RESUMO
The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses Fe73.9Cu1Nb3Si15.5B6.6 and Fe81.2Co4Si0.5B9.5P4Cu0.8 have been investigated and compared. While for Fe73.9Cu1Nb3Si15.5B6.6, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of Fe81.2Co4Si0.5B9.5P4Cu0.8 for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that Fe81.2Co4Si0.5B9.5P4Cu0.8 exhibits HPT-induced crystallization phenomena, while Fe73.9Cu1Nb3Si15.5B6.6 does not crystallize even at the highest HPT-deformation degrees applied. The reasons for these findings are discussed in terms of differences in the deformation energies expended, and the number and composition of the individual crystalline phases formed. The results appear promising for obtaining improved magnetic properties of glassy alloys without additional thermal treatment.
RESUMO
In a previous study (Haas et al. 1995), we reported on preliminary results of 76 Brånemark implants placed in 71 patients with single-tooth gaps. The present study examines the results of the same group over a longer period of time: 55 implants were followed for more than 5 years, 12 for a period between 4 and 5 years and 1 implant for 46 months. One patient died 3 years after implant placement. Five patients lost their implant within 24 months after insertion. The drop-out rate was 2 implants in 2 patients. The recall rate was thus 97%. Of the 5 implant failures, 2 were located in the maxilla and 3 in the mandible. The Kaplan-Meier survival probability was 93% after 120 months. 74% of the sites showed healthy peri-implant soft tissue conditions. At 15 implants (22%) a bone resorption of more than 2 mm was observed on intraoral radiographs. The mean bone resorption was 1.8 mm in the maxilla and 1.3 mm in the mandible and did not increase with time (Pearson correlation coefficient: r = -0.06, P = 0.59). Abutment loosening occurred in 7 implants (10%), however all abutments that were fixed with a defined torque subsequently remained stable. Thus the favourable preliminary results could be maintained over an average 66 months, indicating that if implant loss happens it seems to occur during the first 2 years after insertion.
