Nicolae Ghiban

Cavitation erosion resistance of two steels with the same percentage of Chromium and Nickel but different Carbon content

Hydraulic machinery repair works necessitate new materials with improved cavitation erosion resistance and simultaneously good welding properties. The present paper is concerned with the behavior at cavitation of two steels with close contents of chromium (approximately 12%) and nickel (approximate 6%) but with different carbon content (for the first 0.1% C and the second 0.036% C). The reduced carbon content is necessary for an easy welding repair work. As a result of the different chemical content, as is shown by the Schaffler diagram, the steel containing 0.1% C has a structure formed by 60% austenite and 40% martensite while those with 0.036% C has completely martensitic structure. The laboratory tests were done in two vibratory devices one with piezoelectric crystals, respecting the ASME G32-2010 Standard and the other a magnetostrictive vibratory device with nickel tube. The evaluation of the cavitation resistance was obtained with the help of cavitation erosion characteristic curves MDE (t) and MDER (t). For analyzing the steel degradation, the eroded areas were also subjected to microscopic investigations. The results show that the steel with 0.1% C has better cavitation erosion behavior than that of the steel with 0.036% C.

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.

Structural Analysis of Steels by Cavitation Erosion

Cavitation is an important factor in many areas of science and engineering, including acoustics, chemistry and hydraulics. In this paper the authors analyze the structural analysis of cavitation damages in two steel. The cavitation erosion tests were carried out in a magnetostrictive facility, in Timisoara Hydraulic Machinery Laboratory, in according with ASTM G32-85, using as cavitant liquid drink water at 20 10C. After quantitative and qualitative investigations structural features were put in evidence on experimental steel

Corrosion Behavior in Ringer Solution of Ti-Mo Alloys Used for Orthopedic Biomedical Applications

The present paper take in consideration two titanium alloys, with different molybdenum contents in order to show the corrosion behavior in Ringer body simulated fluid. The samples were corrosion tested in three states, respectively non-treated state, annealed at 850°C/1 h and annealed at 1050°C/1 h.

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.

Stainless Steel Brackets: In Vitro Corrosion Behaviour and Mechanical Debonding Test

The purpose of the study was to investigate the microchemical, morphological, mechanical and anticorrosive characteristics of the metallic brackets by using energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), electrochemical and shear tests. The changes resulted from the exposure of the metallic brackets to artificial saliva and debonding forces were investigated under orthodontic appliances. The results have shown that metallic brackets studied in this paper present a good design, great electrochemical behaviour in artificial saliva for different pH values (2, 5 and 7), and also great mechanical properties. In the case of shear stress the obtained values were higher than the clinical accepted value. The metallic brackets studied in this paper present a good behaviour in artificial saliva, and good mechanical characteristics. The ARI investigation revealed that most of the adhesive was left on the bracket.

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.

Surface Characterization of Some CoCrMo Dental Alloys

The removable partial dentures are made of alloys from CoCrMo system. This survey work paper considers various commercial CoCrMo alloys that were investigated in terms of surface behavior through different processing methods, respectively: sand blasting, grinding, milling, smoothing and polishing, procedures applied in accordance with the necessary standards for prostheses processing in dental labors, regarding their final trimming. Alloys behavior highlighting was performed by macrostructural investigations carried out at stereomicroscope. In the end an alloy hierarchy was achieved according to the method in which the main macrostructural aspects were highlighted.

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.