (0.08 mm·year−1 in Dulbecco's modified Eagle's medium), lower arithmetical mean height (0.05 µm), lower water contact angle (25–35°) and lower micro hardness (35–50 HV 0.1) compared to mechanically and chemically treated surfaces. MgO/Mg(OH)2 could be detected on electropolished surfaces. The localised corrosion mode could be reduced, but not entirely prevented. Electropolishing shows great potential as post-treatment of magnesium-based components, but detailed tests of the long-term corrosion behaviour are an important area of future research.

Comparative investigation on high-pressure flow accelerated corrosion at gradual contraction and gradual expansion pipes

In current study, the flow accelerated corrosion behaviors of X65 steel gradual contraction and gradual expansion pipes under high-pressure conditions were comparatively investigated by establishing dynamic in situ electrochemical tests under high CO2 partial pressure conditions in a loop apparatus. The findings indicate that the corrosion rate is reduced along the flowing direction of gradual contraction pipe. Nevertheless, the corrosion rate firstly descends and subsequently ascends along the flowing direction of gradual expansion pipe, and the lowest corrosion rate is presented in inclination segment close to the straight pipe with large diameter. The corrosion rate at the top wall of gradual contraction pipe is symmetrical to that at the bottom wall, while it is asymmetrically distributed at the top wall and the bottom wall of inclination segment in gradual expansion pipe. The distribution of corrosion rate is correlated with the flow fields at gradual contraction and gradual expansion pipes. Furthermore, the special corrosion rate distribution at inclination segment of gradual expansion pipe is ascribed to the formation of secondary flow and vortexes.

Effect of SrTiO3 incorporation in Mg matrix: Microstructure, mechanical, corrosion and in vitro bioactivity study

In the present study, magnesium-strontium titanate (Mg-SrTiO3) composites were prepared using powder metallurgy route. The physical, mechanical, and electrochemical properties of pure Mg were compared with those of Mg-SrTiO3 composites with varying SrTiO3 concentrations (0, 1 and 5 wt%). X-ray diffraction (XRD) results showed the SrTiO3 and Mg peaks in the composites. Scanning electron microscopy (SEM) of the composite revealed the uniform distribution of reinforcement in the Mg matrix. An electrochemical corrosion study showed that the Mg-SrTiO3 composite has more positive ECORR than pure Mg. The lowest corrosion rate was observed in the Mg-1 %SrTiO3 composite. An in vitro biocompatibility and antimicrobial study revealed that Mg-SrTiO3 composites are non-toxic and have mild antibacterial property.

Multi-Weld Quality Optimization of Gas Tungsten Arc Welding for Aluminium 6061 using the Grey Relation Analysis-Based Taguchi Method

The optimization of parameters is crucial in the joining process, particularly in welding, to attain connections with exceptional mechanical properties. In the present study, the welding of aluminium 6061 was conducted with a TIG, an acronym for tungsten inert gas, is formally referred to as gas tungsten arc welding (GTAW) technique, employing a suitable ER 4043 electrode and argon shielding gas. The investigation of optimal welding parameters, specifically current, voltage, and flow rate, is conducted utilizing statistical methodologies such as the hybrid Grey-based Taguchi process. The desired attributes for high-quality welds were established as having high tensile strength, hardness, and a low rate of corrosion. Given the presence of three responses and one objective, the hybrid Grey-based Taguchi method is employed. The statistical approaches have converged on optimal parameters of 120 A, 20 V, and 15 L/min. The present analysis reveals that the ideal welded junction exhibited the following characteristics: a tensile strength of 190.169 MPa, a hardness value of 77HV, and a corrosion rate of 0.29 mm. The current parameter was found to have the highest contribution, accounting for 65.66% of the overall performance of the weldments. Confirmatory testing was conducted in order to confirm the optimization strategy, and the findings indicated that the Grey-based Taguchi technique is a straightforward yet effective approach for optimizing welded connections across several performance criteria.

Investigating surface integrity, corrosion resistance and biocompatibility of 316L steel using carbon nanotube-assisted EDM process

316L steel employed in biomedical applications has experienced mechanical failure triggered by insufficient biological reactions, a high corrosion rate, and surface impurities. Furthermore, the attenuated surface induced by corrosion and wear releases toxic elements, causing inflammatory effects. The prime aim of this research is to evaluate the carbon nanotube (CNT) based coating for enhancing surface integrity, corrosion resistance, and biological responses. This research also aims to comprehend the relationship between electric discharge machining (EDM) process variables and material properties. Several characterisation techniques, including scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), electron dispersive X-ray (EDX), MTT assays, powder X-ray diffraction (XRD) and potentiodynamic polarisation are utilised. The addition of CNT forms a nanoporous and thin coating of 10.3 μm, resulting in a crack-free surface with an adhesion strength of 23.77 MPa. A low corrosion rate (0.0012 mm/year) and almost 85 % of alive cells are observed on the coated surface of 316L steel. This research shows a method to form carbide and oxide-based coating for biomedical applications.

Mechanical Integrity and In vitro Degradation Behavior of Mg–Zn–Ca Biodegradable Alloy Prepared by Different Casting Technologies

Mg–Zn–Ca alloys have been widely used as biodegradable orthopedic and cardiovascular scaffolds because of their non-cytotoxicity, remarkable biodegradability, good biocompatibility and excellent mechanical properties similar to human bone. However, degradation causes poor corrosion resistance and mechanical properties. In this study, Mg-6%Zn-0.6%Ca alloys were produced using three distinct methodologies: casting, casting via the ultrasonic vibration process (USV), and casting via the mechanical vibration process (MV). Surface characterization, mechanical characteristics and corrosion resistance of the as-cast (untreated) and treated species were studied. The morphology and microstructure showed that the grain size of the as-cast, MV and USV specimens all had average grain sizes of about 191, 93 and 82 µm, respectively. The ultrasonic vibration treated specimen has the greatest degree of grain refinement. Mechanical tests showed that microstructure refinement promotes the mechanical characteristics of Mg alloy, such as compression, ultimate tensile strength as well as elongation. It was observed that the USV-treated sample has exceptional mechanical properties (Compressive strength 360.64 MPa, ultimate tensile strength (UTS) 178.41 MPa and Elongation 3.45%). Corrosion tests revealed that the USV-treated specimen exhibited uniform corrosion and low corrosion rate due to uniform compact fine grains with higher oxide concentration of about 42.82 wt%. The results of electrochemical analyses revealed that the average corrosion rate obtained from Potentiodynamic polarization curves of the as-cast, MV and USV specimens was about 5.3144, 4.5311 and 4.1087 mm/year, respectively and the passive film resistance (Rf) that was obtained from the electrochemical impedance spectroscopy (EIS) model of the USV, MV-treated samples and as-cast sample was 457 Ω, 430 Ω and 204 Ω, respectively. The results of immersion tests revealed that the USV-treated sample lost less weight and exhibits a relatively low degradation rate than the as-cast and MV-treated samples. After two weeks the weight of the as-cast, MV and USV samples decreased by about 18.6%, 18.5%, 16.8%., and the degradation rates were 7.304, 7.097 and 6.78 mm/y, respectively, and then gradually declining over the course of the immersion period.

EFFECT OF HEAT TREATMENT ON CORROSION RESISTANCE OF Al-Ni-Mn EUTECTIC ALLOY IN 3.5% NaCl SOLUTION

In this study, the effects of solution heat treatment (SHT) on how the Al-Ni-Mn eutectic alloy reacts to corrosion were looked into. The composition of the Al-Ni-Mn eutectic alloy was chosen as Al–5.3%Ni–1.3%Mn (wt). In solution heat treatment, firstly, the samples were kept at 570oC and 600oC for 2 hours and quenched with water at room temperature. Then, artificial aging was carried out by keeping 0-2-4 and 8 hours at 180oC. The corrosion behavior of the alloy was investigated by immersion tests in a 3.5% NaCl solution and electrochemical methods such as Tafel polarization curves and Electrochemical Impedance Spectroscopy (EIS). According to the immersion test results, the heat treatment applied at 600oC took the alloy to the more noble side and further increased its corrosion resistance. The α-Al matrix phase in the Al-Ni-Mn alloy system preferentially dissolves in untreated and heat-treated samples, and SEM images reveal the presence of corrosion pits. The corrosion performance of the heat-treated sample at 570oC is the highest. Heat treatment reduced the corrosion current density, indicating a lower corrosion rate and higher corrosion resistance. Also, the open circuit potential of the Tafel polarization curves of heat-treated and unheat-treated samples at 570oC and 600oC was found to be -685 mV, -693 mV and -761 mV, respectively. Similarly, the corrosion resistance of heat-treated and untreated samples at 570oC and 600oC was found to be 58 kΩ, 433 kΩ and 408 kΩ, respectively.

Microstructure, Mechanical and Corrosion Properties of Copper-Nickel 90/10 Alloy Produced by CMT-WAAM Method.

In the case of copper and its alloys, Wire Arc Additive Manufacturing (WAAM) 3D printing technology is mainly used to produce elements for the maritime industry and research has focused on the use of Cu-Al alloys. There is little information devoted to the use of Cu-Ni alloys in this technology, which are also widely used in the maritime industry. In this work, tests were carried out on the microstructure, mechanical properties, and corrosion properties in a 1M NaCl solution of Cu-Ni 90/10 alloy 3D walls printed using the WAAM method. The obtained objects are characterized by a microstructure with elongated column grains and particles of the Ni-Ti phase, hardness in the range of 138-160 HV10, ultimate tensile strength of 495-520 MPa, yield strength of 342-358 MPa, elongation of 16.6-17.9%, and a low average corrosion rate of 7.4 × 10-5 mm/year. The work shows that it is possible to obtain higher mechanical properties of Cu-Ni 90/10 alloy 3D objects produced using the WAAM method compared to cast materials, which opens up the possibility of using this alloy to produce objects with more complex shapes and for use in corrosive working conditions.

Bridge for the thermodynamics and kinetics of electrochemical corrosion: Designing a corrosion–resistant HP–13Cr stainless steel by Cu alloying for use in an H2S–containing geothermal environment

The dissolution–ionization–diffusion–deposition (DIDD) model was used for developing a corrosion–resistant stainless steel (SS) by the means of alloying and the guidelines for the process were proposed. The novel HP–13Cr–Cu SS was designed to resist corrosion in H2S–containing geothermal environment. The results indicated that the preferential deposition of CuS promoted the heterogeneous nucleation rate of Cr2O3, FeCr2O3, and FeS, which formed denser corrosion product layer. As a result, this alloy exhibited a low corrosion rate and a high sulfide stress cracking (SSC) resistance. The results were consistent with the theoretical calculation conducted by the DIDD model.

ANALISIS PENGARUH VARIASI HOLDING TIME ANNEALING TERHADAP LAJU KOROSI TITANIUM PADA LARUTAN CAIRAN TUBUH SINTETIS

Biomaterials are crucial for bone implants due to their biocompatible and inert nature, ensuring no adverse effects within the human body. Titanium is renowned for its exceptional corrosion resistance. This research aims to analyze the impact of annealing holding time and pH of synthetic body fluid on the hardness and corrosion rate of titanium. The annealing process was performed at 700°C, with holding times of 30, 60, and 90 minutes. As an electrolyte medium, a Hanks' solution with pH variations of 4, 6, and 8 was used and maintained at 37°C. Potentiodynamic corrosion testing demonstrated the lowest corrosion rate in specimens treated with 30 minutes of annealing at pH 8, measuring 0.32 x 10-2 mmpy. The 30-minute annealing exhibited the lowest corrosion rate, which was confirmed by Electrochemical Impedance Spectroscopy (EIS) results showing a higher Rp value, indicating a lower corrosion rate. This is attributed to the presence of a passive Rutile TiO2 layer formed during the annealing process, as confirmed by X-ray Diffraction (XRD) analysis. Metallography observations indicated that the microstructure of untreated specimens consisted of α and β phases. Scanning Electron Microscopy (SEM) analysis of specimens annealed for 30 minutes revealed an oxide layer on the surface without any visible pores. However, an increase in annealing holding time led to the formation of pores, particularly noticeable after 90 minutes of annealing. The presence of pores in the oxide layer resulted in an increased corrosion rate with longer annealing holding times. Conversely, hardness testing demonstrated that longer annealing holding times resulted in higher hardness values.

Surface Modification of NiTi Alloy with Sputtered Tantalum Coatings to Improve its Hardness, Corrosion Resistance and Biocompatibility

In this research, titanium alloys including smart nitinol (NiTi) were studied. The (NiTi) alloy tends to emitting (Ni) toxic ions due to its low resistance to corrosion within the body conditions over time. For (NiTi) coating process, the magnetron plasma sputtering (DC) technique was used with Aragon gas ratio of (90%) and Oxygen of (10%) in order to coat the alloy with Tantalum and its Oxide (Ta2O[Formula: see text] thin films. This is one of the methods used to improve the biocompatibility and better adhesion stability of the membrane on the (NiTi) surface, since Tantalum and its oxides are biocompatible and are not affected by the body fluids. Hardness, corrosion and biocompatibility were tested. The results showed improvement in the nominated properties using this coating technique. The hardness for the non-coated sample was (630 Kgf/mm[Formula: see text], meanwhile, the coated sample recorded (762 Kgf/mm[Formula: see text] using sputtering power of (25 W) with a thickness of (226 nm). Tantalum and its precipitated oxides on a pillar of thickness (90.4–226 nm) also exhibited a biocorrosion enhancement, when it was immersed in a Simulated Body Fluid (SBF). The corrosion rate for the non-coated sample was (1.204 × 10[Formula: see text], meanwhile for the coated sample, its value was (3.453 × 10[Formula: see text] at sputtering power of (15 W), considered as the lower corrosion rate. The scanning electron micrographs also showed an increase in the biocompatibility for the coated nitinol alloys (NiTi) in comparison with the non-coated, ones since it showed a clear formation of Hydroxyapatite (HA) on the sample surface after immersion in the SBF. This behavior was confirmed by the XRD measurements, which presented higher HA peaks on the coated samples surface in comparison with the non-coated samples.