Metal Powder Injection Molding for Gas Turbine Components
This paper examines the application of metallic powder injection molding (MIM) to the manufacture of gas turbine components, with a focus on nickel-base superalloys such as INCONEL 625, INCONEL 718, Nimonic 90, and Hastelloy X. The paper begins by outlining the advantages and key attributes of the MIM process, then reviews the material property data relevant to gas turbine component manufacture, including physical, mechanical, and tensile properties. It also surveys recent initiatives to expand MIM technologies beyond small, lightweight parts toward the larger and more complex geometries required by gas turbine engines. The paper concludes that MIM holds considerable promise as a cost-effective, high-precision alternative to traditional manufacturing methods such as precision die forging and investment casting.
- Introduction to Metal Injection Molding for Gas Turbines: MIM defined, advantages listed, gas turbine context established
- Purpose of the Study: Research gap identified, study objective stated
- Types of Material and Material Property Data: Alloy types and detailed property tables for turbine alloys
- Initiatives to Expand MIM Technologies for Gas Turbine Manufacturing: Recent innovations extending MIM to larger, complex components
- Summary and Conclusion: Findings synthesized, MIM potential affirmed
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What makes this paper effective
- Grounds the study in a clear industrial problem — the high cost and complexity of manufacturing gas turbine components — and proposes MIM as a concrete alternative, giving the research a focused practical motivation.
- Anchors technical claims in detailed quantitative data: multiple tables of physical, mechanical, and tensile properties for each alloy allow readers to evaluate material suitability directly rather than relying solely on qualitative assertions.
- Integrates both commercial vendor sources and peer-reviewed literature (Russell, Osada et al., Williams) to triangulate the current state and future potential of MIM technology.
Key academic technique demonstrated
The paper demonstrates systematic comparative analysis across multiple materials. By presenting property data for INCONEL 625, INCONEL 718, Nimonic 90, and Hastelloy X in parallel tabular form, the author enables side-by-side evaluation of candidate alloys against the demanding thermal and mechanical requirements of gas turbine environments — a technique common in materials science and engineering research papers.
Structure breakdown
The paper follows a conventional research-paper structure. An introduction defines MIM, lists its advantages, and contextualizes gas turbine manufacturing needs. A purpose statement frames the research question. A literature review chapter covers material types, detailed property tables, and recent MIM technology initiatives. A brief concluding chapter synthesizes findings and affirms the technology's promise. References follow APA format throughout.
Introduction to Metal Injection Molding for Gas Turbines
Invented by Hans-Joachim Pabst von Ohain and Frank Whittle in the 1930s, gas turbines have become essential technologies for global transportation and international trade (Anderson, 2011). Gas turbines are among the most efficient machines ever designed for transporting large amounts of cargo over long distances, and they boast the lowest carbon dioxide emission rates in terms of per ton-miles compared to other transportation technologies (Anderson, 2011). Additional refinements and innovations in gas turbine technologies are expected to further increase these efficiencies (Anderson, 2011).
One such technology is metallic powder injection molding for gas turbines. Metallic powder injection molding is a technique that can be used to manufacture components and parts in the medical field, aerospace, and other industries. The goal is to apply the metal injection molding (MIM) technique to produce parts and components for gas turbine manufacturing. Conceivably, this technique holds the potential to help reduce costs in producing these parts. According to one commercial vendor, "Metal Injection Molding (MIM), sometimes called Powdered Injection Molding (PIM), is an advanced metal forming technique that uses injection molding equipment for manufacturing both simple and complex metal parts to tight tolerances" (Powder Metal Injection Molding Manufacturing, 2016, p. 2). At present, the optimal applications for metal powder injection molding processes are the production of small components, usually weighing less than 100 grams, which can replace other metal forming processes including machining, investment casting (Powder Metal Injection Molding Manufacturing, 2016), and die forging (Russell, 2015).
Some of the current demonstrated advantages of the metal powder injection molding process include the following:
- High complexity shape capability;
- More efficient use of material and processes;
- Less material waste;
- Repeatability;
- Excellent mechanical properties;
- Lower overall product cost; and
- Tailored solutions using unique materials (Powder Metal Injection Molding Manufacturing, 2016, para. 2).
In addition, some of the key attributes of metallic powder injection molding include the following:
- It is a repeatable process for complex components made from high-temperature alloys;
- Parts are near fully dense, which gives excellent mechanical, magnetic, corrosion, and hermetic sealing properties, and allows secondary operations such as plating, heat treating, and machining to be easily performed;
- The shrinkage from molded parts to sintered parts is high (14–18%) but isotropic and controllable;
- Complex shapes are achieved through tooling techniques used in the plastic injection molding industry; and
- High volumes are attained through multi-cavity tooling (Powder Metal Injection Molding Manufacturing, 2016, para. 3).
Additional innovations in these technologies could expand these advantages further by making it possible to manufacture larger components such as those used in modern gas turbines — an issue that directly relates to the purpose of this study.
Purpose of the Study
In the past, precision die forging has been used to manufacture gas turbine compressor components from nickel-base alloys using a sequential thermo-mechanical processing approach to attain the requisite mechanical and geometric properties (Russell, 2015). The metallic powder injection molding process represents a potentially viable alternative three-dimensional (3D) manufacturing technology for gas turbine components made from nickel-base alloys, given its demonstrated abilities to produce components for transportation and medical applications (Russell, 2015). There remains a dearth of timely and relevant research for this purpose. As Russell (2015) emphasizes, "To date, the Metal Injection Molding process has had limited exposure as a manufacturing process for gas turbine compressor components" (p. 3).
Therefore, the purpose of this study is to identify opportunities to use metallic powder injection molding to produce components and parts cost-effectively for gas turbine manufacturing. The author and associates are currently conducting research on this technique to determine what is being done to push its boundaries, which in turn can inform current and future gas turbine component manufacturing.
Types of Material and Material Property Data
A wide array of alloys and metals can be used in the metallic powder injection molding process, including stainless steel, tungsten alloy, and low-alloy steel; however, the most commonly used materials are nickel, iron, molybdenum, and chromium (Materials Used in Metal Injection Molding, 2016). According to one industry expert, "Iron and nickel are two of the easiest elements to process due to their compatible melt temperature and ease of sintering" (Materials Used in Metal Injection Molding, 2016).
Currently, the majority (greater than 50%) of the total tonnage of materials used for metallic powder injection molding is comprised of iron-nickel alloys (Materials Used in Metal Injection Molding, 2016). Although binder materials are also added to these elements, they are eliminated from the end manufactured product during the sintering stage (Materials Used in Metal Injection Molding, 2016).
While a wide range of metals and alloys can be used in the metallic powder injection molding process, the types of materials of greatest interest are those specifically used for gas turbine component manufacturing, as described below.
Material Property Data
The following describes the various material types used in the manufacture of gas turbine engine components.
INCONEL 625 is a nickel-chromium alloy valued for its high strength, excellent fabricability (including joining), and outstanding corrosion resistance. Service temperatures range from cryogenic to 1,800°F (982°C) (INCONEL 625, 2015, para. 2). Its outstanding strength and toughness across the temperature range from cryogenic to 2,000°F (1,093°C) are derived primarily from the solid solution effects of the refractory metals columbium and molybdenum in a nickel-chromium matrix. The alloy has excellent fatigue strength and stress-corrosion cracking resistance to chloride ions. A typical application for alloy 625 is gas turbine engine ducting (INCONEL 625 Technical Data, 2016, para. 3). Some typical applications have also included heat shields, furnace hardware, and gas turbine engine ducting (INCONEL 625 Technical Data, 2016, para. 4). This alloy produces ASTM grain size 9.0 (INCONEL 625, 2016, para. 2).
INCONEL 718 is a nonmagnetic, corrosion- and oxidation-resistant, nickel-based alloy. Its outstanding strength and toughness across the temperature range from cryogenic to 2,000°F (1,093°C) are derived primarily from the solid solution effects of columbium and molybdenum in a nickel-chromium matrix. Typical annealing involves a continuous process anneal at 1,700°F (927°C) at 15 ft (4.57 m) per minute, which produces ASTM No. 12 grain size (INCONEL 718, 2016, para. 2).
Nimonic 90 is a wrought nickel-chromium-cobalt base alloy strengthened by additions of titanium and aluminum. It has been developed as an age-hardenable, creep-resisting alloy for service at temperatures up to 920°C (1,688°F) and is used for turbine blades (NIMONIC 90, 2016, para. 2).
Hastelloy X is a nickel-base alloy that possesses exceptional strength and oxidation resistance up to 2,200°F. It has also been found to be exceptionally resistant to stress-corrosion cracking in petrochemical applications, and it exhibits excellent forming and welding characteristics (Hastelloy X Technical Data, 2016, para. 3).
The physical properties of IN 625 are summarized below. At room temperature (22°C / 72°F), IN 625 has a density of 8.44 g/cubic cm (0.305 lb/cubic in.) and an electrical resistivity of 1.26 microhm-m (49.6 microhm-in.). Mean coefficients of thermal expansion range from 13.1 × 10⁻⁶ m/m-°C at 20–204°C to 17.3 × 10⁻⁶ m/m-°C at 20–982°C, with corresponding British units ranging from 7.3 to 9.6 microinches/in.-°F. Thermal conductivity at 23°C is 9.8 W/m-°C, rising to 21.3 W/m-°C at elevated temperatures. Specific heat at 0°C is 429 J/kg-°C (0.102 Btu/lb-°F), increasing to 0.134 Btu/lb-°F at higher temperatures (INCONEL 625 Technical Data, 2016).
Average hardness and tensile data for IN 625 at room temperature indicate that annealed sheet (0.014–0.063" thick) achieves an ultimate tensile strength of 132.0 ksi (910 MPa), a yield strength of 67.9 ksi (468 MPa), 47% elongation in 2", and a Rockwell hardness of B94. Annealed plate specimens at various thicknesses (1/4" through 1-3/4") show ultimate tensile strengths ranging from 127.2 to 132.3 ksi (877–912 MPa) and yield strengths from 65.5 to 80.0 ksi (452–552 MPa) (INCONEL 625 Technical Data, 2016).
The mechanical properties of IN 718 include an ultimate tensile strength of 1,120 MPa (162,000 psi), a yield tensile strength of 827 MPa (120,000 psi) at 0.200% strain, elongation at break of 31%, modulus of elasticity of 205 GPa (29,700 ksi), Poisson's ratio of 0.284, and shear modulus of 80.0 GPa (11,600 ksi), with a Rockwell C hardness of 24.
The mechanical properties of IN 625 include an ultimate tensile strength of 915.6 MPa (132,800 psi), a yield tensile strength of 462 MPa (67,000 psi) at 0.200% strain, elongation at break of 48%, modulus of elasticity of 208 GPa (30,200 ksi), Poisson's ratio of 0.28, and shear modulus of 81.4 GPa (11,800 ksi) (INCONEL 625, 2016).
Typical mechanical properties for Nimonic 90 in extruded bar form include, for the precipitation-treated condition at room temperature: minimum yield strength of 695 MPa, minimum tensile strength of 1,080 MPa, minimum elongation of 20%, and minimum hardness of 310 HV. Typical values for the precipitation-treated condition are 672 MPa yield strength, 1,038 MPa tensile strength, and 31% elongation (Nickel Alloy 90 / Nimonic 90, 2016).
The physical properties of Hastelloy X at room temperature include a density of 0.297 lb/cubic in. (8.22 g/cubic cm) and an electrical resistivity of 46.6 microhm-in. (1.18 microhm-m). Mean coefficients of thermal expansion range from 7.7 microin./in.-°F (13.8 × 10⁻⁶ m/m-K) at 79–200°F to 9.2 microin./in.-°F (16.6 × 10⁻⁶ m/m-K) at 79–1,800°F. Thermal conductivity ranges from 63 Btu-in/ft²-hr-°F (9.7 W/m-K) at room temperature to 189 Btu-in/ft²-hr-°F (27.4 W/m-K) at elevated temperatures. Poisson's ratio is 0.320 at room temperature and 0.328 at –108°F/–78°C. Magnetic permeability is less than 1.002 at 200 oersteds (Hastelloy X Technical Data, 2016).
Average room temperature tensile data for Hastelloy X show that sheet (0.012–0.090" thick), heat treated at 2,150°F (1,177°C) and rapid cooled, achieves an ultimate tensile strength of 110.3 ksi (760 MPa), a yield strength of 55.1 ksi (380 MPa), and 44% elongation in 2". Plate (3/8 to 2" thick) under the same heat treatment achieves 107.7 ksi (743 MPa) ultimate tensile strength, 49.1 ksi (339 MPa) yield strength, and 51% elongation (Hastelloy X Technical Data, 2016).
References
Anderson, B. (2011, Fall). Review: Prime movers of globalization: The history and impact of diesel engines and gas turbines. Electronic Green Journal, 32, 1–4.
Ferri, O. M., & Ebel, T. (2011, January 17). The influence of a small boron addition on the microstructure and mechanical properties of Ti-6Al-4V fabricated by metal injection moulding. Advanced Engineering Materials, 13(5), 436–447.
Hastelloy X technical data. (2016). High Temp Metals. Retrieved from http://www.hightempmetals.com/techdata/hitempHastXdata.php
INCONEL 625. (2015). Special Metals. Retrieved from
INCONEL 625 technical data. (2016). High Temp Metals. Retrieved from http://www.hightempmetals.com/techdata/hitempInconel625data.php
INCONEL 718. (2016). MatWeb. Retrieved from http://www.matweb.com/search/datasheet.aspx?matguid=b95db0912b2a4b8bb0c39b34d3672c73&ckck=1
INCONEL 738. (2016). MatWeb. Retrieved from http://www.matweb.com/search/datasheet.aspx?matguid=e76f115155d34f10948662fe3219fdfd
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Osada, T., Sakurai, R., Hashikawa, R., Tsumori, F., Miura, H., & Toda, K. (2015, April 11). Deformation control of large sized MIM parts by changing the powder size distribution. Journal of the Japan Society of Powder and Powder Metallurgy, 62(3), 108–113.
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Russell, A. D. (2015, September). The manufacture of gas turbine compressor components by Metal Injection Molding. Unpublished dissertation.
Williams, B. (2003). Challenges for MIM titanium parts: Cost and contamination are among the concerns of MIM producers working with titanium powder. Metal Powder Report, 58(10), 30.
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