| 1. |
- Malakizadi, Amir, 1983, et al.
(författare)
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The role of microstructural characteristics of additively manufactured Alloy 718 on tool wear in machining
- 2021
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Ingår i: International Journal of Machine Tools and Manufacture. - : Elsevier BV. - 0890-6955. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to provide a fundamental understanding of the role of microstructural characteristics influencing tool wear when machining Alloy 718 fabricated using Powder Bed Fusion (PBF). The effects of preferred crystallographic orientation (texture), shape and distribution of grains, local misorientation, type and amount of precipitates as well as the type, size and amount of abrasive carbides, nitrides and oxides on tool wear are investigated in as-built condition and after the standard solutionising and double-aging treatment. The microstructures of workpiece materials and the surfaces of worn tools were examined using different material characterisation techniques, including Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). A dislocation-based approach was used to reveal the cumulative effects of the microstructural characteristics on deformation behaviour and the thermo-mechanical loads on the tools during cutting. The analyses suggest that texture and the extent of material work-hardening prior to the onset of crack formation markedly influence the amount of plastic work and thus heat generation when machining Electron Beam Powder Bed Fusion (EB-PBF) material. The higher heat generation in the cutting zones provokes thermally-induced wear mechanisms like diffusion-dissolution and oxidation. In addition, the larger amount of hard oxide inclusions present in EB-PBF material leads to higher wear by abrasion. In contrast to the prevailing experimental approaches in this field, the present investigation is built on a physics-based framework to understand the fundamental aspects that govern material deformation and heat generation in cutting and, consequently, tool wear mechanisms. This framework can be used for machinability assessment of any alloy manufactured by different additive manufacturing (AM) technologies and for optimising the process-chain, including printing strategies and thermal post-treatments, to improve the machinability of AM alloys by tailoring their microstructure.
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| 2. |
- Hearn, William, 1992, et al.
(författare)
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In situ tempering of martensite during laser powder bed fusion of Fe-0.45C steel
- 2022
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 23
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Tidskriftsartikel (refereegranskat)abstract
- During laser powder bed fusion (L-PBF), materials experience cyclic re-heating as new layers are deposited, inducing an in situ tempering effect. In this study, the effect of this phenomenon on the tempering of martensite during L-PBF was examined for Fe-0.45C steel. Detailed scanning electron microscopy, transmission electron microscopy, atom probe tomography, and hardness measurements indicated that martensite was initially in a quenched-like state after layer solidification, with carbon atoms segregating to dislocations and to martensite lath boundaries. Subsequent tempering of this quenched-like martensite was the result of two in situ phenomena: (i) micro-tempering within the heat affected zone and (ii) macro-tempering due to heat conduction and subsequent heat accumulation. Hardness measurements showed that although both influenced martensite tempering, micro-tempering had the most significant effect, as it reduced martensite hardness by up to ∼380 HV. This reduction was due to the precipitation of nano-sized Fe3C carbides at the previously carbon-enriched boundaries. Lastly, the magnitude of in situ tempering was found to be related to the energy input, where increasing the volumetric energy density from 60 to 190 J/mm3 reduced martensite hardness by ∼100 HV. These findings outline the stages of martensite tempering during L-PBF and indicate that the level of tempering can be adjusted by tailoring the processing parameters.
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| 3. |
- Hoier, Philipp, 1988, et al.
(författare)
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Tool wear by dissolution during machining of alloy 718 and Waspaloy: a comparative study using diffusion couples
- 2020
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 106:3-4, s. 1431-1440
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Tidskriftsartikel (refereegranskat)abstract
- The wear of metal cutting tools is known to take place by the combined and simultaneous effects of several wear mechanisms. Knowledge of the relative contribution of the individual wear mechanisms is required to understand and predict the tool wear during cutting different workpiece materials and alloys. It has been shown previously that machining two heat resistant superalloys, alloy 718 and Waspaloy, leads to distinctively different tool wears. Even though the subject has been addressed in various studies, there are still open questions regarding the underlying reasons for the differing tool wear rates. In particular, the relative contributions of diffusion/dissolution when machining the two alloys have not been addressed so far. Therefore, a qualitative comparison of the chemical interaction between the tool material and the two superalloys was made by using diffusion couple tests. The aim was to mimic the high temperatures and intimate contact between workpiece and tool material at the tool rake and flank faces during cutting under controlled and static conditions. The obtained results suggest that it is unlikely that differences in flank wear rate when machining the two superalloys are caused by significantly varying magnitudes of tool atoms dissolving into the respective workpiece. Analysis of the tool/superalloy interfaces in the diffusion couples revealed diffusion-affected zones of similar size for both tested superalloys. Increasing test temperature led to enhanced interdiffusion which suggests an increase in tool wear by diffusion/dissolution for higher cutting temperature. For alloy 718, the higher test temperature also led to depletion of carbon together with formation of tungsten within the tool in close vicinity to the interface with the superalloy.
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| 4. |
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| 5. |
- Fisk, Martin, 1981-, et al.
(författare)
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Modelling of induction hardening in low alloy steels
- 2018
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Ingår i: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 144, s. 61-75
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Tidskriftsartikel (refereegranskat)abstract
- Induction hardening is a useful method for improving resistance to surface indentation, fatigue and wear that is favoured in comparison with through hardening, which may lack necessary toughness. The process itself involves fast heating by induction with subsequent quenching, creating a martensitic layer at the surface of the workpiece. In the present work, we demonstrate how to simulate the process of induction hardening using a commercial finite element software package with focuses on validation of the electromagnetic and thermal parts, together with evolution of the microstructure. Experiments have been carried out using fifteen workpieces that have been heated using three different heating rates and five different peak temperatures resulting in different microstructures. It is found that the microstructure and hardening depth is affected by the heating rate and peak temperature. The agreement between the experimental and simulated results is good. Also, it is demonstrated that the critical equilibrium temperatures for phase transformation is important for good agreement between the simulated and experimental hardening depth. The developed simulation technique predicts the hardness and microstructure sufficiently well for design and the development of induction hardening processes.
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| 6. |
- Frost, Robert J. W., et al.
(författare)
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Preliminary results from a study of luminescent materials : For application in the beam imaging system at the ESS
- 2023
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 540, s. 227-233
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Tidskriftsartikel (refereegranskat)abstract
- As part of the development of the beam imaging system at the European Spallation Source, luminescent screens have been fabricated by the flame spraying of scintillating materials onto stainless steel backings. A total of seven screens were produced, three of chromia alumina (Al2O3:Cr), two of YAG (Y3Al5O12:Ce) and two of a 50/50 mix of these. The properties of these screens under proton irradiation were evaluated using a2.55 MeV proton beam at currents of up to 10 μA. Irradiation times were up to 25 h per sample, during which luminescence-, spectrographic-, thermal- and current-data was sampled at a rate of 1 Hz. Preliminary results of these measurements are reported here; with a quantitative analysis presented for one of the chromia alumina screens and a qualitative comparison of all three material types. The luminescent yield for chromia alumina was determined to be around 2000 photons/MeV for a virgin screen, and was found to drop to 1.5% after 167 mC of proton irradiation. A recovery of the luminescence of chromia alumina to >60% was observed after beam current was reduced for an 8 h period. Observations indicate that the YAG and mixed composition screens retain higher luminescence than the chromia alumina even at temperatures of over 200 ◦C. It is indicated that the luminescence from YAG feeds the R-lines of chromia alumina in the mixed composition screens.
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| 7. |
- Johansson, Jakob, et al.
(författare)
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On the function of lead (Pb) in machining brass alloys
- 2022
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Ingår i: International Journal of Advanced Manufacturing Technology. - : Springer Science and Business Media LLC. - 0268-3768 .- 1433-3015. ; 120:11-12, s. 7263-7275
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Tidskriftsartikel (refereegranskat)abstract
- Lead has traditionally been added to brass alloys to achieve high machinability, but the exact mechanisms at work are still debated. Lead-free brass alternatives could be developed if these mechanisms were better understood. Accordingly, machinability characteristics were investigated for two brass alloys with similar mechanical properties and phase composition, but with very different machining characteristics because one has 3 wt.% lead (CuZn38Pb3) while the other has only 0.1 wt.% (CuZn42). The effect of the lead was investigated using infrared temperature measurement, electron microscopy, secondary ion mass spectroscopy, quick-stop methods, and high-speed filming. Neither melting of lead nor its deposition on the tool rake surface takes place during machining thus confirming its limited lubrication and tribological effects. Instead, the main role of lead is to promote discontinuous chip formation. Lead deforms to flake-like shapes that act as crack initiation points when the workpiece material passes through the primary deformation zone. This effect prevents the development of stable tool–chip contact, thus lowering cutting forces, friction, and process temperature.
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| 8. |
- Lindwall, Johan, et al.
(författare)
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Simulation of phase evolution in a Zr-based glass forming alloy during multiple laser remelting
- 2022
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854 .- 2214-0697. ; 16, s. 1165-1178
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing by laser-based powder bed fusion is a promising technique for bulk metallic glass production. But, reheating by deposition of subsequent layers may cause local crystallisation of the alloy. To investigate the crystalline phase evolution during laser scanning of a Zr-based metallic glass-forming alloy, a simulation strategy based on the finite element method and the classical nucleation theory has been developed and compared with experimental results from multiple laser remelting of a single-track. Multiple laser remelting of a single-track demonstrates the crystallisation behaviour by the influence of thermal history in the reheated material. Scanning electron microscopy and transmission electron microscopy reveals the crystalline phase evolution in the heat affected zone after each laser scan. A trend can be observed where repeated remelting results in an increased crystalline volume fraction with larger crystals in the heat affected zone, both in simulation and experiment. A gradient of cluster number density and mean radius can also be predicted by the model, with good correlation to the experiments. Prediction of crystallisation, as presented in this work, can be a useful tool to aid the development of process parameters during additive manufacturing for bulk metallic glass formation.
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| 9. |
- Liu, Yang, et al.
(författare)
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Investigation on residual stress evolution in nickel-based alloy affected by multiple cutting operations
- 2021
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Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 68, s. 818-833
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Tidskriftsartikel (refereegranskat)abstract
- Machining-induced residual stresses in a part can significantly influence its performance and service time. It is common that the final surface of the part is produced after multiple cuts in the machining process. In multiple cuts, the previous cuts could often generate accumulated strain/stress and temperature on the part surface. These accumulated strain/stress and temperature will be brought to the subsequent cut or final cut and continuously affect the cutting forces, process temperatures, deformation zones, etc. in subsequent cut, and eventually affect the final residual stresses on the part. This paper reports on a joint experimental and numerical investigation to explore the influence of previous cuts on surface residual stresses with consideration of cutting parameters, cutting procedure, and tool geometries in multiple cut of Inconel 718 alloy. Coupled Eulerian and Lagrangian (CEL) formulation is used in a two/three-cuts numerical model. The loading cycles of the selected material nodes are characterised based on isotropic constitutive model (Johnson-Cook model) to analyse the underlying mechanism of residual stress evolution during cutting sequences. The results show that accumulated stress/strain induced by previous cuts lead to a more curled chip morphology, a slight decrease in cutting force and a slight increase in feed force in the subsequent cut. An increased magnitude and depth of compressive residual stresses in the finished workpiece are generated owing to the influence of previous cuts, and this is more obvious when the previous cut is implemented at a larger uncut chip thickness, using a more negative rake angle or a larger edge radius tool. The residual stress level might be controlled by optimizing the previous cuts to get the desired surface integrity.
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| 10. |
- Schultheiss, Fredrik, et al.
(författare)
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Machinability of CuZn21Si3P brass
- 2016
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 1743-2847 .- 0267-0836. ; 32:17, s. 1744-1750
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Tidskriftsartikel (refereegranskat)abstract
- New brass alloys containing less or even no lead are being developed, decreasing the environmental impact of the material. One example of an alternative brass is CuZn21Si3P, which contains less than 0.09 wt-% Pb. The research presented in this article evaluates the machinability of CuZn21Si3P as compared to more common, lead-containing free-machining brasses. The results show a marked decrease in the machinability of CuZn21Si3P. When longitudinally turning CuZn21Si3P the cutting tool failed after 142 min of machining. This tool wear was to a large extent remedied through the use of a coating on the cutting tool. CuZn21Si3P appears as a viable substitute for lead-containing brasses, thus implying the possibility for improving the sustainability of modern production.
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