Microstructure and Mechanical Properties of Steel and Ni-Based Superalloy Joints for Rotors of High-Speed Electric Motors

High-speed electric motors, e.g., axially laminated anisotropic synchronous reluctance motors (ALA-SynRM), use a solid rotor manufactured by joining alternating layers of magnetic and non-magnetic metallic sheets. The strength of the dissimilar metallic joints is critical for the rotor's ability to withstand the operating conditions of the high-speed electrical machine. In this work, various dissimilar metallic joint configurations that can be used in high-speed ALA-SynRM rotors are studied by analyzing the shear strength, microstructure, hardness, and composition of the joints. Metallic joints of structural steels and Inconel (R) alloys fabricated by vacuum brazing and hot isostatic pressing (HIP) are studied. Finite element analysis (FEA) was performed to calculate the maximum shear stress of the joints that were subjected to various high speed operating conditions. The shear strength of the test specimens was measured and compared with FEA results. The microstructure and chemical composition of the joints were studied by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) on SEM. The results show that the hot isostatic pressed S1100MC-IN718 joint achieved the highest ultimate shear strength (233.3 MPa) followed by vacuum brazed S355MC-IN600 joint (230.1 MPa) and HIP S355-IN718 (203.5 MPa), thereby showing that vacuum brazing and HIP can be viable manufacturing methods to fabricate a high-speed ALA-SynRM rotor

Fatigue performance of stainless tool steel CX processed by laser powder bed fusion

This study investigates the fatigue performance of additively manufactured steel CX under uniaxial high cycle loading. The results show that surface quality was the most influential parameter that changed the fatigue behavior of the material, compared to combinations of building orientation and heat treatment as other fabrication parameters. Consequently, improving the surface quality from Ra = 3 μm–1 μm increased the fatigue limit from 170 MPa to 250 MPa. However, heat treatment did not significantly influence the fatigue performance of the material, although it increased the hardness of the material from 320 HV to 460 HV.</p

Mechanical performance and design optimisation of metal honeycombs fabricated by laser powder bed fusion

Honeycomb structures have a wide range of applications, from medical implants to industrial components. In addition, honeycombs play a critical role when passive protection is required due to their low density and high energy absorption capabilities. With the transition of additive manufacturing from a rapid prototyping approach to a manufacturing process, this technology has recently offered designers and manufacturers the ability to fabricate and modify lattice structures such as honeycombs. The current study presents the application of laser powder bed fusion, a common additive manufacturing process for producing industrial metal components, for fabricating metal honeycombs. In addition, this study examines three modified designs that can only be practically fabricated using additive manufacturing and compares them with conventional honeycombs. For this purpose, quasi-static and dynamic compression tests are conducted to evaluate and compare the performance of the honeycomb structures. The results show that the structures produced by additive manufacturing have acceptable performance compared to conventional honeycomb structures, and laser powder bed fusion can be considered to be a reliable manufacturing method for honeycomb production. Furthermore, the honeycombs produced according to the modified designs generally outperformed their counterparts made from the typical hexagonal cells. Ultimately, the use of triangular cells as a design modification is proposed to produce honeycombs with promising performance characteristics in all of their principal axes and under various pressure scenarios, from quasi-static to dynamic loading rates. Finally, this study also investigates the applicability of a newly developed maraging steel for additive manufacturing of honeycombs. Microstructural analysis and quasi-static tensile tests have confirmed the material properties for this purpose

Thermomechanical simulation of the heat-affected zones in welded ultra-high strength steels: Microstructure and mechanical properties

Ultra-high strength steels (UHSS) have a determining role in construction and industry. Furthermore, welding as the primary joining process for steel has a similar role in promoting its applications. Therefore, welded UHSS have a vital role in related applications. However, due to their complex microstructures, these steels are more prone to harmful effects of welding heat input on the mechanical properties compared to mild steels. Thus, identifying the correlations between the microstructural transformations triggered by the heat input and the mechanical properties can lead to new insights and hindering the drawbacks. This study investigates the microstructures and mechanical properties of S960 (with a severe softening after welding) and S1100 (with a negligible decrease of the mechanical properties after welding) to understand the mechanisms behind the softening of welded UHSS. Microstructural analysis showed the formation of soft phases, e.g., ferrite and granular bainite, as the primary reason for the softening. Furthermore, tempered forms of martensite and bainite resulted in the simultaneous decrease of hardness and notch toughness. Finally, the applicabilities of two experimental approaches to predict hardness from microstructural constituents were evaluated for welded S960 and S1100 and proved to have relatively good reliability to detect their HAZ softened spots.</p

Mechanical properties of butt-welded ultra-high strength steels at elevated temperatures

Variety of ultra-high strength steels (UHSS) with different microstructural characteristics is becoming available with continuous development of the manufacturing process in the steel industries. In order to effectively design structures made of such steel grades, a detailed knowledge of the mechanical properties is vital. Fire safety design is one of the areas in which such knowledge is essential. Welding process is indispensable in construction of steels structures with inevitable welding-induced degradation of mechanical properties of UHSSs. Thus, conducting experimental research on elevated-temperature constitutive mechanical behavior of welded joints made of UHSSs is of paramount importance. This study addresses elevated-temperature mechanical properties of as-received and as-welded S960 (manufactured via direct quenching technique) and S1100 (quenched and tempered) steel grades. A fully automated gas metal arc welding (GMAW) process with low heat input value was utilized to join the steel plates. Next, steady-state uniaxial tensile tests in the temperature range between room temperature (RT) and 900 °C were carried out. Accordingly, reduction factor-temperature relations for each tested steel in both as-received and as-welded forms are discussed and compared with several design standards, as well as with previous studies in the literature. Finally, predictive equations are proposed to estimate the elevated-temperature mechanical properties reduction factors of the tested UHSSs in as-received and as-welded forms.</p

Bonded CFRP to high strength steels

Research on the bond performance of CFRP-strengthened steel have been done for the past years, but it has mainly focused on lower grades of steel. The performance of the bond between ultra-high modulus (UHM) CFRP and high/ultra-high strength steel (HSS/UHSS) is investigated in this paper. A series of experiments have been conducted, with single/double side-strengthened (SSS/DSS) HSS/UHSS with CFRP laminates using Araldite adhesive. It was found that strengthening up to the ultimate strength of the DSS specimens is feasible. However, debonding happens at the ultimate strength of SSS specimens

CFRP Strengthening of Welded High and Ultra-High Strength Steels

With the increasing demands of the applications of environmentally friendly materials in different engineering fields, especially steel industry, which is one of the highly consumed energy sectors, high and ultra-high strength steels (HSS/UHSS) are potentially capable to meet eco-friendly requirements of the 21st century. With their superior properties, high strength and low weight, it makes it possible to build efficient structures. However, due to their microstructure sensitivity to heat input from welding, these materials may lose a part of their desirable characteristics such as static capacity and fatigue life. Hence it is vital to find possible strengthening solutions for welded UHSS. Carbon fiber reinforced polymers (CFRP) have already proven their superior capability in strengthening metallic structures. There are numerous successful applications of CFRP to enhance fatigue life of different structural details such as: I-beams, biaxial load carrying connections, hollow sections, and plates. However, the strengthened base material in nearly all of them were mild steel, with exceptions of limited work in high strength steels (HSS) up to 700 MPa. This thesis aims to fill the knowledge gap in strengthening of HSS/UHSS welded plates and tubes under quasi-static and fatigue loading using CFRP laminates. Experimental testing, finite element analysis (FEA) were adopted. Microstructure evaluation of welded UHSS using scanning electron microscopy (SEM) as well as electron backscattered diffraction (EBSD) were implemented. Issues such as debonding of CFRP and UHSS were also studied

Molecular detection of genes encoding AcrAB , Qep A efflux pumps in Klebsiella pneumoniae strains isolated from hospitalized patients in selected hospitals in Tehran

Abstract Background and Objectives: Increasing emergence of fluoroquinolone resistance among clinical isolates of Klebsiella pneumoniae&nbsp; (K. pneumoniae), has limited the treatment options for treatment of infections caused by these bacteria. The aim of this study was to investigate the dissemination of genes encoding AcrAB and QepA efflux pumps among K. pneumoniae strains. Methods: This study was carried out on 117 K. pneumoniae strains isolated from patients hospitalized in selected hospitals in Tehran city, 2015-2016, Iran. Antimicrobial susceptibility tests were performed using disk diffusion method (based on CLSI guidelines) and identification of acr A, acr B and qep A genes using PCR assay. Results: In this study, colistin and tigecycline had the best effect against clinical isolates of K. pneumoniae. According to PCR results, 110 (94%) isolates had acrA gene and 102 (87%) isolates had acrB gene, respectively. The qepA gene was not found in any of the K. pneumoniae strains. Conclusion: According to the results of the present study, dissemination of the genes encoding AcrAB efflux pumps among K. pneumoniae strains, which cause resistance to fluoroquinolones, is a matter of concern. Therefore, infection control and prevention of the spread of drug-resistant bacteria requires careful management in drug prescription and identification of resistant isolates

Microstructure and Mechanical Properties of Steel and Ni-Based Superalloy Joints for Rotors of High-Speed Electric Motors

High-speed electric motors, e.g., axially laminated anisotropic synchronous reluctance motors (ALA-SynRM), use a solid rotor manufactured by joining alternating layers of magnetic and non-magnetic metallic sheets. The strength of the dissimilar metallic joints is critical for the rotor&rsquo;s ability to withstand the operating conditions of the high-speed electrical machine. In this work, various dissimilar metallic joint configurations that can be used in high-speed ALA-SynRM rotors are studied by analyzing the shear strength, microstructure, hardness, and composition of the joints. Metallic joints of structural steels and Inconel&reg; alloys fabricated by vacuum brazing and hot isostatic pressing (HIP) are studied. Finite element analysis (FEA) was performed to calculate the maximum shear stress of the joints that were subjected to various high speed operating conditions. The shear strength of the test specimens was measured and compared with FEA results. The microstructure and chemical composition of the joints were studied by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) on SEM. The results show that the hot isostatic pressed S1100MC-IN718 joint achieved the highest ultimate shear strength (233.3 MPa) followed by vacuum brazed S355MC-IN600 joint (230.1 MPa) and HIP S355-IN718 (203.5 MPa), thereby showing that vacuum brazing and HIP can be viable manufacturing methods to fabricate a high-speed ALA-SynRM rotor