Fabrication Process Conditions Research Articles

Exploring the impact of thickness, scale and printing sequence on the tensile and fracture properties of PLA specimens fabricated via fused deposition modeling

Geometrical factors play a key role in determining the dimensional accuracy and mechanical properties of additively manufactured components. This research investigates the influence of thickness, scale, and printing sequence on Polylactic Acid (PLA) specimens produced via Fused Deposition Modeling (FDM) with special focus on tensile and fracture properties of the printed parts. The trends of experimental results were then linked to the microstructures and observations on failure mechanisms and the fabrication process conditions. Tensile test results indicate that increasing the build thickness significantly boosts elongation at failure and slightly raises ultimate tensile strength, while downscaling the printed specimens initially causes minor decreases, but further reductions lead to significant drops in mechanical properties due to higher ratio of intrinsic defect to specimen size. Similar to the tensile properties, fracture analyses revealed that larger build thickness and smaller scale of printed parts lead to lower fracture resistance, with an increasing impact by scale reduction, which is attributed to the formation of defects during fabrication and the thermal history of the printed parts. Printing sequence was found to have limited impact on the mechanical performance of the printed parts with effects below 10%. Additionally, a boundary effect model was employed to evaluate fracture behavior of tested specimens, demonstrating its applicability as an engineering tool for fracture prediction of FDM parts with different scales and thicknesses. The findings of this work underscore the importance of considering geometric factors and printing strategies for effective design and failure analysis of additive manufacturing components.

Effect of casting temperature on the solidification process and (micro)structure of Zr-based metallic glasses

Bulk metallic glasses (BMGs) bear versatile advantages compared to traditional crystalline metallic materials. However, preparation of large size BMG components remains a great challenge due to the lack of understanding the casting dynamics of BMGs. The present work investigates the dynamics of the solidification process during casting of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG by measuring the time-dependent temperature evolution and constructing distance–time curves showing the progress of solidification. The experimentally probed temperature evolution proves that a higher casting temperature causes a lower cooling rate and induces more pronounced nanocrystal phase formation in the final BMG casting. Thus, optimization of the casting temperature is crucial for casting BMG components. The solidification coefficient K of the studied Zr-based BMG in copper mold was determined. The solidification time can be calculated with model: τ=M2K2. The solidification of the Zr-based BMG occurs in a narrow transition layer region following a “layer-by-layer” solidification mode. This feature is vital for designing the casting process appropriately to avoid the formation of casting defects in BMG components. The present work sheds new light on the solidification mechanism of bulk glass-forming liquids and underlines the importance of optimizing the technology and processing conditions for fabrication of BMG components with practical applications.

Diffusivity and solubility of HF gas in polymers and nanocomposites used for automated handling containers of silicon substrates in microelectronic industry

Thermoplastic boxes with internal clean mini-environment (ISO 14644–1:2015, class 2–3), called Front Opening Unified Pods (FOUP), are widely used in microelectronic fabrication for transport and handling of silicon substrates (named wafers) in order to minimize the negative impact of contaminants on integrated circuits. As a type of airborne molecular contaminants (AMC), hydrogen fluoride (HF) outgassed from freshly processed wafers and sorbed (adsorption and absorption) on/in FOUP's walls and then becomes a potential source for subsequent HF cross-contamination. Thin polymeric films which were comprised of available commercial FOUP materials were prepared by hot pressing. They were neat polymers (polycarbonate (PC), Entegris Barrier Materials (EBM)) and nanocomposites (polycarbonate/carbon powder (PCCP), polycarbonate/carbon nanotubes (PCCNT), and EBM/carbon nanotubes (EBMCNT)). The sorption and desorption kinetics of HF in polymers were experimentally established at ultralow HF concentration (part-per-billion-volume, ppbv) and cleanroom conditions (atmospheric pressure, 20 °C and 40%RH); such conditions mimicking fabrication process conditions. Having a polar group in polymeric chains, the PC, PCCP and PCCNT showed a higher affinity to HF rather than EBM and EBMCNT, which resulted in significantly increasing HF diffusivity (nearly two orders of magnitude, 10−10 versus 10−12 cm2.s−1) and HF solubility. The presence of embedded CNT in nanocomposites (PCCNT and EBMCNT) exhibited a significant increase of both HF diffusivity and solubility. Interestingly, based on desorption curves, it was determined that the sorbed HF in nanocomposites made with CNT was composed of two types (i) fixed-HF inside cylindrical voids of CNT and (ii) mobile-HF in polymeric bundle-chains. In addition, the obtained HF transport coefficients were applied as input data in numerical simulation model to simulate the HF concentration profiles and the evolution of HF uptake in FOUP walls in different scenarios.

The Development and Study of Some Composite Membranes Based on Polyurethanes and Iron Oxide Nanoparticles.

To improve the performance of composite membranes, their morphology can be tailored by precise control of the fabrication methods and processing conditions. To this end, the aim of this study was to develop novel high-performance composite membranes based on polyurethane matrix and magnetic nanoparticles with the desired morphology and stability, by selecting the proper method and fabrication systems. These well-prepared composite membranes were investigated from the point of view of their morphological, physico-chemical, mechanical, dielectric, and magnetic properties. In addition, their in vitro cytocompatibility was also verified by the MTT assay and their cell morphology. The results of this study can provide valuable information regarding the preparation of magnetic polyurethane-based composite membranes that could be used to design some suitable devices with tailored properties, in order to improve the image quality in magnetic resonance imaging investigations and to suppress local image artifacts and blurring.

Optically Clear Silk Fibroin Films with Tunable Properties for Potential Corneal Tissue Engineering Applications: A Process-Property-Function Relationship Study.

Owing to the shortage of donor corneas and issues associated with conventional corneal transplantation, corneal tissue engineering has emerged as a promising therapeutic alternative. Biocompatibility and other attractive features make silk fibroin a biomaterial of choice for corneal tissue engineering applications. The current study presents three modes of silk fibroin film fabrication by solvent casting with popular solvents, viz. aqueous (aq), formic acid (FA), and hexafluoroisopropanol (HFIP), followed by three standard modes of postfabrication annealing with water vapor, methanol vapor, and steam, and systematic characterization studies including corneal cell culture in vitro. The results indicated that silk fibroin films made from aq, FA, and HFIP solvents had surface roughness (Rq) of 1.39, 0.32, and 0.13, contact angles of 73°, 85°, and 89°, water uptake% of 58, 29, and 27%, swelling ratios of 1.58, 1.3, and 1.28, and water vapor transmission% of 39, 26, and 22%, respectively. The degradation rate was in the order of aq > HF > FA, whereas the tensile strength was in the order of aq < HF < FA. Further, the results of the annealing process indicated notable changes in morpho-topographical, physical, degradation, and tensile properties. However, the films showed no detectable changes in chemical composition and remained optically clear with >90% transmission in the visible range, irrespective of fabrication and postfabrication processing conditions. The films were noncytotoxic against L929 cells and were cytocompatible with rabbit cornea-derived SIRC cells in vitro. The study demonstrated the potential of fine-tuning various properties of silk fibroin films by varying the fabrication and postfabrication processing conditions.

Application of non-contact quantum efficiency measurement for solar cell fabrication process insights

We demonstrate the application of non-contact external quantum efficiency (EQE) measurements as potential in-line inspection for solar cell mass production. The technique, based on electroluminescence excitation spectroscopy (ELE), is several times faster than conventional contacted EQE measurements, and enables on-the-flight contactless assessment of spectral response. To simulate a manufacturing environment, EQE of a batch of 200 bifacial PERC solar cells are investigated. This allows statistical analysis of the interplay between fabrication process conditions, cell current–voltage characteristics and results from other in-line inspection tools. The study shows that non-contact EQE can be used to detect variation in POCl3 diffusion and PECVD processes at cell level and without direct contact to the device. It is also possible to predict EQE on passivated, non-metallized diffused wafers. This provides powerful information in predicting end-of-line cell parameters, as well as to sort and remove low performing wafers prior to printing to eliminate metal paste wastage.

The Application of Principal Component Analysis (PCA) for the Optimization of the Conditions of Fabrication of Electrospun Nanofibrous Membrane for Desalination and Ion Removal.

Nowadays, acquiring a water supply for urban and industrial uses is one of the greatest challenges facing humanity for ensuring sustainability. Membrane technology has been considered cost-effective, encompasses lower energy requirements, and at the same time, offers acceptable performance. Electrospun nanofibrous membranes (ENMs) are considered a novel and promising strategy for the production of membranes that could be applied in several treatment processes, especially desalination and ion removal. In this study, we apply an unsupervised machine-learning strategy, the so-called principal component analysis (PCA), for the purpose of seeking discrepancies and similarities between different ENMs. The main purpose was to investigate the influence of membrane fabrication conditions, characteristics, and process conditions in order to seek the relevance of the application of different electrospun nanofibrous membranes (ENMs). Membranes were majorly classified into single polymers/layers, from one side, and dual multiple layer ENMs, from another side. For both classes, variables related to membrane fabrication conditions were not separated from membrane characterization variables. This reveals that membranes’ characteristics not only depend on the chemical composition, but also on the fabrication conditions. On the other hand, the process conditions of ENM fabrication showed an extensive effect on membranes’ performance.

Auxetic Polymer Foams: Production, Modeling and Applications

:Auxetic materials have high potential due to their exceptional properties resulting from a negative Poisson’s ratio. Recently, several auxetic polymer-based materials have been developed. In fact, several applications are looking for a lightweight material (less material consumed in production and transport) while having high mechanical performances (impact absorption, rigidity, strength, resistance, etc.). So, a balance between density and toughness/strength is highly important, especially for military, sporting, and transport applications. So auxetic materials (especially foams) can provide high impact protection while limiting the material’s weight. This article presents a review of recent advances with a focus on auxetic polymers, with particular emphasis on the auxetic polymer foams in terms of their fabrication methods and processing conditions (depending on the nature of the cellular structure), the effect of the fabrication parameters on their final properties, as well as their models and potential applications.

Investigation of Vth Distribution Tails of Ground-Select-Line Cells and Edge Dummy Cells in a 3-D NAND Flash Memory

The threshold voltage ( Vth) distributions of ground-select-line (GSL) cells and edge dummy (DMY0) cells in a 3-D NAND flash memory are investigated. We characterize the Vth distributions in 3-D NAND flash samples with different fabrication processes and bitline voltages. Large DMY0 and GSL Vth distribution tails are observed in certain fabrication process and operation voltage conditions. The DMY0 Vth tail is attributed to a random distribution of grain boundary (GB) traps in a poly-silicon channel between GSL and DMY0. The GSL Vth tail is affected by ion implant energy in an epitaxial silicon layer underneath a GSL. A 3-D TCAD simulation is performed to study the effects of a GB trap position and a bitline voltage on the Vth distribution of DMY0. The influence of an implant dose profile in the epitaxial silicon on the GSL Vth distribution is also analyzed by 3-D simulation. The GSL and the DMY0 Vth distributions can be significantly improved by optimizing a fabrication process and choosing an appropriate bitline voltage.

A Physical Model of Contact Resistance in Ti-Contacted Graphene-Based Field Effect Transistors

The effect of device fabrication processing conditions is often overlooked in the evaluation of the contact resistance in metal–graphene contact. In this work, we investigate the Ti–graphene contact resistance theoretically and experimentally. A compact model has been proposed to reveal and evaluate the role of different factors in controlling the value of contact resistance. A layer of oxidized Ti or polymer residues at the Ti–graphene interface has been considered to explain the reduced carrier transmission probability through the interface. Experimental results report a low contact resistance as small as 271.45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega ~\cdot \mu \text{m}$ </tex-math></inline-formula> and our model agrees with the measured values. The proposed model explains the large variation of the contact resistance reported in the literature up to date and help to improve metal–graphene contact for future applications.

Admittance spectroscopy and material modeling for organic electronic applications

Abstract Organic materials, both insulators and semiconductors, led to impressive applications in recent years and particular attention was paid to their performance reliability under realistic atmospheric conditions, fundamental need for the feasibility of organic electronic devices. In this context one of the most critical topics is the investigation of elements affecting device performance, such as trap states at the interface between different materials, and a fundamental target is to provide reliable physical models. By the means of admittance spectroscopy, in this paper, an electrical model was developed to explain the different dynamics of an organic device. Every element of the model was connected to each other through different relationships, each describing a single process. The model provides an efficient parameter extraction method, allowing for example the characterization of the diffusion of mobile ions, the dispersive transport in organic semiconductor bulk, the contact resistance at the metal-organic interface. As a consequence, the model is useful to compare the properties and the performance of devices with respect to the geometries, the materials and the fabrication process conditions.

Simple annealing process for producing unique one-dimensional fullerene crystal named fullerene finned-micropillar

We propose a process for easily fabricating a unique one-dimensional fullerene crystal, i.e., a fullerene finned-micropillar (FFMP). To fabricate a one-dimensional fullerene crystal more easily than when using current processes, fullerene was first annealed at 1173 K for 1 h with an argon gas flow of 0.5 L/min. We then examined how the FFMP structure changed when the fabrication process conditions, such as temperature, annealing time, and argon gas flow rate, were varied. FFMPs can be prepared within a short time and may have the same electrical characteristics as other one-dimensional crystals, e.g., fullerene nanowhiskers, so they are expected to be very useful for field-effect transistors, organic photovoltaics, and so on in the near future.

Thermoelastic Dissipation in Diamond Micro Hemispherical Shell Resonators

Maximizing quality factor (Q) is essential to improve the performance of micro hemispherical shell resonators (μHSRs) which can be used in microelectromechanical system (MEMS) gyroscopes to measure angular rotation. Several energy dissipation mechanisms limit Q, where thermoelastic dissipation (TED) is the major one and studied in this paper. Fully coupled thermo-mechanical equations for calculating TED are formulated, and then temperature distribution in a deformed μHSR and its quality factor related to TED (QTED) are obtained by solving the equations through a finite-element method (FEM). It has been found that different fabrication process conditions can obtain various geometrical parameters in our previous studies. In order to provide guidelines for the design and fabrication of μHSRs, the effects of their geometry on resonant frequency (f0) and QTED are studied. The change of anchor height and small enough anchor radius have no effect on both f0 and QTED, but the shell size including its radius, thickness and height has significant impact on f0 and QTED. It is found that whether a μHSR has lower f0 and higher QTED or higher f0 and higher QTED can be achieved by changing these geometrical parameters. The results presented in this paper can also be applied to other similar resonators.

Preparation and characterization of SnO films via reactive sputtering for ambipolar thin-film transistor applications

SnO films are prepared by reactive magnetron sputtering under various O2 partial pressures along with post-annealing in air. The results indicate that the O2 partial pressure during reactive sputtering process not only influences the composition of the SnO film but also its texture. For the SnO film deposited under 10% O2 partial pressure, its direct bandgap increases from 2.49 to 2.64 eV with elevating the post-annealing temperature from 250 °C to 400 °C. The above SnO-based channel thin-film transistors (TFTs) exhibit a typical ambipolar feature after post-annealing at ≥250 °C in air. For the TFTs annealed at 300 °C for 30 min, the extracted hole and electron field-effect mobility is 1.48 cm2V−1s−1 and 0.21 cm2V−1s−1, respectively. The performance of both p- and n-type TFTs could be further improved by optimizing fabrication process and post-annealing conditions because of a trade-off between hole and electron mobility.

A Technique for Estimation of Residual Stress and Young’s Modulus of Compressively Stressed Thin Films Using Microfabricated Beams

Predictive design of MEMS devices and their performance evaluation require post-fabrication measurement of essential material properties, such as Young's modulus and residual stress, as these are usually affected by fabrication process conditions. To our knowledge, few techniques exist for the measurement of residual stress in micromechanical structures fabricated from compressively-stressed amorphous dielectric thin films. Here, we propose a method for estimating residual stress and Young's modulus from the post-buckling dynamic response of fixed-fixed microbeams and frequency response of cantilevers, respectively. Static deflection profiles and first natural frequencies of buckled beams are used in this analysis. Further, the proposed method uses the length of the beams as an unknown to account for the variation in the actual length of a fabricated beam due to the presence of undercut. The effective length is simultaneously determined from the analysis of the measured data using multi-parameter curve fitting. Use of post-buckling analysis makes this technique useful for thin films with high compressive stresses. Since the proposed method does not involve electrostatic actuation, it is applicable for dielectric thin films in addition to crystalline and conducting films. Using the proposed method, residual stress is estimated in amorphous silicon carbide thin films deposited by PECVD and reactive-sputtering. In addition, the modulus values of three materials (PECVD SiNx, PECVD SiC, and sputtered SiC) are estimated and compared with reported results. [2019-0090]

대형 풍력발전기용 복합재 블레이드의 후단 및 스파-웹 부위 디본딩 손상에 따른 고유주파수 특성 평가

The wind turbine blades are becoming larger because of their energy efficiency, resulting in serious weight increasing problem. To solve this, the blades are manufactured using the composite materials with high specific strength and stiffness. On the other hand, damage modes, such as delamination, cracking, and de-bonding may occur inside depending on the constituents, fabrication process and operating conditions of the composite blades. Therefore, to ensure structural integrity of the blade in operation, the data build-up that can be used to detect this damage is necessary. Therefore, this paper examined the changes in the blade natural frequency characteristics resulting from debonding damage of the trailing edge and the spar-web joints. To this end, the FE model for the 5MW wind turbine blade was generated using geometry, layup information and material properties reported by SANDIA Lab. In addition, the debonding damage that exists at the rear end and on the spar-web joint was modeled by modifying the contact conditions. The modal analysis was performed according to the debonding damage length. Through these, the natural frequency change characteristics according to the size and location of the damage were evaluated.

Parameter Screening of PVDF/PVP Multi-Channel Capillary Membranes.

The increasing research in the field of polymeric multi-channel membranes has shown that their mechanical stability is beneficial for a wide range of applications. The more complex interplay of formation process parameters compared to a single-channel geometry makes an investigation using Design of Experiments (DoE) appealing. In this study, seven-channel capillary membranes were fabricated in a steam–dry–wet spinning process, while varying the composition of the polymer solution and the process temperatures in a three-level fractional factorial linear screening design. The polymers polyvinylidene flouride (PVDF) was the chemically resistant main polymer and polyvinylpyrrolidone (PVP) was added as hydrophilic co-polymer. Scanning electron microscopy and atomic force microscopy were applied to study the membrane morphology. Fabrication process conditions were established to yield PVDF/PVP multi-channel membranes, which reached from high flux (permeability P = ///bar, dextran 500 retention R = 18.3%) to high retention (P = ///bar, R = 80.0%). The concentration of the main polymer PVDF and the molecular weight of the co-polymer PVP showed linear relations with both P and R. The permeability could be increased using sodium hypochlorite post-treatment, although retention was slightly compromised. The obtained membranes may be suitable for micro- or ultra-filtration and, at the same time, demonstrate the merits and limitations of DoE for multi-channel membrane screening.

Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba2CoTeO6 ceramics.

Optimal processing conditions for fabrication of dense single-phase 6L-Ba2CoTeO6 ceramics via the solid-state reaction method were determined. These ceramics possess a room-temperature crystal structure described by the centrosymmetric P3[combining macron]m1 space group. Polarized Raman spectroscopy enabled the observation of all the 25 predicted Raman modes and assignment of their symmetries. On cooling, BCTO ceramics exhibit two antiferromagnetic transitions at 3 K and 12.5 K, in broad agreement with a recent single-crystal study [P. Chanlert, N. Kurita, H. Tanaka, D. Goto, A. Matsuo and K. Kindo, Phys. Rev. B: Condens. Matter Mater. Phys., 2016, 93, 094420]. Low temperature Fourier-transform infrared reflectivity analyses suggest the antiferromagnetic phase transitions to be driven by small distortions of the CoO6 octahedra, lowering locally their C3v symmetry. This causes splitting of the associated vibrational modes, but without a long-range structural change. AC impedance spectroscopy revealed BCTO ceramics to be leaky insulators with an activation energy for conduction of ∼0.15-0.25 eV, which suggests electron hopping between mixed oxidation states of Co.

To study the effect of processing conditions on structural and mechanical characterization of graphite and graphene oxide-reinforced PVA nanocomposite

The aim of this paper is to investigate the effect of processing conditions for fabrication of PVA nanocomposite by varying exfoliation span and to study its surface and mechanical parameters. Graphite (xGnP) and graphene oxide (GO) are used as nanofiller which are prepared by Modified Hummer’s method respectively. PVA nanocomposite has been prepared by solution casting route by varying xGnP and graphene oxide content and also its exfoliation duration. The major concern is to synthesize a hybrid polymer nanocomposite having good interfacial and homogeneous dispersion of nanofiller. Excellent enhancement in tensile strength from 33 to 57.79 MPa is examined on addition of 1% GO content in comparison with pristine PVA which is attributed to the existence of hydroxyl and carboxylic groups into PVA and GO nanoparticles, respectively. Storage modulus of 1% GO-reinforced PVA is two times higher than the neat PVA. Decrement in crystallinity is examined by DSC analysis. Size of crystal is evaluated by XRD analysis. SEM micrographs showed uniform distribution of nanoparticles throughout the polymeric surface. Polarizing optical micrographs displayed difference in exfoliated nanoparticles and its consistent distribution in the polymer matrix by varying exfoliation duration. Thermal studies also support the outcome which is observed from mechanical analysis. Graphical abstract demonstrates tensile strength vs. wt% of nanofiller of A-xGnP, GO (1 h), and B-xGnP, GO (1.5 h), PVA nanocomposite thin films.

Fabrication Process and Pressure Dependence of Critical Current Density in Ba1-xKxFe2As2 Superconducting HIP Wires

We demonstrate the fabrication of (Ba,K)Fe2As2 superconducting wires through a powder-in-tube (PIT) method and hot isostatic press (HIP) technique. Several fabrication processes with different sintering conditions of pressure and time were examined. The measurements of magnetization, I-V characteristics, filling factor, and Vickers hardness clarified that the improvement of fabrication process and sintering condition is effective for the enhancement of critical temperature Tc, which leads to the enhancement of critical current density Jc in HIP round wire. Wires which are fabricated in different processes show significantly different Tc and Jc. The core density, which can be enhanced by sintering at higher pressures, is the main key factor for enhancement of Jc in HIP wires, similar to pressed tapes. Changing the sintering time also slightly affect Jc.