Oxidation Resistance
MULTIMET® exhibits acceptable oxidation resistance up to around 1800°F. However, due to concerns with oxidation resistance, MULTIMET® has been generally replaced by 556® alloy, which has comparable creep-rupture strength but superior oxidation resistance, particularly at temperatures greater than 1800°F.
Short-term Oxidation
Comparative Oxidation Resistance in Flowing Air, 1008 Hours
| Alloy |
1800°F (980°C) |
2000°F (1095°C) |
| Metal Loss |
Average Metal Affected |
Metal Loss |
Average Metal Affected |
| mils |
μm |
mils |
μm |
mils |
μm |
mils |
μm |
| MULTIMET® |
0.4 |
10 |
1.3 |
33 |
8.9 |
226 |
14.3 |
363 |
| 556® |
0.4 |
10 |
2.3 |
58 |
1.5 |
38 |
6.9 |
175 |
Flowing air at a velocity of 7.0 ft/min (213.4 cm/min) past the samples. Samples cycled to room temperature once per week.
Dynamic Oxidation Burner Rig
| Alloy |
1600°F (870°C), 1000 h, 30-min cycles |
1600°F (870°C), 2000 h, 30-min cycles |
| Metal Loss |
Average Metal Affected |
Metal Loss |
Average Metal Affected |
| mils |
μm |
mils |
μm |
mils |
μm |
mils |
μm |
| MULTIMET® |
1.3 |
33 |
2.2 |
56 |
2.7 |
69 |
4.9 |
124 |
| 556® |
1.4 |
36 |
3.1 |
79 |
1.5 |
38 |
3.9 |
99 |
Burner rig oxidation tests were conducted by exposing sampIes 3/8 in. x 2.5 in. x thickness (9 mm x 64 mm x thickness), in a rotating holder, to products of combustion of No. 2 fuel oil burned at a ratio of air to fuel of about 50:1. (Gas velocity was about 0.3 mach). Samples were automatically removed from the gas stream every 30 minutes and fan-cooled to near ambient temperature and then reinserted into the flame tunnel.
Metallographic Technique used for Evaluating Environmental Tests
