| 1. |
- Gauthier, Y., et al.
(författare)
-
Reconstruction of the Pt50Ni50(100) surface : a LEED and STM study
- 1995
-
Ingår i: Surface Science. - 0039-6028. ; 327:1-2, s. 100-120
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of the Pt50Ni50(100) surface was investigated by low energy electron diffraction (LEED) and scanning tunnelling spectroscopy (STM). Superstructures corresponding to 12 × 1 and 19 × 1 reconstructions were observed in the LEED pattern, and these reconstructions were identified with atomic resolution by STM. The reconstructed surface layer has a quasi-hexagonal atomic mesh with almost (111) atomic density and is divided into terraces and domains the size of which can be more than a thousand ångströms. The domains are corrugated with protrusions made up by 5 × 1 subunits of the quasi-hexagonal mesh and with valleys containing depressed atoms or 2 × 1 subunits. The 12 × 1 and 19 × 1 periodicities are determined by the sequence of valleys; depending on the thermal treatment, one or the other dominates but both generally coexist on the terrace. Owing to the complexity of the structure, LEED calculations were performed for a simplified model with surface atoms situated in a planar net and uniform quasi-hexagonal meshes. We find that in both reconstructions the two surface layers are significantly enriched with platinum. The top layer enrichment is consistent with previous Auger measurements. © 1995.
|
|
| 2. |
- Jarfors, A. E. W.
(författare)
-
Influence of carbon on the phases in the copper-titanium system and their precipitation
- 1999
-
Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 34:18, s. 4533-4544
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of carbon on the phases occurring in the copper-titanium system has been experimentally investigated. Samples were fabricated from elemental copper and titanium. Carbon was added in the form of graphite or as titanium carbide. The samples were encapsulated, heat-treated at 1173 or 1373 K for 24 h and subsequently quenched in brine. The phases present at the treatment temperature were identified, as well as the phases occurring during solidification. The microstructure indicates the presence of a miscibility gap. The composition of the phases were determined using EDS-analysis. The composition of the copper phase was found to show a great variation caused by the precipitation sequence during quenching of the melts. The complex precipitation also caused both TiCu4 and the meta-stable TiCu3 to form. The composition of TiCu was found to show a wider compositional interval than earlier found. The variation of its composition with the nominal composition suggests that TiCu can dissolve carbon. The pure Ti phases also showed larger solubility of copper than earlier found. An outline of the precipitation sequence is made.
|
|
| 3. |
- Ruban, AV, et al.
(författare)
-
Ground-state properties of ordered, partially ordered, and random Cu-Au and Ni-Pt alloys
- 1995
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 51:19, s. 12958-12968
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the ground-state properties of ordered, partially ordered, and random Cu-Au and Ni-Pt alloys at the stoichiometric 1/4, 1/2, and 3/4 compositions in the framework of the multisublattice single-site (SS) coherent potential approximation (CPA). Charge-transfer effects in the random and the partially ordered alloys are included in the screened impurity model. The prefactor in the Madelung energy is determined by the requirement that the total energy obtained in direct SS CPA calculations should equal the total energy given by the Connolly-Williams expansion based on Green’s function calculations for the ordered alloys that do not rely on the single-site approximation. We find that the prefactor to a large degree is independent of a lattice constant, concentration, and a long-range-order parameter and may be considered constant for a given alloy system. The calculated heats of formation for the ordered alloys are in good agreement with experimental data. For all the alloys the calculated ordering energy and the equilibrium lattices parameters are found to be almost exact quadratic functions of the long-range-order parameter.
|
|
| 4. |
- Fjellstedt, J., et al.
(författare)
-
Experimental analysis of the intermediary phases AlB2, AlB12 and TiB2 in the Al-B and Al-Ti-B systems
- 1999
-
Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 283:1-2, s. 192-197
-
Tidskriftsartikel (refereegranskat)abstract
- The phases AlB2, AlB12 and TiB2 were studied in Al-rich Al-B and Al-Ti-B alloys produced by several different sample fabrication methods. The samples were examined using light optical microscopy (LOM), energy dispersive X-ray spectroscopic analysis (EDS) and X-ray diffraction analysis (XRD). The results indicate that only a limited solubility of Al in TiB2 and Ti in AlB2 exists, hence a continuous compound (Al,Ti)B2 is not stable. © 1999 Elsevier Science S.A. All rights reserved.
|
|
| 5. |
|
|
| 6. |
- Jemt, Torsten, 1950, et al.
(författare)
-
Laser-welded titanium frameworks supported by implants in the edentulous maxilla: a 2-year prospective multicenter study.
- 1998
-
Ingår i: The International journal of prosthodontics. - 0893-2174. ; 11:6, s. 551-7
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was to evaluate the clinical and radiographic performance of patients who received implants and fixed prostheses with laser-welded titanium frameworks. MATERIALS AND METHODS: Fifty-eight consecutive patients were treated with 349 osseointegrated implants ad modum Brånemark in the edentulous maxilla at 6 implant centers. The patients were randomly arranged into 2 groups at the time of final impression. Twenty-eight patients received laser-welded titanium frameworks and 30 patients received conventional cast frameworks. Clinical and radiographic data were collected for 2 years in function. RESULTS: The 2 groups of patients showed similar results. The 2-year overall cumulative implant survival rate from the time of implant placement and prosthesis insertion was 93.7% and 96.2%, respectively. The corresponding cumulative survival rate for prostheses was 96.6%. Two patients, 1 from each group, failed completely and resumed using conventional complete dentures. The only obvious factor that could possibly be related to the 2 complete failures was a smoking habit. However, it was not possible to significantly correlate implant failures to smoking habits in this study. No fractures were observed in the frameworks or implant components, and both groups experienced the same frequency of resin veneering material fractures. The overall average marginal bone loss was 0.4 mm (SD 0.8 mm). CONCLUSION: Patients treated with implant-supported prostheses fabricated with laser-welded titanium frameworks in the edentulous maxilla presented comparable results to patients with conventional cast frameworks after 2 years in function.
|
|
| 7. |
|
|
| 8. |
- Bäckman, Jonas, et al.
(författare)
-
Potential for improved mechanical properties in cast aluminium alloys
- 1999
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work is to investigate the potential to improve the mechanical properties of some aluminium alloys, in order to obtain castings with optimum properties. Experiments have been made with pure aluminium, aluminium alloyed with 1% Si and 0,9% Mg and four aluminium cast alloys with 7-12% Si and various amounts of iron, magnesium, copper and manganese. To achieve the best possible solidification, gradient solidification technology of tensile specimen has been used, in order to explore the limits of the mechanical properties in relation to the microstructure. The experiments show that it is not possible to obtain good fracture toughness in alloys with a high iron content. The results also show that many of the aluminium alloys frequently used today are not processed in a way that allows optimal mechanical properties to be achieved. The alloys with a maximum of 0,4% Fe can give 10-23% fracture elongation, depending on other alloying elements such as Si, Mg and Cu. For these alloys it is worthwhile to improve the melt treatment and the casting process to obtain properties close to, or even better than can be achieved in other manufacturing processes. The experiments have given results for both columnar and equiaxed primary solidification structures.
|
|
| 9. |
- Das, O. K., et al.
(författare)
-
Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process
- 1998
-
Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. ; 29:8, s. 2173-2188
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with the aluminizing of a directionally cast Ni-base superalloy, namely CM-247, by a single-step process using a high-activity pack. It is observed that significant incorporation of Al into the substrate surface during aluminizing continues over a period of about 1 hour and is not restricted merely to the first few minutes, as reported in the literature. Based on the microstructural details of the coatings formed at various stages of aluminizing, it is concluded that the coating growth in the above process takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion. In the final stages, the outward diffusion of Ni dominates the coating formation process. The above mechanism of coating formation is different from the one that prevails in the conventional two-step high-activity coating process in that the reaction front for the formation of NiAl remains spatially stationary despite the outward diffusion of nickel during the intermediate stage. It is also shown in the present study that the content of the Al source in the pack affects the coating structure significantly. It is further demonstrated that the microstructure of the aluminide coatings depends not only on the amount of Al incorporated in the sample during aluminizing but also on the time over which the uptake of this Al takes place.
|
|
| 10. |
- Jarfors, A. E. W.
(författare)
-
On the design of a rotary spray former : Experimental and theoretical background
- 1997
-
Ingår i: Journal of Materials Processing Technology. - 0924-0136 .- 1873-4774. ; 71:3, s. 440-455
-
Tidskriftsartikel (refereegranskat)abstract
- The phenomenological theory for jet stability and spray formation in centrifugal spraying is reviewed and investigated experimentally. The appropriate set of equations is then adapted to the phenomena found in the present study. The flow on the disk is treated both theoretically, as well as experimentally, leading to the possible design of a spray former. The droplet formation mechanisms are studied implicitly in the experiments, three different modes being found. A bi-modal spray is formed from the disk edge by two modes of disintegration, whilst the third mode is caused by instability at jet impact on the disk and causes a tri-modal spray. The boundary conditions for the release and flight of the droplets are treated theoretically and correlated experimentally. Water was used initially as a model material, due to the ease of direct visual observation, the knowledge acquired then being used to interpret experiments where an A17Si0.3Mg alloy is sprayed. The experimentally-obtained parameters are used in a theoretical treatment to predict the flow on the disk, i.e. the spray directions and the flight of the droplets. The general conclusion is that it is feasible to design a rotary spray former with a directed flow, the key issue being to control the jet width and the actual droplet formation at the disk edge. ©1997 Elsevier Science S.A.
|
|
