Livarski vestnik 53 / 2006 Nr. 1
Peter Schumacher:
Microstructural Control by GrainRefi nement
Alojz Križman, Rebeka Rudolf, Bojan Albreht:
Melting and Casting of Dental Alloys with High Au-Content
Markoli B., Spaić S.:
Microstructure of ZP 0410 (ZnAl4Cu1) alloy in as-cast state
Peter Schumacher,
University of Leoben; Lehrstuhl fűr Gießereikunde
Microstructural Control by Grain Refi nement
Abstract
Abstract
The benefi ts of grain refi ning wrought and foundry Al alloys are widely acknowledged. To induce grain refi nement, Al-Ti-B master alloys are commonly added to the melt prior to casting. Understanding the nucleation mechanisms of these refi ner particles is important with respect to optimizing current commercial casting practices and improving future refi ning potency. However, using conventional solidifi cation casting techniques, heterogeneous nucleation is diffi cult to investigate as α-Al grain growth obscures the nucleation sites. A metallic glass technique has been successfully applied allowing the nucleation mechanisms to be examined using Transmission Electron Microscopy (TEM). The technique freezes the crystalline growth of α-Al at an early stage in a glass and allows the study of the orientation relationship between nucleant and nuclei using diffraction and chemical analysis. The effects of Si which at higher concentrations can have a detrimental effect on the ultimate grain size (UGS) achieved by the grain refi ner addition were examined. It has been found that the chemical composition of the refi ner particles and their interfaces could play an important role in the nucleation mechanism, which has implications for current casting practices.
Key words: Heterogeneous Nucleation, Al Alloys, Grain Refi nement, Metallic Glass Technique
Peter Schumacher,
University of Leoben; Lehrstuhl fűr Gießereikunde
Austrian Foundry Research Institute
Key words: Heterogeneous Nucleation, Al Alloys, Grain Refi nement, Metallic Glass Technique
Peter Schumacher,
University of Leoben; Lehrstuhl fűr Gießereikunde
Austrian Foundry Research Institute
Alojz Križman1, Rebeka Rudolf1, Bojan Albreht2
1University of Maribor,Faculty of Mechanical Engineering, Smetanova 17, Slovenia
2Zlatarna Celje d.d., Slovenia
Melting and Casting of Dental Alloys with High Au-Content
Abstract
This paper deals with the melting and the casting of the dental alloys with high Au content into three-tooth bridgework pieces. These two operations - melting of the dental alloy and casting of the melt into the.mould “on the eliminated wax”- represent the most important process in the fi eld of the dentistry praxis. The process is generaly known as precision casting and is partly different from standard casting methods. The main differences are: the preparation of the mould, the use of plaster instead of moulding sand and the casting of (here) a very small quantity of dental alloy - some grams only. The very important fact in the production of very small castings is the infl uence of the surface tension of the melt which has the tendency to keep the melt surface as small as possible. Because the dental alloys with high Au content have a very high surface tension (~ 1,120 N/m) and because the tooth castings usually have a very small weight and very complicated shape, the dental alloys cannot be processed by gravity casting. The required additional force can be applied by vapour or air pressure, vacuum and air pressure, or by using centrifugal force. In this connection this force represents the most used casting method which is known here as centrifugal horizontal casting.
In this paper we present some results of the investigations dealing with the infl uence of two different kinds of plaster, of the quality of the individual dental alloy charge and of the combination of both on the quality of the tooth casting. The remelted Au dental alloys were centrifugally cast into shaped moulds for three-tooth bridgework. To examine the quality of the tooth casting specimens light microscopy (NIKON Epiphot 300), scanning electron microscopy (SEM-Jeol JSM 849 A) and electronic microanalysis (EDX - Link analytical AN 1000) were used.
On the basis of the received results and analyses the following conclusions can be summarized: The infl uence of the different types of plaster on the quality of the tooth castings is negligible. Depending on the used type of plaster the tooth casting have only a different shade of gold colour. The size of the casting cone depends on the type of plaster mass used for the production of the cuvette. The quality of the tooth castings depends on the initial chemical composition of the dental alloy.
Key words: melting, casting, Au dental alloy, testing, cuvette - metal vessel, made from more parts for making of moulds for dental prosthesis
In this paper we present some results of the investigations dealing with the infl uence of two different kinds of plaster, of the quality of the individual dental alloy charge and of the combination of both on the quality of the tooth casting. The remelted Au dental alloys were centrifugally cast into shaped moulds for three-tooth bridgework. To examine the quality of the tooth casting specimens light microscopy (NIKON Epiphot 300), scanning electron microscopy (SEM-Jeol JSM 849 A) and electronic microanalysis (EDX - Link analytical AN 1000) were used.
On the basis of the received results and analyses the following conclusions can be summarized: The infl uence of the different types of plaster on the quality of the tooth castings is negligible. Depending on the used type of plaster the tooth casting have only a different shade of gold colour. The size of the casting cone depends on the type of plaster mass used for the production of the cuvette. The quality of the tooth castings depends on the initial chemical composition of the dental alloy.
Key words: melting, casting, Au dental alloy, testing, cuvette - metal vessel, made from more parts for making of moulds for dental prosthesis
Markoli B., Spaić S.
Faculty of Natural Sciences and Engineering, University of Ljubljana, Slovenia
Microstructure of ZP 0410 (ZnAl4Cu1) alloy in as-cast state
Abstract
In all three casting methods (sand, permanent mould, die casting) the microstructure in the as-cast state consists of primary multicomponent solid solution based on zinc ηZn, binary eutectic (αAl + ηZn) and ternary eutectic (αAl + ηZn + Θ-Al2Cu). The size of phases and microstructure components is decreasing with increasing cooling rate. The critical temperatures of transformations during the process of solidification are very prone to undercooling. The microstructure of die-castings shows as a rule more tendencies towards the appearance of gas and shrinkage porosity and presence of oxide fi lm.