Metallic Powder Injection Molding for Gas Turbines
Invented by Hans-Joachin Pabst von Ohain and Frank Whittle in the 1930s, gas turbines have become essential technologies for global transportation and international trade today (Anderson, 2011). In fact, gas turbines are among the most efficient machines ever designed for transporting large amounts of cargo for long-distances and these technologies boast the lowest carbon dioxide emission rates in terms of per tons miles compared to other transportation technologies (Anderson, 2011). A typical gas turbine engine and its main constituent components is depicted in Figure 1 below.
http://www.intechopen.com/source/html/47835/media/image1_w.jpg
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/parts in the medical field, aerospace and other industries. The plan is to use metal injection molding technique to produce parts/components for the manufacturing of gas turbines. Conceivably, this technique holds the potential to help reduce costs in producing these parts/components for gas turbine manufacturing. According to one commercial vendor, "Metal Injection Molding (MIM), sometimes called Powdered Injection Molding (PIM), is an advance 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 like 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, however, could expand these advantages 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 as discussed below.
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, though, 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 will be to identify opportunities to use metallic powder injection molding to produce components/parts cheaply for gas turbine manufacturing, The author and his associates are currently conducting research on this technique to find out what is being done to push its boundaries which in turn can help in current and future gas turbine component manufacturing.
Chapter Two: Review of the Literature
Types of material
A wide array of alloys and metals can be used in the metallic powder injection molding process, including stainless steel, tungsten alloy, as well as 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 (>50%) of the total tonnage of materials used for metallic powder injection molding is comprised of iron-nickel allows (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) (see Figure 2 below).
Figure 2. Metal injection molding feedstock preparation
Source: http://www.custompartnet.com/wu/images/metal-injection-molding/mim-feedstock.png
While a wide range of metals and allows can be used in the metallic powder injection molding process, the types of materials that are of interest are specifically those used for gas turbine component manufacturing as discussed below.
Material property data
A description of the various material types used in the manufacture of gas turbine engine components is provided in Table 1 below.
Table 1
Types of materials used in gas turbine component manufacture
Material type
Description
This is a nickel-chromium alloy which is used for its high strength, excellent fabricability (including joining), and outstanding corrosion resistance. Service temperatures range from cryogenic to 1800°F (982°C) (INCONEL 625, 2015, para. 2). The outstanding strength and toughness in the temperature range cryogenic to 2000°F (1093°C) in IN 625 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).
Typical annealing - continuous process anneal, 1700°F (927°C) at 15 ft (4.57 m) per minute. This produces ASTM No. 12 grain size (INCONEL 718, 2016, para. 2).
This is a nonmagnetic, corrosion - and oxidation-resistant, nickel-based alloy. Its outstanding strength and toughness in the temperature range cryogenic to 2000°F (1093°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. Some typical applications for alloy 625 have 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).
Nimonic 90
This 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
(1688°F) and is used for turbine blades (NIMONIC 90, 2016, para. 2).
Hastelloy X
This is a nickel base alloy that possesses exceptional strength and oxidation resistance up to 2200°F. It has also been found to be exceptionally resistant to stress-corrosion cracking in petrochemical applications. The alloy has excellent forming and welding characteristics (Hastelloy X technical...
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