Alexandru Ghiban

Cobalt Based Alloys for Dental Applications

The present paper put in evidence the mechanical behaviour of some commercial dental cobalt alloys, after own classification. The experimental cobalt alloys were classified in according either with molybdenum content, or with Cr+Mo content. A hierarcy of the alloys was finally made. The fractographic surfaces were investigate both by stereomacroscopy and scanning electron microscopy, putting in evidence the main structural features.

Heat Treatments Influence on Corrosion Resistance of some New Dental Cobalt Alloys

A new composition of a dental cobalt alloy was proposed from the system CoCrMoTi, which was compared with a commercial dental alloy, type Wironit. Some heat treatments were applied either for stabilizing the structure, or to simulate welding conditions (such as sensibilization treatments in the range of temperature about 550°C÷-650°C). Corrosion tests were made in two body simulated fluids, respectively infusion NaCl solution and Ringer solution. The results showed that titanium alloying may improve corrosion resistance of the alloy, and also the best state considering corrosion resistance is normalizing at 1100°C with one hour maintaining in air cooling at both alloys, with or without titanium. The worse corrosion resistance is obtained in sensibilized state.

Metallurgical Failure Analysis of Intramedullary Nail Used for Femoral Fracture Stabilization

Currently orthopedics challenge is the use of intramedullary nails to straighten diaphyseal femoral fractures. In this paper it was conducted a case study on an intramedullary nail used for femoral fracture stabilization, in the case of one young patient. The evolution was unfavorable to the fracture site and the implant failed after three month of first surgical intervention. Intramedullary nail dimensions were 300mm length and 10mm in diameter. The following investigations were made in order to establish the failure causes: determination of the chemical composition through spectral analysis, macrostructural analysis using stereomicroscopy, optical microstructural analysis using optical microscopy, fractographic analysis using scanning electron microscopy. The final conclusions showed that the metallic biomaterial used for manufacturing the intramedullary nail was approximately an austenitic stainless steel AISI 316L, but with major microstructural defects. Macro-structural analysis revealed the presence of two zones of cracking, which are very rare at austenitic stainless steels. Also breaking with a fragile character has radial front tear propagation. In longitudinal section, cracks were evidenced due to the extraction operation and also the presence of corrosion products was shown. From fractographic analysis it was determined that intramedullary nail failure was predominantly through the mechanism of brittle fracture that took place at the point of maximum bending of the implant fragile.

Structural Analysis of the Laser Welding Co-Cr-Mo-(Ti) Alloys for Removable Partial Dentures

Optimization of fractured or destroyed removable partial dentures realized from CoCrMo alloys are possible due to modern welding equipments. The aim of study was to offer the processing and welding optimal parameters for some long lasting prosthetic pieces made of a new alloy from the system CoCrMoTi. Laser welding equipments was a Mini Laser XXS (Orotig Italia) and the tested samples were welded in butt joint, without filler material. There are presented in comparison results concerning macro and micro structural analysis made on stereomicroscope and microscope type OLYMPUS. Finally a correlation between different welding parameter values and structural features was made for the new dental cobalt alloy.

Wear Behaviour of New CoCrMoTi Dental Alloys

A new composition of a dental cobalt alloy was proposed from the system CoCrMoTi, which are proposed for dental applications. Three content of titanium were used in commercial matrix of CoCrMo alloy in order to reveal the wear behavior of these alloys. The results showed that titanium alloying may improve wear behaviour by increasing the friction coefficient.

Opportunities and Challenges in Overcoming the Economic Crisis

Abstract This paper presents the main fundamental concepts concerning the methods of economic analysis: necessity of economic analysis, information system, types of economic analysis, methodologies used for the economic analysis of company, study of the factor which explain the results of the economic analysis of company, stage of the practical analysis. However in relation to conditions of economic crisis. In the same context is presented and analyzed the dictum of Nouriel Roubini, who said: “Stop austerity in the crisis!”. So, this paper analyzes “austerity vs crisis”,“insolvency - good or bad?” and “Sustainable Development” too.

Dynamic Mechanical Analysis of Some Ti-Mo Alloys in Correlation with Microstructural Aspects and Surface Properties

The present paper takes into consideration four titanium alloys from the system Ti-Mo, with different molybdenum contents in order to highlight the mechanical and structural behavior of them. The Dynamic Mechanical Analysis was made and this was in correlation with microstructural aspects and surface properties of the experimental alloys. The macrostructural features are the same for all Ti-Mo alloys after bending tests.

Heat Treatments Influence on Corrosion Behaviour of Some Metallic Biomaterials Potentially Used in Metal-Ceramic Prosthesis

The present paper put in evidence the influence of applying different heat treatments on some metallic materials such as cobalt and titanium alloys, usualy used for medical applications. The alloys were cobalt base alloy type CoCrMo (22%Cr, 6%Mo, rest Co), in nontreated state, quenching at 1100°C /1h/aer, quenching at 1100°C /1h/air+ sensiblizing at 550°/4h/ air, 600°/4h/air and/or 650°C/4h/air and titanium base alloys - alloy TiMo0.3Ni0,7 (0.23%Mo, 0.72%Ni, Ti rest), alloy TiAl5Fe2V2Mo1,5(1.52%Mo, 5.15%Al, 2.56%Fe, 2.35%V, Ti rest), each of them in non treated state, annealing at 1050°C/1h/air and annealing at 850°C/1h/air. Corrosion tests were made at potentiostat-galvanostat AUTOLAB, in Ringer solution (for both alloys) and NaCl infusion solution (only for cobalt base alloy) by drawing the polarization curves. Our conclusion is that by applying correct and proper heat treatments to both at cobalt alloys and in titanium alloys there is an improving of the corrosion resistance.