skip to main content


Title: Towards Manufacturing of Ultrafine-Laminated Structures in Metallic Tubes by Accumulative Extrusion Bonding
A severe plastic deformation process, termed accumulative extrusion bonding (AEB), is conceived to steady-state bond metals in the form of multilayered tubes. It is shown that AEB can facilitate bonding of metals in their solid-state, like the process of accumulative roll bonding (ARB). The AEB steps involve iterative extrusion, cutting, expanding, restacking, and annealing. As the process is iterated, the laminated structure layer thicknesses decrease within the tube wall, while the tube wall thickness and outer diameter remain constant. Multilayered bimetallic tubes with approximately 2 mm wall thickness and 25.25 mm outer diameter of copper-aluminum are produced at 52% radial strain per extrusion pass to contain eight layers. Furthermore, tubes of copper-copper are produced at 52% and 68% strain to contain two layers. The amount of bonding at the metal-to-metal interfaces and grain structure are measured using optical microscopy. After detailed examination, only the copper-copper bimetal deformed to 68% strain is found bonded. The yield strength of the copper-copper tube extruded at 68% improves from 83 MPa to 481 MPa; a 480% increase. Surface preparation, as described by the thin film theory, and the amount of deformation imposed per extrusion pass are identified and discussed as key contributors to enact successful metal-to-metal bonding at the interface. Unlike in ARB, bonding in AEB does not occur at ~50% strain revealing the significant role of more complex geometry of tubes relative to sheets in solid-state bonding.  more » « less
Award ID(s):
1727495
NSF-PAR ID:
10311557
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Metals
Volume:
11
Issue:
3
ISSN:
2075-4701
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1.  
    more » « less
  2. Abstract

    We performed a series of extrusion experiments on partially molten samples of forsterite plus 10 vol% of an anorthite‐rich melt to investigate melt segregation in a pipe‐extrusion geometry and test the predictions of two‐phase flow theory with viscous anisotropy. The employed flow geometry has not been experimentally investigated for partially molten rocks; however, numerical solutions for a similar, pipe‐Poiseuille geometry are available. Samples were extruded from a 6‐mm diameter reservoir into a 2‐mm diameter channel under a fixed normal stress at 1350°C and 0.1 MPa. The melt distribution in the channel was subsequently mapped with optical and backscattered electron microscopy and analyzed via quantitative image analysis. Melt segregated from the center toward the outer radius of the channel. The melt fraction at the wall increased with increasing extrusion duration and with increasing shear stress. The melt fraction profiles are parabolic with the melt fraction at the wall reaching 0.17–0.66, values 2 to 16 times higher than at the channel center. Segregation of melt toward the wall of the channel is consistent with base‐state melt segregation as predicted by two‐phase flow theory with viscous anisotropy. However, melt‐rich sheets inclined at a low angle to the wall, which are anticipated from two‐phase flow theory, were not observed, indicating that the compaction length is larger than the channel diameter. The results of our experiments are a test of two‐phase flow theory that includes viscous anisotropy, an essential theoretical frame work needed for modeling large‐scale melt migration and segregation in the upper mantle.

     
    more » « less
  3. Abstract

    This work presents the experimental characterization of pool boiling heat transfer enhancement on cylindrical tubes with circumferential micro-channels using saturated water at atmospheric pressure as the working fluid. Three engineered copper tubes with 300 μm, 600 μm and 900 μm fin width and a fixed 400 μm channel width with 410 μm channel depth were machined using CNC. To compare the boiling enhancement on engineered tubes, one plain copper tube was used as the reference heater. The active heating area on the cylindrical tubes had a dimension of 9.5 mm outer diameter and 10.5 mm length. A custom-built cylindrical heater was designed using a nichrome wire coil of 30 AWG with a resistance of 19.57 Ω/inch of coil to provide joule heating to the cylindrical tubes. The electrical wire was insulated from the copper heater using a thin layer of alumina paste. The saturated pool boiling tests up to critical heat flux (CHF) were conducted at atmospheric pressure. While an approximate CHF of ∼70 W/cm2 was achieved for the plain copper tube, the cylindrical tube with microchannel geometry showed a CHF range of 131–144 W/cm2 that corresponds to 87%–100% enhancement as compared to plain cylindrical tube.

     
    more » « less
  4. Heterogeneous bonding between metals and ceramics is of significant relevance to a wide range of applications in the fields of industry, defense, and aerospace. Metal/ceramic bonding can be used in various specific part applications such as vacuum tubes, automotive use of ceramic rotors, and rocket igniter bodies. However, the bonding of ceramic to metal has been challenging mainly due to (1) the low wettability of ceramics, on which the adhesion of molten adhesive bonders is limited and (2) the large difference between the coefficients of thermal expansion (CTE) of the two dissimilar bonded materials, which develops significant mechanical stresses at the interface and potentially leads to mechanical failures. Vapor-phase deposition is a widely used thin film processing technique in both academic research laboratories and manufacturing industries. Since vapor phase coatings do not require wettability or hydrophobicity, a uniform and strongly adherent layer is deposited over virtually any substrate, including ceramics. In this presentation, we report on the effect of vapor phase-deposited interfacial metal layers on the mechanical properties of bonding between stainless steel and Zerodur (lithium aluminosilicate-based glass ceramic). Direct-current magnetron sputtering was utilized to deposit various thin interfacial layers containing Ti, Cu, or Sn. In addition, to minimize the unfavorable stress at the bonded interface due to the large CTE difference, a low temperature allow solder, that can be chemically and mechanically activated at temperatures of approximately 200 °C, was used. The solder is made from a composite of Ti-Sn-Ce-In. A custom-built fixture and universal testing machine were used to evaluate the bonding strength in shear, which was monitored in-situ with LabView throughout the measurement. The shear strength of the bonding between stainless steel and Zerodur was systematically characterized as a function of interfacial metal and metal processing temperature during sputter depositions. Maximum shear strength of the bonding of 4.36 MPa was obtained with Cu interfacial layers, compared to 3.53 MPa from Sn and 3.42 MPa from Ti adhesion promoting layers. These bonding strengths are significantly higher than those (~0.05 MPa) of contacts without interfacial reactive thin metals. The fracture surface microstructures are presented as well. It was found that the point of failure, when Cu interfacial layers were used, was between the coated Cu film and alloy bonder. This varied from the Sn and Ti interfacial layers where the main point of failure was between the interfacial film and Zerodur interface. The findings of the effect of thin adhesion promoting metal layers and failure behaviors may be of importance to some metal/ceramic heterogeneous bonding studies that require high bonding strength and low residual stresses at the bonding interface. The authors gratefully acknowledge the financial support of the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. 
    more » « less
  5. The bonding of ceramic to metal has been challenging due to the dissimilar nature of the materials, particularly different surface properties and the coefficients of thermal expansion (CTE). To address the issues, gas phase-processed thin metal films were inserted at the metal/ceramic interface to modify the ceramic surface and, therefore, promote heterogeneous bonding. In addition, an alloy bonder that is mechanically and chemically activated at as low as 220 °C with reactive metal elements was utilized to bond the metal and ceramic. Stainless steel (SS)/Zerodur is selected as the metal/ceramic bonding system where Zerodur is chosen due to the known low CTE. The low-temperature process and the low CTE of Zerodur are critical to minimizing the undesirable stress evolution at the bonded interface. Sputtered Ti, Sn, and Cu (300 nm) were deposited on the Zerodur surface, and then dually activated molten alloy bonders were spread on both surfaces of the coated Zerodur and SS at 220 °C in air. The shear stress of the bonding was tested with a custom-designed fixture in a universal testing machine and was recorded through a strain indicator. The mechanical strength and the bonded surface property were compared as a function of interfacial metal thin film and analyzed through thermodynamic interfacial stability/instability calculations. A maximum shear strength of bonding of 4.36 MPa was obtained with Cu interfacial layers, while that of Sn was 3.53 MPa and that of Ti was 3.42 MPa. These bonding strengths are significantly higher than those (∼0.04 MPa) of contacts without interfacial reactive thin metals.

     
    more » « less