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- Angseryd, Jenny, 1979, et al.
(författare)
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An in-depth investigation of the cutting speed impact on the degraded microstructure of worn PCBN cutting tools
- 2011
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 271:9-10, s. 2610-2618
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Tidskriftsartikel (refereegranskat)abstract
- The impact of an increased cutting speed on the degradation of a low content polycrystalline cubic boron nitride (PCBN) tool material is investigated by advanced microscopy techniques. The locally affected microstructure of worn PCBN cutting tools, after dry hard turning, is studied by high precision in situ lift-out cross sections taken from across the crater, formed on the rake face. The cross sections are studied with scanning electron microscopy, transmission electron microscopy (TEM) with electron energy loss spectroscopy and, primarily, energy filtered TEM.Advanced analysis techniques are crucial to illustrate the degradation mechanisms taking place locally at micro- and nano-metre levels during the machining operation. Results show that a higher cutting speed drastically affects the wear surface of the cutting edge. While an adherent layer, consisting of elements from the workpiece material, covers practically the whole wear surface at a lower cutting speed, it is only partially distributed at a higher cutting speed. Results also show significant differences in the local microstructure of the affected worn zone with an increase in cutting speed. The chemical degradation will go from tool-workpiece interface wear with smooth wear surfaces and almost no interaction with material below the wear surface at lower cutting speed to a severe penetration into the tool material by partially oxidised Fe-rich features at higher cutting speed. The more aggressive degradation behaviour at the higher cutting speed is also more localised. Single chemically worn cBN grains are for example shown. The dominating wear mechanism is shown to be chemical degradation, which accelerates with a higher cutting speed. The cBN phase is more affected than the major matrix phase, Ti(C,N).
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- Angseryd, Jenny, 1979
(författare)
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Microstructure of a cubic boron nitride tool material and its degradation during hard turning operations
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abstract. Polycrystalline cubic boron nitride (PCBN) materials are widely used in turning operations of hardened steels due to their beneficial mechanical properties like maintained high hardness at elevated temperatures, adequate toughness and for being more chemically stable towards iron compared to diamond at temperatures typical for turning operations. With the increase of commercially available grades, hard turning is constantly growing as are the new areas of applications. The wear of PCBN tools is influenced by several factors, such as machining parameters, different tool geometries and varying composition of the PCBN tool as well as of the workpiece material. To take full advantage of the beneficial properties of PCBN, the knowledge of the microstructure of unworn materials as well as of how wear progresses and which mechanisms that dominate during machining operations needs to improve.This study reports on several suitable microstructure investigation techniques for PCBN materials. A commercial low content PCBN tool material was used to study the unworn microstructure and its degradation during hard turning operations. The tool material was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) including methods such as energy dispersive X-ray spectrometry, electron energy-loss spectroscopy (EELS) as well as energy filtered TEM and finally atom probe tomography (APT).Cubic boron nitride (cBN) is the major phase in these materials. Quantitative investigations (with both EELS and APT), within the experimental errors, show values corresponding to stoichiometry with no detected impurities. The major matrix phase, Ti(C,N), was found to have a varying C/N ratio, typically between TiC0.5N0.5 and TiC0.7N0.3, in different grains. An Al additive in this material was shown to start a chain of reactions during the high-pressure, high-temperature sintering where several reaction phases form: α-Al2O3, TiB2 and AlN. Alumina networks are formed by Al and surface oxides, while the other phases form by reactions with cBN and Ti(C,N). In-depth microscopy investigations (with EELS) have shown small amounts of hexagonal BN and in rare cases also B2O3, which demonstrates how cBN can participate in reactions. Investigations also showed that the Ti(C,N) phase contains several dissolved elements such as O (~ 2.5 %), Al, B and W (~ 0.2-0.3 at%) and thus acts as a transport medium for elements so that shape adjustments and reactions can take place.The worn PCBN tool exhibited the typical crater wear on the rake face and flank wear, and both faces were covered by an adherent layer containing elements originating from the workpiece material. The degradation behaviour in the crater region of PCBN tools varied with machining parameters such as chemical composition of the workpiece material (a case hardened steel with high and low sulphur content) and cutting speed (150 m/min and 200 m/min). A protective layer of sulphides was found in the crater region when the workpiece material contained a high amount of sulphur. This layer was shown to protect the tool from degradation by iron-rich material. If the layer was missing, iron-rich material was found to make its way into the tool material microstructure by chemically dissolving phases. cBN grains were preferentially worn compared to Ti(C,N) grains, both at the wear surface and below. The strength of the protective sulphides was concluded to be weakened at higher cutting speeds, hence with decreased protection towards the iron-rich material degrading the microstructure.
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| 6. |
- Angseryd, Jenny, 1979
(författare)
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Microstructure of a cubic boron nitride tool material before and after hard turning
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractPolycrystalline cubic boron nitride (PCBN) materials are widely used in turning of hardened steels due to their beneficial mechanical properties like high hardness at elevated temperatures and, compared to diamond, for being more chemically stable towards iron at temperatures typical for turning operations (800-1000˚C). The wear of PCBN tools is influenced by several factors, like machining parameters, different tool geometries and varying composition of PCBN tools as well as workpiece material. The knowledge about how wear progresses and which mechanisms that are dominating is still limited.This study reports on the microstructure of a commercial PCBN tool material with ~55vol% cBN and the degradation of the microstructure after turning. The tool was used for turning a case hardened steel using cutting parameters typical for hard part turning. The tool material has been characterised by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) including spectroscopy methods like energy dispersive X-ray spectroscopy, electron energy-loss spectroscopy and energy-filtered TEM.The microstructure of the tool material contained micron-sized cBN grains, with flat grain boundaries, surrounded by a matrix mainly consisting of Ti(C,N). A fraction of smaller cBN grains, down to nanometre size, were found scattered in the matrix. The matrix also displayed a varying grain size. Both XRD and electron microscopy observations suggested that only limited reactions occur during the sintering process. Al2O3 was the major reaction product identified and some occurrence of TiB2 and AlN phases was also observed. Differences in C and N content in Ti(C,N) were also noted which indicated a material far from equilibrium.The worn PCBN tool exhibited a crater on the rake face and flank wear with an adherent layer covering the affected cutting edge area. Cross section specimens were taken from across the crater, on the rake face of the worn tool, using a lift-out technique in the focused ion beam/SEM. These cross-sections contained both the area close to the wear surface of the PCBN tool and the adherent layer covering it. This allowed a detailed investigation of the interface between them. The adherent layer consisted of elements from the workpiece material. Large Fe-rich areas were found, which were oxidised on the surface and sometimes containing small amounts of Cr and Ni. Mn and S were detected in larger areas, often with rounded shapes. Traces of Al, probably from the PCBN tool material, was found close to the interface in the adherent layer. No B, N or Ti were found in the layer and must have been transported away by the moving chip. cBN grains on the tool wear surface showed concave shapes instead of the common flat shapes. The major degradation mechanism appears to be of chemical nature.Keywords: cBN, PCBN, microstructure, wear, adherent layer, TEM, SEM, EDX, EFTEM, EELS
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- Angseryd, Jenny, 1979, et al.
(författare)
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Nanostructure of a cubic BN cutting tool material
- 2015
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Ingår i: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 283-287
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Tidskriftsartikel (refereegranskat)abstract
- Advanced microscopy techniques, laser assisted atom probe tomography and electron energy loss spectroscopy in transmission electron microscopy are used to investigate in detail the microstructure of a polycrystalline cubic boron nitride tool material. During sintering at high pressure superhard cubic boron nitride combines with hard ceramic Ti(C,N) to form a dense material. Diffusion in Ti(C,N) and reactions between Ti(C,N), cBN and additives result in the formation of several nitride, oxide and boride phases in a complex mixed microcrystalline and nano- crystalline microstructure.
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| 8. |
- Angseryd, Jenny, 1979, et al.
(författare)
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Quantitative APT analysis of Ti(C,N)
- 2011
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 609-614
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Tidskriftsartikel (refereegranskat)abstract
- A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the 13C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified. © 2011 Elsevier B.V.
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| 10. |
- Thuvander, Mattias, 1968, et al.
(författare)
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Quantitative atom probe analysis of carbides
- 2011
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 604-608
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Tidskriftsartikel (refereegranskat)abstract
- Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti 2 AlC grains in different materials as well as on large M 2 3C 6 precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the 13 C isotope, and calculating the concentration of 12 C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) andTi 2 AlC an additional difficulty arises from the overlap between C 2 + ,C 2+ 4 and Ti 2+ at the mass-to-charge 24 Da. © 2010 Elsevier B.V.
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