Induction hardening is one of the finishing processes to improve hardness and wear resistance on ... more Induction hardening is one of the finishing processes to improve hardness and wear resistance on steel products by developing a hard martensite-rich surface layer. Non-destructive Barkhausen noise (BN) evaluation is used for quality assurance. While the routine production is set to develop a desirable hardening depth of this specific structure, the variations of microstructure and grain size overlay the outbound results in the assessment and make the interpretation unambiguous. This work correlates the different parameters in BN-signal with the deviations from the targeted martensite by predictive, physical and numerical modelling means.
Magnetic Barkhausen noise (MBN) method is one of the nondestructive evaluating (NDE) techniques u... more Magnetic Barkhausen noise (MBN) method is one of the nondestructive evaluating (NDE) techniques used in industry to monitor the quality of ferromagnetic products during manufacture. In this article, case depth evaluation of the camshaft lobes by this means after induction hardening is described. A routine industrial monitoring practice is found to have limitation to evaluate the thickness of this process-hardened layer. With the aid of metallography on selected samples, this uppermost layer is found to have one, or more than one microconstituents. This infers that each type possesses different physical properties in response to the MBN measurement. Consequently, the interpretation of the MBN signal/data for case depth evaluation is not straightforward. From metallography, a qualified component should have a uniform layer of martensite with grains ≤ 50 µm and the thickness around 3.0-5.0 mm. This gives the magnetoelastic parameter (i.e. mp) in a range of 20-70 in industrial MBN measurement. The mp outside this range corresponds to either a non-martensitic type or a martensitic type with grains > 50 µm. In fact, the characteristic features of a Barkhausen burst like peak intensity, width and position can be used to categorise different microstructural conditions. Then, the case depth of the qualified components, or the thickness of the qualified martensite, can be estimated. Statistical regression decision tree model helps to divide this qualified group into three subgroups between 3.0 and 6.0 mm, and each can be identified by the decision criteria based on the specific ranges of the mp reading, the RMS of peak intensity and the peak position. In the end, a physical model is used to show how the difference of microstructures is influencing the magnetic flux, and thus the mp. Nevertheless, more information is needed to improve the model for this application.
Binary transition metal silicides based on the systems Ti-Si, Fe-Si, Ni-Si and Cr-Si were fabrica... more Binary transition metal silicides based on the systems Ti-Si, Fe-Si, Ni-Si and Cr-Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti-Si, Fe-Si and Ni-Si systems, single phase thin films of TiSi 2 , β-FeSi 2 and NiSi 2 were generated as the model predicts, while a mixture of CrSi + CrSi 2 phases was obtained for the Cr-Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p 3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0 eV for Ni 2p 3/2 peak of NiSi 2 is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3 eV for the Fe 2p 3/2 level was shown for β-FeSi 2 and negative binding energy shifts of 0.1 and 0.3 eV were determined for CrSi + CrSi 2 and TiSi 2 , respectively.
Induction hardening is one of the finishing processes to improve hardness and wear resistance on ... more Induction hardening is one of the finishing processes to improve hardness and wear resistance on steel products by developing a hard martensite-rich surface layer. Non-destructive Barkhausen noise (BN) evaluation is used for quality assurance. While the routine production is set to develop a desirable hardening depth of this specific structure, the variations of microstructure and grain size overlay the outbound results in the assessment and make the interpretation unambiguous. This work correlates the different parameters in BN-signal with the deviations from the targeted martensite by predictive, physical and numerical modelling means.
Magnetic Barkhausen noise (MBN) method is one of the nondestructive evaluating (NDE) techniques u... more Magnetic Barkhausen noise (MBN) method is one of the nondestructive evaluating (NDE) techniques used in industry to monitor the quality of ferromagnetic products during manufacture. In this article, case depth evaluation of the camshaft lobes by this means after induction hardening is described. A routine industrial monitoring practice is found to have limitation to evaluate the thickness of this process-hardened layer. With the aid of metallography on selected samples, this uppermost layer is found to have one, or more than one microconstituents. This infers that each type possesses different physical properties in response to the MBN measurement. Consequently, the interpretation of the MBN signal/data for case depth evaluation is not straightforward. From metallography, a qualified component should have a uniform layer of martensite with grains ≤ 50 µm and the thickness around 3.0-5.0 mm. This gives the magnetoelastic parameter (i.e. mp) in a range of 20-70 in industrial MBN measurement. The mp outside this range corresponds to either a non-martensitic type or a martensitic type with grains > 50 µm. In fact, the characteristic features of a Barkhausen burst like peak intensity, width and position can be used to categorise different microstructural conditions. Then, the case depth of the qualified components, or the thickness of the qualified martensite, can be estimated. Statistical regression decision tree model helps to divide this qualified group into three subgroups between 3.0 and 6.0 mm, and each can be identified by the decision criteria based on the specific ranges of the mp reading, the RMS of peak intensity and the peak position. In the end, a physical model is used to show how the difference of microstructures is influencing the magnetic flux, and thus the mp. Nevertheless, more information is needed to improve the model for this application.
Binary transition metal silicides based on the systems Ti-Si, Fe-Si, Ni-Si and Cr-Si were fabrica... more Binary transition metal silicides based on the systems Ti-Si, Fe-Si, Ni-Si and Cr-Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti-Si, Fe-Si and Ni-Si systems, single phase thin films of TiSi 2 , β-FeSi 2 and NiSi 2 were generated as the model predicts, while a mixture of CrSi + CrSi 2 phases was obtained for the Cr-Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p 3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0 eV for Ni 2p 3/2 peak of NiSi 2 is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3 eV for the Fe 2p 3/2 level was shown for β-FeSi 2 and negative binding energy shifts of 0.1 and 0.3 eV were determined for CrSi + CrSi 2 and TiSi 2 , respectively.
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Papers by Eric Tam