Surface Engineering Processes Research Articles

System-level integration tools for laser-based powder bed fusion enabled process chains

A multi-setup additive manufacturing (AM) platform that integrates the powder bed fusion (PBF) technology with a range of complementary pre- and post-processing steps has the potential to be an appealing and flexible production solution for addressing the technical requirements of the existing and new products. Especially, such multi-step manufacturing solutions could overcome the limitations of standalone additive, subtractive, replication and surface engineering processes by reinforcing their complementary capabilities. However, the lack of specially developed system-level tools to address interoperability issues in integrating PBF with other technologies leads to high uncertainty and overall risk in producing parts that incorporate geometries with different manufacturing requirements, e.g. parts with areas that can be cost-effectively machined while others require AM solutions. To address such open issues, this paper presents the development of generic hardware and software integration tools that can improve the system level performance of AM enabled process chains. In particular, the research reports the design and implementation of modular workpiece holding system and quality control strategy that can warrant the production of parts encompassing structures with distinctly different manufacturing requirements. An experimental validation of the proposed tools was performed to assess their capabilities in producing parts with high accuracy and repeatability. The results demonstrate that their synergistic utilisation can lead to significant improvements in producing AM sections on top of pre-machined preforms in regards to their positional accuracy and repeatability. It was observed that the positional accuracy in the hybrid additive-subtractive parts was improved thirtyfold with the system level tools from 0.604 mm and 0.442 mm to 21 μm and 10 μm along X and Y axes, respectively.

Highly sensitive wearable strain sensor based on ultra-violet/ozone cracked carbon nanotube/elastomer

To simultaneously achieve high sensitivities (gauge factor > 100) and large stretchability (>50%) is still a grand challenge in developing the wearable strain sensors. In this study, a strain sensor with a high sensitivity up to 1020.2 and a large stretchability of 100% was developed based on ultra-violet/ozone (UV/O3) cracked carbon nanotubes/elastomers. The high sensitivity is ascribed to the widening of the cut-through cracks generated by the UV/O3 surface engineering process. The UV/O3-cracked strain sensors show potential applications in electronic skins to detect various human motion signals such as bending of the wrist, pulsing, and eye blinking.

Improving the surface characteristics of Ti-6Al-4V and Timetal 834 using PIRAC nitriding treatments

Despite the popularity of a number of techniques of thermochemical diffusion for titanium, in many cases the surface engineering processes used may not be economically viable options for industry. This work focuses on the application of Powder Immersion Reaction Assisted Coating (PIRAC), a relatively inexpensive nitriding treatment that can provide a remarkable improvement in the surface characteristics of titanium alloys. The aim of this work was to determine whether PIRAC could be successfully applied to Ti-6Al-4V and the high-performance near-α titanium alloy Timetal 834. In order to study the response of these materials to PIRAC nitriding, techniques such as X-ray diffraction, micro-indentation hardness, surface profilometry, optical and electron microscopy, nano-scratch adhesion testing and ball-on-plate reciprocating-sliding wear testing were employed. These techniques highlighted the markedly different response between the two alloys to the PIRAC treatment; namely, that Ti-6Al-4V forms a thick compound layer, while at the same processing temperature and time Timetal834 does not form any appreciable Ti2N phase instead forming a nitrogen-diffusion case with a thin TiN compound layer at the surface. This inherent difference in nitridability influences the metallurgical response of each alloy. Despite this, the surfaces of both alloys were still hardened considerably and their tribological performance in dry sliding conditions improved compared to the untreated alloys.

Influence of Aliquat 336 on tribological properties of electroless ternary nanocomposite coatings on AZ91 alloy

Incorporation of fine nanoparticles and cationic surfactant (Aliquat 336) within an ENi–P matrix has given a new dimension to the field of nanocomposite coatings. It describes the surface engineering processes currently used for the protection of AZ91 magnesium alloy surface against wear, including electroless nano-composite coatings. The present work aims to investigate the influence of Aliquat 336 cationic surfactant on the microhardness and tribological properties of electroless (Ni–P–ZnO) ternary alloy nanocomposite coatings on AZ91 magnesium alloy substrate from acidic bath. The results revealed that there was a significant improvement in the microhardness and wear resistance of the coated surface by the addition of cationic surfactant at a concentration of 1.5 g/L as compared to the coating obtained without the addition of cationic surfactant in the chemical bath. These results are thus clearly indicative of the fact that the component of life of members made from substrate subjected to nanocomposite coatings with varying the concentration of surfactant can be greatly improved, thereby preventing early or regular failures, and increasing service life.

Key Equipments for O3-based Wet-Chemical Surface Engineering and PVD Processes Tailored for High-Efficiency Silicon Heterojunction Solar Cells

SINGULUS TECHNOLOGIES AG has been dedicated to realizing multiple HJT-projects worldwide up to gigawatt dimension. In this contribution key equipments including advanced wet-chemical texturing and cleaning processes based on ozone (O3) and PVD (Physical Vapour Deposition) for ITO (Indium Tin Oxide) layers are reviewed, which are developed and optimized together with industrial and institutional partners.

Enhanced erosion performance of cold spray co-deposited AISI316 MMCs modified by friction stir processing

The present study reports on the erosion properties of a novel surface engineering process combining cold spray and friction stir processing. Tungsten carbide (WC-CoCr) and aluminium oxide (Al2O3) powders were cold spray co-deposited with AISI316 using a twin powder feed system. The deposited coatings were subsequently friction stir processed to refine and redistribute the reinforcing particles and remove the coating-to-substrate interface layer, thus generating a new metal matrix composite surface. Microstructural analysis of the SprayStirred (cold sprayed then friction stirred) specimens revealed significant particle refinement and improved particle distribution over the as-deposited coatings. The erosion performance of these SprayStirred surfaces was evaluated using a flowing slurry and demonstrated an 80% decrease in volume loss over the as-received AISI316 at 30° angle of attack. For SprayStirred WC-CoCr, microhardness measurements indicated an increase of approx. 530% over the unaltered AISI316 and 100% over the cold sprayed coating. These findings highlight the considerable increase in erosion performance of the SprayStirred specimens, and thus demonstrate the benefits of this innovative surface engineering process. This outcome is attributed to dispersion strengthening, imparted by the refined tungsten carbides. Furthermore, the SprayStirred WC-CoCr coating exhibited an 85% reduction in volume loss over an HVOF sprayed WC-CoCr coating.

Tribology of nitrided-coated steel-a review

Abstract Surface engineering such as surface treatment, coating, and surface modification are employed to increase surface hardness, minimize adhesion, and hence, to reduce friction and improve resistance to wear. To have optimal tribological performance of Physical Vapor Deposition (PVD) hard coating to the substrate materials, pretreatment of the substrate materials is always advisable to avoid plastic deformation of the substrate, which may result in eventual coating failure. The surface treatment results in hardening of the substrate and increase in load support effect. Many approaches aim to improve the adhesion of the coatings onto the substrate and nitriding is the one of the best suitable options for the same. In addition to tribological properties, nitriding leads to improved corrosion resistance. Often corrosion resistance is better than that obtainable with other surface engineering processes such as hard-chrome and nickel plating. Ability of this layer to withstand thermal stresses gives stability which extends the surface life of tools and other components exposed to heat. Most importantly, the nitrogen picked-up by the diffusion layer increases the rotating-bending fatigue strength in components. The present article reviews mainly the tribological advancement of different nitrided-coated steels based on the types of coatings, structure, and the tribo-testing parameters, in recent years.

Influence of friction stir process parameters on surface quality of aluminum alloy A2017

Friction stir processing is an environment friendly surface engineering process that enhances mechanical properties and refines microstructure of processed zones. The aim of this paper is to study the influence of process parameters during friction stir processing of aluminium alloy A2017 plates on surface quality of the processed zones.

Where physics meets chemistry: Thin film deposition from reactive plasmas

Functionalising surfaces using polymeric thin films is an industrially important field. One technique for achieving nanoscale, controlled surface functionalization is plasma deposition. Plasma deposition has advantages over other surface engineering processes, including that it is solvent free, substrate and geometry independent, and the surface properties of the film can be designed by judicious choice of precursor and plasma conditions. Despite the utility of this method, the mechanisms of plasma polymer growth are generally unknown, and are usually described by chemical (i.e., radical) pathways. In this review, we aim to show that plasma physics drives the chemistry of the plasma phase, and surface-plasma interactions. For example, we show that ionic species can react in the plasma to form larger ions, and also arrive at surfaces with energies greater than 1000 kJ∙mol–1 (>10 eV) and thus facilitate surface reactions that have not been taken into account previously. Thus, improving thin film deposition processes requires an understanding of both physical and chemical processes in plasma.

Effects of Different Plasma Nitrided Layers on the Tribological Performance of DLC Coatings

When multifunctional surface engineering processes that combine purpose-oriented phases are applied to soft substrates, a combination of high wear resistance, high load support and low coefficients of friction can be achieved. In this study, the effects of different nitrided layers on the tribological behaviour of a diamond-like carbon (DLC) film deposited on a SAE 1040 steel were investigated. The nitriding was carried out under different temperatures and gas mixtures to create three distinct nitrided layers: two compound layers with predominant e and γ' phases and a diffusion layer. All of the surfaces were then coated with DLC deposited via plasma-enhanced chemical vapour deposition (PECVD). The tribological tests indicated that the best performance was achieved for a specific combination of hardness, surface roughness and nitride type. The best load-bearing capacity between the DLC coating and the soft substrate was achieved when the nitrided layer was primarily a diffusion layer.

Finite element simulation of shot peening of an aluminum alloy considering hardening models

Shot peening is a surface engineering process acknowledged for its potential to develop fatigue strength and erosion-corrosion resistance of metallic materials. In the present study, a 3-D finite element model is employed to predict the effective parameters through a single shot impact and the accuracy of the simulation is validated using previous literatures. In order to induce uniform compressive residual stress patterns across the specimen, processing parameters such as shot velocity, impact angle and friction coefficient should be controlled. It is observed that by increasing the shot velocity and the friction coefficient, the depth of compressive residual stress increases. Moreover, a comparative study between isotropic and kinematic hardening models is performed to evaluate the significant role of the hardening models on the compressive residual stress. It is observed that the kinematic hardening model shows better compatibility with the experimental results compared to the isotropic hardening.

The "Pure Marriage" between 3D Printing and Well-Ordered Nanoarrays by Using PEALD Assisted Hydrothermal Surface Engineering.

For the first time, homogeneous and well-ordered functional nanoarrays were grown densely on the complex structured three-dimensional (3D) printing frameworks through a general plasma enhanced atomic layer deposition (PEALD) assisted hydrothermal surface engineering process. The entire process was free from toxic additives or harmful residues and, therefore, can meet the critical requirements of high-purity products. As a practical example, 3D customized earplugs were precisely manufactured according to the model of ear canals at the 0.1 mm level. Meanwhile, well-ordered ZnO nanoarrays, formed on the surfaces of these 3D printed earplugs, could effectively prevent the growth of five main pathogens derived from the patients with otitis media and exhibited excellent wear resistance as well. On the basis of both animal experiments and volunteers' investigations, the 3D customized earplugs showed sound insulation capabilities superior to those of traditional earplugs. Further animal experiments demonstrated the potential of as-modified implant scaffolds in practical clinical applications. This work, exemplified with earplugs and implant scaffolds, oriented the development direction of 3D printing in biomedical devices, which precisely integrated customized architecture and tailored surface performance.

Developments in laser-based surface engineering processes: with particular reference to protection against cavitation erosion

With the increasing demands of economical, reliable and durable hydraulic and pneumatic systems, it is necessary to minimize the material damage from cavitation erosion (CE) when systems are handling cavitating and corrosive fluids. Cavitation erosion is a nausea for many engineering components, such as ship propellers & rudders, turbine, diesel engine, cylinder liner, pump impeller vanes, control valves, hydraulic turbines, bearings, pipes, ultrasonic cleaners and mechanical heart valves, which are exposed to the high-speed flowing or vibratory fluids. This paper reviews the rationale behind the application of laser surface modification for achieving CE resistant surfaces of fluid handling components. The problem of CE may be tackled by enhancing the surface properties of the base materials (ferrous and non-ferrous alloys) with various laser surface modification techniques including laser transformation hardening (LTH), laser surface melting (LSM), laser surface alloying (LSA), laser cladding (LC), laser dispersion (LD) and laser plasma hybrid spraying (LPHS). The CE performance of a variety of laser-surface modified layers/coatings is discussed in this review. In particular, coatings of hard-facing alloys, shape memory alloys, surface metal or intermetallic matrix composites and cermets on ferrous and non-ferrous alloys are included. The mechanisms of the enhancement in cavitation erosion resistance (Re) are discussed.

Towards near-permanent CoCrMo prosthesis surface by combining micro-texturing and low temperature plasma carburising

An advanced surface engineering process combining micro-texture with a plasma carburising process was produced on CoCrMo femoral head, and their tribological properties were evaluated by the cutting-edge pendulum hip joint simulator coupled with thin film colorimetric interferometry. FESEM and GDOES showed that precipitation-free C S-phase with a uniform case depth of 10μm was formed across the micro-textures after duplex treatment. Hip simulator tests showed that the friction coefficient was reduced by 20% for micro-metre sized texture, and the long-term tribological property of microtexture was enhanced by the C-supersaturated crystalline microstructure formed on the surface of duplex treated CoCrMo, thereby enhancing biotribological durability significantly. In-situ colorimetric interferometry confirmed that the maximum film thickness around texture area was 530nm, indicating that the additional lubricant during sliding motion might provide exceptional bearing life.

Active screen plasma surface co-alloying of 316 austenitic stainless steel with both nitrogen and niobium for the application of bipolar plates in proton exchange membrane fuel cells

Austenitic stainless steel has been researched as a promising candidate material for bipolar plates in proton exchange membrane fuel cells. However, its interfacial contact resistance (ICR) is about 16 times higher that of the Department of Energy (DOE) target (10 mΩ cm2), which leads to undesirable fuel cell performance. In this work, a new hybrid plasma surface engineering process, based on active screen plasma co-alloying, has been developed to simultaneously alloy 316 austenitic stainless steel (316 SS) surfaces with both nitrogen and niobium. The results demonstrated that the layer structure of the modified surfaces can be tailored by adjusting the treatment conditions. All the plasma treated 316 SS samples exhibited significantly reduced ICR below the DOE target of 10 mΩ cm2. The corrosion resistance of the N/Nb co-alloyed 316 SS was much better than active screen plasma nitrided and marginally better than the untreated material.

Effect of pulse laser parameters on TiC reinforced AISI 304 stainless steel composite coating by laser surface engineering process

In this work, TiC reinforced steel composite layer has been produced by laser scanning over the preplaced TiC powder on AISI 304 steel substrate, using a pulse Nd:YAG laser. Depending on the pulse laser parameters, TiC either deposited or dispersed on the surface of steel substrate. Depth and width of laser processed TiC–steel composite layer has been deliberated from the SEM images at the transverse cross section of the laser scanned samples. Hardness of the laser processed composite layer has been measured through Vickers micro-hardness tester. Effect of pulsed laser parameters i.e. peak power, pulse duration, overlapping factor (corresponding to scan speed and frequency) on micro-hardness, composite layer profile (depth and width) and microstructure of the laser processed TiC–steel composite layer has been studied. From the experimental analysis, it is revealed that, laser peak power and overlapping factor have significant effect on the TiC–steel composite layer profile and its hardness value.

Hard TiC Coating on AISI304 Steel by Laser Surface Engineering Using Pulsed Nd:YAG Laser

The surface mechanical property of AISI304 stainless steel was improved by TiC coating deposited through laser surface engineering process using a pulsed Nd:YAG laser. The produced coating exhibited significantly higher hardness (650–1900 HV0.1) compared to the steel substrate (190 HV0.1). Coating thickness, dilution of TiC on substrate surface, and hardness of the coating were determined using various pulse laser processing parameters, i.e., peak power and pulse frequency. At low pulse frequency and peak power condition, relatively thick and uniform coating of TiC was deposited over the substrate. However, at higher pulse frequency and peak power condition, TiC-dispersed steel composite coating was produced.

Functionalization of liposomes: microscopical methods for preformulative screening

The development of smart delivery systems able to deliver and target a drug to the site of action is one of the major challenges in the field of pharmaceutical technology. The surface modification of nanocarriers, such as liposomes, is widely investigated either for increasing the blood circulation time (by pegylation) or for interacting with specific tissues or cells (by conjugation of a selective ligand as a monoclonal antibody, mAb). Microscopical analysis thereby is a useful approach to evaluate the morphology and the size owing to resolution and versatility in defining either surface modification or the architecture and the internal structure of liposomes. This contribution aims to connect the outputs obtained by transmission electron (TEM) and atomic force (AFM) microscopical techniques for identifying the modifications on the liposomal surface. To reach this objective, we prepared liposomes applying two different pegylation technologies and further modifying the surface by mAb conjugation. This work demonstrates the feasibility to apply the combined approach (TEM and AFM analysis) in the evaluation of the efficacy of a surface engineering process.

윤활영역에서 멀티크기 Laser Surface Texturing 효과

Laser Surface Texturing(LST) is a surface engineering process used to improve tribological characteristicsof materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsatedlaser beam is used to create arranged dimples on a surface by a material ablation process, which can improve such asload capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect ofmulti-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples withsome specific formula arrays were fabricated by combining circles, ellipses and the laser ablation process. The tri-bological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubri-cation and the results compared with that of the non-textured surface. Through an increase in sliding speed, thebeneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower frictioncoefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.Keywords: laser surface texture (레이저 표면 텍스처), lubrication regime (윤활영역), friction (마찰), surfacemodification (표면개질)

Influence on friction behavior of micro-texturing under lubricated non-conformal contact

Laser surface texturing (LST) is a well-known surface engineering process used to create arranged dimples on surface using a material ablation process. In this process, a well arranged micro-dimple can produce significant improvements of engineering components in aspects such as load carrying capacity, wear resistance, wetting characteristics and reduction of friction coefficient. In the present work, we investigated the effect of multi-dimple LST steel surfaces on tribological properties under non-conforming contact. The multi-dimple textured surfaces with some specific formula arrays were fabricated by laser ablation process on steel disc by combining patterns of circles and triangles, and circles and squares, having different dimple densities to optimize the surface texturing effect on tribological performance. The tribological test of multi-dimple textured surface was performed by a ball-on-flat unidirectional tribometer in lubricated condition, and the results compared with that of a single-dimple and untextured (polished and ground) surfaces. The results indicate that the surface with multi-dimple textured patterns had better friction performance than the untextured and single-dimple textured surfaces. The beneficial effect of multi-dimple textured patterns was associated with transition of lubrication from boundary to mixed lubrication regime.