1. Product Overview

INCONEL 939 is a precipitation-hardened, cast nickel-based superalloy developed for demanding high-temperature applications in gas turbines and aerospace propulsion systems.

The alloy derives its high-temperature strength primarily fromγ′ (gamma-prime) precipitation strengthening, combined with solid-solution strengthening and grain-boundary strengthening. Its combination of creep resistance, stress-rupture capability, oxidation resistance, and thermal-fatigue performance makes it particularly suitable for hot-section components exposed to prolonged thermal and mechanical loading.

INCONEL 939 was developed specifically forprecision investment casting, enabling the production of complex geometries such as turbine blades, nozzle guide vanes, combustion-system hardware, and other hot-gas-path components.

Typical applications include:

· Gas-turbine turbine blades

· Nozzle guide vanes (NGVs)

· Combustion-system hardware

· Hot-gas-path components

· Aerospace propulsion components

· High-temperature stationary turbine components

INCONEL 939 is generally considered suitable for high-temperature service in the approximate800–1000 °C range, depending on stress level, exposure duration, oxidation environment, cooling conditions, coating system, casting condition, and component design.

2. Material Classification

Item	Description
Alloy	INCONEL 939
UNS Number	N09939
Material Type	Nickel-based precipitation-hardened superalloy
Manufacturing Route	Vacuum induction melting+casting
Primary Strengthening Mechanism	γ′ precipitation strengthening
Typical Supply Condition	Solution-treated and age-hardened
Primary Service	Gas-turbine and aerospace hot-section components

3. Supply Condition

INCONEL 939 is typically supplied in aninvestment-cast, solution-treated, and age-hardened condition.

A representative heat-treatment route for cast IN939 consists of:

·Solution treatment:approximately1160 °C / 4 h

·Cooling:controlled cooling / furnace or gas-fan cooling according to the applicable process specification

·Primary aging:approximately1080 °C / 4 h, where applicable

·Secondary aging:approximately843–850 °C / 16–20 h

Heat-treatment schedules should be selected according to the applicable material specification, casting process, component geometry, and customer/OEM requirements.

Solution treatment is important not only for controlling the γ′ precipitation state but also for reducing undesirable phases such as theη phasethat may form during solidification of cast IN939.

4. Chemical Composition

Table 1 — Typical Chemical Composition

Element	Typical / Specified Range (wt.%)	Primary Function
Nickel (Ni)	Balance	Matrix element; high-temperature strength
Chromium (Cr)	21.5–23.5	Oxidation and hot-corrosion resistance
Cobalt (Co)	18.0–20.0	Solid-solution strengthening and thermal stability
Molybdenum (Mo)	≤0.30	Solid-solution strengthening
Aluminum (Al)	1.70–2.10	γ′ formation and precipitation strengthening
Titanium (Ti)	3.50–3.90	γ′ strengthening
Tantalum (Ta)	1.20–1.60	Strengthening and microstructural stability
Carbon (C)	0.12–0.18	Carbide formation and grain-boundary strengthening
Niobium (Nb)	0.80–1.20	partitions to the γ′ phase, forming stable NbC carbides that strengthen grain boundaries and improve high-temperature strength, creep resistance and microstructural stability.
Boron (B)	0.004–0.015	Grain-boundary strengthening and ductility
Zirconium (Zr)	0.05–0.014	Grain-boundary stability
Silicon (Si)	≤0.30	Melting/casting control
Manganese (Mn)	≤0.20	Melting/casting control

5. Physical Properties

Table 2 — Typical Physical Properties

Property	Typical Value	Test Method / Condition
Density	~8.27 g/cm³	Typical literature data
Melting Range	~1235–1338 °C	Typical literature data
Thermal Conductivity	10.0 W/m·K（100°C）	ASTM E1225
Electrical Resistivity	1.38 µΩ·m（20°C）	ASTM B193
Coefficient of Thermal Expansion	Temperature dependent	ASTM E228
Specific Heat	440 J/kg·Kat room temperature	ASTM E1269
Elastic Modulus	~190 GPa at room temperature	ASTM E111

Physical Property Notes

Physical properties of INCONEL 939 vary with temperature, alloy chemistry, casting condition, heat treatment, and microstructure.

The reported melting range should be treated as areference range rather than a guaranteed specification limit. A literature source reports approximately1235–1338 °Cfor IN-939.

The coefficient of thermal expansion, thermal conductivity, specific heat, and electrical resistivity should preferably be provided astemperature-dependent curveswhen the data are intended for thermal or structural design.

6. Mechanical Properties

Table 3 — Typical Mechanical Properties

Cast, Heat-Treated Condition

Property	Typical Value	Test Standard / Condition
Ultimate Tensile Strength	Typically ~1000–1180 MPa	ASTM E8/E8M
0.2% Yield Strength	Typically 950–1050 MPa	ASTM E8/E8M
Elongation	Typically ~5–8%	ASTM E8/E8M
Hardness	~330–390 HB, condition dependent	ASTM E10

Mechanical properties are strongly dependent on casting quality, grain structure, heat-treatment condition, specimen orientation, section thickness, and test temperature.

For this reason, values in this table are intended astypical engineering reference datarather than universal guaranteed minimum properties.

7. Creep and Stress-Rupture Properties

Creep and stress-rupture performance is strongly dependent on temperature, applied stress, casting condition, grain structure, heat treatment, specimen orientation, and exposure time.

Table 4 — Creep / Stress-Rupture Performance

Test Temperature	Applied Stress	RuptureLife	Elongation
850 °C	350MPa	30 h	≥2%

8. Key Material Characteristics

8.1 γ′ Precipitation Strengthening

INCONEL 939 obtains its high-temperature strength primarily through precipitation strengthening associated with the γ′ phase.

The γ′ precipitates provide resistance to dislocation motion and contribute to strength retention during elevated-temperature exposure.

8.2 High-Temperature Creep and Stress-Rupture Resistance

The alloy is designed for prolonged high-temperature loading and provides strong resistance to creep deformation and stress rupture when appropriately cast and heat treated.

8.3 Oxidation and Hot-Corrosion Resistance

The relatively high chromium content promotes the formation of protective oxide scales, while the alloy’s overall chemistry provides resistance to oxidation and corrosive combustion environments.

IN939 was developed specifically for gas-turbine hot-section service with an emphasis on corrosion and oxidation resistance together with precipitation-strengthened mechanical properties.

8.4 Thermal-Fatigue Capability

The alloy is suitable for components subjected to repeated thermal cycling and combined thermal-mechanical loading.

Actual thermal-fatigue life depends on component geometry, thermal gradients, cooling conditions, surface condition, stress concentration, and coating system.

8.5 Investment-Casting Capability

INCONEL 939 is particularly suited to precision investment casting of complex geometries.

Typical cast components include:

· Airfoils

· Turbine blades

· Nozzle guide vanes

· Platforms

· Shrouds

· Combustion-system hardware

9. CNC Machining Characteristics

INCONEL 939 presents machining challenges typical of precipitation-strengthened nickel-based superalloys.

Table 5 — Machining Challenges and Recommended Approaches

Challenge	Description	Recommended Approach
High strength and γ′ strengthening	High cutting forces and accelerated tool wear	Use rigid tooling, stable fixturing, and appropriate cutting conditions
Work hardening	Repeated tool engagement can produce a hardened surface layer	Avoid tool dwelling and rubbing; maintain consistent engagement
Low thermal conductivity	Heat is concentrated near the cutting zone	Use effective coolant delivery and optimized cutting parameters
Carbide / hard second phases	Can contribute to localized abrasive and mechanical wear	Select suitable tool grade and edge geometry
Tool-edge chipping	High cutting forces and interrupted cuts can destabilize the cutting edge	Use appropriate edge preparation and controlled tool engagement
Chip control	Tough chips may interfere with stable machining	Use suitable chipbreaker geometry and controlled feed
Thin-wall deformation	Investment-cast airfoils may be susceptible to vibration and distortion	Use rigid workholding and optimized multi-axis tool paths

10.Heat Treatment

10.1Heat Treatment

Heat treatment is an essential part of the INCONEL 939 manufacturing process.

A representative route includes:

· Solution treatment at approximately1160 °C

· Controlled cooling

· Aging at approximately843–850 °C

· Optional intermediate aging step depending on the applicable specification

The purpose is to establish the desired γ′ precipitation structure while controlling undesirable phases and grain-boundary microstructure.

Published studies report solution treatment around 1160 °C followed by aging around 850 °C for cast IN939.

10.2Welding and Repair Welding

INCONEL 939 can be challenging to weld and repair because of its precipitation-strengthened microstructure and susceptibility to cracking under unsuitable thermal cycles.

Repair procedures should use:

· Controlled heat input

· Appropriate preheating/interpass control where applicable

· Qualified filler metal

· Controlled welding sequence

· Appropriate post-weld heat treatment where required

TIG/GTAW or other qualified repair-welding processes may be used depending on component geometry and customer requirements.

Welding procedures should be qualified before use on critical components.

11. Material Testing and Quality Control

Material and component qualification may include:

· Chemical composition verification

· Heat-treatment records

· Hardness testing

· Tensile testing

· Creep / stress-rupture testing

· Metallographic examination

· Grain-size evaluation

· Radiographic inspection

· Fluorescent penetrant inspection

· Dimensional inspection

· Surface-finish inspection

· Internal-defect evaluation

Typical Standards

Test / Inspection	Reference Standard
Tensile Testing	ASTM E8/E8M
Hardness	ASTM E10
Creep / Stress Rupture	ASTM E139
Elastic Modulus	ASTM E111
Thermal Expansion	ASTM E228
Thermal Conductivity	ASTM E1225
Specific Heat	ASTM E1269
Electrical Resistivity	ASTM B193
Metallographic Preparation	ASTM E3
Radiographic Examination	Applicable casting/NDT specification
Penetrant Inspection	Applicable ASTM / OEM specification

The applicable specification should always take precedence over general ASTM test methods.

12. Typical Applications

12.1 Aerospace and Gas-Turbine Turbines

Typical applications include:

· Turbine blades

· Nozzle guide vanes

· Turbine airfoils

· Blade platforms

· Combustion-system hardware

· Hot-gas-path components

IN939 was developed specifically as an investment-cast alloy for gas-turbine hot-section applications.

12.2 Power Generation

Typical applications include:

· Gas-turbine stator components

· Nozzle guide vanes

· Hot-gas-path hardware

· Combustor components

· Heat shields

· Selected stationary turbine components

The alloy is suitable for prolonged exposure to elevated temperatures and combined thermal-mechanical loading.

12.3 Aerospace and Defense

Potential applications include:

· Aero-engine hot-section components

· Combustor hardware

· Exhaust-system components

· High-temperature structural hardware

· Nozzle and hot-gas-path components

The alloy is particularly attractive where oxidation resistance and long-term high-temperature mechanical performance are required.

12.4 Industrial Gas Turbines

Potential applications include:

· Turbine vanes

· Blade platforms

· Combustor hardware

· Transition components

· Hot-gas-path structural components

IN939 is particularly suited to components manufactured by investment casting where complex geometry and high-temperature performance are required.

13. Manufacturing and Quality Considerations

For investment-cast INCONEL 939 components, final performance depends on:

·VacuumMeltingpractice

· Casting process

· Mold design

· Solidification behavior

· Grain structure

· Internal porosity

· Carbide morphology

· η-phase control

· Heat-treatment condition

· HIP treatment where applicable

· Surface condition

· Machining integrity

For critical aerospace and power-generation components, a complete manufacturing route should include appropriate process qualification and inspection.

14. Engineering Design Considerations

INCONEL 939 should be selected based on the complete service environment rather than nominal temperature alone.

Important design factors include:

· Metal temperature

· Applied stress

· Exposure duration

· Thermal cycling

· Oxidation environment

· Hot corrosion

· Cooling conditions

· Coating system

· Casting orientation

· Section thickness

· Internal casting defects

For safety-critical components, design allowables should be generated from qualified material and component test data.

15. Material Summary

Category	INCONEL 939
Material	INCONEL 939
UNS	N09939
Material Class	Nickel-based precipitation-hardened superalloy
Manufacturing Route	Precision investment casting
Strengthening Mechanism	γ′ precipitation strengthening
Typical Supply Condition	Solution-treated + age-hardened
Density	~8.27 g/cm³
Melting Range	~1235–1338 °C
Ultimate Tensile Strength	~1000–1180 MPa, condition dependent
Yield Strength	~950–1050 MPa, condition dependent
Elongation	~5–8%, condition dependent
Hardness	~330–390 HB, condition dependent
High-Temperature Capability	Approx. 800–1000 °C, application dependent
Main Advantages	Creep resistance · Stress-rupture resistance · Oxidation resistance · Thermal-fatigue capability · Investment castability
Main Applications	Turbine blades · NGVs · Combustion hardware · Hot-gas-path components · Industrial gas turbines