| 1. |
|
|
| 2. |
- Hardell, Jens, et al.
(author)
-
Abrasive wear behaviour of hardened high strength boron steel
- 2014
-
In: Tribology - Materials, Surfaces & Interfaces. - 1751-5831 .- 1751-584X. ; 8:2, s. 90-97
-
Journal article (peer-reviewed)abstract
- Abrasive wear in industrial applications such as mining, materials handling and agricultural machinery constitutes a large part of the total wear. Hardened high strength boron steels are known for their good wear resistance and mechanical properties, but available results in the open literature are scarce. This work aims at investigating how different quenching techniques affect the two-body abrasive wear resistance of hardened high strength boron steels. Furthermore, the wear as a function of depth in thicker hardened high strength boron steel plates has also been studied. The material characterisation has been carried out using microhardness, SEM/energy dispersive spectroscopy and three-dimensional optical surface profilometry. The results have shown that water quenched and tool quenched high strength boron steel had similar wear resistance. The main wear mechanisms appear to be microcutting combined with microfatigue. Workhardening during the abrasion process has been found to affect the abrasive wear.
|
|
| 3. |
|
|
| 4. |
- Yang, Qigui, et al.
(author)
-
Cu precipitation in electron-irradiated iron alloys for spent-fuel canisters
- 2022
-
In: Journal of Nuclear Materials. - : Elsevier B.V.. - 0022-3115 .- 1873-4820. ; 572
-
Journal article (peer-reviewed)abstract
- In this work, the Cu clustering in Fe under irradiation is investigated using experiments, cluster dynamics and atomistic kinetic Monte Carlo (AKMC) simulations. In experiments, cast iron and model FeCu alloy samples were irradiated with 2 MeV electrons for 143 h at 140 °C. The post-irradiation microstructure was characterized using atom probe tomography. Cluster dynamics and AKMC methods were used to simulate the Cu clustering under the same irradiation conditions. Both simulation methods show satisfactory agreement with experiments, lending strength to the validity of the models. Finally, the Cu clustering in spent-fuel repository conditions for 105 years at 100 °C was simulated using both methods. The results indicate that potential hardening by Cu clustering is insignificant over 105 years.
|
|
| 5. |
- Yousfi, Mohamed Amine, 1986, et al.
(author)
-
Chromium segregation at phase boundaries in Cr-doped WC-Co cemented carbides
- 2018
-
In: Materials Characterization. - : Elsevier BV. - 1044-5803. ; 144, s. 48-56
-
Journal article (peer-reviewed)abstract
- Atom probe tomography has shown (Cr,W)C to be present as a thin WC grain surface layer in an as-sintered Cr-doped WC-Co cemented carbide microstructure slowly cooled from the sintering temperature. The Co-rich binder phase contained a segregation of Cr in front of this surface layer. The mixed carbide layer was not observed when the as-sintered material had been heat treated at 1000 °C for 3000 s and then quickly cooled. A reduced amount of segregated Cr was, however, still present in the binder phase in front of the WC grain surface. These observations are supported by predictions from thermodynamic modelling; (Cr,W)C becomes stable at temperatures below 940 °C in the absence of other secondary carbides. The equilibrium segregation of Cr in the binder phase was estimated to 0.8 and 0.4 monolayer in the as-sintered and heat treated materials, respectively. The energy of segregation was calculated to 0.22 eV/Cr atom from the atom probe data. This value would result in a Cr segregation of 0.3 monolayer at the sintering temperature 1410 °C, provided that the energy of segregation in the Co-rich liquid phase sintering medium is the same as in the Co-rich binder phase. This Cr segregation may explain the WC grain growth inhibiting effect of Cr additions to WC-Co cemented carbide materials.
|
|
| 6. |
- Yousfi, Mohamed Amine, 1986, et al.
(author)
-
Creep of un-doped and Cr-doped WC-Co at high temperature and high load
- 2023
-
In: International Journal of Refractory Metals and Hard Materials. - 0263-4368 .- 2213-3917. ; 117
-
Journal article (peer-reviewed)abstract
- Un-doped and Cr-doped WC-10 vol% Co cemented carbides with a WC grain size of 1.4 μm have been investigated before and after hot compressive creep tests under an applied load of 900 MPa at 1000 °C and 300 MPa at 1100 °C. The Cr-doped material showed a much higher creep resistance at 1000 °C and a somewhat higher creep resistance at 1100 °C than the un-doped material. Quantitative microscopy showed that WC grain growth occurred in the plane perpendicular to the load axis during creep deformation and that the growth process was slower in the Cr-doped material. In addition, binder phase redistributed and a number of WC grain boundaries were infiltrated with binder phase. This suggests that accommodated WC grain boundary sliding occurred during creep deformation. The formation of intergranular cavities implies that also unaccommodated grain boundary sliding occurred, especially at 1000 °C. It is suggested that WC grain growth perpendicular to the load axis is rate limiting in the creep deformation process, and that Cr segregation to WC/binder phase boundaries hinders grain growth. The weak effect of Cr on creep resistance at 1100 °C at 300 MPa is explained by Cr giving a larger volume fraction of binder phase and therefore a larger number of infiltrated grain boundaries, facilitating grain growth.
|
|
| 7. |
- Yousfi, Mohamed Amine, 1986, et al.
(author)
-
Deformation mechanisms in a WC–Co based cemented carbide during creep
- 2015
-
In: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 81-87
-
Journal article (peer-reviewed)abstract
- The microstructure of a WC–Co based cemented carbide has been investigated before and after plastic deformation at high temperatures. The material was fabricated with a Co binder phase content of 16 vol.% and smaller additions of Cr. Hot compressive creep tests were performed under an applied load of 900 MPa at 1000 and 1100 °C. The test bars were deformed to 10 or 20% strain at 1000 °C, and to 7% strain at 1100 °C. Quantitative microscopy using SEM suggests that WC grain growth took place during the creep tests, and that the growth took place preferentially in the plane perpendicular to the load axis. TEM showed that there was an increased dislocation density in the WC grains after creep deformation. Deformation was also associated with a redistribution of the WC grains resulting in the formation of intergranular binder phase lamellae and cavities. EBSD showed that there was an increased spread in the crystallographic orientation of the binder phase after deformation.
|
|
| 8. |
- Yousfi, Mohamed Amine, 1986
(author)
-
Evolution of WC-Co cemented carbide microstructure during creep testing
- 2014
-
Licentiate thesis (other academic/artistic)abstract
- The aim of this work is to understand the mechanisms behind the plastic deformation of WC-Co based cemented carbides. The microstructures of two materials have been investigated before and after creep deformation using quantitative microscopy, atom probe tomography, and transmission electron microscopy. One material was a pure WC‐Co material with 10 vol % binder phase. The other material had a higher fraction of binder phase, 16 vol %, and contained a small addition of Cr.High temperature compressive creep tests have been performed under a load of 900 MPa at 900, 1000 and 1100 °C and the test bars were deformed to different strains. Grain size measurements by the linear intercept method showed that WC grain growth took place during compressive creep testing of the Cr doped material, and that this growth took place preferentially in the plane perpendicular to the load axis. Transmission electron microscopy showed that the WC grains in the crept materials had a significantly increased dislocation density, with a large number of dislocation lines merging at the grain surfaces. It is suggested that merging matrix dislocations having a screw component may act as nucleation points to grow new layers of WC. The binder phase grains became, on the other hand, smaller during creep deformation, and lost their dendritic morphology. This may be explained by binder phase grain rotation caused by dislocation glide. The crept microstructures had an increase number of binder phase lamellae separating adjacent WC grains. This suggests that a redistribution of the WC grains occured, and that the associated grain boundary sliding was accommodated by the lamella formation. Intergranular cavities were also formed during creep deformation. This cavity formation indicates that also unaccommodated grain boundary sliding took place during creep deformation. Atom probe tomography revealed an increased amount of C in the binder phase after creep deformation at 1000 °C. This could possibly be related to the comparatively rapid cooling from the test temperature.
|
|
| 9. |
- Yousfi, Mohamed Amine, 1986
(author)
-
Microstructure Development of WC-Co Based Cemented Carbides During Creep Testing
- 2016
-
Doctoral thesis (other academic/artistic)abstract
- The aim of this work is to understand the mechanisms behind the plastic deformation of WC‐Co based cemented carbides. The microstructure of two series with different WC grain size was investigated before and after creep deformation using quantitative microscopy, atom probe tomography, and transmission electron microscopy. The first series consisted of two WC-Co based cemented carbides with fine WC grain size used for machining applications, an un-doped WC-Co material with 10 vol % binder phase and a Cr-doped WC-Co material with a higher fraction of binder phase, 16 vol %. The second series consisted of two WC-Co based cemented carbides with coarser WC grain size used for mining applications, an un-doped and a Cr-doped WC-Co based materials. In both materials, the binder phase represented 10 vol% of the total volume. High temperature compressive creep tests were performed under a stress of 900 MPa at 900, 1000 and 1100 °C and 300 MPa at 1100 °C, and the test bars were deformed to different strains. A heat treatment was also performed at 1000 °C in order to see the effect of an applied load on WC grain growth.Preferential WC grain growth perpendicular to the applied load was found to occur during creep deformation at 1000 and 1100 °C. WC grains in the crept materials had a significantly increased dislocation density, with a large number of dislocation lines merging on the grain surfaces. It is suggested that merging matrix dislocations having a screw component may act as nucleation points to grow new layers of W and C. The binder phase grains became, on the other hand, smaller during creep deformation at 1000 °C, and lost their finger-like morphology. This may be explained by binder phase grain rotation caused by dislocation glide. The crept microstructures had an increased number of density of WC/WC grain boundaries infiltrated by the binder phase. This suggests that grain boundary sliding occurred, accommodated by binder phase infiltration. Some WC grain surfaces facing the infiltrated grain boundaries had a step surface of an angle of 90 and 120 °. The atoms at the surface were rearranged to reduce the surface energy. Intergranular cavities were also formed during creep deformation. This cavity formation indicates that also unaccommodated grain boundary sliding took place during creep deformation.APT revealed a variation in the concentration of W and C in the binder phase, and that the solubility of W and C increased with increase of temperature. The rapid cooling from the creep test temperature ensures that the composition of the binder phase in crept materials represents the composition during the test. WC/binder phase boundaries of the as-sintered fine grained Cr-doped material showed an enrichment in Cr at the phase boundary and formation of thin (Cr, W) carbide layer on the surface of WC grains at the phase boundary. This (Cr, W) carbide layer seems to disappear when the material is heat treated at 1000 °C. The thermodynamic calculations found that this cubic layer is stable below 940 °C when no M7C3 carbides are formed.
|
|
