In the Directed Energy Deposition (DED) process, when the mass flow of metal particles is relatively high, the thickness of the layers increases, leading to a more productive process. The higher the mass flow is, the more difficult it becomes to get a stable melt pool. The accumulation of residual heat in the previously consolidated material constitutes a thermal input affecting the balance at the laser-material interaction zone. An accurate control of the temperature of the laser-material interaction zone is critical to maintain the dynamic viscosity of the liquid metal within the narrow margin in which it can be managed in a stable way. The present work introduces a thermal model in which domains with tunable properties are considered to reproduce the growing of the manufactured sample. Concurrently, a virtual closed-loop PID regulator has been implemented in order to calculate suitable values of laser power to compensate the heat accumulated in the material, offering the results from the model as input process parameters to be directly applied in the real process. The levels of laser power proposed by the model have been experimentally applied, leading to a stable process capable of carrying out in reality the desired component.

Laser Metal Deposition (LMD) allows the fabrication of complex shapes onto non-planar surfaces. This manuscript presents a 3D-scanning strategy for the dimensional inspection of LMD-manufactured gear teeth onto cylindrical substrates. The standard registration (alignment) methods are ineffective in the context of LMD because they minimize the global distance between the reference model and the 3D-scanning point cloud. This global minimization wrongfully biases the alignment. In response to this limitation, this manuscript discusses a registration procedure that avoids global distance minimization by sequentially aligning the datums (gear root cylinder and planar faces) of both datasets. This datum-alignment procedure fixes 5 out of 6 Degrees of Freedom (DOF). The final DOF is determined by finding the optimal rotation angle that minimizes the distance between the gear teeth of both datasets. The strategy is validated with actual LMD-manufactured spur and helical gear teeth onto cylindrical substrates. This strategy would also save time during the grinding process. (c) 2024 The Authors. Published by Elsevier B.V.

Laser Shock Processing (LSP) has been demonstrated as an effective technology for improving surface and mechanical properties of metals. The main recognized advantages of the technique consist in its capability of inducing a relatively deep compression residual stresses field allowing an improved mechanical behaviour against fatigue crack initiation and growth, mechanical wear and stress corrosion. Although significant experimental work has been performed in order to explore the optimum conditions for the application of the treatments and to assess their capability to provide enhanced mechanical properties, only limited attempts have been developed in the way of physical understanding of the characteristic processes and transformations taking place under the LSP regime. In the present paper, the integrated numerical-experimental approach to LSP processes design developed by the authors is presented, the incorporation of increasingly more accurate models for the characterization of metallic materials behaviour under LSP conditions being an always present objective. Different practical results at laboratory scale on the application of the LSP technique to different materials with different irradiation parameters are presented along with physical interpretations of the induced mechanical effects. Concrete issues as laser-plasma interaction in the ns, GW/cm(2) regime, material behaviour description for cyclically compressed matter, numerical simulation methods for the coupled plasma-thermomechanic analysis, practical implementation of the technique according to different approaches, etc. are discussed in the view of the last developments contributed by the authors and, finally, a tentative summary of the still open questions for the better knowledge and control of the process is presented.

Processing the electroceramics by cold sintering is an effective and emerging technique in recent research investigations. Among several existing approaches, this method has energy efficiency and cost-effectiveness advantages. BaTiO3 (BT) perovskites are currently receiving tremendous attention in electronic industries. This material is non-toxic, suitable, low-cost, and has excellent stability. This article recapitulates the in-depth review of the BaTiO3 with various elements by a cold sintering process. Considering microstructure and electrical properties, researchers feel cold-sintered BaTiO3 can provide a breakthrough in future electronic applications. The work also reviews the crystal structure of the barium titanate and the external processing parameters that influence synthesis conditions, element substitution, grain size, and density measurements to trigger further research into advanced perovskite materials. A thorough review is presented on the various investigations performed so far on microstructure dielectric-ferroelectric properties of BaTiO3 by a cold sintering process. Furthermore, future research on these functional materials should be conducted in depth. We believe this article contains precious data that would assist future researchers in understanding the behavior of cold-sintered barium titanate better and help them develop more excellent materials for several industrial applications.

Laser Shock Processing (LSP) is increasingly applied as an effective technology for the improvement me- chanical and surface properties of metallic materials for different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields allowing an improved mechanical behavior. In this paper, the special case of Ti-6Al-4 V alloy is considered with specific consideration of the microstructural changes and residual stresses fields justi- fying those macroscopic effects. In particular, the effect of the application of different typical LSP intensities on the microstructure and residual stresses fields introduced in this material and their possible correlation to the associated surface effects are analyzed. Emphasis is placed on the study of the thermal stability of these fields after an aging heat treatment at typical high temperature working conditions. The results show that, according to expectations, a certain level of residual stresses and dislocation density remains after in - work thermal aging. The combination of different material characterization techniques has made possible to obtain a correlated set of results highlighting the complementarity of different scale approaches from surface (X-ray) to bulk (neutrons) methods. A model based on the evolution of immobile dislocation density is proposed to rationalize the distribution of dislocation densities, pointing out that plastic deformation is retained. The results clearly show such material improvement stability under typical heavy-duty conditions, thus endorsing the use of the LSP for Ti-6Al-4 V as a suitable technology for industrial applications in relatively high temperature conditions.(c) 2022 Elsevier B.V. All rights reserved.

In this paper, the experimentally observed significant increase in yield stress for strain rates beyond 104 s−1 (viscous regime) is explicitly considered in laser shock processing (LSP) simulations. First, a detailed review of the most common high-strain-rate deformation models is presented, highlighting the expected strain rates in materials subject to LSP for a wide range of treatment conditions. Second, the abrupt yield stress increase presented beyond 104 s−1 is explicitly considered in the material model of a titanium alloy subject to LSP. A combined numerical–analytical approach is used to predict the time evolution of the plastic strain. Finally, extended areas are irradiated covering a squared area of 25 × 25 mm2 for numerical–experimental validation. The in-depth experimental residual stress profiles are obtained by means of the hole drilling method. Near-surface-temperature gradients are explicitly considered in simulations. In summary, the conventionally accepted strain rate range in LSP (106–107 s−1) is challenged in this paper. Results show that the conventional high-strain-rate hardening models widely used in LSP simulations (i.e., Johnson Cook model) clearly overestimate the induced compressive residual stresses. Additionally, pressure decay, whose importance is usually neglected, has been found to play a significant role in the total plastic strain achieved by LSP treatments.

The development of superhydrophobic surfaces is significant due to the industrial applications in various fields, from energy to biomedical implants. The surface morphology and chemistry primarily govern the characteristics of the interface between the water droplet and the surfaces. Herein, a combination of laser patterning and low-pressure technique has been adopted to generate the superhydrophobic TiN surface. The superhydrophobic surface was subjected to wetting property and chemical analysis with respect to the surface geometry. The impact dynamics of water droplets at the laser-patterned superhydrophobic surface have been studied. The droplet impacts result in finger formation at the start of the spreading, and the droplets formed at the tip of fingers detached from the rim during the retraction. The resulting fragmentation favors decreased travel distance and time required for recoiling the water droplets. The fragmentation during the recoiling results from modified hydrodynamics induced by the surface morphology and wetting property. The laser-processed hierarchical surface structures are a potential method to reduce the contact time at the solid-liquid interface.

Laser surface texturing (LST) is a method to obtain micro-structures on the material's surface for improving tribological performances, wetting tuning, surface treatment, and increasing adhesion. The material selected for LST is AISI 430 ferritic stainless steel, distinguished by the low cost in manufacturing, corrosion resistance, and high strength at elevated temperature. The present study addresses the morphology of new pattern designs (crater array, ellipse, and octagonal shapes). The patterns are applied on the stainless-steel surface by a non-contact method with high quality and precision nanosecond pulsed laser equipment. The investigation of laser parameter influence on thermal affected area and micro-structures is accomplished by morphological and elemental analysis (SEM + EDX). The parameters of the laser micro-patterning have a marked influence on the morphology, creating groove-type sections with different depths and recast material features. From the SEM characterization, the highest level of recast material is observed for concentric octagon LST design. Its application is more recommended for the preparation of the metal surface before hybrid welding. Additionally, the lack of the oxygen element in the case of this design suggests the possible use of the pattern in hybrid joining.

The interaction of water droplets to the engineered hierarchical surface structures depends on the synergy between the topographical and chemical modifications. In this work, we develop an ultrafast laser processing technology to create a robust superhydrophobic nanostructured titanium nitride (TiN) surface. The process is based on the manipulation of the surface geometry and the low-pressure technique's accelerated adsorption of Volatile Organic Compounds (VOC). The laser-processed surfaces are composed of nanoscale geometry overlapped with porous, spongy structures. The metal oxides formed on the TiN surface were hydrophilic and subjected to accelerated VOC adsorption by low-pressure technique via condensation reaction with surface hydroxyl groups formed by heterolytic adsorption of water molecules from the environment. The decrease of surface energy due to the presence of adsorbed hydrocarbons and the topography of the nanostructures allow the trapping of small volumes of air. The presence of a layer of air favour the Cassie-Baxter state of wetting state. Static contact angles ranging from 155 to 180° have been reached depending on the geometry of the nanostructures. A comparative study of vacuum processed and aged (15 days) samples under atmospheric conditions were also performed. The chemical analysis by XPS demonstrates that the water molecules attached to hydroxyl groups passivate these reactive sites and hinder the adsorption of VOC, decreasing the adsorption rate drastically under aging in atmosphereic conditions. In contrast, it is enhanced under low-pressure conditions due to the reduced amount of water vapour.

The paper envisages the development of specific toolpaths for additive repair and cladding of full 3D geometry components by the Laser Metal Deposition Additive Manufacturing technique. Due to the essential difference between substractive and additive manufacturing approaches, the use of traditional substractive CAD-CAM programs is hardly suitable for a proper design and manufacturing of 3D additive manufactured AM’d components. The main key points for the development of CAD-CAM tools specifically applicable to Additive Manufacturing - AM processes are the need for an intrinsic process stability in terms of coating and layer growth, the need for a well-tailored additive track overlapping over the whole selected surface area and the need for integration of specific features relative to the laser, addition material and surface properties monitoring and control. The expected result of the full AM process based on the appropriate design tools is an efficient capability to meet not only the full 3D geometry according to the specified tolerances, but, very importantly, the microstructure specifications for the deposited material, avoiding the existence of critical defaults invalidating the fabrication or repair of the component. Moreover, the developed AZALA software must comply with the geometric specifications usual for manufacturing workstations, detecting preventively possible part-tool collisions with part and assuring an overall efficient manufacturing chain.

Laser-generated surface patterns provide the means for local mechanical interlocking between the joined materials, tunes the wettability of surfaces that come in contact, and generally are the main factor for bonding strength enhancement, especially between dissimilar materials. This paper presents the influence of different patterning overlays generated with a pulsed laser on the surface of stainless-steel sheets. For all experiments, an overlapping degree of 90% has been chosen between three different patterns, while the engraving speed, pulse frequency and number of passes have varied. The textured surfaces’ morphology was assessed through optical microscopy, and the roughness of the surfaces was correlated with the corresponding experimental parameters. The results have indicated promising insights for joining stainless steel to plastic materials, which is otherwise difficult to assess through usual welding techniques.

Due to its wide applicability in industry, devising microstructures on the surface of materials can be easily implemented and automated in technological processes. Laser Surface Texturing (LST) is applied to modify the chemical composition, morphology, and roughness of surfaces (wettability), cleaning (remove contaminants), reducing internal stresses of metals (hardening, tempering), surface energy (polymers, metals), increasing the adhesion (hybrid joining, bioengineering) and decreasing the growth of pathogenic bacteria (bioengineering). This paper is a continuation and extension of our previous studies in laser-assisted texturing of surfaces. Three different patterns (crater array-type C, two ellipses at 90° overlapping with its mirror-type B and 3 concentric octagons-type A) were applied with a nanosecond pulsed laser (active medium Nd: Fiber Diode-pumped) on the surface of a ferritic stainless steel (AISI 430). Micro texturing the surface of a material can modify its wettability behavior. A hydrophobic surface (contact angle greater than 90°) was obtained with different variations depending on the parameters. The analysis performed in this research (surface roughness, wettability) is critical for assessing the surface functionality, characteristics and properties of the stainless steel surface after the LST process. The values of the surface roughness and the contact angle are directly proportional to the number of repetitions and inversely proportional to the speed. Recommendations for the use of different texturing pattern designs are also made.

This paper addresses the metallurgical and mechanical characterization of dissimilar joints made by laser autogenous welding between thin sheets of low-carbon steel (CS) and austenitic stainless steel (SS). The welding technology applied, previously optimized to produce sound dissimilar joints, is based on the heat source displacement from the weld gap centerline towards CS, in order to reduce the SS overheating. The research includes optical microscopy observations, energy dispersive X-ray analysis (EDX) to assess the wt% of Cr, Ni, and Fe in all regions of the dissimilar welded joint, hardness measurements, and tensile tests of transverse-welded flat specimens. In comparison with classical determination of the joint overall mechanical characteristics, the novelty of this research consists of experimental assessment of the local mechanical behavior of the fusion and heat affected zones by using a digital image correlation technique (VIC-2D). This is an efficient tool for determining the constitutive properties of the joint, useful for modelling the mechanical behavior of materials and for verifying the engineering predictions. The results show that the positive difference in yielding between the weld metal and the base materials protects the joint from being plastically deformed. As a consequence, the tensile loading of flat transverse specimens generates the strain localization and failure in CS, far away from the weld.

An inverse approach for the Laser Surface Hardening Process is proposed. It departs from specific austenization requirements in terms of a desired size for the austenized region at any cross section of the treated sample, aiming at calculating suitable process parameters to obtain it. This approach contrasts with conventional direct procedures, from process parameters to thermal cycles and austenite distribution, where stochastic design strategies, falling on the dynamics of successive approximations, are performed. A thermo-metallurgical numerical model is used to determine the irradiance distribution capable of meeting the prescribed austenization requirements. This theoretical irradiance distribution is implemented by means of an adaptative high-frequency scanning of the treated surface. The minimum scanning frequency to guarantee the equivalence between the pursued theoretical irradiance distribution and the scanning is established attending to the evolution of temperature and its influence on the austenization rate by means of Avrami Law. A value of 100 Hz grants a continuous heating of the material. Considering this threshold, equations to calculate the parameters of the scanning to achieve the desired irradiance distribution are built. These equations are used to approach a design case where real hardened cross sections are achieved, confirming the utility of the proposed systematic methodology.

In recent years, an increasing interest in designing magnesium biomedical implants has been presented due to its biocompatibility, and great effort has been employed in characterizing it experimentally. However, its complex anisotropic behaviour, which is observed in rolled alloys, leads to a lack of reliable numerical simulation results concerning residual stress predictions. In this paper, a new model is proposed to focus on anisotropic material hardening behaviour in Mg base (in particular AZ31B as a representative alloy) materials, in which the particular stress cycle involved in Laser Shock Processing (LSP) treatments is considered. Numerical predictions in high extended coverage areas obtained by means of the implemented model are presented, showing that the realistic material's complex anisotropic behaviour can be appropriately computed and-much more importantly-it shows a particular non-conventional behaviour regarding extended areas processing strategies.

The use of pulsed laser irradiation techniques has proven to be a clearly effective procedure for the achievement of surface properties modification via micro-/nano-structuration, different conceptual approaches having been the subject of research and extensively reported in the literature. Beyond the broad spectrum of applications developed for the generation of structured surfaces of metallic materials with specific contact, friction and wear functionalities, the application of laser sources to the surface structuration of metal surfaces for the modification of their wettability and corrosion resistance properties is considered. Multi-scaled hierarchical surface microstructures fabricated on characteristic alloys (the concrete case of Ti6Al4V alloy is considered as example) by the combination of two complementary laser micro/nano-structuring techniques (Direct Laser Writing and Direct Laser Interference Patterning) are reported. Static contact angle measurements show a clearly hydrophobicity enhancement for both types of processing options and a clear improvement on the corrosion resistance of patterned samples of either type is observed. A discussion of the reported features in view of the applicability of the technique to industrial-scope problems is provided.

The effect of process parameters and the orientation of the cladding layer on the mechanical properties of 316L stainless steel components manufactured by laser metal deposition (LMD) was investigated. High aspect-ratio walls were manufactured with layers of a 4.5 mm wide single-cladding track to study the microstructure and mechanical properties along the length and the height of the wall. Samples for the tensile test (according to ASTM E-8M-04) were machined from the wall along both the direction of the layers and the direction perpendicular to them. Cross-sections of the LMD samples were analyzed by optical and scanning electron microscopy (SEM). The orientation of the growing grain was observed. It was associated with the thermal gradient through the building part. A homogeneous microstructure between consecutive layers and some degree of microporosity was observed by SEM. Uniaxial tension tests were performed on samples extracted from the wall in perpendicular and parallel directions. Results for ultimate tensile strength were similar in both cases and with the wrought material. The σ0.2 were similar in both cases but slightly superior to the wrought material.

Ultralow water adhesion aluminum surface has been fabricated by eco friendly low pressure processing technique. The laser patterned surface shows interconnected spongy porous nanostructures with micro packets at regular intervals. The micro volume of air present inside the interconnected porous surface structure together with the adsorbed hydrocarbons by low pressure processing leads to ultralow water adhesion surface. Application of bigger droplet volumes to the patterned surface showed a decrease in static contact angle measurement due to larger radius of curvature and axisymmetrical compared to the smaller droplets. (C) 2020 Elsevier B.V. All rights reserved.

The use of pulsed laser irradiation techniques has proven to be a clearly effective procedure for the achievement of surface properties modification via micro-/nano-structuration, different conceptual approaches having been the subject of research and extensively reported in the literature. Completing the broad spectrum of applications developed mostly involving the generation of structured surfaces (particularly of metallic materials) with specific contact, friction and wear functionalities, the application of laser sources to the surface structuration of metal surfaces for the modification of their wetability and corrosion resistance properties is considered. The particular problems found for the generation of the appropriate surface microstructure able to replicate the hydrophobic behaviour of some live structures present in nature, their long term stability and their amenability to macroscopic scale are discussed along with innovative methods to generate the required hierarchical micro-/nano-structures by a combination of the DLW and DLIP techniques.

Laser shock processing (ISP) is increasingly applied as an effective technology for improving the properties of different metallic components. This is done principally to enhance their corrosion and fatigue life behaviour, stress corrosion cracking resistance, etc. In this paper, LSP has been applied to a commercially pure Mg and a Mg-1Zn alloy (wt%) which is aimed to be used as a biodegradable material for biomedical applications. The rational for microalloying with Zn is not only influencing the bacterial response, but also enhancing corrosion resistance and mechanical strength of Mg without causing any toxic effect. The present work is focussed on the examination of the effects of the LSP treatment on the relevant surface related properties of the samples and their correlation with the surface and subsurface induced modifications such as residual stress state, microstructural, roughness, hardness, etc. Central to this investigation is the study of the corrosion response and antibacterial properties against Staphylococcus epidennidis of the different samples as a function of material and LSP parameters. The results show that the application of LSP introduces compressive residual stresses up to 1 mm deep. This occurs together with a significant improvement in corrosion resistance, and less bacterial colonization.