Tribo-Behavior and Corrosion Properties of Welded 304L and 316L Stainless Steel

The present study investigates the electrochemical corrosion response and tribo-behavior of 304L and 316L stainless steel welded by gas metal arc welding (GMAW), which offered a high deposition rate. During this research, the metallurgically prepared welded samples were subjected to a tribological test and a corrosion test. The wear results were favorable for 316L steel, and it showed a lower coefficient of friction than the 304L specimen. These samples also underwent characterization studies, such as X-ray diffractometry (XRD) and scanning electron microscopy (SEM), to identify the different phases obtained on the cooling of the weld pool. Finally, both specimens were compared against their mechanical properties. Owing to the above properties, the 316L sample showed lasting durability, as compared to the 304L steel. The primary compositional difference is the higher presence of molybdenum and chromium in the 316L steel, compared to the 304L stainless steel.

Analysis of Metal Transfer and Weld Forming Characteristics in Triple-wire Gas Indirect Arc Welding

Triple-wire gas indirect arc welding (TW-GIA) has the advantages of low heat input and high deposition rate. However, the simultaneous melting of triple wires makes the metal transfer mode complicated. The unknown of the metal transfer mode restricts the development of this technology. In this paper, high-speed camera systems and electrical signal acquisition sensors were used to explore the TW-GIA metal transfer mode. The static force model and the arc conductive channel model were used to discuss the droplet force and energy conversion characteristics respectively. Results showed that the TW-GIA metal transfer modes can be divided into: short-circuit transfer (SCT), main wire projected transfer + side wire globular transfer (PGT), main wire streaming transfer + side wire projected transfer (SPT) and main wire streaming transfer + side wire streaming transfer (SST). Moreover, the process parameter ranges corresponding to the four modes were summarized. Due to the stable arc and the uniform metal transfer process, SPT and SST can form desirable weld seam. The gravity and z-axis components of electromagnetic force are the main forces that promote metal transfer. The x-axis and y-axis components of the electromagnetic force deviate the metal transfer path from the arc coverage. Due to the change of arc conductive channel, the energy transferred from TW-GIA to the base metal is less than that of GMAW, showing the advantages of small welding deformation, narrow heat affected zone and grain refinement.

Vision-Based Melt Pool Monitoring for Wire-Arc Additive Manufacturing Using Deep Learning Method

Wire-arc additive manufacturing (WAAM) technology has been widely recognized as a promising alternative for fabricating large-scale components, due to its advantages of high deposition rate and high material utilization rate. However, some anomalies may occur during the deposition process, such as humping, spattering, and robot suspend. this study proposed to apply Deep Learning in the visual monitoring to diagnose different anomalies during WAAM process. The melt pool images of different anomalies were collected for training and validation by a visual monitoring system. The classification performance of several representative CNN architectures, including ResNet, EfficientNet, VGG-16 and GoogLeNet, were investigated and compared. The classification accuracy of 97.62%, 97.45%, 97.15% and 97.25% was achieved by each model. The results proved that the CNN models are effective in classifying different types of melt pool images of WAAM. Our study is applicable beyond WAAM and should benefit other additive manufacturing or arc welding techniques.

Experimental Investigation on Bead Geometry Parameter and Mechanical Property of Part Fabricated by Wire Arc Additive Manufacturing

In additive manufacturing process, wire arc additive manufacturing process (WAAM) is a technique which can produce a metal 3D printed part. In Industries product are produced by wasting one third of its material, from this process time consumption and material wastage is more comparing in Subtractive Manufacturing over Additive Manufacturing. Additive Manufacturing stepped from 1925 in manufacturing industry and it has gained its remarkable growth in past few decades, as of now metal 3D oriented parts have come to play a major role in aerospace industry. This research work focused on Gas Metal Arc Welding (GMAW) welding. It has high deposition rate, ultimate build volume and good structural integrity compare with other additive manufacturing process. MACH3 controller is used to control the welding torch motion for addition of material by 3 axis movement (X, Y and Z). To identify the correct parameters for metal part we have done numbers of samples by changing values in the MIG machine from that we finalize the three parameters through visualizes on the printed materials after that a wall like structure is built and post processing like cutting the materials from base plate, grinding the uneven surface on printed materials. The printed materials are ready for material testing like bead geometry analysis of various parameter and tensile testing to identify the printed material strength, elongation, stress and strain.

ZnO thin-film optimization towards the fabrication of high-frequency ultrasound transducers

<p>Zinc oxide is a popular wide bandgap semiconductor material with versatile electrical and optical properties. In its wurtzite crystal form, this semiconductor is piezoelectric, and has material properties that make it an attractive candidate for fabricating high frequency ultrasound transducers. This thesis describes the development of an RF sputtering process for creating zinc oxide films with thicknesses ranging from 3μm to 10μm, aiming for transducer frequencies of 300MHz to 1 GHz. Sputtering parameters are optimized to meet the dual requirements of a c-axis film orientation while maintaining a high deposition rate. These constraints and the dimensional characteristics of the utilized sputtering system, such as the short substrate-to-target distance, introduce high levels of strain in the deposited zinc oxide films. Various anneal procedures are developed to reduce film strain and optimize the resulting microstructure. It is found that annealing temperatures > 600°C eliminate the inherent film strain, but simultaneously result in the dewetting of the bottom metal contact, making this thermal treatment unsuitable for device processing. As an alternative to traditional metal contacts used in ultrasound transducers, the use of highly doped zinc oxide contacts is then investigated. It is shown that aluminium doped zinc oxide contacts provide an improved seed layer for device growth while eliminating the dewetting problems associated with metal contacts at high anneal temperatures. In addition, the use of such transparent conductive oxide contacts can lead to novel ultrasound applications, which benefit from the integration of optical and acoustic imaging in a single lens. A proof of concept all-zinc oxide single element ultrasound transducer structure is finally fabricated, to highlight the potential of an integrated optical-acoustic lens design.</p>

ZnO thin-film optimization towards the fabrication of high-frequency ultrasound transducers

<p>Zinc oxide is a popular wide bandgap semiconductor material with versatile electrical and optical properties. In its wurtzite crystal form, this semiconductor is piezoelectric, and has material properties that make it an attractive candidate for fabricating high frequency ultrasound transducers. This thesis describes the development of an RF sputtering process for creating zinc oxide films with thicknesses ranging from 3μm to 10μm, aiming for transducer frequencies of 300MHz to 1 GHz. Sputtering parameters are optimized to meet the dual requirements of a c-axis film orientation while maintaining a high deposition rate. These constraints and the dimensional characteristics of the utilized sputtering system, such as the short substrate-to-target distance, introduce high levels of strain in the deposited zinc oxide films. Various anneal procedures are developed to reduce film strain and optimize the resulting microstructure. It is found that annealing temperatures > 600°C eliminate the inherent film strain, but simultaneously result in the dewetting of the bottom metal contact, making this thermal treatment unsuitable for device processing. As an alternative to traditional metal contacts used in ultrasound transducers, the use of highly doped zinc oxide contacts is then investigated. It is shown that aluminium doped zinc oxide contacts provide an improved seed layer for device growth while eliminating the dewetting problems associated with metal contacts at high anneal temperatures. In addition, the use of such transparent conductive oxide contacts can lead to novel ultrasound applications, which benefit from the integration of optical and acoustic imaging in a single lens. A proof of concept all-zinc oxide single element ultrasound transducer structure is finally fabricated, to highlight the potential of an integrated optical-acoustic lens design.</p>

Grain Boundary Propagation and Epitaxy on (111) Surfaces of FCC Substrates: A Kinetic Monte Carlo Study with Lennard-Jones and Iridium Potentials

<p>A Kinetic Monte Carlo (KMC) method was developed to model homoepitaxy and grain boundary propagation on a (111) surface. Barrier energies were calculated using the Nudged Elastic Band (NEB) technique. A recently reported inertial relaxation technique named FIRE (the Fast Inertial Relaxation Engine) was used to relax the NEB images. Both the Lennard-Jones potential and a Sutton-Chen Iridium potential were used and compared. A doubly-refined lattice mesh was developed to incorporate atoms in Face-Centred-Cubic (FCC) and Hexagonal-Close-Packed (HCP) sites as well as atoms in decorated row sites (i.e. supported by 4 atoms). A look-up table was developed to identify hops in the KMC algorithm. The KMC results show that a small difference in energy barriers between FCC and HCP sites on the substrate can cause a substantial bias in the direction of grain boundary propagation. We also investigated the effect of the geometry of the grain boundary on its propagation, as well as the atomistic processes involved in grain boundary propagation and the merger of grain boundaries. Our deposition simulations produced islands with loosely triangular envelopes, where FCC islands are rotated 180° with respect to HCP islands. The results are similar to scanning tunneling microscopy (STM) images of Iridium deposition, although lack of computing power forced us to use a high deposition rate and this caused some differences.</p>

Grain Boundary Propagation and Epitaxy on (111) Surfaces of FCC Substrates: A Kinetic Monte Carlo Study with Lennard-Jones and Iridium Potentials

<p>A Kinetic Monte Carlo (KMC) method was developed to model homoepitaxy and grain boundary propagation on a (111) surface. Barrier energies were calculated using the Nudged Elastic Band (NEB) technique. A recently reported inertial relaxation technique named FIRE (the Fast Inertial Relaxation Engine) was used to relax the NEB images. Both the Lennard-Jones potential and a Sutton-Chen Iridium potential were used and compared. A doubly-refined lattice mesh was developed to incorporate atoms in Face-Centred-Cubic (FCC) and Hexagonal-Close-Packed (HCP) sites as well as atoms in decorated row sites (i.e. supported by 4 atoms). A look-up table was developed to identify hops in the KMC algorithm. The KMC results show that a small difference in energy barriers between FCC and HCP sites on the substrate can cause a substantial bias in the direction of grain boundary propagation. We also investigated the effect of the geometry of the grain boundary on its propagation, as well as the atomistic processes involved in grain boundary propagation and the merger of grain boundaries. Our deposition simulations produced islands with loosely triangular envelopes, where FCC islands are rotated 180° with respect to HCP islands. The results are similar to scanning tunneling microscopy (STM) images of Iridium deposition, although lack of computing power forced us to use a high deposition rate and this caused some differences.</p>

Paleoenvironment and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shales: Outcrop Characterizations of the Carboniferous–Permian Strata, Ordos Basin, North China

In the Carboniferous–Permian period, several organic-rich black shales were deposited in a marine–continental transitional environment in the Linfen area on the eastern margin of the Ordos Basin. Integrated sedimentological and organic geochemical analyses are performed on an outcrop in order to clarify the relationship between paleoenvironment and organic matter accumulation. The results of this study show that the marine–continental transitional strata of the Upper Carboniferous Benxi Formation to Lower Permian Taiyuan and Shanxi Formation exposed in the Linfen area are composed of sandstone, shale, coal, and limestone. Total organic carbon (TOC) contents of the studied samples were mainly distributed in the range of 0.59%–35.4%, with an average of 7.32%. From Benxi Formation to Shanxi formation, the humidity gradually increased, and the climate gradually changed from hot and humid to warm and humid during Carboniferous to Permian. The deposition of the Shanxi Formation ended with the climate returning to hot and humid, having an oxic-suboxic conditions and a high paleoproductivity. Paleoredox conditions and paleoproductivity are the two vital factors controlling the formation of organic matter in black shales. The transitional environment characterized by oxic-suboxic, relatively high deposition rate, and various source of organic matter, although different from the marine environment, provides a good material basis for the deposition of organic-rich shales.