Incoloy 909 Introduction

Precipitation
Strengthened Alloy

Nickel

Iron

Cobalt

Corrosion
Resistance

63

Mechanical
Behavior

89

Purity

97

Overview

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INCOLOY® alloy 909 (UNS N19909) is a nickel-iron-cobalt alloy whose outstanding characteristics are a constant low coefficient of thermal expansion, a constant modulus of elasticity, and high strength. The alloy is strengthened by a precipitation-hardening heat treatment made possible by additions of niobium and titanium.

The combination of low expansion and high strength makes INCOLOY alloy 909 especially useful for gas turbines. The low expansion enables closer control of clearances and tolerances for greater power output and fuel efficiency. The high strength increases strength-to-weight ratios for lower weight in aircraft engines. For those reasons, INCOLOY alloy 909 is used for gas-turbine vanes, casings, shafts, and shrouds.

The properties of INCOLOY alloy 909 are attractive also for rocket-engine thrust chambers, ordnance hardware, springs, steam-turbine bolts, gauge blocks, instrumentation, and glass-sealing applications.

Physical and Mechanical Properties

Values for some physical properties of INCOLOY alloy 909 were determined for age-hardened material. Curie temperature varies within the range shown depending on specific chemical composition of the material.

INCOLOY alloy 909 maintains its rigidity over a wide temperature range. The modulus of elasticity remains nearly constant from room temperature to 1200°F (650°C). Elastic modulus was determined for age-hardened material, and testing was by a dynamic method.

The composition of INCOLOY alloy 909 is designed to provide a low and constant coefficient of thermal expansion. The alloy’s expansion rate is about half the rate of other alloys having comparable strength. Figure 1 compares thermal expansion of INCOLOY alloy 909 and other high-strength alloys. The coefficient of expansion of INCOLOY alloy 909 is approximately 4.3 x 10-6 in/in/°F (7.7 μm/m/°C) from room temperature to the inflection point (Curie temperature). At the inflection point, which is in the region of 800°F (425°C), the alloy changes from ferromagnetic to paramagnetic and displays higher expansion coefficients with increasing temperature.

The combination of low expansion and constant elastic modulus, in conjunction with relatively high thermal conductivity, makes INCOLOY alloy 909 highly resistant to thermal fatigue and thermal shock.

Corrosion Resistance

INCOLOY alloy 909 contains no chromium because the presence of that element would increase thermal expansion rate. The absence of chromium, however, makes the alloy more susceptible to oxidation in high-temperature atmospheres. In some applications, INCOLOY alloy 909 may require a protective coating to prevent excessive oxidation. Figure 6 compares INCOLOY alloy 909 with INCONEL alloy 718 (19% chromium) in a cyclic oxidation test at 1200°F (650°C).

A characteristic of INCOLOY alloy 909 is that, unlike other materials of comparable strength, it resists embrittlement by high-pressure hydrogen.

Physical Properties

Mechanical Properties

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