The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

This study aims at evaluating the effect of microstructure imperfections on the corrosion fatigue performance of an ER70S-6 alloy produced by wire arc additive manufacturing (WAAM) process, in a 3.5% NaCl solution. For reference, a regular ST-37 alloy with relatively similar chemical composition was considered as a counterpart alloy. This was justified by the fact that the ER70S-6 alloy is usually used for conventional welding of ST-37 steel. The results obtained indicated that while the ST-37 alloy exhibited fatigue strength of 240 MPa in the corrosive solution, the additively manufactured ER70S-6 alloy showed fatigue strength of only 140 MPa. These differences were related to microstructural imperfections that are inherently produced during the WAAM process.</jats:p

Corrosion Behavior of AlSi10Mg Alloy Produced by Additive Manufacturing (AM) vs. Its Counterpart Gravity Cast Alloy

The attractiveness of additive manufacturing (AM) relates to the ability of this technology to rapidly produce very complex components at affordable costs. However, the properties and corrosion behavior, in particular, of products produced by AM technology should at least match the properties obtained by conventional technologies. The present study aims at evaluating the corrosion behavior and corrosion fatigue endurance of AlSi10Mg alloy produced by selective laser melting (SLM) in comparison with its conventional counterpart, gravity cast alloy. The results obtained indicate that the corrosion resistance of the printed and cast alloys was relatively similar, with a minor advantage to the printed alloy. The corrosion fatigue endurance of the printed alloy was relatively improved compared to the cast alloy. This was mainly attributed to the significant differences between the microstructure and defect characteristics of those two alloys

Effect of HIP Defects on the Mechanical Properties of Additive Manufactured Ti6Al4V Alloy

The expanding use of Additive Manufacturing (AM) technology enables engineers and designers to plan and manufacture highly complex geometries that are impossible to manufacture with any other conventional technology. When comparing this with building parts using powder bed technology, the main differences found in the quality of the products concern fracture toughness, fatigue, and inferiority in tensile tests. To overcome these issues, the Hot Isostatic Press (HIP) procedure may be used to improve the material quality by reducing product porosity. Regarding fatigue, the standard procedure consists of HIP and the machining of specimens to their final geometry. However, in many AM parts, geometrical complexity does not enable complementary machining. Recently, some AM vendors integrated in-process milling capabilities into their machines, in an attempt to address this challenge. In this study, the authors examine the effect of the HIP procedure on representative samples in order to demonstrate its effect on the final products of TI-6Al-4V parts. The results indicate that the fatigue limit of HIPed parts can increase by 12%; however, a dramatic decrease in the fatigue limit was observed if any failure in the HIP process occurred. The authors suggest an optional procedure to improve performance in such cases

The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

This study aims at evaluating the effect of microstructure imperfections on the corrosion fatigue performance of an ER70S-6 alloy produced by wire arc additive manufacturing (WAAM) process, in a 3.5% NaCl solution. For reference, a regular ST-37 alloy with relatively similar chemical composition was considered as a counterpart alloy. This was justified by the fact that the ER70S-6 alloy is usually used for conventional welding of ST-37 steel. The results obtained indicated that while the ST-37 alloy exhibited fatigue strength of 240 MPa in the corrosive solution, the additively manufactured ER70S-6 alloy showed fatigue strength of only 140 MPa. These differences were related to microstructural imperfections that are inherently produced during the WAAM process

In vitro behavior of bioactive hybrid implant composed of additively manufactured titanium alloy lattice infiltrated with Mg-based alloy

We have developed a novel bioactive hybrid metallic implant that integrates the beneficial characteristics of a permanent matrix and a biodegradable substance. Such a combination may generate a material system that evolves into a porous structure within weeks to months following implantation and can be used to form strong interfacial bonding and osseointegration for orthopedic and dental applications. Presently, traditional technologies such as casting, powder metallurgy and plastic forming have limited ability to produce the complex bioactive implant structures that are required in practical applications. The present study aimed to develop an innovative bioactive Ti[sbnd]Mg (BTiMg) hybrid system using a Ti-lattice (Ti-6Al-4 V) produced by an additive manufacturing (AM) process, in combination with a new Mg-based alloy (Mg-2.4%Nd −0.6%Y -0.3%Zr) as a biodegradable filling material. We evaluated the in-vitro behavior of the BTiMg system in a simulated physiological environment, along with cytotoxicity assessment. The microstructure was evaluated by scanning electron microscopy and X-ray diffraction, mechanical properties were examined in terms of compressive strength, environmental performance analysis was conducted by electrochemical testing using potentiodynamic polarization and impedance spectroscopy (EIS), and cytotoxicity characteristics were assessed by indirect cell viability analysis. The results demonstrated the feasibility to produce geometrically complex implants by AM technology, as well as the strength and non-cytotoxic effects of the BTiMg system. Benefits included a relatively high ultimate compressive strength (UCS) and a high yield point (YP), along with an adequate cell viability response in the range between 70 and 120%

Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process

Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy consumption, and the sizes of the components, that are limited by the size of the printing cell. The aim of the present study was to evaluate the environmental behavior of low carbon steel (ER70S-6) produced by a relatively inexpensive AM process using wire feed arc welding. The mechanical properties were examined by tension testing and hardness measurements, while microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. General corrosion performance was evaluated by salt spray testing, immersion testing, potentiodynamic polarization analysis, and electrochemical impedance spectroscopy. Stress corrosion performance was characterized in terms of slow strain rate testing (SSRT). All corrosion tests were carried out in 3.5% NaCl solution at room temperature. The results indicated that the general corrosion resistance of wire arc additive manufacturing (WAAM) samples were quite similar to those of the counterpart ST-37 steel and the stress corrosion resistance of both alloys was adequate. Altogether, it was clearly evident that the WAAM process did not encounter any deterioration in corrosion performance compared to its conventional wrought alloy counterpart

The Effect of a Slow Strain Rate on the Stress Corrosion Resistance of Austenitic Stainless Steel Produced by the Wire Laser Additive Manufacturing Process

The wire laser additive manufacturing (WLAM) process is considered a direct-energy deposition method that aims at addressing the need to produce large components having relatively simple geometrics at an affordable cost. This additive manufacturing (AM) process uses wires as raw materials instead of powders and is capable of reaching a deposition rate of up to 3 kg/h, compared with only 0.1 kg/h with common powder bed fusion (PBF) processes. Despite the attractiveness of the WLAM process, there has been only limited research on this technique. In particular, the stress corrosion properties of components produced by this technology have not been the subject of much study. The current study aims at evaluating the effect of a slow strain rate on the stress corrosion resistance of 316L stainless steel produced by the WLAM process in comparison with its counterpart: AISI 316L alloy. Microstructure examination was carried out using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis, while the mechanical properties were evaluated using tensile strength and hardness measurements. The general corrosion resistance was examined by potentiodynamic polarization and impedance spectroscopy analysis, while the stress corrosion performance was assessed by slow strain rate testing (SSRT) in a 3.5% NaCl solution at ambient temperature. The attained results highlight the inferior mechanical properties, corrosion resistance and stress corrosion performance, especially at a slow strain rate, of the WLAM samples compared with the regular AISI 316L alloy. The differences between the WLAM alloy and AISI 316L alloy were mainly attributed to their dissimilarities in terms of phase compositions, structural morphology and inherent defects

The Influence of Intralayer Porosity and Phase Transition on Corrosion Fatigue of Additively Manufactured 316L Stainless Steel Obtained by Direct Energy Deposition Process

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking