Mirror-polished Surface Research Articles

Experimental investigations of chemo-mechanical magneto-rheological finishing of Al-6061 via composite magnetic abrasive

ABSTRACT To achieve flawless soft material surfaces, defects and irregularities must be eliminated. Traditional abrasive-mixing techniques frequently produce surface flaws as a result of abrasive embrittlement, resulting in poor surface-quality. As a result, ensuring an immaculate finish is critical for these surfaces. In contrast, the chemo-mechanical magneto-rheological finishing (CMMRF) process, which employs a composite magnetic abrasive (CMA)-based smart fluid, has proven to be extremely effective at producing nano-finished surfaces. This study used a central-composite-rotatable design (CCRD) based on response surface methodology (RSM) to analyze how CMAs variables, slurry-based parameters, and polishing time affect final surface roughness (R a ) and percentage change in roughness (%∆R a ) for Al-6061. The CMMRF process resulted in a superior Al-surface finish (R a ) of 29 nm and a %∆R a of 91.23%. Statistical models predicted R a and %∆R a values, which matched experimental results. Characterization tests on the final Al-surface revealed significant reduction in initial machining scratches and valleys, resulting in a superior mirror-polished surface via CMA-based polishing.

Elaboration of highly hydrophobic surface by coupling femtosecond laser texturing and fluorine-free chemistry

The elaboration of a nylon surface with highly hydrophobic properties is achieved. These properties are obtained by coupling a physical texturing and a hydrophobic chemical coating. The texturing is done by femtosecond laser with parameters designed to obtain a micrometric pillar network. The chemical coating is obtained by deposition of a fluorine-free dendritic solution, terminated by isobutyl-polyhedral oligomeric silsesquioxanes (iBuPOSS). The apparent contact angle of chemically and physically textured surface is evaluated at 142°. Its hysteresis is estimated around 24°. The wetting properties and topography of the textured-coated surface are compared to the properties of a mirror-polished surface, a coated surface and a textured surface. Both the coated and the textured surfaces present a higher contact angle than the mirror polished surface. Nevertheless, the hysteresis is strongly increased on these surfaces. Whereas for the textured-coated surface, thanks to the physico-chemical coupling, the increase of the static contact angle is associated with a significant reduction of the hysteresis. The wetting mechanisms of these surfaces are interpreted in the sense of Wenzel and Cassie–Baxter models and the interest of the coupling laser texturing - dendritic chemistry without fluorine is discussed with regard to the Extrand model.

Development of Ge Isotropic Wet Etching Solution and its Application to High Quality Ge-on-Insulator Fabrication through the Etchback Method

Ge has many unique characteristics, such as high carrier mobility and a narrow bandgap corresponding to near-infrared wavelengths. To take advantage of the attractive characteristics of Ge, Ge-on-Insulator (GOI) structures are necessary. In this study, we focus on a direct wafer bonding and etchback method to fabricate GOI structures and explore appropriate etching solutions for the etchback. An HF + H2O2 + CH3COOH solution can isotropically etch Ge and improve surface uniformity. The resulting surfaces were sufficiently flat to achieve Schottky and MOS diodes showing good electrical characteristics of the same level as devices based on commercial mirror-polished Ge surfaces. We discuss the role of the chemicals in the etching solution in achieving the flat surface. We fabricated GOI structures and a back-gate GOI capacitor through direct wafer bonding of SiO2/Si and Al2O3/Ge with the etchback method using the solution. The resulting electrical characteristics are also explained using theoretical calculations. This approach might offer an alternative route to high-quality GOI fabrication.

Experimental analysis of a compact cooling system containing an enhanced-surface spray heat sink

This paper examines the performance of a heat sink that combines an evaporator and an expansion device into a single component within a compact vapor compression refrigeration system designed for applications with high heat fluxes. The liquid refrigerant at high pressure expands through orifices, generating a spray that impacts a copper heater. The heated surface is enhanced with laser-micromachined micropillars featuring a square cross-section to improve the thermal conductance of the boiling liquid film. Qualitative evaluations of the enhanced surfaces using interferometry analyses determined the heat transfer surface area and assessed the effectiveness of the fabrication technique. The experiments involved using R-134a, a two-orifice expansion device, and enhanced surfaces with pillar edge sizes ranging from 200 to 600μm. This analysis encompasses the cooling system’s thermodynamic performance, including compressor power and coefficient of performance, as well as steady-state heat transfer parameters such as convection coefficient and critical heat flux. The system achieved a cooling capacity of 230 W (35.9 W/cm2), with the heater surface temperature staying below 22.9 °C and the highest average heat transfer coefficient reaching as high as 55 kW/(m2-K). This represents a 129% increase in thermal conductance compared to mirror polished surfaces, leading to a significant reduction in the temperature of the heated surface. Additionally, the area-corrected heat transfer coefficient is computed to verify the thermal resistance reduction unrelated to the surface area enhancement, and a 60% reduction is found. Furthermore, although this heat transfer enhancement shows minor to no influence on the thermodynamic performance of the refrigeration system, the heater cooling efficiency, defined as the ratio of the enthalpy rise delivered by the heat source to its ideal maximum, increased by 13%. The findings are supported by high-speed video sequences illustrating the boiling heat transfer features.

Surface structuring of β-TCP and transition to α-TCP induced by femtosecond laser processing

Tricalcium phosphate (Ca3(PO4)2, TCP), is one of the most studied and used as material for bioresorbable implants. The β phase has a slower dissolution dynamic and ensures mechanical support for a longer time in biological environment, while a faster release of ions characterize the α phase that trigger a stronger biological response. In this work a femtosecond laser system was used to process β-TCP pellets surface. The femtosecond laser processing results in surface morphology modification, by turning the flat mirror polished surface into a rough and opaque one. The morphological and phisycochemical characteristics of material surface were studied by means of SEM, AFM, Raman, XRD and contact angle measurement. The processed surface showed the formation of micro and nano roughness alongside, furthermore a partial phase transformation from β-TCP to α-TCP was detected. A significant improvement in surface wettability for three different liquids (i.e.water, ethylene glycol and diiodo-methane) is reported. This implies an increase in surface free energy as well. The combination of α and β phase, together with the increased roughness obtained by laser processing, could positively affect the cell adhesion and metabolic activity.

Probing the reaction mechanism between a laser welded polyamide thin film and titanium with XPS and ToF-SIMS

The biomedical industry uses more and more polymer/metal hybrid assemblies because of the ability to combine the advantages and lower the inconveniences of both materials. The key is to assemble them. Among the high variety of existing assembling techniques, laser welding appears as an excellent option. It is a quick process allowing a great design flexibility, high reproducibility without intermediate material needed to create the adhesion, which is advantageous for biomedical applications. The laser welding process creates strong adhesion between dissimilar materials, but the root cause for adhesion is still unclear. The analytical challenge is to gain an information at the molecular level from an interface that is deeply buried between the two materials. Such a study requires extremely surface sensitive analytical methods, such as ToF-SIMS or XPS in order to detect chemical bonds, but also a method to expose the interface to the X-ray or ion beam. In order to investigate the chemical bonding at the interface between polyamide-6.6 and titanium, mirror polished titanium surfaces were prepared, on which a thin polyamide-6.6 film was spin-coated. The samples were laser welded, and after dissolving the polymer thin film, XPS and ToF-SIMS measurement were performed. The ToF-SIMS data interpretation was assisted by a principal component analysis. This multivariate analysis is rather common for ToF-SIMS data but is more rarely used to solve adhesion problems. This allowed to show the nature of the chemical bond at the interface and to propose a reaction mechanism.

Simultaneous measurement of heat flux and droplet population during dropwise condensation from humid air flowing on a vertical surface

A new experimental apparatus for the investigation of dropwise condensation from humid air flowing over a vertical aluminum surface at controlled velocity is presented. Differently from other works on this subject, here we measure simultaneously, during condensation of flowing moist air, the total heat flux (by a heat flux sensor), the latent heat flux (by weighing the mass of condensate), the small and the large droplet population. Experimental tests were performed on two aluminum specimens that display different wettability: a mirror-polished surface (56° advancing contact angle, 46° contact angle hysteresis) considered as a baseline, and a coated surface functionalized by using a sol–gel coating (87° advancing contact angle, 15° contact angle hysteresis). The effects of the wall subcooling, moisture content, relative humidity and air velocity on the heat and mass transfer during dropwise condensation (DWC) are investigated. Enhanced condensation is observed on the coated surface but, with the increase of relative humidity and wall subcooling, the advantage of using the coated surface diminishes. Time-lapse videos of the condensation process, featuring droplets detection down to three microns, are used to investigate droplet population (both large and small droplets) and nucleation sites density. Usually, DWC models assume tentative values of the nucleation site density and tentative trends of the droplet population. In this paper we measure and discuss such parameters. The determination of the nucleation site density is crucial because it affects the droplet interactions and the drop size distribution, determining the overall heat transfer. The measurement of the nucleation site density is currently rare in the literature, especially during condensation of flowing humid air. Here the nucleation site density is determined with a double approach and it is found to vary between 3.3 × 108 sites/m2 and 6.1 × 108 sites/m2 in the investigated range of experimental conditions. The experimental droplet population is also compared against the predicted one, finding some disagreement which should be properly addressed for the development of improved DWC models.

Fabrication of Punch and Die Using Plasma-Assisted 3D Printing Technology for Piercing Sheet Metals

A pair of punch and die was often fabricated using subtractive manufacturing processes such as milling and other machining processes. However, additive manufacturing could be used to perform the same processes. This study explored this possibility. In particular, this study fabricated a pair of T-shaped punch and die made of AISI316L austenitic stainless steel using an additive manufacturing process called plasma-assisted 3D printing. Accordingly, T-shaped negative and positive 2D patterns were screen-printed onto the mirror-polished surfaces of the substrates made of AISI316L austenitic stainless steel. The printed film worked like a mask to prevent the printed substrate surfaces from nitriding. In order to form a thick nitrided layer, the unprinted substrate surfaces were selectively nitrided at 673 K for 14.4 ks. The un-nitrided segments of the substrates were uniformly removed by sand-blasting that involved shooting silica particles on the substrate’s surfaces. As a result, the substrates printed with negative and positive T-shaped patterns were transformed into the punch head and die cavity. In order to see the efficacy of the fabricated punch and die pair, this pair was used for piercing the electrical steel sheets under a controlled clearance. Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) was used to measure surface topography after piercing. In addition, SEM and a 3D profilometer were used to measure the punch and die profiles after piercing. The abovementioned measurement results showed that the fabricated punch and die exhibited highly accurate piercing behavior. Thus, the plasma-assisted 3D printing was useful for punch and die fabrication.

Plasmon resonance measurements in pool boiling, condensation and evaporation experiments on a nanostructured surface

Surface plasmon resonance (SPR) is used in a wide range of applications, including biology, physics and materials science, because of its ability to obtain sub-wavelength measurements from a simple white light source, in real time and non-invasively. Surprisingly, this technique is just beginning to be used in the field of phase change heat transfer, whereas fundamental phenomena occurring near interfaces, such as ice, liquid or vapour nucleation, require the development of innovative techniques capable of reaching this little-explored scale. In this paper, the grating-coupled SPR method is implemented on aluminium samples on which different liquid-vapour phase change phenomena take place. The first goal of this work was the study of the influence of the surface topography on the boiling phenomenon, in particular in the presence of geometrical patterns of micrometric and sub-micrometric scales, typical of those necessary for the implementation of the grating-coupled SPR method. The results show that mirror-polished surfaces covered with periodically structured sub-micrometric grooves have the best thermal characteristics amongst the different surfaces tested, similar to those of a mirror-polished surface with a small number of holes evenly distributed over the surface. Sub-micrometre scale corrugated surfaces being also ideally suited for SPR, they were also used in the second part of the paper to evaluate the potential of this method for the study of boiling, condensation and evaporation. Although our optical SPR test bench, limited by its acquisition frequency, was not able to detect the very fast birth of the first vapour nuclei at the beginning of nucleate boiling, the results yet show the interest of the method as a non-intrusive technique to measure the temperature of the liquid in the very vicinity of the wall, which is also an essential measurement. In addition, measurements from the condensation and evaporation experiments show that SPR provides a useful means to monitor the formation of a nanoscale condensation film and the evaporation of an acetone film in real time. This exploratory study opens perspectives to understand the small-scale phenomena that occur during phase changes and thus help develop functional surfaces that promote or delay their occurrence.

Evaluation of the Repolished Surface Properties of a Resin Composite Employing Structural Coloration Technology.

Resin composites employing structural coloration have recently been developed. These resins match to various tooth shades despite being a single paste. To accomplish this, the filler and base resin are tightly bonded, which is thought to provide excellent discoloration resistance. Here, we investigated the surface properties of one of these resins, including the discoloration of the repolished surface. We developed an innovative in vitro method to adjust the repolished surface, in which structural degradation is removed according to scanning electron microscopy (SEM) observation rather than by the naked eye. The resin samples (20 mm (length) × 10 mm (width) × 4 mm (depth)) were manufactured using this resin material. After accelerated aging of the resin by alkaline degradation, the resin was repolished and the discoloration (ΔE*ab), surface roughness (the arithmetic mean roughness (Ra)), and glossiness (the 60° specular) were measured. SEM observation showed that the appearance of the bond between the organic composite filler and base resin on the repolished surface was different from that on the mirror-polished surface. This revealed that according to our in vitro method it was difficult to make the repolished surface structurally identical to the mirror-polished surface. Among the properties of the repolished surface, the degree of discoloration did not change despite the rougher and less glossy surface. It can be concluded that the factors that induce discoloration in this resin composite are independent of the surface roughness and glossiness.

Prediction of maximum spreading time of water droplet during impact onto hot surface beyond the Leidenfrost temperature

When a water droplet impacts on a heated surface in the film boiling regime, it will spread, recede, and finally bounce off from the heated surface. These unique liquid-solid interactions only occur at high surface temperatures. Our main objective in this research is to measure the maximum spreading and residence time of the droplet and the findings were compared to theory. We focused our study in the film boiling regime. Brass material was selected as the test surface and was polished until it became a mirror polished surface. The temperature range for this experimental work was between 100 °C up to 420 °C. Degassed and distilled water was used as the test liquid. The high speed video camera recorded the images at the rate of 10,000 frames per second (fps). As a result, it was found that the experimental value of maximum spreading and residence time agreed closely with the theoretical calculation. A new empirical formula that can be used to predict the maximum spreading time in the film boiling regime is also proposed.

Picosecond laser-induced nanopillar coverage of entire mirror-polished surfaces of Ti6Al4V alloy

The goal of this study was to investigate a study for the efficient generation of pillar-like nanostructure (nanopillar) on a material surface over a large area. In this research, a vertical cross-scanning (VCS) strategy using two linearly-polarized lasers with different laser conditions was proposed for the generation of nanopillars on a mirror-polished surface on a large scale. It found that the laser fluence and scanning speed of the second laser scanning should be controlled within a specific range to generate the nanopillars. Additionally, the distance between scan lines, which is defined as hatch distance, h, of the second scan, is also a non-negligible factor to induce nanopillars to cover the entire surface. This work demonstrated that the VCS method is a feasible strategy for the fabrication of nanopillars on the entire mirror-polished surface of Ti6Al4V alloy by linearly-polarized picosecond laser conveniently and efficiently.

Adhesion of various dental luting cements to the mirror-polished surface of metallic dental materials

本研究の目的は，鏡面研磨されたJIS2 種チタン表面に対する各種市販合着用セメントの引張接着強さを検討し，金銀パラジウム合金および金合金への引張接着強さと比較することである．3 種類の歯冠修復用合金・金属（JIS 第2 種鋳造用チタン12％金銀パラジウム合金，およびタイプ3 金合金）平坦面を鏡面研磨し，表面処理後に合着用コンポジットレジンセメント（パナビア®V5），コンポジット系接着性レジンセメント（リライエックスTM アルティメット），4-META / MMA-TBB 系接着性レジンセメント（スーパーボンド®），合着用従来型グラスアイオノマーセメント（ハイ－ボンドグラスアイオノマーCX）のいずれかを用いてステンレス棒を接着した．なお表面処理にはパナビアV5 の場合ではクリアフィル® セラミックプライマープラスまたはアロイプライマーのいずれかを， リライエックスTM アルティメットではスコッチボンドTM ユニバーサルアドヒーシブを，スーパーボンドではV- プライマーをそれぞれ塗布した．またチタン鏡面研磨面ではスーパーボンドの応用方法の相違についても検討した．12％金銀パラジウム合金の場合，V- プライマー/ スーパーボンドでの接着が最も高い接着強さを示した．タイプ3 金合金の場合においてもV- プライマー/ スーパーボンドでの接着で最も高い接着強さを示したが，その値は12％金銀パラジウム合金の場合よりも大幅に低いものであった．JIS2 種純チタンの場合，スーパーボンド使用時に被着面に対してあらかじめ活性化液（クイックモノマー（5％ 4-META + 95％ MMA）とキャタリストV（TBB-O）の混合液）を塗布した場合に接着強さの向上を認めた．本研究結果から，鏡面研磨された歯冠修復用合金・金属に対する金属用プライマー/ 合着用セメントの効果は金属材料の種類に依存すると結論付けられた．【顎咬合誌 40（ 3 ）：219-230，2020】

Direct correlation between martensitic transformation and incubation-acceleration transition in solution-treated AISI 304 austenitic stainless steel cavitation

This work shows in details how the γ→α′(ε) (austenite (γ), martensite (α′, ε)) strain-induced martensitic transformation affects the cavitation erosion behavior of the solution-treated AISI 304 austenitic stainless steel. For this purpose, mirror-polished surface samples initially presenting ~93 vol% γ + ~7 vol% α′ were subjected to cavitation erosion testing according to ASTM G32-10, being carefully characterized by X-ray diffraction and hardness measurements at the tested surfaces. Under cavitation, the studied steel surface showed total γ→α′ transformation fraction of ~89 vol% (which supposedly is directly related to the needed ~4 vol% expansion for the transformation), with no effective mass loss for 180 min testing time, clearly defining the transition from the incubation period (IP) to the acceleration stage of the cavitation testing. For this transformation condition, initially presenting remaining ~11 vol% γ fraction, successive material removal steps and XRD analysis were carried out aiming at determining the actual depth at which this cavitation-related transformation takes place into the steel austenitic matrix. In this case, ~57 μm depth was found when XRD patterns before testing (leading to ~93 vol% γ results) were obtained. Finally, the variation of the average γ→α′ transformation rate along all IP presented a maximum level of ~0.60% min−1 between 60-120 min, which is attributed to the great difference on the mechanical properties of the γ and α′ phases, whose volume fractions continuously change at the surface under cavitation, thus affecting the evolution of the referred surface transformation.

Strong variant selection observed in the α−ε martensitic transition of iron under quasihydrostatic compression along [111]α

The $\ensuremath{\alpha}$ (bcc) phase of single-crystalline iron was compressed along the ${[111]}_{\ensuremath{\alpha}}$ direction under quasihydrostatic and nonhydrostatic conditions. The emergence of the $\ensuremath{\epsilon}$ (hcp) phase variants via the pressure-induced martensitic transformation was investigated using x-ray diffraction and optical observations of the sample surface. In quasihydrostatic compression, the $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\epsilon}$ transition occurred at approximately 14 GPa accompanied by the sudden appearance of texture structures on the mirror-polished sample surface. The texture structure divided the sample surface into two characteristic regions: distorted regions with undulations and flat regions without undulations. Although martensitic transformation based on the Burgers model allows for the emergence of 12 $\ensuremath{\epsilon}$ variants from one single-crystalline phase, the transition proceeded according to the Burgers model, but selected variants preferably emerged depending on the regions in the texture structure. The flat region consisted of only three variants whose $c$ axes were parallel to the sample surface. The region near the undulation exhibited a large number of variants whose $c$ axes aligned parallel and nonparallel to the sample surface. The $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\epsilon}$ transition under nonhydrostatic compression deviated from the Burgers model, and the variant selection was not observed. This study demonstrates that the quasihydrostatic compression along ${[111]}_{\ensuremath{\alpha}}$ reduces the number of variants via strong variant selection. The strong preferred orientation is useful for investigating the anisotropy of physical properties in the $\ensuremath{\epsilon}$ phase.

Clinical application of the mirror irradiation technique in photodynamic therapy for malignant glioma.

Intraoperative photodynamic therapy (PDT) using talaporfin sodium for malignant glioma is effective both in the experimental and in the clinical setting. Because the irradiation unit is fixed to the objective lens of the operating microscope, blind spots for irradiation exist. To overcome this problem, we developed a mirror reflecting system using a modified dental mirror. The developed mirror is made of stainless steel, has a mirror-polished surface, and is rhodium coated on 1 side, which is the reflecting surface. The reflection rate was measured using He-Ne laser irradiation. The reflection intensity was measured using a laser power meter when the incident angle to the mirror was changed to 60°, 45°, and 30°, and the reflectance was calculated by the direct received light intensity from the laser. After confirming the safety of the fundamental experiment, PDT was performed with this developed mirror on 9 patients with malignant glioma (4 with recurrence and 5 newly diagnosed). The energy efficiency of the mirror was approximately 70 %, and apparent irregular reflection was not observed. Even during clinical use, apparent complications, such as irregular reflection, did not occur upon using the mirror in any of the patients. In all patients, recurrence did not occur in the site where mirror irradiation was performed, but in a deep site or a distant site to which sufficient laser irradiation did not reach. PDT using our newly developed mirror involves few instrumental changes compared with the conventional irradiation method, and is effective, safe, and inexpensive.

Adhesion of streptococci to titanium and zirconia.

The purpose of this study was to evaluate the adherence of streptococci to disks of titanium (commercially pure titanium: CpTi) and zirconia (tetragonal zirconia polycrystals: TZP). CpTi and yttria-stabilized TZP disks with a mirror-polished surface were used as specimens. The arithmetic mean surface roughness (Ra and Sa) and the surface wettability of the experimental specimens were measured. For analyzing the outermost layer of the experimental specimens, X-ray photoelectron spectroscopy (XPS) analysis was performed. Streptococcus sanguinis, S. gordonii, S. oralis, and S. mutans were used as streptococcal bacterial strains. These bacterial cultures were grown for 24 h on CpTi and TZP. The number of bacterial adhesions was estimated using an ATP-bioluminescent assay, and scanning electron microscope (SEM) observation of the adhered bacterial specimens was performed. No significant differences in surface roughness or wettability were found between CpTi and TZP. In XPS analyses, outermost layer of CpTi included Ti0 and Ti4+, and outermost layer of TZP included Zr4+. In the cell adhesion assay, the adherences of S. sanguinis, S. gordonii, and S. oralis to TZP were significantly lower than those to CpTi (p < 0.05); however, significant difference was not observed for S. mutans among the specimens. The adherence to CpTi and TZP of S. mutans was significantly lower than that of S. sanguinis, S. gordonii, and S. oralis. These results were confirmed by SEM. S. sanguinis, S. gordonii, and S. oralis adhered less to TZP than to CpTi, but the adherence of S. mutans was similar to both surfaces. S. mutans was less adherent compare with the other streptococci tested in those specimens.

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.

(Invited) A Combined Femtosecond Laser Treatment and Anodization Approach to Control Fibroblast Cell Growth on Titanium Alloys

Intra cardiac pace makers are an emerging technology. In case of revisions however they should not be found completely overgrown by fibroblasts. Titanium alloys which are used for their housings can be engineered. For this purpose the titanium alloy is surface treated by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples or periodic nanoplate-like structure (LIPSS). To make the surface hydrophilic anodization was 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 vs. standard hydrogen electrode. The obtained electrochemical active surface area (ECSA) is approximately 8-9 times larger as compared to flat mirror polished titanium surface. Combined chemical analysis by Pourbaix diagram and (XPS) analysis reveal that titanium and aluminium are passivating into TiO2 and Al2O3 but the dissolution of aluminium in the form of solvated ion is inevitable. Finally, after exposing the anodized + laser treated titanium alloy sample to murine fibroblast environment, it is found that murine fibroblast cell growth is significantly restricted due to unique surface texture of the laser treated and anodized titanium alloy sample.

High Machinability of Plasma-Nitrided HPM80 Dies at 673K by PCD-Tools for Hot Mold-Stamping

HPM80 had been utilized as one of the martensitic stainless steel mold and die substrates for stamping. In particular, HPM80 mold was often used as hot-stamping molds for oxide glasses and optical polymers to fabricate the optical elements and DOE (Diffractive Optical Elements) with the aid of NiP (Nickel Phosphate) and NiWP (Nickel-Tungsten Phosphate) coatings. These machinable amorphous coatings were indispensable to cut and finish the tailored micro textures for DOE since HPM80 was difficult or nearly impossible to be finished by using the PCD (Poly-Crystal Diamond)-chipped tools. However, those coatings were fragile above 473 K; the original HPM80 must be modified to be fine machinable even by the diamond-chipped and coated tools for fine finishing to mirror-polished die surfaces with far less damage to cutting tools. These HPM80 substrates were plasma nitrided at 673 K under the nitrogen and hydrogen mixed gas flow to form the high content nitrogen super-saturated layer. Precise machinability experiment was performed with the use of the PCD coated WC (Co) tools to investigate the machinability of these nitrogen supersaturated HPM80 substrates. Two-phase fine-grained layer with higher nitrogen solute content than 2 mass% was machined in the ductile mode with adaptively high quality to shaping and finishing the mold die surface for stamping. Through the hardness testing, this nitrogen super-saturated die surface had higher hardness than 1400 HV; it had sufficient durability for long-term stamping operations. Finally, the turning test was employed to demonstrate that this nitrogen supersaturated HPM80 layer with the thickness of 40μm was machined with high quality to form the mirror-polished surface.