Arithmetic Average Roughness Research Articles

The Effect of Assist Gas Type on Nitinol Microsecond Laser Cut Edges: A Study on the Use of Oxygen, Argon, Nitrogen, Helium, and Compressed Air

Abstract Historically, the published literature for laser cutting atomically balanced nickel-titanium alloy (Nitinol) tubular devices assumes slow cut rates with an inert argon assist gas. Herein, a novel application of an exothermic reactive oxygen assist gas was employed during Nitinol laser micromachining, which enabled a 38.1 mm/s cut rate, a 4.5-times improvement from traditional argon cutting. Furthermore, this led to the realization of improved cut quality: 2-times less dross, a 2-times lower surface roughness, and a minimal heat-affected zone. Of the tested assist gases (oxygen, argon, nitrogen, helium, and compressed air), oxygen was found to provide the best cut quality, achieving dross-free cuts. Additionally, oxygen was shown to produce a relatively low arithmetic mean average surface roughness of 0.48 μm, when compared to argon at 0.85 μm. A decrease in surface roughness was found to be associated with an increase in cut rate. These findings suggest that assist gas melt flow dynamics has a higher contributing factor than laser pulse energy parameters. In-situ thermographic monitoring of the melt flow during processing demonstrated a clear difference in the melt flow pattern between a reactive oxygen assist gas and inert argon assist gas. Furthermore, with the culmination of nanoindentation analysis and microstructural characterization, it was concluded that long-pulse laser micromachining can produce cuts with negligible microstructural alterations to the bulk material. This study quantitatively demonstrates the benefits observed during laser cutting Nitinol with a reactive oxygen assist gas when compared to previous studies that employ an inert argon assist gas.

Interaction of contour and hatch parameters on vertical surface roughness in laser powder bed fusion

In Laser Powder Bed Fusion (L-PBF), surface roughness is pivotal for controlling the mechanical and functional performances, as well as the geometrical accuracy of the final product. This study extensively investigated the interactions of hatch and contour processing parameters, along with contour offset distance, on vertical surface roughness for 316L stainless steel in L-PBF. Melt pool morphology and surface arithmetic average roughness (Sa) were quantified using confocal microscopy, while scanning electron microscopy was employed to interpret the detailed microstructure of surface features. Under low volumetric energy density (VED) hatch conditions (e.g., 66.7 J/mm3), varying the contour offset distance has a negatable effect on the surface roughness when the contour VED is lower than 121.6 J/mm3, remaining relatively smooth surfaces dominated by bare melt tracks with sparely attached partially melted particles. Increasing the hatch or contour VED (e.g., 166.7 J/mm3), dross formation, identified by the microstructural differences and explained by the melt pool instability and migration, is inevitable, which dictates the surface roughness with higher Sa values. The larger contour offset distance further promotes the dross occurrence with irregularity and increases Sa. Employing a low contour VED with an appropriate offset distance and adopting the contour-first scan strategy was demonstrated as an effective solution to reduce the dross formation. Through the analysis of melt pool behavior, surface topography, and microstructure, this study elucidates the mechanisms governing dominant surface characteristics under the combined influence of hatch and contour parameters. It lays the foundation for precise control of surface roughness without altering hatching parameters, enabling the tailored manipulation of performance in additively manufactured structures.

Investigation of film Physical properties under various starch thermal treatments with emphasis on Retrogradation effects

This study investigated the changes in the physical properties of cornstarch-based films as they were retrogradely aged at different temperatures. Using a casting method, the films were fabricated, and their effects on the mechanical properties, thermal stability, barrier properties, and essential properties were analyzed. With prolonged aging and retrogradation periods, reductions in film thickness, solubility, water content, and water vapor permeability of 5.35%, 9.92%, 29.61%, and 20.94%, respectively, were observed. In addition, the surface roughness decreased by 44.46% for Rq (root-mean-square roughness) and 45.61% for Ra (arithmetic average roughness), while the elongation at break decreased by 72.64%. Conversely, the tensile strength, maximum degradation rate, and maximum degradation temperature increased by 116.98%, 99.5%, and 3.21%, respectively. These results provide a fundamental understanding of the changes that occur in the properties of cornstarch-based films during aging and retrogradation.

Relationship between topographic parameters and BRDF for tungsten surfaces in the visible spectrum

In metallic fusion devices, parasitic light originating from multiple reflections on the wall is a major problem for the interpretation of optical diagnostics. Strong stray light affects several optical diagnostics in ITER. One possibility to cope with this reflected light is to use photonic simulation, which can accurately predict the behavior of light within complex 3D geometry. A prerequisite is to get a good description of the reflection model, represented by the Bidirectional Reflectance Distribution Function (BRDF), based on optical measurements of in-vessel materials. To avoid complicated measurements using goniophotometer to get the BRDF, one possibility is to link surface optical properties and topography characteristics, such as roughness measurements, for example, using the classical Bennett’s formula. Measurements were performed using two experimental goniophotometers to fully characterize the BRDF of tungsten samples with different roughness values. Surface topography was measured using a three-dimensional laser scanning confocal microscope. Several parameters were extracted from these measurements including the arithmetic average roughness (Ra), the root mean square roughness (RMS), the Surface Inclination Angle Distribution and furthermore its mean value δm and the power spectral density (PSD). The correlations of BRDF model parameters deduced from the measurements are compared with the previous topographic parameters. The initial results on several tungsten samples show that Ra, which is the usual measure of surface roughness, is not the most suitable metric to link with the reflection behavior of the surface. In contrast, the PSD and the surface inclination angle are interesting metrics for describing the reflected light.

Empirical modeling of profile roughness parameters during end milling of aluminium alloy 5052/tungsten carbide/graphite hybrid composite

AbstractThis study presents an empirical modeling approach to reveal the effect of end milling parameters on the profile roughness parameters. Aluminium hybrid composite was melt‐stir die cast into the required work material, setting a predetermined weight fraction of reinforcements. The experimental design was adopted using the Taguchi meta‐heuristic algorithm for the selection of the levels of the end milling parameters. The profile roughness parameters namely arithmetic average roughness (Ra), root mean square roughness (Rq), and mean roughness depth (Rz) were considered as output responses, which were measured using stylus type surface roughness tester. Non‐linear second‐order empirical models were formulated and from them, the profile response parameters were predicted with 95 % accuracy. The results revealed that the depth of cut and spindle speed are contributing 54.22 % and 38.6 % respectively among the selected input parameters on the cumulative output.

Effect of the addition of silver nanoparticles on the mechanical properties of an orthodontic adhesive

ObjectivesThis study evaluated the effects of adding silver nanoparticles on the shear bond strength, microhardness, and surface roughness of orthodontic adhesives. Material and MethodsFifty upper premolars were randomly allocated to five groups (n = 10). Orthodontic brackets were bonded with silver nanoparticle (AgNP)-modified adhesives (1 %, 0.5 %, 0.1 %, 0.05 %), and conventional adhesive was used as a control. The shear bond strength was recorded using a universal testing machine, and the adhesive remnant index was evaluated using a stereomicroscope. Ten discs of each adhesive were subjected to the microhardness and surface roughness tests. The Vickers microhardness values were measured under a constant load of 100 g for 30 s using a microhardness tester. The samples were analyzed using a surface profilometer, and the arithmetic average roughness was used as the measurement parameter. Data were analyzed using one-way analysis of variance and chi-square tests. A significance level of 5 % was considered significant. ResultsAgNP concentration > 0.1 % significantly reduced the shear bond strength (p < 0.05). At higher AgNP concentration, the bonding failure pattern occurred mainly at the bracket-resin interface. The Vickers microhardness increased with increasing concentration, and significant differences were observed between the group with 1 % AgNP and the other groups (p < 0.05). The average roughness values were similar between the groups with AgNP concentrations > 0.1 % (p > 0.05). ConclusionThe incorporation of AgNP into an orthodontic adhesive has the potential to decrease the shear bond strength while increasing the microhardness and surface roughness.

Color stability of bleached tooth enamel brushed with different stain-removing toothpastes.

The effects of four toothpastes on the color stability of in-office bleached tooth specimens were determined. We evaluated an experimental toothpaste (EXP) and three commercially available toothpastes: Colgate Optic White (OPW), Aquafresh White & Protect (AWP), and Crest 3D White (CDW). OPW, AWP, and CDW contained inorganic abrasives, whereas EXP and AWP contained sodium polyphosphate. Forty-eight randomly selected human-extracted maxillary central incisors were bleached and brushed twice daily over 30 days. We analyzed the final color difference (ΔE*ab, ΔE00 , ΔWID ), arithmetic average surface roughness (Ra) of the enamel measured on days 0 and 30, and scanning electron microscopy images of enamel surfaces and toothpastes. ΔE*ab, ΔE00 , ΔWID , and Ra were analyzed using one-way analysis of variance and Tukey's test (α = 0.05). ΔE*ab and ΔE00 values were significantly lower after toothbrushing with EXP, OPW, and CDW than with AWP. OPW induced the greatest positive ΔWID . Ra was significantly increased by OPW and CDW, but slightly increased by AWP, with cube-like particles, and EXP, with no particle-like structures. Only EXP stabilized the color of bleached teeth without increasing the enamel surface roughness. Sodium polyphosphate with approximately 10 phosphate groups was effective at removing stains. The effect of toothpaste on the color stability of bleached teeth depends on the constituting abrasives and chemical components. Polyphosphoric acid has different stain-removal effects depending on its degree of polymerization. Additionally, although certain types of abrasives may be effective for color stability, they also increase the surface roughness of the enamel.

Development of analytical models for tip, root, and end relieving of spur gears by pulsed electrochemical finishing process

This paper describes analytical modelling for the non-contact tip, root, and end relieving of spur gears and their associated volumetric material removal rate (MRR) by the pulsed electrochemical finishing (PECF) process. The models were developed using Faraday’s law of electrolysis and involute geometry of spur gears. The developed models are validated experimentally using the innovatively designed and developed cathode gears and experimental apparatus by varying voltage, pulse-on time, and pulse-off time at four levels each. It found that minimum prediction errors for the developed models for the amount of tip, root, and end relief are 0.8%, 0.3%, and 1.3%, respectively, and minimum prediction error for models of volumetric MRR of tip, root, and end relief are 6.9%, 0.6%, and 9.8% respectively. A study of microgeometry along the profile and lead direction of spur gear confirmed that the PECF process not only successfully imparted tip, root, and end relief but also reduced their arithmetical average roughness and maximum height by 61.1% and 62.5% for tip relief, 67.7% and 67.8% for root relief, and 63.8% and 66.6% for end relief respectively. It also removed hob cutter marks and cracks revealed from the comparison of surface morphology of spur gear flank surfaces before and after tip, root, and end relieving. Maximum values of % reductions in maximum height and arithmetical average roughness occurred for pulse-on and pulse-off times as 3 and 4 ms (i.e., 43% duty cycle). The developed models will be very useful in designing or predicting the amount of tip, root, and end relief that can be imparted for a given modification duration. Conversely, they can be used for parametric optimization of the PECF process and to compute the required duration for the PECF process to impart the desired amount of tip/root/end relief to spur gears.

Chemical Composition, Structure, and Physical Properties of AlN Films Produced via Pulsed DC Reactive Magnetron Sputtering

The chemical composition, structure, and physical properties of aluminum nitride (AlN) films obtained using pulsed DC reactive magnetron sputtering in asymmetric bipolar mode have been studied. X-ray diffraction and electron diffraction confirmed the composition of c–axis textured hexagonal AlN films required for piezoelectric applications. The surface of the films obtained is quite smooth; the arithmetic average roughness does not exceed 2 nm. Transmission electron microscopy has shown the presence of a transition layer at the film–substrate interface. Transmission electron microscopy and X-ray photoelectron spectroscopy depth profile analysis have shown that the films have an oxidized surface layer which has an influence on the optical model of the films derived from ellipsometric data. However, it does not significantly influence the films’ piezoresponse. Piezoelectric force microscopy indicated a piezoelectric effect in the films that is uniform over their surface.

A Response Surface Modeling Study on Effects of Powder Rate and Machining Parameters on Surface Quality of CoCrMo Processed by Powder Mixed Electrical Discharge Machining

Due to the high mechanical strength of the metals used in implant manufacture, which makes them difficult to work with using other machining techniques, electrical discharge machining (EDM) is frequently employed in the production of implants. In this study, the effect of powder ratio and other EDM parameters used in the machining of CoCrMo alloy, which used in implant production widely, with powder-mixed EDM on the surface roughness of the machined part was investigated through the response surface methodology. AISI 316L stainless steel was chosen as the electrode material, and Ti6V4Al was chosen as the additive powder, taking into account their biocompatibility properties. Using a Taguchi L16 array, an experimental design was created by selecting 4 levels for each parameter of additive ratio, discharge current, pulse on time (Ton), and pulse off time (Toff). The response surface method was used, along with the experimental data, to estimate how the parameters affected the arithmetic average roughness (Ra) and mean roughness depth (Rz).

Laser surface polishing of 3D printed polylactic acid (PLA) with different levels of absorption

Fused deposition modeling (FDM) based 3D printed polymer parts have received extensive attention in the industries. However, their high surface roughness due to the intrinsic layer deposition method limits the applicability, necessitating the printed parts' post-processing. Herein, we used colored (white, blue, and gray) 3D-printed polylactic acid (PLA) parts and investigated the color influence on the laser polishing process in detail. Interestingly, the level of laser absorption at an irradiated wavelength of 1060 nm differed in the order of PLA-gray > PLA-blue > PLA-white. Laser-polished PLA-white samples showed a negligible difference in the arithmetic average surface roughness (Ra) compared to the printed sample, corresponding to the low absorption level and melting behavior. On the other hand, the laser-polished PLA-blue sample exhibited a 96.4 % reduction in Ra value at a laser power of 15 W. The PLA-gray sample showed a 98.6 % reduction at 3 W. The Ra variation of the laser-polished samples confirmed a dramatic surface roughness improvement that could be made by controlling laser processing parameters and varying light absorption levels of the colored PLA substrates. Besides, PLA-blue and PLA-gray samples had different polishing conditions; Scanning electron microscope (SEM) images, thermal studies, and finite element model simulation results confirmed the polishing and melting behavior of the PLA samples. The comparative experimental results followed by statistical analysis also showed the significant effect of PLA color and laser parameters such as the power and scan speed. Through the advantages of the highly improved laser finishing results with optimal process parameters considering the different light absorption, this approach will broaden the application of efficient laser polishing of 3D printed materials.

Surface finishing of an additively manufactured part using electrochemical jet machining

The development and expansion activities of additive manufacturing (AM) are at their peak as complex parts with intricate features can be easily manufactured by various AM processes. However, obtaining a good surface finish for the AM parts has remained a challenging task. The surface defects and irregularities over intricate parts pose challenges during machining with conventional processes. Therefore, a simple, cost-effective, non-contact surface finishing approach is required to post-process the external and internal surfaces of AM metallic parts. This article reports the surface finishing of the SS316L part made by laser powder bed fusion (L-PBF) using a toolless electrochemical jet machining (ECJM), and investigations were performed to evaluate the different aspects of surface integrity. The experimental results revealed that surface irregularities and defects highlighted on the as-deposited samples were eliminated after ECJM.Moreover, after post-processing, the overlaid layer of oxides and carbides over the as-deposited sample surfaces was also removed. The maximum peak and valley height of the as-deposited surface were 30.1 µm and 41.6 µm, respectively. These heights have been reduced to 13.3 µm and 9.9 µm, respectively, while the arithmetical average roughness value 'Ra' has been reduced from 7.8 µm to 3 µm. The improvement in the mean value of 'Rz' and 'Ra' after post-processing was found to be 72%, and 61%, respectively. Therefore, the study concluded that the unique characteristic of the toolless electrochemical machining process is suitable for finishing the AM part.

Design of GH4169 diaphragm for combined improvements of yield strength and surface roughness

AbstractDiaphragm compressors have become the primary source of on-site hydrogen compression for hydrogen fuelling stations around the world. The most common hydrogen-compressor-failure mechanism has been identified as diaphragm fracture due to low tensile strength and poor surface properties. In this study, a new type of GH4169 diaphragm with high yield strength and low surface roughness was fabricated. Microstructures, tensile behaviours and surface properties of the specimens were characterized by using scanning electron microscopy, an electronic universal testing machine and atomic force microscopy, respectively. The evolution of the γ′′ and γ′ phases with temperature has been examined. Both γ′′ and γ′ phases were precipitant-strengthened phases for GH4169 and the volume and size of γ′′ and γ′ phases increase with ageing time. In addition, the γ′′ phase is the main strengthening phase and γ′ is the supportive strengthening phase. Tensile strength was increased due to the strengthening phases at the cost of ductility. The roughness of the diaphragm could reach an arithmetic average roughness (Ra) of 0.1 μ m by applying a cooling-assisted polishing process. This work improves the reliability and reduces the auxiliary steps and down-time for diaphragm compressors.

Durability and wettability of varnishes on the modified and aged surfaces of short rotation teak wood

PurposeThe surface characteristics of thermally and chemically modified wood, such as surface roughness, surface free energy (SFE) and wettability, are important properties that influence further manufacturing processes such as gluing and coating. The aim of this paper was to determine the influence of the surface roughness of thermally and chemically modified teak wood on their SFE, wettability and bonding quality for water-based acrylic and solvent-based alkyd varnishes. In addition, durability against subterranean termites in the field of these modified teak woods was also investigated to give a valuable information for their further application.Design/methodology/approachThe woods tested in this study were fast-growing teak woods that were prepared in untreated and treated with furfuryl alcohol (FA), glycerol maleic anhydride (GMA) and thermal. SFE values were calculated using the Rabel method. The wettability values were measured based on the contact angle between varnish liquids and wood surfaces using the sessile drop method, and the Shi and Gardner model model was used to evaluate the wettability of the varnishes on the wood surface. The bonding quality of the varnishes was measured using a cross-cut test based on ASTM 3359-17 standard. In addition, durability against subterranean termites in the field of these modified teak woods was also investigated according to ASTM D 1758-06.FindingsThe results showed that furfurylated and GMA-thermal 220°C improved the durability of teak wood against termites. The furfurylated teak wood had the roughest surface with an arithmetic average roughness (Ra) value of 15.65 µm before aging and 27.11 µm after aging. The GMA-thermal 220°C treated teak wood was the smoothest surface with Ra value of 6.44 µm before aging and 13.75 µm after aging. Untreated teak wood had the highest SFE value of 46.90 and 57.37 mJ/m2 before and after aging, respectively. The K values of untreated and treated teak wood increased owing to the aging treatment. The K values for the water-based acrylic varnish were lower than that of the solvent-based alkyd varnish. The untreated teak wood with the highest SFE produced the highest bonding quality (grades 4–5) for both acrylic and alkyd varnishes. The solvent-based alkyd varnish was more wettable and generated better bonding quality than the water-based acrylic varnish.Originality/valueThe originality of this research work is that it provides evaluation values of the durability and SFE. The SFE value can be used to quantitatively determine the wettability of paint liquids on the surface of wood and its varnish bonding quality.

Understanding surface roughness on vertical surfaces of 316 L stainless steel in laser powder bed fusion additive manufacturing

Laser powder bed fusion (L-PBF) offers high degrees of freedom to create complex geometries with fine features. Controlling surface roughness is one of the means of improving mechanical and functional properties. This is critical for those surfaces that post-treatments cannot process. This study investigated the effects of a wide range of processing parameters grouped by energy density on surface roughness, particularly at vertical surfaces in L-PBF. The surface arithmetic average roughness, Sa, was measured via confocal microscopy. Scanning electron microscope was used to examine the detailed characteristics and the solidification microstructure on and near surfaces. Increasing laser power and speed under the identical energy density or increasing energy density under the equal speed results in rough vertical surfaces. Solidified melt tracks and partially remelted particles dominate the vertical surface roughness in cases with low energy densities. In contrast, the dross formation contributes to the high vertical surface roughness in cases with high energy densities. By examining the melt pool morphology and the solidification microstructure near the surfaces, the mechanism grounded on a multi-layer melt pool instability is proposed to explain the dominant factors for vertical surfaces. The insights into the formation of key surface characteristics can assist in designing process parameters and generating innovative methods to improve surface roughness. • Vertical surface roughness is positively correlated to melt pool width and depth. • Powder and melt tracks dominate vertical surface roughness at low energy densities. • The dross dominates vertical surface roughness at high energy densities. • Inhomogeneous thermal distribution and melt pool instability drive dross formation.

The effect of NiFeCr seed layer composition on the giant magnetoresistance properties of [FeCoNi/Cu] multilayers

We present a systematic study on the giant magnetoresistance (GMR) and interlayer exchange couplings (IEC) in polycrystalline [Fe16Co66Ni18/Cu]5/Fe16Co66Ni18 multilayer films deposited on NiFeCr seed layers with various compositions. We observed that the GMR ratio (ΔR/R) depends on bilinear and biquadratic IEC coefficients, J1 and J2, and varies linearly with their ratio, J1/J2. The maximum ΔR/R of 35 ± 2.5% and strong antiparallel IEC (J1/J2 > 1) were observed for the seed layers with a particular Ni:Fe ratio of (Ni0.55Cr0.45)100-yFey with 0 ≤ y ≤ 47 at. %. Structural studies confirm that the high ΔR/R and J1/J2 for these NiFeCr compositions are related to a strong fcc [111] crystallographic texture and a coarse grain size of the FeCoNi/Cu mutilayers. In addition, we observed that the film deposited on a Ni32Fe33Cr35 seed layer showed a stronger [111] texture, but a lower ΔR/R (17%) than those deposited on a Ni36Fe51Cr13 seed layer (ΔR/R = 28%). Detailed microstructural analysis indicated an increased arithmetic average roughness (Ra) of the interfaces between FeCoNi and Cu layers for the films with the Ni32Fe33Cr35 seed layer. We argue that the lower ΔR/R in the film despite the relatively strong [111] texture is due to its higher Ra which causes a reduction in antiparallel IEC. This indicates that two conditions of (i) a strong [111] crystallographic texture and (ii) small interface roughness must be satisfied in the FeCoNi/Cu multilayer to achieve a strong antiparallel IEC and thus large ΔR/R.

Effects of Bifidobacterium animalis subsp. lactis Bl-04 on Skin Wrinkles and Dryness: A Randomized, Triple-Blinded, Placebo-Controlled Clinical Trial

The effects of orally consumed probiotics on skin wrinkles and dryness are not fully known. A randomized, placebo-controlled, triple-blinded study was conducted with 148 healthy Korean female volunteers aged between 33 and 60 years, who were administered 1.75 × 109 colony-forming units (CFUs) of Bifidobacterium animalis subsp. lactis Bl-04 (Bl-04) (N = 74) or matching placebo (N = 74) for 12 weeks. Facial wrinkles (with 3-dimensional (3D) imaging), skin hydration, transepidermal water loss (TEWL), elasticity, and gloss were assessed at baseline and after every 4 weeks of the intervention. Questionnaire-based subjective evaluations of product efficacy and usability were also analyzed. The consumption of Bl-04 was safe and ameliorated significantly facial skin wrinkle parameters (total wrinkle area and volume, average depth of wrinkles, and arithmetic average roughness (Ra)) versus placebo at 4 weeks, but there were no differences at Week 8 or 12 between groups. Skin hydration, TEWL, elasticity, and gloss were similar between treatment groups, as were the subjective evaluation scores. Oral consumption of Bl-04 indicated promising short-term effects on skin appearance from the winter toward the spring. In future study designs, special attention should be paid to environmental conditions as well as to the skin condition and age of the participants.

Ion Release and Surface Changes of Nickel-Titanium Archwires Induced by Changes in the pH Value of the Saliva-Significance for Human Health Risk Assessment.

The aim of this study was to explore whether changes in the salivary pH influence mechanical properties, surface roughness, and ion release from NiTi archwires with various surface coatings, and discuss the clinical significance of the findings. The uncoated, rhodium-coated, and nitrified NiTi wires were immersed into artificial saliva of different pH values (4.8, 5.1, 5.5, and 6.6). Released nickel and titanium ions were measured with inductively coupled plasma-optical emission spectroscopy at the end of 28 days. Atomic force microscopy was used to measure the arithmetic average surface roughness Ra, the root-mean-square roughness Rq, and the maximum height of the asperities RZ. The nanoindentation hardness (HIT) and Young’s modulus (EIT) measurements were performed. The change in the pH of artificial saliva is inversely proportional to the release of titanium from both coated and uncoated wires, and the release of nickel from uncoated wires. The surface roughness parameters of both coated and uncoated wires are unaffected by the change in the pH of artificial saliva. The change in the pH of saliva has minor influence on the hardness and Young’s modulus of elasticity of both coated and uncoated wires. The concentration of released metal ions measured was below the recommended upper limit for daily intake; nevertheless, hypersensitivity effects cannot be excluded, even at lower concentrations and at low pH.

Benchmarking of 316L Stainless Steel Manufactured by a Hybrid Additive/Subtractive Technology

This research study investigated the hybrid processing of 316L stainless steel using laser powder bed (LPB) processing with high-speed machining in the same build envelope. Benchmarking at four laser powers (160 W, 240 W, 320 W, and 380 W) was undertaken by building additively with machining passes integrated sequentially after every ten deposited layers, followed by the final finishing of select surfaces. The final geometry was inspected against the computer-aided design (CAD) model and showed deviations smaller than 280 µm for the as-built and machined surfaces, which demonstrate the good efficacy of hybrid processing for the net-shape manufacturing of stainless steel products. The arithmetic average roughness values for the printed surfaces, Ra (linear) and Sa (surface), were 11.4 um and 14.9 um, respectively. On the other hand, the vertical and horizontal machined surfaces had considerably lower roughness, with Ra and Sa values ranging between 0.33 µm and 0.70 µm. The 160 W coupon contained layered, interconnected lack of fusion defects which affected the density (7.84 g·cm−3), yield strength (494 MPa), ultimate tensile strength (604 MPa), Young’s modulus (175 GPa), and elongation at break (17.3%). By contrast, at higher laser powers, near-full density was obtained for the 240 W (7.96 g·cm−3), 320 W (7.94 g·cm−3), and 380 W (7.92 g·cm−3) conditions. This, combined with the isolated nature of the small pores, led to the tensile properties surpassing the requirements stipulated in ASTM F3184—16 for 316L stainless steel.

Atomic force microscopy study on the effect of different irrigation regimens on the surface roughness of human root canal dentin.

Endodontic irrigants could alter the mechanical properties of root canal dentin, such as its roughness. To compare the effect of various irrigation protocols on root canal dentin roughness with respect to their application time, concentration, and additional ultrasonic activation. Forty single-rooted, non-endodontically treated upper incisors were decoronated and further sectioned longitudinally in a buccolingual direction. The surfaces of all eighty samples were polished and randomly segregated to eight equal groups (n = 10): Group A: 2% NaOCl/2 min followed by 17% EDTA/2 min; Group B: 2% NaOCl/5 min followed by 17% EDTA/5 min; Group C: 5.25% NaOCl/2 min followed by 17% EDTA/2 min; Group D: 5.25% NaOCl/5 min followed by 17% EDTA/5 min; Group E: 2% NaOCl solution, ultrasonically activated for 2 min; Group F: 5.25% NaOCl, ultrasonically activated for 2 min; Group G: 2% NaOCl/2 min followed by 17% EDTA/2 min, both ultrasonically activated; Group H: Control group (distilled water). All irrigation regimens increased root dentin surface roughness in comparison with the control group. The analysis of the values revealed significant differences between the arithmetical average roughness values (Ra) in the groups (p < 0.001). A statistically significant increase in the Ra parameter was observed in groups E, F, G, and D. The irrigation protocol in Group A showed a significantly smoother dentin surface than those with the ultrasonic activation. All tested irrigants increased root canal dentin roughness and the effect was time and concentration-dependent. The ultrasonic activation of the disinfection solutions roughened the root dentin surface significantly.