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|Equal Grade:||Ni-Span-C 902, Alloy 902, 3J53|
0.025mm rolled foil,
NI-SPAN-C alloy 902 rolled foil
NI-SPAN-C alloy 902(N09902) is a Fe-Ni Alloy with controllable thermoelastic coefficient. The desired thermoelastic coefficient is then obtained by using cold work and the proper thermal treatment. Cold work produces internal strains, making the coefficient more negative. Thermal treatments, in the lower temperature ranges, relieve strain. They also cause complex ordering phenomena which make the coefficient more positive. Heating at temperatures above about 900°F causes the precipitation of an intermetallic compound of titanium and nickel, withdrawing nickel from the matrix and moving the coefficient further in the positive direction.
The thermoelastic coefficient (TEC) of an alloy is the rate of change of its modulus of elasticity with change in temperature. It is usually expressed as parts per million per degree F (e.g. 5 x 10-6/°F).
The first measurements of the TEC of NI-SPAN-C alloy 902 were made using a torsion pendulum operating at about one cycle per second. These tests are the basis for much of the published data on the alloy. However, when these data were used to design high frequency devices they were found to produce incorrect results, and a confused situation arose.
Recent work has solved the problem of the conflicting results. It has been found that operating frequency has a marked effect on TEC. Tests run at Special Metals showed that the TEC of a given sample increased with increase in test frequency up to about 800 cps. Above 800 cps there was no frequency effect. Samples from the same heat of materialtested at about 1500 cps, and in another laboratory at
455,000 cps, gave identical results. Burnette at the National Bureau of Standards found that a heat treatment which produced zero TEC on a sample tested in a torsion pendulum at 1 cps developed a TEC of +40 on a sample tested in freefree vibration at 1000 cps. Figure 2 shows these data and a schematic indication of the frequency effect.
Because of the frequency effect, it is necessary to delineate two areas of application of NI-SPAN-C alloy 902, each requiring different processing to achieve best results.
1. Low frequency devices. These include springs, Bourdon tubes, aneroid capsules, etc.
2. High frequency devices. Tuning forks, vibrating reeds, mechanical filters and similar instrumentation fall in this category.
Density: 8.05 g/cm3
Curie Temperature: 190°C
Electrical Resistivity: 1.02 µΩ•m
Cold work causes an increase in the modulus. Raising the temperature of heat treatment also causes an increase.
Although the alloy was designed for use above -50°F, it has been used successfully at lower temperatures and some cryogenic data have been
published. The alloy exhibits low damping capacity (high Q). The Q of cold worked material has been reported to be about 8000, about 4 times greater than the values for annealed forms.
Contact Person: Allen Sun