Academia.eduAcademia.edu

Figure 4 – uploaded by Lizelle Glaner

See full PDFdownloadDownload figure
Hardnesses of Pt-, Ru-, Rh-, Ir-, Zn- and Co-containing sample in different conditions

Table 4 Hardnesses of Pt-, Ru-, Rh-, Ir-, Zn- and Co-containing sample in different conditions

Related Figures (22)

The Au-Ag-Cu system is the basis of the most common gold jewellery and dental alloys used today and dates back several millennia. Conventional 18 carat alloys are no exception. As a rule, pink or red 18 carat alloys are harder than yellow or The Au-Cu binary alloy phase diagram (4,
The Au-Ag-Cu system is the basis of the most common gold jewellery and dental alloys used today and dates back several millennia. Conventional 18 carat alloys are no exception. As a rule, pink or red 18 carat alloys are harder than yellow or The Au-Cu binary alloy phase diagram (4,
Figure 2 The Au-Cu system’s ordering regions (AuCu and AuCus) also extend into the ternary Au-Ag-Cu system (5) (although ordering in the AuCus region (Figure 1) has relatively little effect on the development of hardness during annealing of Au-Cu alloys, as the ordering involves no structural and negligible dimensional changes.) These ordered phases, depending on their size and distribution, can therefore effect considerable strengthening in 18 carat Au-Ag-Cu gold alloys
Figure 2 The Au-Cu system’s ordering regions (AuCu and AuCus) also extend into the ternary Au-Ag-Cu system (5) (although ordering in the AuCus region (Figure 1) has relatively little effect on the development of hardness during annealing of Au-Cu alloys, as the ordering involves no structural and negligible dimensional changes.) These ordered phases, depending on their size and distribution, can therefore effect considerable strengthening in 18 carat Au-Ag-Cu gold alloys
Figure 3
Figure 3
Figure 4 Isopleth at gold content 75 wt% (18 carat) of the Au-Ag-Cu ternary phase diagram (6)
Figure 4 Isopleth at gold content 75 wt% (18 carat) of the Au-Ag-Cu ternary phase diagram (6)
Co is already known to act as grain refiner, especially in the annealed and cold worked state (10). Grain refining has already been mentioned as a strengthening mechanism, but would never induce the hardening that was required in this investigation. However, according to the binary Au-Co alloy phase diagram (Figure 5), the addition of small amounts of Co could potentially induce a precipitation hardening reaction. A Co-rich e-Co phase will precipitate from metastable Au-rich Au-Co solid solutions during ageing at temperatures below ~422°C. The Au-Co binary alloy phase diagram (4)
Co is already known to act as grain refiner, especially in the annealed and cold worked state (10). Grain refining has already been mentioned as a strengthening mechanism, but would never induce the hardening that was required in this investigation. However, according to the binary Au-Co alloy phase diagram (Figure 5), the addition of small amounts of Co could potentially induce a precipitation hardening reaction. A Co-rich e-Co phase will precipitate from metastable Au-rich Au-Co solid solutions during ageing at temperatures below ~422°C. The Au-Co binary alloy phase diagram (4)
* 50% cold worked Hardnesses of Co-containing samples in different conditions Table 1
* 50% cold worked Hardnesses of Co-containing samples in different conditions Table 1
Hardnesses of Ti-containing samples in different conditions Table 2
Hardnesses of Ti-containing samples in different conditions Table 2
In order to increase the hardness Co was added and to improve the colour Zn was added and the gold content increased to 80 wt%. From Table 3 one can see that a high hardness can be readily achieved by the Ti-Co combination, but the colour of the alloy remained pale. Furthermore, the formability of the alloy was also compromised. It was therefore concluded that Ti is not an acceptable alloying addition for hardening 18 carat gold. The Au-Ti binary alloy phase diagram (4)
In order to increase the hardness Co was added and to improve the colour Zn was added and the gold content increased to 80 wt%. From Table 3 one can see that a high hardness can be readily achieved by the Ti-Co combination, but the colour of the alloy remained pale. Furthermore, the formability of the alloy was also compromised. It was therefore concluded that Ti is not an acceptable alloying addition for hardening 18 carat gold. The Au-Ti binary alloy phase diagram (4)
Hardnesses of Ti-, Co- and Zn-containing sample in different conditions The addition of platinum group metals (PGMs)
Hardnesses of Ti-, Co- and Zn-containing sample in different conditions The addition of platinum group metals (PGMs)
Table 4 shows the compositions and properties of a first batch of experimental alloys containing Pt, Ru, Rh and Ir respectively. Note that the Ru, Rh and Ir were all added in the form of a Cu-20 wt% PGM master alloy to ensure even
Table 4 shows the compositions and properties of a first batch of experimental alloys containing Pt, Ru, Rh and Ir respectively. Note that the Ru, Rh and Ir were all added in the form of a Cu-20 wt% PGM master alloy to ensure even
The Au-Rh binary alloy phase diagram (4)
The Au-Rh binary alloy phase diagram (4)
Pt-containing alloys can be hardened to values well in excess The Au-Pt binary alloy phase diagram (4)
Pt-containing alloys can be hardened to values well in excess The Au-Pt binary alloy phase diagram (4)
Hardnesses of B-containing sample in different conditions Table 6
Hardnesses of B-containing sample in different conditions Table 6
Hardnesses of Al, Co and Zn containing samples in different conditions
Hardnesses of Al, Co and Zn containing samples in different conditions
Hardnesses of Zr- and Co-containing sample in different condition Table 8
Hardnesses of Zr- and Co-containing sample in different condition Table 8
Figure 11 The Au-Zr binary alloy phase diagram (4,
Figure 11 The Au-Zr binary alloy phase diagram (4,
the chemical compositions (wt%) of the 18 carat alloys, 75 weight per cent gold, that can be hardened to a value in excess of 300 points on th /ickers scale
the chemical compositions (wt%) of the 18 carat alloys, 75 weight per cent gold, that can be hardened to a value in excess of 300 points on th /ickers scale
Alloys 1 to 4 in Table 9 were chosen for further evaluation. Although the alloys containing PGMs were also very promising as 18 carat hard gold alloys, their high melting points and price made them less attractive options. Regardless of the fact that it was suspected that the Zr- and Al-containing alloys might not behave well during investment casting, it was decided to test them further. Figure 4 shows
Alloys 1 to 4 in Table 9 were chosen for further evaluation. Although the alloys containing PGMs were also very promising as 18 carat hard gold alloys, their high melting points and price made them less attractive options. Regardless of the fact that it was suspected that the Zr- and Al-containing alloys might not behave well during investment casting, it was decided to test them further. Figure 4 shows
Figure 13
Figure 13
Figure 14 Standard form fill test grids. From left to right: alloys containing Co, B, Al+Co and Zr+Co The form filling properties of all the alloys (including, surprisingly, the Al- and Zr-containing alloys) were excellent, the respective grids being completely filled in all dimensions. Figure 6 shows each of the standard form fill test grids.
Figure 14 Standard form fill test grids. From left to right: alloys containing Co, B, Al+Co and Zr+Co The form filling properties of all the alloys (including, surprisingly, the Al- and Zr-containing alloys) were excellent, the respective grids being completely filled in all dimensions. Figure 6 shows each of the standard form fill test grids.
Figure 15 Metallographic section of the as-cast grid of the Co-containing alloy. The B-containing alloy was similar in appearance
Figure 15 Metallographic section of the as-cast grid of the Co-containing alloy. The B-containing alloy was similar in appearance
Related topics:
Materials EngineeringInorganic Chemistry
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved