Sergio Lorenzi

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Verified

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• PhD
• Associate Professor at University of Bergamo

In the metal additive manufacturing (MAM) scenario, metal-polymer-based systems such as material extrusion (MEX) and binder jetting (BJ) are gaining increasing interest as they are expected to provide production cost savings alongside increased productivity compared with well-established powder bed fusion (PBF) and direct energy deposition (DED) te...

Additive manufacturing (AM) is gaining increasing interest in various strategic industrial sectors such as Oil & Gas, aerospace, and chemical industries. This group of technologies includes both innovative yet well-established techniques and more recent methods like Material Extrusion (MEX). This technique shows several advantages over other AM tec...

Electrochemical impedance spectroscopy (EIS) is a modern and efficient method for the evaluation of the protective abilities of coatings. However, the interpretation of the experimental data is a difficult task. This paper aims to investigate the effect of the addition of a nano clay, Cloesite 30B®, on the barrier properties of an epoxy-based syste...

WE43B is one of the newest Mg alloys with practical application in biomedical implant technology. This work attempts to scrutinize the corrosion characteristics of WE43B alloy in a simulated body fluid (SBF) at a typical body temperature. The dynamic-electrochemical impedance spectroscopy with the capacity to track changes on surfaces in a dynamic...

The aim of this paper is to evaluate the mass loss rates of two magnesium and rare earths alloys, specifically WE43B and EV31A, in comparison with commercially pure magnesium. The growing interest for magnesium alloys in the field of bioabsorbable osteosynthesis devices is because they simultaneously fulfil the needs of biocompatibility and superio...

Additive manufacturing (AM) is becoming a consolidated reality for nickel alloys production in recent years. Among the several technologies available, material extrusion (MEX) is gaining industrial interest. However, its qualification is fundamental to achieve high-value applications. In this work, Ni alloy 625 produced using different AM technique...

Additive manufacturing (AM) technologies are gaining increasing attraction for biomedical applications due to the granted customizability and optimal surface topography for osteointegration. Ti-6Al-4V is one of the most promising materials due to its biocompatibility. However, excessive ions release can occur, leading to a relevant immunologic resp...

Calcium chloride is one of the main de-icing salts for removing snow and ice from roads, infrastructures and service areas. It is well known that reinforced concrete structures, if exposed to calcium chloride, can suffer from severe damages due to both corrosion of steel reinforcement and chemical attack of the cement paste. This paper aims at eval...

The topic of sustainability of reinforced concrete structures is strictly related with their durability in aggressive environments. In particular, at equal environmental impact, the higher the durability of construction materials, the higher the sustainability. The present review deals with the possible strategies aimed at producing sustainable and...

The carbon steel B450C and low chromium SS 430 ferritic samples were exposed for 30 days to chloride-containing (5 g L⁻¹ NaCL) cement extract solution. The initial pH ≈ 13.88 decreased to pH ≈ 9.6, associated mainly with the consumption of OH⁻ ions and the formation of γ-FeOOH, α-FeOOH, Fe3O4 and Cr(OH)3, as suggested by XRD and XPS analysis, in th...

Laser bed powder fusion (LPBF) is an additive manufacturing technology for the fabrication of semi-finished components directly from computer-aided design modelling, through melting and consolidation, layer upon layer, of a metallic powder, with a laser source. This manufacturing technique is particularly indicated for poor machinable alloys, such...

The paper deals with the evolution of the microstructure of AlSi10Mg alloy obtained by laser powder bed fusion (LPBF), as a function of the post-processing heat treatment temperature. This was approached by complementary methods including FE-scanning electron microscopy, scanning Kelvin probe force microscopy and exo-electron emission techniques. T...

This study compares corrosion activities of carbon steel B450C and SS 430 (Mn in low content) exposed for 30 days in cement extract solution. Iron oxide and hydroxide were formed as corrosion products, in addition to CaCO3, in the presence of Cr2O3 on SS 430. Because of the decrease in pH, B450C lost the passive state when OCP shifted to negative v...

The paper is devoted to the study of stress corrosion cracking phenomena in friction stir welding AA-2024 T3 joints. Constant load (CL) cell and slow strain rate (SSR) tests were carried out in aerated NaCl 35 g/L solution. During the tests, open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were measured in the different...

The paper focuses on the corrosion behavior of aluminum joints made by friction stir welding as a function of loading conditions. A four-points bend-beam test, constant loading test, and slow strain-rate test were carried out on AA 7075-T6 alloy in aerated NaCl 35g/L solution at room temperature monitoring the free corrosion potential. The penetrat...

The aim of this work is the evaluation of the inhibition effect of tartrate ions with respect to the localized corrosion of steel reinforcements in alkaline solution as a function of the concentration of chlorides ions. Weight loss tests and electrochemical tests were carried out in saturated Ca(OH)2 solution with NaOH at pH 12.7 and 13.2. The resu...

Surface characteristics and machining performances of micro-pockets manufactured by μEDM as a function of different process conditions are studied in this paper. The micro-pockets were obtained using different combinations of process parameters on different ultra-high temperature ceramics (UHTCs) with the same base matrix (ZrC) and different volume...

This experimental work analyzes the hydrogen embrittlement mechanism in quenched and tempered low-alloyed steels. Experimental tests were performed to study hydrogen diffusion under applied cyclic loading. The permeation curves were fitted by considering literature models in order to evaluate the role of trapping—both reversible and irreversible—on...

The paper is aimed to the study of the corrosion-fatigue behavior of high strength steels for offshore pipelines. Tests have been performed in order to study fatigue crack growth in synthetic seawater under cathodic protection. The tests have been carried out on three different steel grades from 65 to 85 ksi with tempered martensite and ferrite-bai...

The paper is aimed at the evaluation of intergranular corrosion of friction stir welded AA2024-T3 joints as a function of manufacturing parameters and loading conditions. Tests for intergranular corrosion assessment, long terms exposure tests, corrosion monitoring through electrochemical impedance spectroscopy and microstructural characterization o...

The aim of this work is to compare the corrosion resistance of nickel-base Alloy 625 (UNS N06625) produced by laser powder bedfusion with that obtained via conventional casting and hot working. Cyclic potentiodynamic polarization and potentiostatic tests wereperformed in order to evaluate the corrosion resistance of the differently manufactured all...

The effect of microstructure on the susceptibility to selective corrosion of Alloy 625 produced by laser powder bed fusion (LPBF) process was investigated through intergranular corrosion tests according to ASTM G28 standard. The effect of heat treatment on selective corrosion susceptibility was also evaluated. The behavior was compared to commercia...

The aim of this work is to analyze hydrogen transport in a low alloy steel by applying the electrochemical permeation technique to matrices subject to cyclic loading conditions, up to the yield strength and beyond this limit. The results indicate that, with an increase in the applied maximum stress, a decrease in the apparent diffusivity takes plac...

Tissue-engineered decellularized matrices can progress clinical replacement of full-thickness ruptures or tendon defects. This study develops and validates a custom-made automated bioreactor, called oscillating stretch-perfusion bioreactor (OSPB), consisting of multiple, independent culture chambers able to combine a bidirectional perfusion with a...

Potentiodynamic tests were performed on AlSi10Mg alloy produced using laser powder bed fusion. As corrosion depends on the surface conditions, we compared the rough as-built surface with that formed after mechanical polishing and passivation in air. The as-built samples showed lower pitting potentials than polished samples. Corrosion initiation dep...

Laser powder bed fusion (LPBF) is one of the most widespread additive manufacturing (AM) technologies for metals, in which the components are built additively layer upon layer along the z-axis (the building direction) perpendicular to the building platform (xy-plane). Here, we evaluated the effect of post-processing heat treatments at 200, 300, and...

Electrical Discharge Machining (EDM) is a process used to remove material by means of electrical discharges between the tool electrode and the workpiece. During the process, particles of the electrode migrates to the workpiece and vice versa, causing contamination. This can result in modifications of the physical and mechanical properties of the wo...

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduce...

span lang="EN-US">The paper deals with the effect of microstructure on the hydrogen diffusion in traditional ferritic-pearlitic HSLA steels and new high strength steels, with tempered martensite microstructures or banded ferritic-bainitic-martensitic microstructures. Diffusivity was correlated to the hydrogen embrittlement resistance of steels, eva...

Aim of the present paper is to analyze if and how the process parameters (namely rotational speed S and feed rate f) affect both the mechanical properties and the corrosion behavior of friction stir welded (FSWed) butt joints made of AA7075 and AA2024 alloys and their combination. Tensile tests were performed orthogonally to the welding direction o...

This review presents "a state of the art" report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1-the present paper-focuses on the use of binders alternative...

The paper represents the "state of the art" on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditio...

This experimental work is aimed at studying the effect of microstructural modifications induced by post-processing heat treatments on the corrosion behavior of silicon-aluminum alloys produced by means of laser powder bed fusion (LPBF). The manufacturing technique leads to microstructures characterized by the presence of melt pools, which are quite...

The presence of a conductive layers of hot-formed oxide on the surface of bars for pre or post-compressing structures can promote localized attacks as a function of pH. The aggressive local environment in the occluded cells inside localized attacks has as consequence the possibility of initiation of stress corrosion cracking. In this paper, the str...

The paper deals with the general corrosion of carbon steel in geothermal plants for conveying and re-injecting condensates. The results of electrochemical and weight loss tests are discussed in function of sulphite and thiosulphate concentrations typical of Italian geothermal power plants. Thiosulphates can inhibit the reactions between oxygen and...

Semi-scale tests were performed with the aim of evaluating the influence on the resistance against SSCC of as-produced inner surface of steel pipes. The activity includes the design of tests on specimens sampled by preserving the inner surface of pipe and preliminary tests, which covers four samples taken from a commercial pipe. Two of the specimen...

The experimental work is aimed to the study of the hydrogen embrittlement mechanism in carbon and low-alloy steels. In particular, the theme of hydrogen diffusion within the metal in matrices subjected to cyclic loading is addressed. Literature models have been applied to fit experimental hydrogen permeation curves obtained in the presence and in t...

The present study was carried out to evaluate how the process parameters affect the mechanical properties and the corrosion behavior of joints obtained by friction stir welding (FSW). The experimental study was performed by means of a CNC machine tool for the friction stir welding of two aluminum alloys, namely AA7075 and AA2024, taking also into a...

The paper is aimed to the evaluation of the corrosion behavior of corrosion resisting alloys (CRAs) in geothermal fluids operating at the dew point. Several test series were carried out in geothermal production sites of Tuscany (Italy) under continuous flow. The vapor was extracted directly from the main flow and it was conveyed in an experimental...

The paper deals with the effectiveness of an innovative phosphonate-based superplasticizer (PNH) for ready mixed concrete. Concrete specimens were manufactured by considering a constant initial workability, equal to 220 mm slump at the end of the mixing procedure. Workability was measured at 0, 30, and 60 min to evaluate the workability retention p...

Present case study investigates the rheological, mechanical and in-placing performances of fiber-reinforced shotcrete manufactured with different fibers (steel, glass and polypropylene) and with sodium silicate based set-accelerating admixture for tunnel linings. The study compares the performances of concretes manufactured and fully compacted with...

The paper deals with the corrosion behavior of stainless steels as candidate materials for biofuel production plants by liquefaction process of the sorted organic fraction of municipal solid waste. Corrosion tests were carried out on AISI 316L and AISI 304L stainless steels at 250 °C in a batch reactor during conversion of raw material to bio-oil (...

The paper summarizes the results obtained by authors concerning near-neutral stress corrosion cracking (SCC) phenomena on buried pipelines. Stress corrosion tests according to different methodologies and fatigue propagation tests were executed on traditional steel grades. Tests were performed also on specimens pre-corroded according to a procedure...

Aim of this study is to analyse how the process parameters affect the mechanical properties and the corrosion behaviour of butt joints obtained by friction stir welding (FSW). The experimental study was performed by the friction stir welding of sheets having a thickness equal to 4 mm and made of three aluminum alloys, namely AA7075, AA6060 and AA20...

The paper reports on the corrosion behavior of two aluminum alloys, with different silicon content, manufactured by means of laser powder bed fusion. The results of potentiodynamic tests and intergranular corrosion tests are discussed in order to evaluate the effect of film formed during manufacturing and successive stress relieving and plane orien...

The production of components by means of additive manufacturing (AM) technology modifies the materials properties, giving them particular microstructures. In the present work, the corrosion resistance in chloride solutions of a AISMOMg alloy obtained by "Direct Metal Laser Sintering" (DMLS) process was evaluated. The alloy was studied by means of a...

The paper focuses on the reuse of crushed asphalt (GA) as a partial replacement (up to 20%) of natural aggregates for concrete manufacture. Addition of GA aggregates produced a positive effect on workability loss. The GA mixes, however, showed a significant tendency to bleed and segregate at the highest replacement percentage applied. GA led to a d...

The paper investigates the corrosion behavior of AlSi10Mg alloy produced by direct metal laser sintering (DMLS). Potentiodynamic tests were performed in aerated diluted Harrison solution, on specimens with different orientation with respect to the building plane. Different surface finishing were analyzed, covering rough surfaces as produced by DMLS...

This paper deals with the use of industrial by-products from electric arc furnace (EAF) granulated slag for the partial replacement of natural aggregates commonly used to manufacture concrete. Three different gradings of EAF granulated slag were considered. The rheological and mechanical properties of concrete manufactured with a partial replacemen...

The paper reports the results of an experimental research devoted to the study of the damage mechanism of steel in contact with fresh flowing cementitious mixtures. It focuses on the damage caused by both erosion and corrosion. Weight-loss tests, potentiodynamic tests and electrochemical impedance spectroscopy tests were carried out on stationary a...

The paper deals with the effect of heat treatments on corrosion resistance of an AlSi10Mg alloy obtained by means of Direct Metal Laser Sintering. The tests were performed on as-processed alloy and after different post-heat treatment, covering stress relieving, annealing at high temperature and water quenching. Potentiodynamic and electrochemical i...

The paper deals with the effectiveness of blended phosphonate-based superplasticizers (PHN) for ready mixed concrete. Two phosphonates (PNH1 and PNH2) were added in different percentage to naphthalene sulphonate (NSF) or polycarboxylates (PCEs) based admixtures to improve both compatibility with different cements and workability retention of concre...

The paper reports the results of an experimental work on the effect of steel microstructures on morphology and protectiveness of the corrosion scale formed in water saturated by supercritical CO 2 . Two HSLA steels were tested. The microstructures were modified by means of different heat treatments. Weight loss was measured after exposure at CO 2 p...

The paper focuses on the evaluation of the rheological and mechanical performances of cement-based renders manufactured with phase-change materials (PCM) in form of microencapsulated paraffin for innovative and ecofriendly residential buildings. Specifically, cement-based renders were manufactured by incorporating different amount of paraffin micro...

The paper deals with the effectiveness of blended phosphonate-based superplasticizers (PHN) for ready mixed concrete. Two phosphonates (PNH1 and PNH2) were added in different percentage to naphthalene sulphonate (NSF) or polycarboxylates (PCEs) based admixtures to improve both compatibility with different cements and workability retention of concre...

This article deals with the risk of environmentally assisted cracking of steel structures that are kept under cathodic protection (CP). The experimental results collected on both hydrogen diffusion and hydrogen embrittlement (HE) of high-strength low-alloy (HSLA) steels under CP are discussed. Hydrogen diffusion was evaluated by permeation experime...

Con la fine del secolo scorso e, soprattutto, con l'inizio del 21° secolo, il mondo ha acquisito la consapevolezza di essere entrato nell'era dello sviluppo sostenibile [1]. La sfida più importante che, in quest'ottica, si presenta per il settore delle costruzioni è quella di sostenere la crescita della popolazione, e la conseguente industrializzaz...

The inhibition properties of aspartic and lactic acid salts are compared with nitrite ions with regard to their effect on critical chloride concentration. The tests were carried out on carbon steel specimens in simulated pore solutions with initial pH in the range of 12.6 to 13.8. The critical chloride concentrations were estimated through multiple...

The role of thiosulfate on Corrosion has been extensively studied in literature and its effects have been known since the,40s especially in the oil and paper industry. The studies revealed stress corrosion cracking phenomena by polythionic acids and thiosulfate formed due to presence of air and moisture in the the systems. Other failures were evide...

Friction stir welded butt joints were performed on 8 mm thick sheets made of AA6060 T6 aluminum alloy by means of a CNC machine tool, at feed rates between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm. Tensile tests, metallographic analyses and micro-Vickers tests were carried out to evaluate the mechanical properties of th...

This work deals with the study of innovative biocompatible coatings for magnesium resorbable osteosynthesis devices. Conversion layers based on magnesium fluoride and "diamond like carbon" coatings (DLC) obtained by chemical vapor deposition were considered in order to reduce the corrosion rate of magnesium to levels compatible with the time needed...

The paper deals with the effect of pressure, temperature and time on corrosion rate of pipeline steels in CO2 saturated water and in humid saturated CO2 gas in the range from 25 to 60°C and pressure from 20 to 145 bar, up to 400 hours of exposure. The results of weight loss tests show very high rates in the aqueous phase, one or two order of magnit...

The role of thiosulfate on corrosion has been extensively studied in literature and its effects have been known since the 40s especially in the oil and paper industry. The studies revealed stress corrosion cracking phenomena by po- lythionic acids and thiosulfate formed due to the presence of air and moisture in the the systems. Other failures were...

The paper is oriented to the study of chlorides corrosion of carbon steel in simulating alkaline concrete pore solutions. Cyclic voltammetries (CV) were performed in order to evaluate the influence of pH, in the range of 12.6-13.8, on the inhibiting properties of nitrite and anions of two organic acid, lactate and aspartate, on localized corrosion...