The actual service life of wind turbine gearboxes is often well below the desired 20 years. One of the prevalent failure modes in gearbox bearing raceways is white structure flaking (WSF) in as ...little as 6-24 months of operation by the formation of axial cracks and white etching cracks (WECs) with associated microstructural change called white etching areas (WEAs). Despite these failures having been observed for two decades in various industries, the drivers and mechanisms for their formation are still highly contested. Discussed in this review are methods for searching and analysing WECs, mechanisms for WEA microstructural change, WEC initiation and propagation theories, WSF formation drivers and finally technologies and processes offering resistance to WSF. This updated review serves as a recap, comprehensive update on findings, current focus areas and remaining challenges.
This paper is part of a Themed Issue on Recent developments in bearing steels.
Conventional engineering methods oftentimes have challenges in the quantification of crack nucleation processes from manufacturing defects that are relevant for engineering component lifing. In this ...work, we present peridynamic simulation framework for the description of the crack nucleation process from cluster of non-metallic inclusions in aluminum alloys. Our non-local simulation framework characterizes crack nucleation process as multiple micro-crack nucleation events from individual inclusions, and eventually one micro-crack dominates. We define individual stages of the crack nucleation process, i.e., nucleation, micro-crack, technical, and crack initiation, that allow a quantification and meta model development of both the individual stages and the entire crack nucleation process.
Behavior of collision and agglomeration between solid inclusion particles MgO · Al2O3 and Al2O3 on H13 molten steel surfaces is observed in situ through a confocal scanning laser microscope (CSLM) ...equipped with a gold image furnace, and the attractive force between these solid inclusions is calculated by using Newton's second law. Results and analysis show that the attractive force between alumina particles in H13 steel without magnesium is stronger than that between MgO · Al2O3 particles in H13 steel containing magnesium, and the action radius of attractive force between alumina particles is larger than that between MgO · Al2O3 particles. MgO · Al2O3 particles have a much weaker tendency to collide, agglomerate, grow, and form clusters than alumina particles in H13 steel. Therefore, the collision, agglomeration and growth of inclusions, as well as the formation of clusters in H13 steel can be effectively impeded by the adding of magnesium.
The formation sequence of MgO · Al2O3 cluster is the same as that of alumina cluster, but the MgO · Al2O3 clusters cannot form the outside branch and attract more distant particles. The collision, agglomeration and growth of inclusions, as well as the formation of clusters in H13 steel can be effectively impeded by the adding of magnesium.
The contact angles between three non-metallic inclusion-type oxide substrates, viz. Al2O3, MgO, and MgO·Al2O3, and molten Fe and molten Fe-based stainless steel (Fe–Cr–Ni alloy) were measured using ...the sessile drop method in Ar atmosphere at 1873 K. The contact angles between molten Fe and oxide substrates ranged between 111° and 117°, while that between molten Fe–Cr–Ni alloy and substrates ranged between 103° and 105°. The angles between the alloy and each of the substrates were smaller than the corresponding values for Fe, which was attributed to the superior wettability of molten Fe–Cr–Ni alloy on the substrates. The wettability of the molten materials is related to the interfacial tension between the molten metals and each substrate. Thus, the interfacial tension between the molten metals and the non-metallic substrates was quantitatively evaluated using Young’s equation and the measured contact angles; the interfacial tension for molten Fe ranged from 1.862 to 2.781 N·m−1, while that for molten Fe–Cr–Ni alloy ranged from 1.513 to 2.286 N·m−1. Owing to the higher reactivity between molten Fe–Cr–Ni alloy and the substrates, the interfacial tension and energy between them were lower than those between molten Fe and the substrates.
The behaviors of non‐metallic inclusions in a new tundish and SEN design enabling a swirling flow are investigated by using a Lagrangian particle tracking scheme. The results show that 99% of both ...Al2O3 and Ce2O3 inclusions are removed from both the top surface and the other tundish walls with a “trap” boundary condition, while only around 60% are removed from the top surface of tundish for a “reflect” boundary condition at the other tundish walls. Large size non‐metallic inclusions of different densities show a large difference under a “reflect” boundary condition at tundish walls, due to a high buoyancy of light inclusions. In the swirling flow SEN, a much smaller number of large Al2O3 inclusions touches the wall compared to Ce2O3 inclusions. This is due to that they have larger deviations from the steel flow path compared to heavy Ce2O3 inclusions, due to the centripetal force. For small size inclusions, the centripetal separation is not effective neither for the light Al2O3 inclusions nor for the heavy Ce2O3 inclusions in the current swirling flow SEN with a swirl number of 0.4. Light Al2O3 inclusions larger than 40 µm can be influenced by the current centripetal force.
The behaviors of non‐metallic inclusions in a new tundish design enabling a swirling flow SEN are investigated using a Lagrangian tracking scheme. Large non‐metallic inclusions of different densities show a large difference under a “reflect” boundary condition at tundish walls. In the swirling flow SEN, a much smaller number of large Al2O3 inclusions touches the wall compared to Ce2O3 inclusions.
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•First time to investigate inclusion characteristics in Co-based entropic alloys.•Quantitatively discuss size evolution of different inclusions in the proposed alloys.•Experimental ...findings of inclusion agglomeration potency is predicted by the theory.
Co-based duplex entropic alloy is designed very recently to replace pure Co as a major component of the binder phase for cemented carbide cutting tools. This work aims to provide a fundamental study of oxide inclusion characteristics in the duplex fcc + hcp Co-based entropic alloys. It is found that the Co85−xCrxFe7.5Ni7.5 (x = 15, 30 at.%) alloys hold the highest liquidus (Tliq) and solidus (Tsol) temperatures, compare with the Co85−xCrxMn7.5Ni7.5 (x = 15, 30 at.%) and Co77.5−xCrxFe7.5Mn7.5Ni7.5 (x = 15, 30 at.%) alloys. For each grade, the increasing Cr content leads to a decrease of Tsol and Tliq temperatures. It is also noted that there is an approximate 100 °C of undercooling exists in each grade during the solidification. The stable oxide inclusion in the Co85−xCrxMn7.5Ni7.5 and Co77.5−xCrxFe7.5Mn7.5Ni7.5 alloys is the MnCr2O4 type, while Cr2O3 is the main stable inclusion in the Co85−xCrxFe7.5Ni7.5 alloy. Furthermore, the size range of the MnCr2O4 particles is larger than that of Cr2O3. The theoretical calculation shows that MnCr2O4 has a higher coagulation coefficient than Cr2O3 does. This is due to the influence of the thermo-physical parameters, i.e. the interfacial energy between the oxide and the alloy and the viscosity of liquid alloy. The theoretical calculation fits well with the experimental findings.
The composition, morphology, number, area, size and average distance of inclusions in Fe-23Mn-xAl-0.7C steels were evaluated through an inclusion automatic analysis system (INCA Feature). According ...to their composition and morphology, six types of inclusions are classified in the present steels: MnS(Se), AlN, Al
2
O
3
, AlN-MnS(Se), Al
2
O
3
-MnS(Se), and other inclusions (i.e. Al
2
O
3
-AlN and MgO-Al
2
O
3
). Thermodynamic calculation results show that AlN inclusions are formed in molten steel with Al contents of 3.28 and 6.76 wt-%. Irregularly shaped MnS(Se) inclusions precipitate during the solidification processe. AlN and Al
2
O
3
generally serve as sites for the heterogeneous nucleation of MnS(Se). Sometimes, AlN particles can precipitate on the surfaces of Al
2
O
3
and MnS(Se) inclusions in the solidification process. As the Al content increases to 6.76 wt-%, a large number of agglomerated AlN and AlN-MnS(Se) inclusions are observed. Agglomerated AlN inclusions normally form in the smelting process due to the combined effects of the cavity bridge force and viscous resistance.
Calcium aluminate (CaO–Al2O3) phases play a critical role in the study of non-metallic inclusions in aluminium killed, and calcium treated steels. In this study, the Raman spectroscopy technique, a ...versatile and non-destructive approach, was used to characterise binary calcium aluminate phases qualitatively and quantitatively. Calcium aluminate samples with varying CaO/Al2O3 ratios were synthesised to produce a binary phase samples mixture of C12A7–C3A and C12A7–CA. Quantitative estimation was based on plotting a linear regression calibration model between the ratio of Raman band intensities and the phase fraction in the samples. With the linear regression, the phase fraction of C12A7–C3A and C12A7–CA was estimated with average absolute errors of 2.97 and 2.55 percentage points. This work demonstrates the potential suitability of using Raman spectroscopy technique for evaluating whether calcium aluminate phases in oxide inclusions fall within the liquidus region at steelmaking temperatures.
Based on the tensile test in two-phase region, the damage evolution mechanism around AlN non-metallic inclusions in Fe-8.5Mn–3Al-0.2C lightweight medium-Mn steel during warm forming was elucidated. ...The findings indicate that voids primarily originate from the bonding interfaces between AlN non-metallic inclusions and ferrite. According to the numerical simulation results, strain eventually concentrates at the bonding interface where the AlN inclusion is connected to the high-strain ferrite in the direction parallel to the load, which is in good agreement with the experimental results. TEM analysis reveals the semi-coherent interface between AlN and austenite as well as the incoherent interface between AlN and ferrite. The incoherent interface between AlN and ferrite exhibits higher interfacial energy and worse mechanical stability, accelerating the separation of the bonding interface between AlN and ferrite.
The contact angles between three non-metallic inclusion-type oxide substrates, viz. Al2O3, MgO, and MgO·Al2O3, and molten Fe and molten Fe-based stainless steel (Fe–Cr–Ni alloy) were measured using ...the sessile drop method in Ar atmosphere at 1873 K. The contact angles between molten Fe and oxide substrates ranged between 111° and 117°, while that between molten Fe–Cr–Ni alloy and substrates ranged between 103° and 105°. The angles between the alloy and each of the substrates were smaller than the corresponding values for Fe, which was attributed to the superior wettability of molten Fe–Cr–Ni alloy on the substrates. The wettability of the molten materials is related to the interfacial tension between the molten metals and each substrate. Thus, the interfacial tension between the molten metals and the non-metallic substrates was quantitatively evaluated using Young's equation and the measured contact angles; the interfacial tension for molten Fe ranged from 1.862 to 2.781 N·m-1, while that for molten Fe–Cr–Ni alloy ranged from 1.513 to 2.286 N·m-1. Owing to the higher reactivity between molten Fe–Cr–Ni alloy and the substrates, the interfacial tension and energy between them were lower than those between molten Fe and the substrates.
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