Metallographs of a biphasic platinum-copper-cobalt alloy characterised by small grain size. Some excellent metallographs illustrated how alloy microstructure varied between the platinum alloys (some are two-phase) and with metallurgical conditions (an example is shown in Figure 1). ![]() He examined a range of platinum alloys, including dental and other alloys as well as the standard jewellery alloys, with compositions ranging from 70%–95% platinum with rhodium, iridium, gold, copper, cobalt, copper-cobalt or indium-gallium-zirconium, in various metallurgical conditions. Electrolytic etching was preferred over chemical etching. In this presentation, Battaini described how to best prepare specimens for optical examination, with some emphasis on etching techniques to show up the microstructural features. Paolo Battaini (8853 SpA, Italy) made a significant contribution to our understanding in his presentation ‘Metallography of Platinum and Platinum Alloys’. This involves a process of metallography, in which specimens are polished and etched and examined under a microscope. Understanding the microstructure of platinum jewellery alloys and how it is influenced during processing is important if good quality jewellery is to be produced. ![]() This work has shown that casting of platinum alloys is a complex process and that careful selection of casting conditions is important if acceptable castings are to result. In contrast, 950 PtRu did not show any investment reaction despite its higher casting temperature. Investment reactions were observed for the 950 PtCo alloy, independent of casting atmosphere, and resulted in a blue layer of cobalt silicate. 950 PtCo was superior in this regard to 950 PtRu alloy 950 PtCo showed few but large pores, while 950PtRu often showed scattered pores built by intersecting dendrites įorm-filling was a critical issue for filigree items. Shrinkage porosity was the main issue for heavy items and for lightweight filigree pieces. From these trials, the following observations were made: ![]() ![]() Four types of investment powder were investigated and many casting trials were carried out to analyse the influence of casting parameters: melt temperature, flask temperature, atmosphere, alloy and investment type. Segregation effects, especially of silicon, lead to a substantial extension of the melting range by lowering the solidus temperature.Ĭasting trials were conducted in a centrifugal casting machine with induction heating, atmosphere control and temperature measurement. In his presentation, entitled ‘The Role of Process Parameters in Platinum Casting’, Klotz looked at the casting of two platinum alloys: 950 PtRu (platinum with 5 wt% ruthenium) and 950 PtCo (platinum with 5 wt% cobalt). Funded by Platinum Guild International, this is perhaps the first significant basic research carried out on the platinum casting process for some years and should lead to improved casting technology. One of the highlights of the Symposium was the presentation by Ulrich Klotz (FEM, Germany) on a major research project carried out, with several industrial partners, on the investment casting of platinum alloys.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |