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The ability to adjust topological features of lattice structures offers a great potential to finely calibrate their physical and mechanical response to precisely meet specific requirements. This study explores a new topological design that leverages the internal porosity of Triply Periodic Minimal Surfaces (TPMS) unit cells to optimize and control their mechanical properties. A smaller-scale TPMS lattice structure was integrated within the internal volume of the sheet-network Schwarz Primitive TPMS cell, culminating in a hybrid hierarchical architecture. Various TPMS topologies with distinct mechanical behavior and varying relative density combinations were examined. Experimental and numerical approaches were developed to reveal the structure’s deformation behaviour and quantify stiffness, anisotropy, quasi-static uniaxial compressive strength, and energy absorption capacity. The topological design of the internal lattice was found to play a key role in defining the mechanical performance of the integrated structures, leading to enhanced energy absorption up to 4 times that of the reference structure. Moreover, all the studied hierarchical topologies exhibited a lower Emax/Emin ratio in comparison to the reference topology, indicating more isotropic performance of the hybrid designs (upto 40% reduction of anisotropy). The findings underscore the significant promise of hybrid hierarchical design methodologies in attaining lattice structures with tailored properties.

Wettability is a crucial surface feature of polymers due to their numerous interaction-destined applications. This study focuses on the application of sand blasting process for investigating the wettability of polymeric materials to produce hydrophobic behavior. Four different polymeric materials, Acrylonitrile Butadiene Styrene (ABS), Poly(methyl methacrylate) (PMMA), Polypropylene (PP), and Polycarbonate (PC) underwent sand blasting with varying process parameters, following a comprehensive plan for the design of experiments. Subsequent analyses included surface roughness measurement and wettability tests, supplemented by scanning electron and confocal microscopy observations to gain deeper insights into the blasted surfaces. A predictive model based on a machine learning algorithm was developed using the backpropagation technique to correlate the surface treatment parameters to surface roughness and wettability indexes. From the experimental results sand blasting proved to be efficient in creating hydrophobic surfaces on all the tested materials. The developed neural network demonstrated high fitting degrees between the predicted and measured values. ABS exhibited the most hydrophobic behavior and emerged as a strong candidate for further investigations.

CSAM (cold spray additive manufacturing) of Ti6Al4V is a challenging task and high-quality deposits conforming to the AM application standards have not been developed so far. In our study, two distinct feedstock Ti6Al4V powders with different morphology and microstructure, spherical and crystalline, were used and their influence on the deposits was investigated in terms of microstructure as well as tensile properties. The results indicate the mechanical strength and ductility of the as-deposited samples to be in the range of 8–30 % compared to wrought Ti6Al4V and highlight a significant anisotropy in different in-plane directions. The post-treatments of the deposits from the spherical, plasma atomized powder effectively reduced the porosity and triggered microstructural homogenization and recrystallization, leading to a significant increase in the yield and tensile strengths, reaching 892 MPa and 954 MPa, respectively, while achieving an enormous enhancement in the elongation to 21.6 % at the same time. This was in a striking contrast to the deposits from the crystalline powder: despite the yield and tensile strength increase to 853 MPa and 1058 MPa, respectively, the elongation remained virtually zero, highlighting the importance of the feedstock powder selection in cold spray additive manufacturing of Ti6Al4V.

Post-processing methods are widely used to address the issues caused by surface imperfections and bulk defects in additive manufactured materials. In our previous studies, we analysed the effects of different peening-based treatments of shot peening (SP), severe vibratory peening (SVP) and laser shock peening (LSP) on fatigue performance of V-notched laser powder bed fusion AlSi1Mg samples. Herein, the fracture surfaces of failed samples were further analyzed and obtained experimental data were further elaborated by machine learning (ML)-based approach to identify the correlation between residual stress, hardness and surface roughness (all affected by the applied post-treatments) with the depth of crack initiation site and fatigue life of the post-treated samples. ML-based model was developed via a six layer deep neural network (DNN) as well as using stacked auto-encoder (SAE) for pre-training of the used data set. Taking the advantages of SAE, the accuracies of more than 0.96 were obtained for the predicted results. Correlations were obtained by performing parametric analyses and the importance of each input factor was assessed through sensitivity analyses. The obtained results revealed that by enhancing surface hardening and inducing higher compressive residual stresses as well as more efficient surface roughness reduction, deeper crack initiation site and superior fatigue life can be obtained. In addition, it was found that the depth of sub-surface crack initiation had direct relation with fatigue life improvement in the samples.

In the current study, the effects of different post-processing methods, including heat treatment (HT) and electro-chemical polishing (ECP) as well as their combination on the surface texture, porosity, microstructure, mechanical properties, and rotating bending fatigue behavior of U-notched laser powder bed fused AlSi10Mg specimens were comprehensively investigated. In addition, to better understand the effects of the applied post-processing methods on the sensitivity of the notched specimen to surface and near-surface defects, finite element analysis was performed. Chemical treatment was found to be very influential on surface texture modification of the very narrow notched parts, for which the application of other treatments can be quite challenging. It was also found that the fatigue behavior of the notched specimens was more sensitive to the surface texture rather than to the near-surface defects. The hybrid treatment involving HT+ECP was the most effective for fatigue behavior improvement due to simultaneous homogenization of the microstructure, released tensile residual stresses, enhanced ductility and high surface texture modification.

Extraordinary fretting fatigue endurance is critical for engineering structures prone to contact with expected long service lifetimes. Here, we propose a strategy to achieve ultrahigh fretting fatigue endurance in titanium alloy. A special hierarchical structure, i.e. gradient amorphous-nanocrystalline grain/coarse grain, was designed in a TB8 titanium alloy via surface severe plastic deformation, which forms an nanocomposite structure comprising of amorphous-nanocrystalline and nano-lamellae and β to α phase transformation upon repeated fretting wear. The nanocomposite surface and phase transformation suppress cracks initiation and propagation, resulting in the high fretting fatigue life that was 30.2-times higher than that of the original TB8 titanium alloy via triggering an exceptional fretting fatigue phenomenon where damage-crack initiate towards the interior of non-fretting contact zone. This study provides a new insight into improving the fretting fatigue endurance of titanium alloys.

Abstract A hybrid post-treatment combining tumble finishing as a final step after shot peening and heat treatment was developed to alleviate the adverse effects of internal and surface defects on the fatigue performance of laser powder bed fusion AlSi10Mg samples. The effects of each post-treatment were investigated individually and synergistically on microstructure, surface morphology and roughness, hardness, residual stresses, porosity, and rotating bending fatigue behavior of V-notched AlSi10Mg samples. The results reveal that tumble finishing can highly reduce surface roughness by 28 and 32% compared to the as-built and heat-treated states while inducing extra surface layer hardening and compressive residual stresses. The hybrid post-treatment of heat treatment + shot peening + tumble finishing significantly increased the fatigue life of the samples by over 500 times higher compared to the as-built series.

AISI316L stainless steel components produced via additive manufacturing techniques have quickly found new applications across several industrial sectors. However, parts manufactured through this method generally exhibit poor surface quality and performance in the as-built state. This work addresses the influence of laser polishing and water jet assisted recirculating shot peening on the surface quality, microstructure and electrochemical properties of AISI316L samples produced by the laser powder bed fusion method. To do so, surface roughness analysis, residual stress measurement, scanning electron microscope and electron backscatter diffraction analysis were employed along with electrochemical tests, including cyclic potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky analysis. Laser polished samples exhibited a smooth surface with high tensile residual stress on the surface, which led to the reduction of pitting potential and formation of passive layers, including more crystal defects. Microscopical analysis evidenced that the higher density of lattice defects and local microstrain on the surface of the shot peened samples promoted surface hardness and induced compressive residual stress. Therfore, the shot peened samples exhibited a wider passive range in cyclic potentiodynamic polarization measurements, higher polarization resistance in electrochemical impedance spectroscopy measurements, and less defective passive film in Mott-Schottky analysis. Moreover, it was calculated that the passive film thickness of the shot peened sample was slightly larger than the other samples. Low surface roughness, high crystal defect density, and compressive residual stresses enhanced the passive layer's resistance to defect transport, lowered the point defect concentration in the passive film, and improved the pitting resistance of the samples.

In view of the recent interest in modifying the surface functionality and esthetics of polymeric materials by sand blasting treatment, a numerical model was developed as a tool to predict the evolution of surface morphology as a function of blasting parameters. The wide range of shot size and shape variations, typical of blasting media, were parametrized based on microscopical observations. Thus, the developed numerical model accounts for the media inhomogeneity and also implements randomness in both the sequence and position of the multiple impacts. To make the model as realistic as possible, the velocity of individual shots was calculated based on their interaction with the airflow. Systematic experiments were performed using Polycarbonate (PC) as the substrate material and Alumina as the blasting media. A comparison of the experimental and numerical results demonstrated the ability of the developed model to successfully predict the surface roughness generated by sand blasting, as the shot arrangement and distribution were varied. This model establishes a potential basis for future studies regarding the performance of the sand blasted surfaces such as wettability using numerical approaches.

Abstract Metallization of polymers using cold spray technology has reached wide consideration in recent years. However, an effective modeling approach to address the deposition phenomena able to assess bonding formation in polymer metallization is still lacking. This study aims to develop a finite element model to simulate the solid-state deposition of metallic particles on thermoplastic polymeric substrates. Single copper particle impact on the Polyether Ether Ketone substrate was modeled using the coupled Lagrangian–Eulerian approach. Emphasis was given to the polymer material properties and substrate thermal history to account for the sensitivity of the physical and mechanical properties of polymers to temperature. Experimental coating depositions were performed to select an optimized set of spray parameters while single-particle impact tests were conducted for model validation. The substrate temperature was measured using an infrared thermal camera and was used to model the sub-surface temperature gradient during gas spray exposure. The proposed numerical model is shown to be capable of predicting various impact features includi mechanical interlocking and the effect of particle velocity fluctuations and temperature gradients on the extent of bonding. Substrate heating was found to have a distinct effect on the correct prediction of particle bonding. The proposed model enables tuning the appropriate processing conditions for successful copper particle adhesion on PEEK polymeric substrates.

Nickel-based coatings are well known for their good corrosion resistance performance. However, these materials suffer from inferior mechanical properties that limit their wider application. This work investigates the synthesis, and performs an exhaustive characterization, of Ni–P–B4C nanocomposite coatings developed through conventional electrodeposition using a modified Watts bath. The study examines the effect of an increase in the concentration of boron carbide nanoparticles (BCNPs) on the structural, morphological, topographical, mechanical and electrochemical properties of the nanocomposite coating. Vickers microhardness tester and nanoindentation technique were utilized to elucidate the role of BCNPs in modifying the mechanical response of nanocomposite coatings. Furthermore, corrosion resistance of the nanocomposite coatings was investigated through d.c potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Comparison of the properties of the developed coatings revealed the remarkable improvement in the properties of Ni–P–B4C nanocomposite coatings when compared to the bare mild steel substrate and the Ni–P coatings. The enhanced corrosion resistance and superior mechanical properties of Ni–P–B4C nanocomposite coatings make them attractive for many industries. Based upon the experimental findings, a possible mechanism for the synthesis and improved corrosion resistance of Ni–P–B4C nanocomposite coatings was also proposed.

Microstructural characterization has a key role in analyzing the properties of additive manufactured materials. Electron backscatter diffraction (EBSD) can offer a unique set of information on the microstructural state of these materials. However, EBSD analyses is extremely sensitive to the quality of the prepared sample and requires a seamless preparation eliminating any risk of contamination, oxidation or surface imperfections. Despite the wide use of EBSD analysis in AM, there is no universally accepted sample preparation protocol and the variety and sequence of the steps that can guarantee high quality data remain unclear. In this study, the efficiency of sample preparation methods with various final steps of vibrational polishing, vibrational polishing + cleaning, vibrational polishing + electro-chemical polishing and vibrational polishing + chemical etching was surveyed and compared for EBSD analyses of notched AM AlSi10Mg part. The obtained results help selecting the most efficient approach indicating that vibrational polishing + chemical etching with hit rate of 95.41% lead to the lowest zero solutions followed by vibrational polishing + electro-chemical polishing, vibrational polishing + pad cleaning and just vibrational polishing, respectively.

An experimental campaign of stainless-steel specimen tests has been completed. Three different types of tests have been performed: UTS (Ultimate Tensile Strength), LCF (Low Cycle Fatigue) and HCF (High Cycle Fatigue). This experimental campaign has been conceived and performed to validate the fatigue damage initiation prediction capabilities of UMT (Unified Mechanics Theory). Two different formulations have been used for LCF and HCF. For the latter, a modification to the existing approach is proposed in this paper. Good agreement has been found between UMT predictions and experimental results.

Abstract The roughness of material surfaces is of greatest relevance for applications. These include wear, friction, fatigue, cytocompatibility, or corrosion resistance. Today’s descriptors of the International Organization for Standardization show varying performance in discriminating surface roughness patterns. We introduce here a set of surface parameters which are extracted from the appropriate persistence diagram with enhanced discrimination power. Using the finite element method implemented in Abaqus Explicit 2019, we modelled American Rolling Mill Company pure iron specimens (volume 1.5 × 1.5 × 1.0 mm3) exposed to a shot peening procedure. Surface roughness evaluation after each shot impact and single indents were controlled numerically. Conventional and persistence-based evaluation is implemented in Python code and available as open access supplement. Topological techniques prove helpful in the comparison of different shot peened surface samples. Conventional surface area roughness parameters might struggle in distinguishing different shot peening surface topographies, in particular for coverage values > 69%. Above that range, the calculation of conventional parameters leads to overlapping descriptor values. In contrast, lifetime entropy of persistence diagrams and Betti curves provide novel, discriminative one-dimensional descriptors at all coverage ranges. We compare how conventional parameters and persistence parameters describe surface roughness. Conventional parameters are outperformed. These results highlight how topological techniques might be a promising extension of surface roughness methods.

Abstract Shot peening is widely used for improving mechanical properties especially fatigue behavior of metallic components by inducing surface hardening, compressive residual stresses and surface grain refinement. In air blast shot peening, projection pressure and surface coverage (an index of peening duration) have been considered as major controlling process parameters; the combination of these parameters plays a critical role in the beneficial effects of shot peening. Generally in severe shot peening aimed at obtaining surface grain refinement, constant values of pressure are considered with different peening durations. Considering very high peening duration, however, the phenomenon of over shot peening, which can be identified with the formation of surface defects could occur. The present study introduces a novel shot peening treatment, here called gradient severe shot peening (GSSP) that instead of using constant projection pressure, implements gradually increasing or decreasing pressures. The gradual increase of the projection pressure acts as a pre-hardening stage for the following higher projection pressure boosting the potential of the material to tolerate the sequential impacts and thus become less prone to the formation of surface defects. The results of the experiments indicate significant fatigue life improvement obtained for GSSP treated specimens compared to the standard treatment with constant pressure. GSSP avoids the detrimental effects of over-peening, while maintaining the beneficial effects of surface nano-crystallization, surface hardening and compressive residual stresses. The notable difference in fatigue strength enhancement for GSSP treated material can be also attributed to the modulated surface morphology with lower surface roughness compared to a standard shot peening treatment with the same exposure time.

Currently, the onset of bone damage and the interaction of cracks with the surrounding micro-architecture are still black boxes. With the motivation to address this issue, our research targets isolating lacunar morphological and densitometric effects on crack advancement under both static and cyclic loading conditions by implementing static extended finite element models (XFEM) and fatigue analyses. The effect of lacunar pathological alterations on damage initiation and progression is evaluated; the results indicate that high lacunar density considerably reduces the mechanical strength of the specimens, resulting as the most influencing parameter among the studied ones. Lacunar size has a lower effect on mechanical strength, reducing it by 2%. Additionally, specific lacunar alignments play a key role in deviating the crack path, eventually slowing its progression. This could shed some light on evaluating the effects of lacunar alterations on fracture evolution in the presence of pathologies.

Gradient microstructures on the surface of metals induced by severe shot peening (SSP) is relatively a new research topic in the field of severe plastic deformation processing. The treated surface is known to show three distinct features: a spectrum of grain size from nanometer to sub-micron to micron regime, a work-hardened surface layer, and a compressive residual stress profile near the surface. The current study is defined to investigate the effects of SSP pre-preprocessing on the anodization behavior of Aluminum. Gradient microstructures were obtained on AA1050 Al substrate using SSP with different coverage levels. SSP was performed with ceramic media to prevent contamination of the treated surface. Then the treated surface was anodized at a constant voltage in a sulfuric acid solution. The current-time responses were recorded to study the reaction kinetics. The average grain size on the surface treated by SSP was evaluated to be 255.6 nm and 181.5 nm for 1000% and 2000% coverage levels, respectively, using X-ray diffraction; while the Vickers microhardness was increased from 10.8 HV for the untreated sample to 19.8 HV and 25.8 HV by SSP with 1000% and 2000% coverage levels, respectively. It was found that the nanocrystalline microstructure of Al substrate enhances the growth rate of anodic oxide. A variable growth rate is detected within the treated layer. The nucleation of anodic oxide nanopores is discussed in terms of underlying oxide formation mechanisms and the extent of surface grain refinement.

Used with the right combination of parameters, shot peening process can be regarded as a severe plastic deformation method that can greatly enhance the strength of mechanical components by inducing surface grain refinement, increasing the hardness, and generating compressive residual stresses in the top surface layer. The present experimental study explores the effects of gradual rise of shot peening kinetic energy on microstructure, mechanical properties, and fatigue behavior of AISI 1045 carbon steel by changing the process parameters over a wide range of Almen intensity (20-32A) and surface coverages (100-3000%). Microstructural observations, X-ray diffraction, microhardness and residual stress measurements were carried out to analyze the effects of grain refinement as the kinetic energy of the peening process increased. In addition to compression-tension axial fatigue tests, fatigue crack growth measurements were also performed on specimens in both smooth and notched configurations. The results demonstrated that increasing the kinetic energy of the process is an effective technique to achieve nanostructured surface layer combined with superior mechanical properties. Severe shot peening treatment significantly improved the fatigue strength of the treated specimens, while the continuous growth of surface coverage proved to have detrimental effects on fatigue behaviour.

Thanks to the low working temperature, less product size limitations and one order of magnitude higher deposition rates compared to the established additive manufacturing techniques, more attention has been brought to the potential of cold spraying for additive manufacturing . As a process dealing with deformation of solid particles possibly leaving non-bonded interfaces and causing work hardening, any optimization should (i) adjust spray parameters to obtain high performance as-sprayed parts and (ii) tune ductility and internal stresses by post-treatments. The present study first deals with strategies to optimize spray parameters for fabrication of high performance steel 316 L deposits. Next, the performances of deposits are further adjusted by various heat treatments. The structural strength of the freestanding samples before and after the heat treatments is evaluated under static and cyclic axial loading and supported by fatigue crack growth rate analysis. The results highlight the feasibility of obtaining high quality steel 316 L deposits using N2 as process gas, rather than the costly He that is commonly suggested. This study demonstrates the potential of cold spraying to be used for deposition of freeform structural components with a static strength comparable to that of bulk and laser-based additive manufactured materials and a fatigue strength similar to that of bulk cast material.

The aim of the present study is to investigate the role of Ti on corrosion and the wear properties of Mg-5Sn-xTi (x = 0, 0.15, 0.75, 1.5 wt.%) alloys. The samples were fabricated by conventional casting followed by hot extrusion, and the studies were examined by means of a pin-on-disc tribometer at various loads of 6, 10, and 20 N with constant sliding velocities of 0.04 m/s at ambient temperature. The corrosion performance, using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), was studied in a basic solution containing 3.5 wt.% NaCl. The observation indicated a drop in the wear rate with an increase in Ti, while the average coefficient of friction was raised in higher Ti contents compared to the base material. The sample with 0.75 wt.% Ti exhibited superior wear properties at 6 and 10 N of normal force, while the sample with 0.15 wt.% Ti presented better wear resistance for 20 N. Electrochemical test observations demonstrated that the Ti deteriorated the corrosion features of the Mg-5Sn alloy, owing to the galvanic effects of Ti. The Mg-5Sn alloy exhibited excellent corrosion behavior (corrosion potential (Ecorr) = −1.45V and current density (Icorr) = 43.92 A/cm2). The results indicated the significant role of Ti content in modulating wear and corrosion resistance of the Mg-5Sn alloy.

Cold Spray is an innovative technology to create coatings through the impact of metallic particles on substrates. Its application to composites’ surfaces is recently attracting the attention of the scientific community thanks to the possibility to functionalize and improve their thermal and wear properties. Within this context, the generation of the first metal-to-composite layer is fundamental. This work presented an experimental investigation of a composite panel, reinforced with glass fibers and coated with aluminum particles. The coating investigation was carried out through active pulsed thermography, analyzing the thermal response of single and double hatches. The thermal outputs were compared with a standard microscopic analysis, with a critical discussion supporting the identification of factors that influence the thermal response to the pulse: (1) layer’s thickness; (2) cold spray coverage; (3) layer compactness; (4) particle-substrate adhesion; (5) particle’s oxidation; and (6) surface roughness.

The solutions provided through natural evolution of living creatures serve as an ingenious source of inspiration for many technological and applicative fields. Along these lines, bone-inspired concepts lead to fascinating advances in product design, architecture and garments, thanks to the bone’s exceptional combination of strength, toughness and lightness. Structural applications are inspired by the bone’s ability to resist fracture under a large spectrum of forces, while the high surface area and pore connectivity of bone architecture present exciting opportunities from an aesthetic point of view. Behind these inspirations, a disruptive common belief emerges: “down to the bone”, a journey in search of equality, universality and substantiality. Herein, we explore the current state of the art in bone-inspired applications in these fields, considering the two major categories of structural and aesthetic inspirations and discussing further technological developments.

Impact surface treatments are well-known for their efficiency in enhancing the mechanical properties of metallic materials, especially under cyclic loadings. These processes, which encompass a wide range of surface treatments based on repetitive impacts of tools of various types, induce surface plastic deformation, compressive residual stresses, and grain refinement alter the surface roughness as a side effect. Thus, it is essential to have suitable indexes to quantify the surface features caused by the typically random nature of these treatments. Herein, we evaluated the rationality of using standard roughness parameters for describing the morphological characteristics of surfaces treated by shot peening as a representative and widely used treatment of the category. A detailed numerical model of the peening process was developed. The output data were elaborated to extract the surface roughness parameters following the standard procedures. The results revealed the validity of the surface roughness parameters to describe the topography of material treated with adequate surface coverage, also highlighting the necessity to use a set of parameters rather than the common practice of relying on single parameters. Not considering a comprehensive set of amplitude and spacing parameters can result in significant, inconsistent, and misleading results while comparing the performance of surfaces.

Glass ceramics are widely used to enhance the functionality of inert metallic materials typically used for hard-tissue engineering. Biofunctionality of glass ceramics can in turn be significantly boosted with the addition of trace element dopants. Herein, we synthesized a nanostructured glass ceramic and used magnesium (Mg), which is known to promote osteoblast adhesion and proliferation, for further functionalization. The nanostructured akermanite glass ceramic (Ca 2 MgSi 2 O 7 ) was used to coat Ti6Al4V substrates by the sol-gel method. Scanning and transmission electron microscopy as well as X-ray diffraction were used to assess the structural morphology and phase composition of the coating, respectively. The micrographs showed a uniform and crack-free coating structure. Atomic force microscopy observation revealed a disordered surface roughness for coated samples. In vitro cytocompatibility tests revealed that Saos-2 cells cultured on bare samples adopted a rounded morphology, whereas cells cultured on the coated samples represented a more spread out configuration and also increased proliferation. The characterizing tests confirmed the efficiency of the synthesis method and the in vitro biocompatibility of the synthesized coating, indicating its suitability to be used for bone implants.

Almen intensity and surface coverage are well-known to be the defining parameters of shot peening-based surface treatments. These parameters are directly affected by material properties, the extension of the contact zone, the geometry of the impact pair, as well as the impact rate and velocity. Such intricate relationships have resulted in often dissimilar predictions of shot peening effects even while using an identical combination of Almen intensity and surface coverage. With the fast pace introduction of new generation impact-based surface treatments, there is a need to find a more widespread parameter that would facilitate the direct comparison of all different treatments and relate the main process parameters to the resultant mechanical characteristics. Herein, we propose to use an energy-based parameter to describe the peening process in a more widespread approach, which collectively incorporates the effects of the Almen intensity and surface coverage, as well as the diameter, material, and velocity of the impact media. A set of finite element analyses was developed to demonstrate the correlation of the peening process effects with this energetic approach. Comparisons with the experimental data served as proof of concept, confirming that the proposed method could provide a quite good estimation of the effect of peening parameters on the treated material.