Ivan Anzel

The influence of the microstructure of high noble gold-platinum dental alloys on their corrosion and biocompatibility in vitro

The aim of this work was to compare the microstructures of two high noble experimental Au-Pt alloys with similar composition with their corrosion and biocompatibility in vitro. We showed that Au-Pt II alloy, composed of 87.3 wt.% Au, 9.9 wt.% Pt, 1.7 wt.% Zn and 0.5 wt.% Ir + Rh + In, although possessing better mechanical properties than the Au-Pt I alloy (86.9 wt.% Au, 10.4 wt.% Pt, 1.5 wt.% Zn and 0.5 wt.% Ir + Rh + In), exerted higher adverse effects on the viability of L929 cells and the suppression of rat thymocyte functions, such as proliferation activity, the production of Interleukin-2 (IL-2), expression of IL-2 receptor and activation — induced apoptosis after stimulation of the cells with Concanavalin-A. These results correlated with the higher release of Zn ions in the culture medium. As Zn2+, at the concentrations which were detected in the alloy’s culture media, showed a lesser cytotoxic effect than the Au-Pt conditioning media, we concluded that Zn is probably not the only element responsible for alloy cytotoxicity. Microstructural characterization of the alloys, performed by means of scanning electron microscopy in addition to energy dispersive X-ray and X-ray diffraction analyses, showed that Au-Pt I is a two-phase alloy containing a dominant Au-rich α1 phase and a minor Pt-rich α2 phase. On the other hand, the Au-Pt II alloy additionally contained three minor phases: AuZn3, Pt3Zn and Au1.4Zn0.52. The highest content of Zn was identified in the Pt3Zn phase. After conditioning, the Pt3Zn and AuZn3 phases disappeared, suggesting that they are predominantly responsible for Zn loss, lower corrosion stability and subsequent lower biocompatibility of the Au-Pt II alloy.

Development of an Al–Mn–Be–Cu alloy with improved quasicrystalline forming ability

Abstract An Al94Mn2Be2Cu2 cast alloy was developed displaying increased quasicrystalline formation ability at moderate cooling rates. The as-cast microstructure consisted of a mainly icosahedral phase in the Al-matrix. The microstructure remained stable during uniform heating to 580 °C and isothermal annealing at 400 °C. Most of the icosahedral phase was preserved even after 24 h annealing at 500 °C. For that reason, this alloy presents a promising basis for further development of cast Al-alloys containing quasicrystals.

Dispersion strengthening of copper by internal oxidation of rapidly solidified Cu–RE alloys: Part I: The microstructure and stability of rapidly solidified ribbons

Abstract Rapidly solidified ribbons of Cu-0.5-at.% Er and Cu-0.5 at.% Yb alloys have been prepared by melt spinning. An overall assessment of the ribbons has shown that up to three microstructural regions are distinguished: fine equiaxed grains, zone with a columnar structure and coarse equiaxed grains. Their number, type and height are controlled by wheel velocity. The growth behavior of dispersed intermetallic particles depends on the obtained microstructure, i. e., on the ribbon thickness. The large particles in thin ribbons coarsened by bulk diffusion, controlled by the diffusivity of the rare earth (RE) elements, and grow with the cube root of time at all temperatures. In thick ribbons with a high fraction of the coarse equiaxed zone, the coarsening takes place much more rapidly along the grain boundaries, which became a dominant transport mechanism.

In Situ Monitoring of Vacuum Carburizing

The present article describes development and testing of a new measurement method that enables nondestructive and in situ monitoring of a vacuum carburizing process. The principle of the method is based on monitoring the carbon diffusion during vacuum carburizing by the in-situ measurement of electrical resistance changes in the carburizing sample. Using this method the electrical resistance changes during vacuum carburizing of pure iron were acquired and analyzed. The experiments were performed in a laboratory vacuum furnace under a low pressure acetylene atmosphere (5 mbar) at a temperature of 950°C. The results of monitoring the kinetics of carburized zones obtained by the novel measurement method were compared with kinetics obtained by metallographic analysis of carburized samples.

Metallographic techniques for the characterization of quasicrystalline phases in aluminium alloys

Abstract Several Al-alloys strengthened by quasicrystalline phases have been developed over the last few years showing the considerable potential for practical application. Therefore there is a strong need for developing new metallographic methods or adapting the traditional ones in order to identify and characterize quasicrystalline phases in a reliable, quick and economical way. This paper describes different techniques: the classical metallographic method, deep etching, particle extraction technique and cross-sectioning using focused ion beam (FIB), and discusses their advantages and disadvantages when identifying quasicrystalline particles. It was discovered that particle extraction techniques are very powerful methods for the identification of phases according to their morphology, and preparation of quality samples for X-ray diffraction (XRD). Transmission electron microscopy (TEM) analyses are also possible provided the extracted particles are thin enough.

Microstructure and Properties of Shape Memory Alloys

Shape memory effects are very interesting functional properties of certain metallic alloys such as NiTi, CuZnAl or CuAlNi, to name the most popular ones. After considerable seemingly plastic deformation at low temperatures the elements restore their original shape just by raising the temperature by about 50-100°C, thereby seeming to remember their former shape. The reasons for this phenomenon are reversible martensitic transformations from one ordered structure to another ordered one with almost the same specific volume. This so called one-way shape memory effect has been thoroughly investigated and is well-understood nowadays and therefore many technical and some medical applications are in use or could be used. The so-called two-way shape memory effect changes the shape of an element not only during heating but also during cooling without external forces. Therefore this effect would be even more attractive for technical applications but it is not quite well understood from a scientific point of view, and this effect is smaller and less stable than the one-way effect.

The response of peripheral blood mononuclear cells to shape memory alloys

The aim of this work was to study the response of human peripheral blood mononuclear cells (PB-MNCs) to Cu-Al-Ni and Ni-Ti shape memory alloys (SMAs). The alloys were prepared as rapidly solidified thin ribbons via melt spinning. It has been shown that the ribbons were non cytotoxic for PB-MNCs as determined by the viability and apoptosis assay. In 18 cultures out of 20 cultures of individual donor PB-MNCs cultivated with Cu-Al-Ni SMAs, no significant changes in the production of Th1 (IFN-γ), Th2 (IL-5 and IL-10) and proinflammatory (IL-1s, TNF-α, IL-6 and IL-8) cytokines were detected compared to controls. In two cultures out of 20, a significant increase in the production of Th1 and proinflammatory cytokines was observed. Microstructural analyses confirmed the formation of thin oxide on the surface of both SMA ribbons.

Dispersion strengthening of copper by internal oxidation of rapidly solidified Cu-RE alloys Part II: Experimental study of internal oxidation

Combination of rapid solidification and internal oxidation was used for producing a fine dispersion of rare earth oxide particles in the copper matrix. An overall microstructural analysis has shown that the internal oxidation temperature, the rapidly solidified microstructure and its changing ahead of the internal oxidation front strongly influence the mechanism of the internal oxidation process and the resulting microstructure. The internal oxidation in a Cu-Yb alloy took place mainly by direct oxidation of intermetallic particles. Contrary to this, in a Cu-Er alloy two mechanisms of internal oxidation have been clearly observed: (i) Dissolution of intermetallic particles ahead of the internal oxidation front and oxidation of the erbium from the solid solution and (ii) direct oxidation of the Cu-Er intermetallic particles. While a reasonable optimum combination of processing conditions at internal oxidation in the solid state, yielding suitable oxide dispersions, seems to have been identified for the Cu-Er alloy, the same was not true for the Cu-Yb alloy. However, the internal oxidation of the Cu-Yb alloy in the semisolid state, which occurs by alternation of two processes - Yb oxides precipitation and Cu matrix solidification - led to a relatively uniform dispersion of Yb oxide particles.

Characterization of Oxidation Resistance of Stainless Steels at High Temperature by Metallographic Examinations and In-Situ Electrical Resistance Measurements

Abstract Practically all metals and alloys survive high-temperature exposure by growing oxide scales and/or by precipitation of the oxide particles in the matrix. Formed products can grow in shape of external oxide layers on surfaces, or as discrete oxide particles precipitated in a metal matrix. The first case represents external oxidation, and the other case is called internal oxidation. These processes are very important, because they determine the properties and applicability of metallic materials. Generally, they are undesired, because they cause deterioration of the mechanical properties and decomposition of metallic material. On the other side, the controlled process of external oxidation could be used for formation of protective coatings and the internal oxidation for dispersion strengthening of materials. In this paper we present monitoring of high-temperature oxidation of X12Cr13 stainless steel by in-situ electrical resistance measurements at different annealing temperatures in the air atmosphere. We determined the kinetics of oxide scale formation and its morphology with additional metallographic examination made by optical and scanning electron microscopy. The results of this research work show that in-situ monitoring and characterization of high-temperature oxidation present a strong tool that will contribute to a better fundamental understanding of the phenomena that occur during high-temperature oxidation of metallic materials.

Microstructural Changes during Vacuum Carburizing of Steels

Abstract Vacuum carburizing is a modern, very efficient and environmentally friendly process for case hardening of steels. Nowadays the technology has replaced atmosphere carburizing in many cases due to better repeatability and uniformity of heat treated samples. The process of vacuum carburizing is performed under oxygen free hydrocarbon gas atmosphere (usually pure acetylene) at partial pressure lower than 20mbar and in conditions which are far from thermodynamic equilibrium. The process consists of the cycles of active (saturation) and passive (diffusion) stages. Desired case depth and corresponding target concentration profile of carbon can be supervised by controlling the duration of these two stages.