Ti6Al4V Surfaces Research Articles

Lightweight refractory high entropy alloy coating by laser cladding on Ti–6Al–4V surface

In order to improve the Ti–6Al–4V (TC4) alloy's defects of low surface hardness and weak high-temperature oxidation resistance, an AlTiVMoNb lightweight refractory high-entropy alloy (RHEA) coating was developed. The AlTiVMoNb coating was successfully deposited on the TC4 substrate by laser cladding. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed that the coating and the TC4 substrate are metallurgically bonded, and the coating structure is composed of a single BCC HEA phase, and its lattice constant aXRD = 0.31246 nm, aTEM = 0.31234 nm. Due to the decrease of the d value has a more significant hindering effect on dislocation slip, the decomposition of spinodal in the bcc RHEA coating, the microhardness of the coating is 885.5 HV0.2, which is 2.52 times that of the TC4 substrate, and 1.66 times of the arc-melting alloy. The effect of complex mixed oxides such as Al2O3, TiO2, Al0·2Nb0·2Ti0·6O2, AlMoVO7, and Nb10·7V2·38O32.7 makes the coating continuously oxidized in the air at 800 °C for 120 h, and its oxidation weight is only 10.58% of the TC4 substrate.

Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters.

Ti6Al4V alloy was shot peened by using stainless-steel shots with different sizes (0.09–0.14 mm (S10) and 0.7–1.0 mm (S60)) for two durations (5 and 15 min) using a custom-designed peening system. The shot size was the main parameter modifying the roughness (0.74 µm for S10 vs. 2.27 µm for S60), whereas a higher peening time slightly increased roughness. Hardness improved up to approximately 35% by peening with large shots, while peening time was insignificant in hardness improvement. However, longer peening duration with large shots led to an unwanted formation of micro-cracks and delamination on the peened surfaces. After dry sliding wear tests, the mass loss of peened samples (S60 for 15 min) was 25% higher than that of un-peened samples, while the coefficient of friction decreased by 12%. Plastically deformed regions and micro-scratches were observed on the worn surfaces, which corresponds to mostly adhesive and abrasive wear mechanisms. The present study sheds light on how surface, subsurface and tribological properties of Ti6Al4V vary with shot peening and peening parameters, which paves the way for the understanding of the mechanical, surface, and tribological behavior of shot peened Ti6Al4V used in both aerospace and biomedical applications.

Surface properties and bacterial behavior of micro conical dimple textured Ti6Al4V surface through micro-milling

Although several techniques have been utilized to alter micro/nanotopographies of implant surfaces to improve the osseointegration rate, it has been challenging to fabricate micro/nano directional textures of desired shape size and accuracy. In the present study, mechanical micro-milling is utilized to create orderly conical dimple textures on the Ti6Al4V surface. The surface characterization, 3D surface topography, form measurement, and surface roughness were performed using FESEM and 3D surface analyzer. The wetting behavior of surfaces assisted by measuring advancing, receding contact angle, and contact angle hysteresis with ultrapure water and diiodomethane. Further, the Surface free energy of implants using the Chibowski approach, Neumann's equation, and Owen &Wendt method were calculated. The surface properties were studied with the roughness factor. The bacterial cell behavior of textured surfaces was studied in detail. Bacterial response studies on various surfaces are highly essential to gain insightful information about the usage of implants. Results indicate that the formed textures are uniform, dimensionally accurate with no defects, and as per the design of the experiment. The area surface roughness, hydrophilicity rate, and surface free energy increased in all cases, and all the surface properties alter with a change in textures density. Further, the results show that bacteria respond to surface modifications through changes in cell surface membrane, cellular roughness, morphological changes, the appearance of cellular appendages, and EPS production. The present study provides insight details about the surface properties of the Ti6Al4V implant and will be helpful to facilitate cell attachment, adhesion, proliferation, and protein adsorption.

Fabrication of highly ordered nanoporous oxide layer on Ti6Al4V surfaces for improved corrosion resistance property

Self-organized nanoporous oxide layer was successively prepared on the Ti6Al4V surface in an ethylene glycol electrolyte containing 0.1 mol dm−3 NH4F, 5 wt% H2O and 0.1 mol dm−3 lactic acid solution. Morphology, composition and crystal structure of the developed oxide layer were evaluated using FESEM, EDX and XRD analysis. FESEM study shows that the average diameter of the nanopores is ~ 89 nm and the thickness of the developed oxide layer is ~ 5.412 µm. XRD and EDX analyses indicate that the as-anodized nanoporous oxide layer are mainly amorphous in nature and contained significant amount of fluoride species. To remove the fluoride species and formed more chemical stable oxide layer thermal treatment is performed at 723 K for 3 h duration. XPS study confirms the presence of TiO2 and Al2O3 in the oxide layer. Potentiodynamic polarization study has been carried out to evaluate the corrosion inhibition property of the developed nanoporous oxide layer in an 8 g/l NaCl medium. It was concluded that the nanoporous oxide layer fabricated on Ti6Al4V surfaces shows good corrosion inhibition property than that of bare Ti6Al4V.

Surface-grafted zwitterionic polymers improve the efficacy of a single antibiotic injection in suppressing S. aureus periprosthetic infections.

Implant-associated bacterial infections are difficult to treat due to the tendency of biofilm formation on implant surfaces, which protects embedded pathogens from host defense and impedes antibiotic penetration, rendering systemic antibiotic injections ineffective. Here, we test the hypothesis that implant coatings that reduce bacterial colonization would make planktonic bacteria within the periprosthetic environment more susceptible to conventional systemic antibiotic treatment. We covalently grafted zwitterionic polymer brushes poly(sulfobetaine methacryate) from Ti6Al4V surface to increase the substrate surface hydrophilicity and reduce staphylococcus aureus (S. aureus) adhesion. Using a mouse femoral intramedullary (IM) canal infection model, we showed that the anti-fouling coating applied to Ti6Al4V IM implants, when combined with a single vancomycin systemic injection, significantly suppressed both bacterial colonization on implant surfaces and the periprosthetic infections, outperforming either treatment alone. This work supports the hypothesis that grafting anti-fouling polymers to implant surfaces improves the efficacy of systemic antibiotic injections to combat periprosthetic infections.

90. Nanoroughened microstructured orthopedic implant surfaces induce osteogenesis via soluble signaling factors produced by MSCs

BACKGROUND CONTEXT There is a growing clinical need to create implants with material properties that promote accelerated osseointegration and reduced recovery time for interbody fusion healing. We have shown that machined Ti-based implants possessing biomimetic surface topographies can direct osteoblast differentiation of multipotent bone marrow stromal cells (MSCs) in vitro and improve osseointegration in vivo in both animals and in humans following dental implant placement. PURPOSE This study examined the hypothesis that MSCs grown on nanotextured microstructured Ti6Al4V surfaces produce factors that regulate osteogenic differentiation of MSCs not on the surface. STUDY DESIGN/SETTING Not applicable. PATIENT SAMPLE Not applicable. OUTCOME MEASURES Not applicable. METHODS Ti6Al4V discs were grit-blasted and acid-etched, producing complex topography at the macro/micro/nanoscale (MMN; Medtronic/Titan Spine). All cultures were grown in MSC growth media (GM). Co-cultures were used to examine paracrine effects of factors released by human MSCs cultured on MMN surfaces. MSCs were grown on tissue culture polystyrene (TCPS) or MMN discs in 24-well plates. At 24 hours, inserts containing MSCs were placed into the wells and cultured in GM for 7 days, then moved to fresh GM for 24 hours. Alternatively, MSCs were cultured on MMN surfaces and TCPS for 7 days. Inserts with MSCs were added to the wells on day 7 and the co-culture was incubated for another 4 days. Inserts were moved on day 11 and cultured for 24 hours. In each experiment, a group of MMN discs received GM+15µg/mL BMP2 blocking antibody (abBMP2). BMP2, OPN, OPG, OCN, IL6, and VEGF-A in the conditioned media (CM) were assayed by ELISA and normalized to DNA. Athymic mice were divided into 3 groups: inactive demineralized bone matrix (iDBM), iDBM+rhBMP2 (MMN-CM concentration), and iDBM+MMN-CM proteins. MMN-CM was derived by culturing MSCs on MMN surfaces for 10 days and lyophilizing the CM from days 5-10. Gel capsules were implanted bilaterally into intramuscular pockets created in the hind limbs (N=8 capsules/group). Legs were harvested at 35 days. Bone formation was assessed by micro-CT and histomorphometry. RESULTS MSCs grown directly on MMN discs and on inserts above MMN discs increased production of OCN, OPN, BMP2, and VEGF-A compared to MSCs above TCPS, MMN discs+abBMP2, and insert control. Blocking BMP2 after surface mediated differentiation reduced OCN, OPN, and BMP2 compared to MMN groups. Total DNA content was increased on MMN discs+abBMP2. Micro-CT revealed greater mineralized tissue in MMN-CM groups compared to iDBM and iDBM+BMP2. There was more live bone in the MMN-CM group compared to iDBM. CONCLUSIONS MSCs cultured on nanoroughened microtextured biomimetic Ti6Al4V surfaces differentiate and produce local factors that can induce MSC differentiation above the surface through paracrine signaling factors such as BMP2. Reducing BMP2 function via abBMP2 inhibits MSC differentiation in contact with the surface and above the surface, indicating that BMP2 produced by cells on the surface is involved in the surface-dependent osteogenic differentiation process. Factors produced by the MSCs increased bone formation in a mouse model compared to control and BMP2-only treatment groups, suggesting that the engineered biomimetic surface topography may improve bone formation. FDA DEVICE/DRUG STATUS Interbody Fusion Implants (Approved for this indication)

Numerical analyses of molten pool evolution in laser polishing Ti6Al4V

Abstract As one advanced manufacturing process, laser polishing has been widely used in precision machining of metal or nonmetal materials. However, the evolution mechanism of molten pool formed during polishing process has not been thoroughly studied. This paper studies the polishing process of Ti6Al4V with a continuous wave (CW) fiber laser under the top-hat distributed heat source. A two-dimensional (2D) axisymmetric numerical transient model is established to simulate the formation process of the surface of Ti6Al4V after laser heating to form a molten pool and then cooling. It reveals that the evolution mechanism of physical processes involved in heat transfer, heat radiation, heat convection, melting and solidification during the polishing process. Particularly, the capillary and thermocapillary regimes (Marangoni flow) play a key role in smoothing the free-form surface of molten pool. The freedom surface can be smoothed effectively before the solidification of molten pool. In order to verify the correctness of the simulation model and explore the influence of laser irradiation duration on the material, the surface topography of the polished sample was investigated. It is found that the errors of the depth and width of the remelting zone are respectively less than 8 % and 22 % by the comparison of simulation and experimental results. Likewise, the depth and width of molten pool expand with the laser radiation duration increasing. Meanwhile, the polished surface topography becomes smoother.

Fabrication of Superhydrophobic Ti-6Al-4V Surfaces with Single-Scale Micotextures by using Two-Step Laser Irradiation and Silanization.

Laser irradiation is a popular method to produce microtextures on metal surfaces. However, the common laser-produced microtextures were hierarchical (multiscale), which may limit their applicability. In this paper, a method of two-step laser irradiation, combining first-step strong ablation and sequentially second-step gentle ablation, was presented to produce micron-rough surface with single-scale microtextures. The effect of laser fluence on the Ti–6Al–4V surface morphology and wettability were investigated in detail. The morphology results revealed that the microtextures produced using this method gradually evolved from multiscale to single-scale meanwhile from microprotrusions to microholes with increasing the second-step laser fluence from 0.0 to 2.4 J/cm2. The wettability and EDS/XPS results indicated that attributing to the rich TiO2 content and micron roughness produced by laser irradiation, all the two-step laser-irradiated surfaces exhibited superhydrophilicity. In addition, after silanization, all these superhydrophilic surfaces immediately turned to be superhydrophobic with close water contact angles of 155–162°. However, due to the absence of nanotextures, the water-rolling angle on the superhydrophobic surfaces with single-scale microtextures distinctly larger than those with multiscale ones. Finally, using the two-step laser-irradiation method and assisted with silanization, multifunctional superhydrophobic Ti–6Al–4V surfaces were achieved, including self-cleaning, guiding of the water-rolling direction and anisotropic water-rolling angles (like the rice-leaf), etc.

Polydopamine Linking Substrate for AMPs: Characterisation and Stability on Ti6Al4V.

Infections are common complications in joint replacement surgeries. Eradicated infections can lead to implant failure. In this paper, analogues of the peptide KR-12 derived from the human cathelicidin LL-37 were designed, synthesised, and characterised. The designed antimicrobial peptides (AMPs) were attached to the surface of a titanium alloy, Ti6Al4V, by conjugation to a polydopamine linking substrate. The topography of the polydopamine coating was evaluated by electron microscopy and coating thickness measurements were performed with ellipsometry and Atomic Force Microscopy (AFM). The subsequently attached peptide stability was investigated with release profile studies in simulated body fluid, using both fluorescence imaging and High-Performance Liquid Chromatography (HPLC). Finally, the hydrophobicity of the coating was characterised by water contact angle measurements. The designed AMPs were shown to provide long-term bonding to the polydopamine-coated Ti6Al4V surfaces.

Bio-Functional Coating on Ti6Al4V Surface Produced by Using Plasma Electrolytic Oxidation

One way to improve the biofunctionality of titanium alloys is by implementing plasma electrolytic oxidation (PEO) to incorporate bioactive elements such as fluoridated hydroxyapatite, into surface coatings of orthopaedic and dental implants. Hydroxyapatite (HAp) is known as a bioactive coating while fluorapatite (FAp) has an antibacterial effect that would enhance the bio-functionality and reduce the failure rate of orthopaedic and dental implants. The purpose of this study was to develop fluoridated hydroxyapatite as a bio-functional coating on Ti6Al4V with electrolyte containing trisodium orthophosphate, potassium hydroxide, and calcium fluoride. The coating surface and cross-section morphologies were evaluated, and the species in the electrolyte solution were found, and irregular micropores shapes were observed by field emission scanning electron microscopy (FESEM) and energy dispersive spectrometer (EDS). The phase composition of the coating surface containing TiO2 (anatase and rutile), tricalcium orthophosphate, HAp, and FAp was characterized by X-ray diffractometer (XRD). The adhesive strength of the coating was analysed by a micro-scratch test. Simulated body fluid (SBF) immersion test was performed to investigate the bioactivity of the coating. In this study, we demonstrated that the PEO technique has a good potential to develop bio-functional surface modifications that can affect the chemical composition and roughness of the coating surface. The FAp coating may provide insights for subsequent bioactive coatings while improving the antibacterial properties for orthopaedic and dental implants. Future work shall investigate the optimal amount of fluoride in the coating layer that obtains excellent results without causing adverse effects on adjacent tissue.

Structuring of the Ti6Al4V alloy surface by pulsed laser remelting

In this work, we present experimental data on the structure, chemical composition and wear resistance of a titanium alloy Ti6Al4V after pulsed laser treatment. The material was investigated to get a better understanding of the nature of laser melting, ablation of the surface layer by using nanosecond, picosecond, and femtosecond lasers. Melting and subsequent rapid solidification forms a new changed microstructure of the Ti6Al4V surface layer. This rapid solidification of the surface layer affects the new microstructure as well as its surface’s topography (texture). It is shown that using different laser’s pulse parameters the desired surface topography (texture) of the Ti6Al4V can be obtained.The laser treatment with femtosecond and picosecond pulse allows creating periodical micro/nano structures on the surface. These structure are characterized by good wear resistance as compared with the non-texturized surface of Ti6Al4V. In the case of nanosecond laser surface treatment of the Ti6Al4V elements, it is possible to obtain the strongly extended surface of Ti6Al4V elements in the form of metal-oxide foam that is also characterized with good wear resistance. The laser treatment with femtosecond and picosecond pulse allows creating periodical micro/nano structures on the surface. These structure are characterized by good wear resistance. In the case of nanosecond laser surface treatment of the Ti6Al4V elements, it is possible to obtain the strongly extended surface of Ti6Al4V elements in the form of metal-oxide foam. Analysis of the foam microstructure shows that the α-Ti phase was transformed mostly into β-Ti, and is significantly fragmented.

In situ preparation of antibacterial Ag particles on Ti6Al4V surfaces by spray deposition

In this study, spray deposition technology was used for in situ preparation of silver (Ag) particles on additively manufactured Ti6Al4V alloy surfaces. An amount of silver particles (200 nm) was uniformly achieved on pristine or acid-etched titanium (Ti) alloy surfaces by designing the spraying passes. Energy-dispersive X-ray spectroscopy and X-ray diffraction were used to confirm their composition and crystal structure. The antibacterial activity of the prepared silver particles was investigated against Staphylococcus aureus and Escherichia coli bacteria. Thereafter, the antibacterial activity of silver particles on Ti6Al4V alloy surfaces against S. aureus and E. coli bacteria was investigated by utilizing the bacterial counting method. The damaged cell membranes around the silver particles revealed excellent antibacterial properties, indicating the possibility of harnessing the spray deposition method to take advantage of the in-situ-produced antibacterial silver coatings on additively manufactured metallic materials. The excellent antibacterial activity of the surfaces suggests that silver particles prepared by spray deposition are potential candidates for future dental implant applications.

Tribological investigations of wear resistant layers developed through EDA and WEDA techniques on Ti6Al4V surfaces: Part I – Ambient temperature

The incompetent tribological behavior of Ti6Al4V (Ti64) poses an imperative need to develop new techniques or improve existing processes for surface characteristic enhancement of the alloy. Given the above, the tribological characteristics of the wear-resistant layers deposited through electrical discharge machining assisted alloying (EDA) and wire electrical discharge machining assisted alloying (WEDA) got investigated at ambient condition. The electrical discharge machined and alloyed Ti64 (ETi64), and wire-electrical discharge machined and alloyed Ti64 (WETi64) specimens demonstrated a decrement (62.89%) and increment (11.01%) in specific wear rate (SWR), respectively as compared to the bare Ti64 (BTi64). The near similar friction and wear behavior associated with the BTi64, and WETi64 is subject to the occurrence of the wear mechanisms, viz. adhesion, abrasion, and delamination. For ETi64 specimens, the continuous squashing and sintering of the spalls/flakes and the ability of the deposited layer (through EDA) to impart ceramic characteristics aided in achieving superior wear-resistant characteristics. They also assist the formation/existence of the distinct oxides (TiO and Ti8O15). The failure of the WEDA specimens during dry interactive sliding attributes to the inadequate thickness of the protective layers and the absence of high carbon (C) diffusion achievable through the utilization of hydrocarbon dielectrics.

Surface machining of Ti6Al4V by means of Micro-Electrical Discharging to improve adhesive joining

The Micro-Electrical Discharge Machining (Micro-EDM) technique has been employed to machine micro-patterns with shaped micro-slots on Ti6Al4V surfaces. Ti6Al4V substrates, with and without micro-slots, were bonded using a commercial epoxy adhesive. Optical microscopy and SEM were used to observe the micro-patterned Ti6Al4V surfaces before and after joining and to analyse the fracture surfaces after mechanical tests. The joints were mechanically characterised, with and without micro-patterns, by means of Single Lap Offset (SLO) shear tests under compression to understand the effect of differently shaped micro-slots. The effects of the shape of the micro-slots, their interlocking or overlapping, and their orientation, with respect to the applied load, are presented and discussed in terms of mechanical performance of the joints.

Impact of Femtosecond Laser Treatment Accompanied with Anodization of Titanium Alloy on Fibroblast Cell Growth

Herein, Ti6Al4V alloy is surface modified by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples (laser‐induced periodic surface structures). To make the surface hydrophilic, anodization is performed resulting in further smoothness of microstructure and a final thickness of 35 ± 4 nm is estimated for oxide produced after anodization at 10 V (scan rate = 0.1 V s−1) versus standard hydrogen electrode. The obtained electrochemically active surface area (ECSA) is approximately 8 times larger compared with flat mirror polished Ti6Al4V surface. Combined chemical analysis by Pourbaix diagram and X‐ray photoelectron spectroscopy (XPS) analyses reveal that titanium and aluminum are passivating into TiO2 and Al2O3, but the dissolution of aluminum in the form of solvated ion is inevitable. Finally, cell seeding experiments on anodized and laser‐treated titanium alloy samples show that the growth of murine fibroblast cells is significantly suppressed due to unique surface texture of the laser‐treated and anodized titanium alloy sample.

Deposition of biphasic calcium phosphate film on laser surface textured Ti–6Al–4V and its effect on different biological properties for orthopedic applications

Abstract The present study reports laser surface texturing (LST) of Ti–6Al–4V using a Nd-YAG laser with a particular set of parameters and three different overlapping factors (OF): 0%, 25% and 50%. Biphasic calcium phosphate (BCP) film was deposited on bare as well as textured Ti–6Al–4V specimens by using radio frequency (RF) sputtering. The simultaneous effect of texturing as well as BCP coating on different physical and biological properties was investigated. The study revealed that the surface wettability of bare Ti–6Al–4V enhanced after laser texturing (as contact angle reduced from 89° to 71°-77°). It was further improved upon BCP deposition to make the Ti–6Al–4V superhydrophilic (contact angle ≈ 17°-21°). It was also observed that the surface roughness of bare Ti–6Al–4V significantly increased from Ra ≈ 94 nm to Ra ≈ 0.98–1.84 μm for different micro-dimpled texture substrates. The dimensions of micro-dimpled texture did not change after BCP deposition; however, a non-uniform film is deposited with increase in surface roughness. Protein adsorption was found as a function of surface hydrophobicity, which increased from 5.3 to 7.11 μg/cm2 with the rise in hydrophobicity of modified surfaces. Compared to bare Ti–6Al–4V and BCP deposited bare-Ti-6Al–4V surfaces, the BCP deposited textured surfaces exhibit higher number of well spread MG63 osteoblast cells. For the same surface chemistry, increase in surface area (roughness) improves cellular behavior. With texturing of the substrate, the cell adhered percentage and average cell area improved significantly and BCP-(50% OF)–Ti–6Al–4V was found to have the maximum cell spreading and proliferation. Overall, these findings revealed that a micro-dimpled textured surface followed by BCP film deposition strategy improved the physio-chemical properties of surfaces such as surface roughness and wettability. This in turn enhanced the bioactivity, cell adhesion and proliferation of bone cells (MG63) on modified Ti–6Al–4V surfaces and based on the results we envisage that can be potentially used for orthopedic and dental applications.

One-step synthesis of nano-hydroxyapatite/graphene nanosheet hybrid coatings on Ti6Al4V alloys by hydrothermal method and their in-vitro corrosion responses

The nano-hydroxyapatite (nHA) matrix coatings doped with different graphene nanosheets (GNSs) weight percentages on the Ti6Al4V alloy were synthesized by hydrothermal method, successfully. Surface roughness, porosity, hardness and, in-vitro responses of the coatings have been detailly investigated. The surface morphologies of the nHA/GNS coatings characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). The surfaces crystalline nature and phases of the coating were confirmed by using X-ray diffraction (XRD) and electron dispersive spectroscopy (EDS). An attenuated total reflection infrared (ATR-IR) spectroscopy was used to characterize the functional groups of the coatings. A partially porous structure with nano-scale HA nucleation in the coating was obtained and, the number of nHA nucleation in the layers increased significantly with increasing GNS weight percentage in hybrid structures. The micro Vickers hardness of the hybrid coatings increased with the increasing GNS weight percentage in the coating layer. The electrochemical studies showed that the nHA/GNS hybrid structure progress the in-vitro corrosion resistance of hydrothermal treated Ti6Al4V surfaces. However, there is a certain ratio of GNS in the nHA matrix structure to achieve good surface property. The highest surface area and the high corrosion resistance were obtained in nHA/5GNS coating due to its better surface property than others.

Molecular arrangement mechanisms within phosphate films on Ti6Al4V regulated by intermolecular forces based on sum frequency generation vibrational spectroscopy

Self-assembled films of phosphonic acid on Ti6Al4V surfaces can improve the interface properties, mainly in terms of biocompatibility. In this study, different phosphoric acid films were formed on Ti6Al4V surfaces and the intermolecular forces in the films were explored by sum frequency generation (SFG) vibrational spectroscopy due to its intrinsic sub-monolayer interfacial selectivity. With the surface and interface resonance signals analysis and theoretical calculation, it is found that when the molecular polarity is the same, there is an extreme value of carbon chain length, near which van der Waals (vdW) forces can more effectively drive the self-assembly arrangement. However, for the phosphonic acids with polarity groups, the stronger polarity of the terminal functional groups generated the electrostatic interactions between the phosphonic acid molecules, further enhancing the distance between molecules and weakening the vdW interactions. Moreover, the new electrostatic force participated in the final molecular interactions. The synergistic effect of vdW and electrostatic forces constituted the final molecular interaction force, driving the molecular arrangement. A larger molecular interaction force results in lager inclination angles of the carbon chains, which is beneficial to resisting molecular collapse within the films. This research can be an effective guidance for improving SAMs properties.

Modification of Ti6Al4V surface properties by combined DLW-DLIP hierarchical micro-nano structuring

Abstract The use of pulsed laser irradiation techniques has proven to be a clearly effective procedure for the achievement of surface properties modification via micro-/nano-structuration, different conceptual approaches having been the subject of research and extensively reported in the literature. Completing the broad spectrum of applications developed mostly involving the generation of structured surfaces (particularly of metallic materials) with specific contact, friction and wear functionalities, the application of laser sources to the surface structuration of metal surfaces for the modification of their wetability and corrosion resistance properties is considered. The particular problems found for the generation of the appropriate surface microstructure able to replicate the hydrophobic behaviour of some live structures present in nature, their long term stability and their amenability to macroscopic scale are discussed along with innovative methods to generate the required hierarchical micro-/nano-structures by a combination of the DLW and DLIP techniques.

Surface engineering of a titanium alloy for tribological applications by nanosecond-pulsed laser

In many applications, surface engineering is needed in order to overcome the poor wear properties of titanium alloys. A fiber laser was used in different operation modes for remelting a Ti6Al4V surface and subsequently smoothing it again, resulting in a smooth, glossy and crack-free surface. The laser treated surface was characterized by tribological experiments, nanoindentation and (transmission) electron microscopy and compared to samples treated by plasma nitridation and thermal oxidation. All surface treatments improved the tribological behavior of Ti6Al4V to different extents. Nanoindentation measurements showed no strict correlation of mechanical properties and tribological behavior. It is hypothesized that apart from mechanical properties, binding of titanium electrons by interstitials plays a role in the occurrence or absence of adhesive wear.