Papers by Keyword: Ni-Cr Alloys

Abstract: The characteristics of Ni-Cr porous alloys containing 0.5 wt%Cr up to 12 wt%Cr were determined. The alloys were prepared from a mix of Ni-particles with filamentary shape and Cr-particles with irregular shape which then mixed with 0.5 wt% paraffin wax as a binder. The samples were formed by compaction and then sintered at 1200 °C for 1 h. The microstructure of samples was found to consist of a Ni-Cr solid solution matrix with X-ray energy dispersive analysis of Cr% less than 0.33 wt%. The matrix microstructure which composed of equiaxed grains (20-60 μm) surrounded high Cr content islands which also contained γ phase (Ni_2.88 Cr_1.22). The apparent density of the alloys was found to decrease with Cr content from 8.32 g/cm³ for samples containing 0.5 wt%Cr to 7.26 g/cm³ for samples containing 12 wt%Cr. Therefore, the estimated porosity was found to increase from 6.4% to 16.6% with increasing Cr content from 0.5 wt% to 12 wt%. The microhardness of the samples varied from 153.6 to 284.2 VHN for the equiaxed grains and from 119.6 to 240.6 VHN for the island areas.

Abstract: Microstructure and mechanical properties of Ni-Cr alloys with various contents of Phosphorus (P) have been investigated. It is found that the increase of phosphorus refined dendritic structures in as-cast alloys and decreased micro-segregation of Chromium (Cr) element. α-Cr which precipitated during hot-rolling process was obviously inhibited by phosphorus because of its prior occupancy on grain boundaries and decreasing precipitation driving force of α-Cr. Tensile and impact properties were examined on samples under different heat treatments. Though the yield strength of as-rolled alloys was increased by precipitation of α-Cr, the elongation and impact energies were reduced. It is worthy to note that impact energies of samples solutioned at 950°C increased with the increasing phosphorus. The results indicated that dislocations are markedly effected by phosphorus which is probably the reason for improving impact energies.

Abstract: The purpose of this study was to evaluate the chemical and metallurgical aspects, mechanical properties and hardness of the Co-Cr alloy powders manufactured by sintering process DMLS and compared with Ni-Cr alloys used for personalized dental crowns.In dentistry are develop new methods to obtain personalized dental crowns quickly, the cost is not expensive and is identically with the dental scan realized by dentist. DMLS sintering manufacturing is a new method who permits to realize in the same day the dental crowns with the first control.Powders of Co-Cr alloys presents good sintered properties, good mechanical properties and the sintered probes don’t present tensile strength in the material after DMLS process.

Abstract: Ni-30Cr and Fe-47Cr alloys have been oxidized at 900 and 1000°C in air. The influence of the oxidation and cooling conditions on the magnitude of residual stresses present in the oxide scale as well as the existing relaxation modes are studied. A rigorous determination of the residual stresses at both macroscopic scale in the oxide film adherent to the substrate and local scale over the damaged areas allows a comparison with models describing thin film delamination. A multi-scale approach is then proposed : Residual stress levels are determined thanks to conventional x-ray diffraction and Raman spectroscopy while mappings are done over different types of buckling using Raman micro-spectroscopy and synchrotron micro-diffraction. Additional morphological information combined to associated stress levels is injected in the mechanical laws for buckling in order to extract the interfacial toughness.

Abstract: The papers focus is to establish the criterion for the transition from internal to external oxidation. This criterion is a simple value of oxide volume fraction where the coalescence of the nodular oxide in the continuous layer is considered as inevitable. It is obtained by the Wagners analytical solution and by the data of Giggins et al. [1], which give the experimental transition from internal to external oxidation between 10 and 11 weight percent of chromium in the initial alloy. This paper also enables to obtain the oxygen diffusion coefficient in pure nickel thanks to the experimental results of oxidation at 950 °C during 10 hours on Ni-0.2Cr, Ni-1Cr and Ni-5Cr model alloys.

Abstract: The aim of the work was evaluation of electrochemical properties of Co-based alloys (Remanium GM 800+ and Biosil F) and Ni-based alloys (Heraenium NA and Remanium G-Soft) commonly used on frameworks for porcelain faced cast partial dentures. First stage of the work was evaluation of surface roughness by means of direct linear contact measurement (SURTRONIC 3+ profiler, Taylor/Hobson) of samples after casting and surface treatment. Electrochemical properties of surface were assessed by means of potentiodynamic and impedance methods. In potentiodynamic tests, in order to evaluate pitting corrosion resistance of the analyzed alloys, anodic polarization curves were recorded. The VoltaLab® PGP 201 system was applied in corrosion tests. Moreover, in order to evaluate structure and properties of the surface layer the electrochemical impedance spectroscopy (EIS) was applied. Selection of this method enabled to determine the impedance of the material – surface layer – solution interface with the use of approximation of impedance data by means of equivalent electric circuit model. The EIS tests were carried out with the use of the AutoLab PGSTAT 302N system equipped with the FRA2 Faraday impedance module. Electrochemical tests were carried out in artificial saliva at the temperature of 37°C and pH = 7,0±0,1.