Twinning-induced strain hardening in dual-phase FeCoCrNiAl0.5 at room and cryogenic temperature.

A face-centered-cubic (fcc) oriented FeCoCrNiAl0.5 dual-phase high entropy alloy (HEA) was plastically strained in uniaxial compression at 77K and 293K and the underlying deformation mechanisms were studied. The undeformed microstructure consists of a body-centered-cubic (bcc)/B2 interdendritic network and precipitates embedded in 〈001〉-oriented fcc dendrites. In contrast to other dual-phase HEAs, at both deformation temperatures a steep rise in the stress-strain curves occurs above 23% total axial strain. As a result, the hardening rate associated saturates at the unusual high value of ~6 GPa. Analysis of the strain partitioning between fcc and bcc/B2 by digital image correlation shows that the fcc component carries the larger part of the plastic strain. Further, electron backscatter diffraction and transmission electron microscopy evidence ample fcc deformation twinning both at 77K and 293K, while slip activity only is found in the bcc/B2. These results may guide future advancements in the design of novel alloys with superior toughening characteristics.

Composition optimization of low modulus and high-strength TiNb-based alloys for biomedical applications.

The effect of chemical composition on microstructure and tensile properties of a series of low modulus Ti-Nb-Cu-Ni-Al alloys was studied. These alloys consist of primary micrometer-sized ß-Ti dendrites surrounded by intermetallic phases. The morphology of the intermetallic phases is strongly affected by composition. Due to the composite microstructure, the alloys exhibit a low Young's modulus (77-84GPa) together with a high yield strength of about 1000MPa as well as moderate tensile ductility. The results demonstrate that complete substitution of Al by Ti reduces the Young's modulus by 5%. Increasing Nb content at the expense of Ti causes a significant improvement of tensile ductility.

[Healing process of cartilage attached to a polydioxanone implant]. / Heilungsprozess des Knorpels in Verbindung mit PDS-Folie.

BACKGROUND AND OBJECTIVE: To correct severe septal deformities, it is often necessary to perform an extracorporal septoplasty with temporary removal of the deviated septal cartilage, followed by straightening and reimplantation into the nose as free graft. The utilization of a compound graft, which sutures the cartilage fragments to a resorbable polydioxanon (PDS) foil, facilitates this technique immediately while simultaneously ensuring support of the nasal dorsum. PATIENTS/METHODS: On account of the good clinical experiences (during the past 3 years 71 patients have been treated using this method), we investigated the biological properties of the foil and its degradation products in connection with cartilage in an animal model from a histological point of view. In five rabbits, a 0.15-mm-thick PDS foil was implanted in combination with the cartilage into the outer ear. The follow-up period was between 2 and 25 weeks. RESULTS: The results showed the following: (1) Up to the tenth week, the foil maintains the original structure; (2) The foil will be completely resorbed after 25 weeks; (3) The cartilage underneath the foil is protected from necrosis; (4) The degradation products of the polydioxanon do not interfere with the healing process; (5) Concerning the regeneration of cartilage, the foil acts as a guarding splint; (6) After resorption, almost no scar tissue remains. CONCLUSIONS: Due to the fact that the PDS foil endonasal implant means no additional risk to the patient, we can recommend the compound graft for simplification of extracorporal septoplasty.

[Septum reconstruction with PDS implant]. / Septumrekonstruktion mit PDS-Folie.

To achieve septoplasty without compromising the surgical goal of attaining a straight and solid septum, even in cases of marked deviations or severe post-traumatic deformities, we now use a new technique in which the septal reconstruction includes the placement of a resorbable implant as a "compound graft." For this purpose the entire septal cartilage is removed, and the severely deviated part is divided into straight sections that are reconnected to each other to form a straight and solid plate. As connecting material we use a polydioxanon (PDS) foil. The sections of cartilage are sutured to the foil with PDS suture material. The compound graft thus constructed consists of the septal cartilage and resorbable alloplastic material and is reimplanted into the nose. The PDS and suture material are usually resorbed within 8 months, excluding long-term complications. During the past 2 years this method was used in treating 38 patients. The surgical goal was attained in every case, and no immediate or long-term complications occurred. This method of combining septal cartilage with a resorbable implant leads to a better, significant correction of even severe septal deviations.