| 1. |
- Hassila, Carl Johan
(författare)
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Additive Manufacturing of Ni-Fe Superalloys : Exploring the Alloying Envelope and the Impact of Process on Mechanical Properties
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive manufacturing of metals has received a lot of attention in the last decade as this family of manufacturing processes allows the manufacturing of complicated geometries which would be difficult to produce using conventional manufacturing techniques. Additive manufacturing of the Ni-Fe based superalloys 625 and 718 using the Powder Bed Fusion – Laser Beam (PBF-LB) process is facilitated by the fact that these alloys were developed as weldable alternatives to other high-strength, high-temperature Ni-based superalloys. However, given that these alloys were developed with casting and forging as the main manufacturing route, the alloying composition of these alloys may possibly be tuned to better suit the PBF-LB process. In this thesis, small changes to the alloy 625 and 718 alloy compositions were made, with the goal of either improving material properties or reducing the environmental footprint of the produced materials. For alloy 718, the influence of carbon content on the resulting microstructure and mechanical properties was investigated both in the as-built and heat-treated conditions using tensile and impact testing. A similar study, but also including corrosion experiments, was performed on an alloy 625 composition which had been tuned to allow it to be atomized using nitrogen instead of argon, a transition that results in environmental benefits as argon gas carries with it a larger environmental footprint compared to nitrogen gas. In addition to the above, as the process conditions in the PBF-LB process have a strong influence on the developing microstructure, their influence on rolling contact fatigue and residual stresses in printed alloys 625 and 718 were investigated. Rolling contact fatigue experiments were performed on alloy 625 and were complemented by a fractographic study which showed that the different grain structures achieved depending on the used process condition affected the pitting damage development. Meanwhile, the residual stress experiments were performed on PBF-LB processed alloy 625 and 718. The residual stresses in the materials were first calculated using experimental data attained from high energy synchrotron diffraction experiments. These results were then compared to the predicted stresses from a thermo-mechanical model. The thermomechanical model included a built-in mechanism-based material model which was shown to successfully simulate relaxation effects stemming from the cyclic heating of the material during the PBF-LB process. Lastly, a modelling approach using the thermo-mechanical model was developed which allowed the model to successfully predict the stresses also when using different scanning strategies.
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| 2. |
- Heinrichs, Jannica, et al.
(författare)
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Exploring the tribochemical wear and material transfer caused by Cu15Zn alloys on shearing tools
- 2024
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 542
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Tidskriftsartikel (refereegranskat)abstract
- Cemented carbide tools are extensively used in the zipper industry, including shearing of a pre-formed Cu15Zn wire into individual zipper elements. Although the work material is significantly softer than the tool, wear is the life limiting factor for the tools and is considered to be of tribochemical nature. So far it has not been explained, however, it is known that the wear rate of uncoated, as well as CrC and CrN coated, cemented carbide increases dramatically when Zn is omitted from the Cu alloy. In this paper, worn tool surfaces, including any transferred material, were studied to investigate the tribochemical wear mechanism in detail. Material transfer occurred onto all tool surfaces. Cu and Zn were separated on the sub-micron scale, and preferential transfer of one of the constituents was observed. This is reflected in the outermost surface of the sheared element, which shows a homogeneous composition elsewhere. Oxidation was observed of all tool surfaces, which indicates elements of oxidative wear. Further, any Zn transferred to the tool surfaces was oxidized. Thus, it is suggested that the presence of Zn reduces the oxygen available and consequently reduces the oxidation rate of the tool surfaces, leading to the protective effect previously observed. © 2024 The Authors
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| 3. |
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| 4. |
- Heinrichs, Jannica, 1982-, et al.
(författare)
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Wear mechanisms of WC-Co cemented carbide tools and PVD coated tools used for shearing Cu-alloy wire in zipper production
- 2019
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 420, s. 96-107
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Tidskriftsartikel (refereegranskat)abstract
- To form the individual elements, that together form a zipper, a pre-formed Cu-alloy wire is sheared using cemented carbide tools. The wear caused by the relatively soft copper alloy on the much harder tool is generally quite slow. However, millions of elements are to be sheared so eventually the wear becomes unacceptable and the tool needs to be exchanged. To improve product quality, as well as minimize down time and material consumption, the tool life needs to be prolonged. To achieve this the wear process needs to be better understood. Uncoated tools used for an increasing number of shearing events have been studied in detail using high resolution SEM and EDS, to map the propagating wear and get an insight into the wear mechanisms. Transfer of material from the Cu-alloy to the tool occurs and the wear is highly concentrated to specific areas. This wear occurs on a very fine scale, limited to within individual WC grains at each event. Tools coated with PVD CrC and PVD CrN have been studied for comparison with the uncoated cemented carbide. Both coatings successfully protect the cemented carbide tool from wear, however occasional flaking occurs and then the cemented carbide becomes exposed and subsequently worn. The differences in performance and wear mechanisms between the uncoated and coated tools are discussed, with focus on the capability of the coatings to prolong the tool life.
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| 5. |
- Heinrichs, Jannica, et al.
(författare)
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Wear of cemented carbide forging dies used in zipper production
- 2022
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 492-493
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Tidskriftsartikel (refereegranskat)abstract
- Cemented carbide tools are commonly used in both cutting and forging processes associated to zipper produc-tion. In production, the tools experience many millions of repeated contacts, hence they must be very durable to keep the wear at acceptable levels. Although the zipper elements in this investigation are made in a relatively soft CuZn alloy, the wear becomes significant and the tool life a production limiting factor. The wear process is to a large extent unknown. To increase the understanding, forging dies used for an increasing number of forgings in actual production, have been studied in detail. Initially the Co binder is preferentially worn off, and transferred CuZn partly fills the cavities. Interestingly, the repeating forging contacts lead to modification of the composition of the transferred material, which partly separates into Cu rich and Zn rich parts, where the Zn rich parts show a high presence of oxygen. During the life span of the tool, represented by the controlled use of forging tools to different percentages of their estimated life, the WC grains are gradually worn into faceted shapes. The most severely worn region of the forging dies develops an increasing surface roughness, which act to shape a corre-sponding pattern on the zipper elements.
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| 6. |
- Heinrichs, Jannica, et al.
(författare)
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Wear of uncoated and PVD coated cemented carbide tools for processing of copper based materials part II : Exploring the sliding contact with pure copper
- 2021
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 466-467
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Tidskriftsartikel (refereegranskat)abstract
- Cemented carbide tools are successfully used to shear Cu alloy wire into zipper elements in the zipper industry. However, wear of the tools is the limiting factor for the production rate and the industry would benefit from more wear resistant tools. Previous investigations have indicated that the wear is tribochemical, and to investigate the role of Zn in commonly used Cu alloy testing is repeated against pure Cu in this work. The tool material used is a cemented carbide, in uncoated, CrC coated and CrN coated versions. The tests are performed in a simplified sliding test rig, combined with intermittent scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis.The tools are gradually worn and Cu is adhered and transferred to all tool surfaces. This process results in a pattern consisting of ridges and valleys on uncoated cemented carbide and CrC. Both are worn significantly faster than CrN, where much of the original surface roughness still remains after the full test. These worn surfaces are similar to the corresponding surfaces worn against the previously tested Cu–Zn alloy. However, the wear rate is dramatically higher in the pure Cu tests.
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| 7. |
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| 8. |
- Mikado, Hiroko, et al.
(författare)
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Wear of cemented carbide tools in a copper alloy forging process : Verification of a new lab test
- 2023
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; , s. 528-529
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Tidskriftsartikel (refereegranskat)abstract
- Cemented carbide tools are commonly used in both shearing and forging processes associated to zipper production. In the actual production, the tool life is often limited by wear after many millions of repeated contacts with copper alloys. A series of previous investigations has shown that the wear of the tools is tribochemical for both shearing and forging, however with different features. The mechanisms causing this wear are not well understood.To gain deeper insights into the active wear mechanisms during the copper alloy forging process, a new tribotester was proposed and developed. By this tester, a cemented carbide cylinder is repeatedly put in sliding contact with a rotating copper alloy cylinder in a crossed cylinders arrangement. The test was interrupted at selected intervals so that the cemented carbide cylinder could be repeatedly evaluated by SEM and EDS. It was revealed that the characteristic wear of actual tools, tribochemical smooth wear in common, and preferential removal of Co binder and partially Zn rich transfer for the forging tool, can be reproduced by this tribotester.
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| 9. |
- Mikado, Hiroko, et al.
(författare)
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Wear of Uncoated and PVD Coated Cemented Carbide Tools for Processing of Copper Based Materials Part I : Lab test verification in dry and lubricated sliding
- 2020
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 462-463
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Tidskriftsartikel (refereegranskat)abstract
- In the manufacturing of metal zippers, including several complicated forming and shearing process steps, the tool wear is a limiting factor, since it deteriorates the quality of the zipper elements. Hence, an increased understanding of the tool wear mechanisms occurring in the zipper production is important to prolong the tool life.To gain deeper insights into the tool wear mechanisms active in the process of shearing Cu alloy wire into separate zipper elements, the present study utilizes a simplified sliding test rig. The rig comprises a small tool material cylinder sliding against a large rotating work material cylinder, in a crossed cylinders configuration. One uncoated and two PVD-coated cemented carbide cylinders were tested under contact conditions similar to those of the actual shearing. The tool material cylinder was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) at selected intervals during the test. The surface appearance was investigated and compared with observations on tools used in actual zipper production. The degradation was found to include gradual wear against the Cu alloy, transfer of the Cu alloy and characteristic modifications of the topography, indicative of wear mechanisms operating at a very small scale, confirming that the wear of the shearing tools can be mimicked by the test.
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