62 research outputs found
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Process Parameters Optimization for Ultrasonically Consolidated Fiber-Reinforced Metal Matrix Composites
As an emerging rapid prototyping technology, Ultrasonic Consolidation (UC) has
been used to successfully fabricate metal matrix composites (MMC). The intent of this
study is to identify the optimum combination of processing parameters, including
oscillation amplitude, welding speed, normal force, operating temperature and fiber
orientation, for manufacture of long fiber-reinforced MMCs. The experiments were
designed using the Taguchi method, and an L25 orthogonal array was utilized to
determine the influences of each parameter. SiC fibers of 0.1mm diameter were
successfully embedded into an Al 3003 metal matrix. Two methods were employed to
characterize the bonding between the fiber and matrix material: optical/electron
microscopy and push-out tests monitored by an acoustic emission (AE) sensor. SEM
images and data from push-out tests were analyzed and optimum combinations of
parameters were achieved.Mechanical Engineerin
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Multi-Material Ultrasonic Consolidation
Ultrasonic consolidation (UC) is a recently developed direct metal solid freeform
fabrication process. While the process has been well-demonstrated for part fabrication in Al alloy
3003 H18, including with intricate cooling channels, some of the potential strengths of the
process have not been fully exploited. One of them is its flexibility with build materials and the
other is its suitability for fabrication of multi-material and functionally graded material parts with
enhanced functional or mechanical properties. Capitalizing on these capabilities is critical for
broadening the application range and commercial utilization of the process. In the current work,
UC was used to investigate ultrasonic bonding of a broad range of engineering materials, which
included stainless steels, Ni-base alloys, brass, Al alloys, and Al alloy composites. UC multimaterial part fabrication was examined using Al alloy 3003 as the bulk part material and the
above mentioned materials as performance enhancement materials. Studies were focused on
microstructural aspects to evaluate interface characteristics between dissimilar material layers.
The results showed that most of these materials can be successfully bonded to Al alloy 3003 and
vice versa using the ultrasonic consolidation process. Bond formation and interface
characteristics between various material combinations are discussed based on oxide layer
characteristics, material properties, and others.Mechanical Engineerin
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Improving Linear Weld Density in Ultrasonically Consolidated Parts
Ultrasonic consolidation is a novel additive manufacturing process with immense
potential for fabrication of complex shaped three-dimensional metallic objects from metal foils.
The proportion of bonded area to unbonded area along the layer interface, termed linear weld
density (LWD), is perhaps the most important quality attribute of ultrasonically consolidated
parts. Part mechanical properties largely depend on LWD and a high level of LWD must be
ensured in parts intended for load-bearing structural applications. It is therefore necessary to
understand what factors influence LWD or defect formation and devise methods to enhance bond
formation during ultrasonic consolidation. The current work examines these issues and proposes
strategies to ensure near 100% LWD in ultrasonically consolidated aluminum alloy 3003 parts.
The work elucidates the effects of various process parameters on LWD and a qualitative
understanding of the effects of process parameters on bond formation during ultrasonic
consolidation is presented. The beneficial effects of using elevated substrate temperatures and its
implications on overall manufacturing flexibility are discussed. A preliminary understanding of
defect morphologies and defect formation is presented, based on which a method (involving
surface machining) for minimizing defect incidence during ultrasonic consolidation is proposed
and demonstrated. Finally, trade-offs between part quality and build time are discussed.Mechanical Engineerin
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Interface Microstructures and Bond Formation in Ultrasonic Consolidation
The quality of ultrasonically consolidated parts critically depends on the bond quality
between individual metal foils. This necessitates a detailed understanding of interface
microstructures and ultrasonic bonding mechanism. There is a lack of information on interface
microstructures in ultrasonically consolidated parts as well as a lack of consensus on the
mechanism of metal ultrasonic welding, especially on matters such as plastic deformation and
recrystallization. In the current work, interface microstructures of an ultrasonically consolidated
multi-material Al 3003-Ni 201 sample were analyzed in detail using optical microscopy,
scanning electron microscopy, energy dispersive spectroscopy, and orientation imaging
microscopy. Based on the results of microstructural studies, the mechanism of metal ultrasonic
welding has been discussed. The reasons for formation of defects/unbonded regions in
ultrasonically consolidated parts have also been identified and discussedMechanical Engineerin
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Maximum Height to Width Ratio of Freestanding Structures Built Using Ultrasonic Consolidation
Ultrasonic consolidation (UC) is a process whereby metal foils can be metallurgically
bonded at or near room temperature. The UC process works by inducing high-speed differential
motion (~20kHz) between a newly deposited layer and a substrate (which consists of a base plate
and any previously deposited layers of material). This differential motion causes plastic
deformation at the interface, which breaks up surface oxides and deforms surface asperities,
bringing clean metal surfaces into intimate contact, where bonding occurs. If the substrate is not
stiff enough to resist deflection during ultrasonic excitation of newly deposited layers, then it
deflects along with the newly deposited layer, resulting in no differential motion and lack of
bonding. Geometric issues which control substrate stiffness and deflection were investigated at
Utah State University by building a number of free-standing rib structures with varying
dimensions and orientations. Each structure was built to a height where lack of bonding between
the previously deposited layers and the newly deposited layer caused the building process to fail,
a height to width ratio (H/W) of approximately 1:1. The parts were then cut, polished, and
viewed under a microscope. An ANSYS model was created to investigate analytically the cause
of this failure. It appears build failure is due to excessive deflection of the ribs around a 1:1 H/W,
resulting in insufficient differential motion and deformation to achieve bonding. Preliminary
results show, when the H/W reaches 1:1, the von Mises stress is found to be tensile along
portions of the bonding interface, which eliminates the compressive frictional forces necessary
for plastic deformation and formation of a metallurgical bond. These tensile stresses are shown
to be concentrated at regions near the edges of the newly deposited foil layer.Mechanical Engineerin
Wire-arc additive manufacturing of nickel aluminum bronze/stainless steel hybrid parts – Interfacial characterization, prospects, and problems
Hybrid parts of nickel aluminum bronze (NAB) and 316L stainless steel were fabricated using a commercially available wire-arc additive manufacturing (WAAM) technology to evaluate the feasibility and cracking tendency. Focused Ion beam (FIB) based Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and Transmission Electron Microscopy (TEM) were used to characterize the built (NAB)-substrate (SS) interfacial characteristics. FIB extracted a selected region of the interface, and the spatial distribution of the interface across several sections was characterized by using the state-of-the-art technique for 3D EBSD mapping. A metallurgically bonded interface without any pores and cracks, with the inter-diffusion region in a thickness of 2 μm, was formed, which was further confirmed by a video with the results of 3D reconstructed EBSD maps. The interface did not exhibit any strong texture orientation owing to the control of the thermal gradient as NAB is more conductive than 316L. EDS elemental mapping confirmed that Fe3Al intermetallic was formed at the NAB/SS bimetallic-joint interface. Occasional liquation cracks on the grain boundaries in the heat-affected zone (HAZ) of 316L substrate were observed. Fe-Al based intermetallic formation, along with the penetration of copper along the HAZ cracks, was noticed. The problems associated were highlighted, and remedial measures were suggested to open up the possibilities of additive manufacturing to fabricate NAB-Stainless steel hybrid parts for industrial repair and maintenance applications. © 2020 Acta Materialia Inc
Wire-arc additive manufactured nickel aluminum bronze with enhanced mechanical properties using heat treatments cycles
Wire-arc additive manufacturing (WAAM) technique was used to develop nickel aluminum bronze (NAB) components for naval applications. The microstructural changes were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). As-built WAAM-NAB consists of κII (globular Fe3Al) and κIII (lamellar NiAl) phases in the interdendritic regions and fine Fe-rich κIV particles in the Cu-matrix. Along the build direction, the WAAM-NAB flat samples exhibited yield and ultimate tensile strength values of 380 and 708 MPa, respectively, and 34 % elongation. Furthermore, three different heat-treatments were performed on the samples in a view to evaluating their effect on mechanical properties. When heat-treated to 350 °C for 2 h (HT-1), there are no significant microstructural changes, and tensile properties along the build direction are similar to the as-built WAAM-NAB. Heat-treatment at 550 °C for 4 h (HT-2) produced a new needle-like κv phase in the α-matrix, coarsening of globular κII, partial spheroidization of lamellar κIII, and reduced amount of κIV precipitation. As compared to the WAAM-NAB, HT-2 samples exhibited a significant increase in yield strength (∼90 MPa), and ultimate tensile strength (∼60 MPa); however, tensile ductility was observed to drop by 20 %. After heat-treatment at 675 °C for 6 h (HT-3), globular κII and needle-like κv were coarsened, lamellar κIII was completely spheroidized, and the amount of κIV was significantly reduced. HT-3 samples showed better tensile strength (∼37 MPa) than the WAAM-NAB with marginal loss (6%) in the ductility. © 202
Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite
Laser-engineered net shaping (LENS (TM)), a commercial additive manufacturing process, was used to modify the surfaces of 316 L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32 J/mm(2) to 59 J/mm(2) the thickness of the modified surface increased from 222 +/- 12 mu m to 355 +/- 6 mu m, while the average surface hardness decreased marginally from 403 +/- 18 HV03 to 372 +/- 8 HV0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316 L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316 L samples. (C) 2013 Elsevier B.V. All rights reserved
Effects of grain refinement on cast structure and tensile properties of superalloy K4169 at high pouring temperature
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