| 1. |
- Bejjani, Roland, et al.
(författare)
-
Multi-scale study of initial tool wear on textured alumina coating, and the effect of inclusions in low-alloyed steel
- 2016
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 100, s. 204-212
-
Tidskriftsartikel (refereegranskat)abstract
- When turning low-alloyed steel with hard inclusions, scores and grooves have been observed in the wear of the alumina coating in CVD coated cutting tools. This study focuses on detailed understanding of flank wear in the textured alumina coating and the relation to the workpiece's inclusions. For chip formation studies, a quick stop device has been used. A topography analysis for the worn coating was performed in the micro scale. Studies at lower scales were performed using TEM. This allowed the study of wear on the coating crystalline structure and the embedment of workpiece material on its surface. Based on the results, the mechanism behind the initial wear was analyzed and an abrasion wear model is proposed.
|
|
| 2. |
- Collin, Marianne
(författare)
-
Analysis of thermal shock in brittle materials
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns thermal shock damage of ceramicmaterials. More specifically the work is focused on theoreticaland practical aspects of a new technique for determining thethermal shock resistance of brittle materials. The principalidea of this Indentation-Quench Test is to study the growth ofVickers indentation cracks after exposing them to a transientthermal load (thermal shock) obtained by rapid cooling(quenching).It is established that relatively light quenches causestable crack growth whereas more severe quenches result inunstable growth. A model is derived that clarifies that theregime with stable growth is due to the combination of thermalstress from the quenching and residual stress from the indent.Based on the model an equation for the transition to unstablecrack growth is derived. This equation can be used forprediction of thermal shock resistance and it is shown thatfracture toughness is of great importance. Another valuable useof the equation is for estimating unknown parameters, such asthe surface heat transfer coefficient. It is also demonstratedhow crack growth data obtained in the stable regime can be usedfor making a rough estimate of the thermal stress pattern oncomponents.Thermal conductivity is evaluated for alumina siliconcarbide whisker composites and a new procedure for evaluatingthe thermal conductivity of the whiskers is suggested.A significant part of the thesis focuses on changes in crackshape and fracture mode when indentation cracks are subjectedto thermal stress. Crack shapes in cross-section show that thecrack growth rate is higher in the surface direction comparedto the downward direction. To simplify estimation of the crackdepth, an algorithm is suggested which reveals the crack depthfrom surface crack length data. The fracture mode in aluminavaries from intergranular to transgranular and it is suggestedthat the stress intensity at the crack tip is one importantparameter that determines the fracture path. When the stressintensity is close to the fracture toughness of the materialthe fracture path is predominantly intergranular, while thetransgranular contribution increases for higher levels ofstress intensity.All of the major aspects of the Indentation-Quench Test havebeen thoroughly explored. Due to the use of artificialprecracks and the presence of residual stress the test has manyadvantages compared to other methods. Practical parameters forthe test are well established and firmly linked to models whichidentify the influence of various physical parameters. Thisleads to a reliable test that can be extremely suitable toevaluate thermal shock resistance of materials and can be usedto map thermal shock effects in components.Keywords:Thermal shock, thermal stress, stressintensity, Vickers indentation, alumina, silicon carbidewhisker reinforced alumina, silicon nitride, high speed steel,water quench, thermal conductivity, fracture toughness, crackshape, intergranular, transgranular,
|
|
| 3. |
|
|
| 4. |
- Gerth, Julia, et al.
(författare)
-
Adhesion phenomena in the secondary shear zone in turning of austenitic stainless steel and carbon steel
- 2014
-
Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 214:8, s. 1467-1481
-
Tidskriftsartikel (refereegranskat)abstract
- This paper aims to increase the understanding of the adhesion between chip and tool rake face by studying the initial material transfer to the tool during orthogonal machining at 150 m/min. Two types of work material were tested, an austenitic stainless steel, 316L, and a carbon steel, UHB 11. The tools used were cemented carbide inserts coated with hard ceramic coatings. Two different CVD coatings, TiN and Al2O3, produced with two different surface roughnesses, polished and rough, were tested. The influences of both tool surface topography and chemistry on the adhesion phenomena in the secondary shear zone were thus evaluated. Extensive surface analyses of the inserts after cutting were made using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). As expected, cutting in the stainless steel resulted in a higher amount of adhered material, compared to cutting in the carbon steel. Remnants of built-up layers were found on the surfaces of the 316L chips but not on the UHB 11 chips. Moreover, it was shown that for both materials the tool roughness had a profound effect, with the rougher surfaces comprising much higher amounts of adhered material than the polished ones. Non-metallic inclusions from both types of workpiece steels accumulate in the high temperature area on the inserts. The general tendency was that higher amounts of transferred material were found on the TiN coating than on the Al2O3 coating after cutting.
|
|
| 5. |
|
|
| 6. |
- Trinh, David, 1981-, et al.
(författare)
-
Coated Insert
- 2006
-
Patent (populärvet., debatt m.m.)
|
|
| 7. |
- Trinh, David Huy, 1981-
(författare)
-
Nanocrystalline Alumina-Zirconia Thin Films Grown by Magnetron Sputtering
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alumina-zirconia thin films have been deposited using dual magnetron sputtering. Film growth was performed at relatively low-to-medium temperatures, ranging from ~300°C to 810 °C. Different substrates were applied, including silicon (100), and industrially relevant materials, such as WC-Co hardmetal. Both radio-frequency sputtering and direct-current magnetron sputtering were utilised to achieve a range of film compositions. The influence of sputtering target was investigated; both ceramics and metals were used as sputtering sources. Microstructural characterisation was performed with a range of electron microscopy and x-ray diffraction techniques which show that the pure zirconia was deposited in the monoclinic phase. Reduced mobility of depositing species, as in the case of direct-current sputtering, yielded preferred crystallographic orientation in the {100} directions. The initial nucleation layer consisted of the metastable tetragonal zirconia phase. This phase could be grown over film thicknesses ~1 μm through the addition of ~3 at.% Al under similar low mobility conditions. For cases of higher mobility, as obtained through radio-frequency sputtering, the metastable cubic zirconia phase formed in the film bulk for alumina-zirconia nanocomposites. A combination of two mechanisms is suggested for the stabilisation of metastable zirconia phases: oxygen-deficiency and aluminium segregations with resultant restraint on the zirconia lattice. The sputter deposition process was investigated through energy resolved mass spectrometry in the case of radio-frequency sputtering; the sputter deposition flux contained a mixture of metallic ions, metaloxygen clusters, and oxygen ions. The presence of metal-oxygen clusters was found to be important in oxygen-stoichiometry and thus the phase selection of the resultant film. The energy distributions were similar when comparing sputtering from ceramic and metallic targets. A mass-balance model has also been developed for the transport phenomena and reactions of particles in reactive sputtering of two targets in a two-gas scenario for the alumina-zirconia system. Addition of nitrogen to the working gas was found to eliminate the hysteresis in the target poisoning for oxygen reactive sputtering. The higher reactivity of oxygen contributed to a higher oxygen content in resultant films compared to the oxygen content in the oxy-nitride working gas. The model was thus shown to be successful for tuning depositions in the alumina-zirconia oxy-nitride system.
|
|
| 8. |
- Wiklund, Urban, et al.
(författare)
-
Experimental and theoretical studies on stainless steel transfer onto a TiN-coated cutting tool
- 2011
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 59:1, s. 68-74
-
Tidskriftsartikel (refereegranskat)abstract
- Stainless steel is a good example of a metal that is not easily machined. To explain such behavior an understanding of the fundamental adhesion between the workpiece and the tool is invaluable. It is a well-known fact that build-up layers form in the interface, but little attention has been given to the very first layer that adheres to the tool surface. Although this layer rapidly becomes covered by successive material transfer, this layer and its ability to stick to the tool surface control the successive material transfer and influence the cutting properties. In this work, a quick stop test is employed to interrupt the cutting of a 316L stainless steel using a TiN-coated cemented carbide cutting insert. Different analytical techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy, as well as theoretical atomistic modeling, were used to study the early adhesion.
|
|
