Using Metal Injection Molding for Gas Turbine Component Manufacture

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 data, 2016, para. 3). This alloy possesses good oxidation resistance, high temperature strength (Materials used in metal injection molding, 2016, para. 3).

A description of the physical properties of IN 625 is provided in Table 2 below.

Table 2

Physical properties of IN 625

Physical Property

°C

Metric Units

°F

British Units

Density

22

8.44 g/cubic cm

72

0.305 lb/cubic in.

Electrical

Resistivity

23

1.26 microhm-m

1.27

1.28

1.29

1.30

1.31

1.32

74

49.6 microhm-in.

50.0

50.4

50.8

51.2

51.6

52.0

Mean Coefficient

of Thermal

Expansion

20-204

20-316

20-427

20-538

20-649

20-760

20-871

20-982

13.1 x 10(-6)m/m-°C

13.5

13.9

14.4

15.1

15.7

16.6

17.3

68-400

68-600

68-800

68-1000

68-1200

68-1400

68-1600

68-1800

7.3 microinches/in.-°F

7.5

7.7

8.0

8.4

8.7

9.2

9.6

Thermal

Conductivity

23

9.8 W/M-°C

11.4

13.4

15.5

17.6

19.6

21.3

74

68 Btu-in./ft2.-hr.-°F

79

93

Specific

Heat

0

429 J/kg-°C

32

0.102 Btu/lb-°F

0.107

0.111

0.115

0.118

0.123

0.134

Source: INCONEL 625 technical data (2016) at http://www.hightempmetals.com/techdata / hitempInconel625data.php

A description of the tensile strength for IN 625 is provided in Table 3 below.

Table 3

IN 625 Average Hardness and Tensile Data, Room Temperature

Condition

Form

Ultimate

Tensile

Strength,

ksi (MPa)

Yield

Strength

at 0.2%

offset, ksi (MPa)

Elongation

in 2"

percent

Hardness,

Rockwell

Annealed at

1925°F (1052°C),

rapid cooled

Sheet

0.014-0.063"

thick

132.0 (910)

67.9 (468)

47

B94

Annealed at

1925°F (1052°C),

rapid cooled

Sheet,*

0.0.78-0.155"

thick

131.5 (907)

67.4 (465)

45

B97

Annealed at

1925°F (1052°C),

rapid cooled

Plate,***

1/4"

1/2"

3/4"

1.00"

1-1/2"

1-3/4"

132.0 (910)

130.0 (896)

132.3 (912)

127.2 (877)

127.3 (878)

128.0 (883)

65.5 (452)

67.0 (462)

80.0 (552)

75.3 (519)

73.7 (508)

66.0 (455)

46

44

44

42

43

44

B94

B98

B98

B97

B97

C20

Source: INCONEL 625 technical data (2016) at http://www.hightempmetals.com/techdata / hitempInconel625data.php

The mechanical properties of IN 718 are set forth in Table 3 below.

Table 3

Mechanical properties of IN 718

Mechanical Properties

Metric

English

Hardness, Rockwell C

24

24

Tensile Strength, Ultimate

1120 MPa

162000 psi

Tensile Strength, Yield

827 MPa

@Strain 0.200%

120000 psi

@Strain 0.200%

Elongation at Break

31%

31%

Modulus of Elasticity

205 GPa

29700 ksi

Poissons Ratio

0.284

0.284

Shear Modulus

80.0 GPa

11600 ksi

The mechanical properties of IN 625 are set forth in Table 4 below.

Table 4

Mechanical properties of IN 625

Mechanical Properties

Metric

English

Tensile Strength, Ultimate

915.6 MPa

132800 psi

Tensile Strength, Yield

462 MPa

@Strain 0.200%

67000 psi

@Strain 0.200%

Elongation at Break

48%

48%

Modulus of Elasticity

208 GPa

30200 ksi

Poissons Ratio

0.28

0.28

Shear Modulus

81.4 GPa

11800 ksi

Source: INCONEL 625 (2016) at http://www.specialmetals.com/assets / documents/alloys / inconel/inconel-alloy-625.pdf

The typical mechanical properties for Nimonic 90 are set forth in Table 5 below.

Table 5

Typical mechanical properties for Nimonic 90

Material

Extruded Bar

Temperature °C

Yield Strength 0.2% (MPa)

Tensile Strength (MPa)

Elongation (%)

Hardness HV

Nimonic 90 bar

Solution Treated (BS HR2)

RT

295 max

Nimonic 90 bar

Precipition Treated (BS HR2)

RT

695 min

1080 min

20 min

310 min

Nimonic 90 Bar

Precipitation Treated (BS HR2)

672 (typical)

1038 (typical)

31

Source: Nickel Alloy 90 / Nimonic 90 (2016) at http://www.aircraftmaterials.com/data/nickel / nimonic90.html

The physical properties of Hastelloy X are provided in Table 6 below.

Table 6

Physical properties of Hastelloy X

Physical Properties

°F

British Units

°C

Metric Units

Density

72

0.297 lb./cubic in.

22

8.22 g/cubic cm.

Melting Range

Electrical

Resistivity

72

46.6 microhm-in.

22

1.18 microhm-m

Mean Coefficient

of Thermal

Expansion

79-200

7.7 microin./in.-°F

26-100

13.8 X 10(-6)m/m-K

79-1000

8.4 microin./in.-°F

26-500

14.9 X 10(-6)m/m-K

79-1200

8.6 microin./in.-°F

26-600

15.3 X 10(-6)m/m-K

79-1350

8.8 microin./in.-°F

26-700

15.7 X 10(-6)m/m-K

79-1500

8.9 microin./in.-°F

26-800

16.0 X 10(-6)m/m-K

76-1650

9.1 microin./in.-°F

26-900

16.3 X 10(-6)m/m-K

79-1800

9.2 microin./in.-°F

26-1000

16.6 X 10(-6)m/m-K

Thermal

Conductivity

70

63 Btu-in/ft2-hr-°F

20

9.7* W/m-K

76 Btu-in/ft2-hr-°F

11.1 W/m-K

98 Btu-in/ft2-hr-°F

14.7 W/m-K

144 Btu-in/ft2-hr-°F

20.6 W/m-K

159 Btu-in/ft2-hr-°F

22.8 W/m-K

174 Btu-in/ft2-hr-°F

25.0 W/m-K

189 Btu-in/ft2-hr-°F

27.4* W/m-K

Poisson's Ratio

-78

22

0.328

0.320

-108

72

0.328

0.320

Magnetic

Permeability

Room

Source: Hastelloy X technical data (2016) at http://www.hightempmetals.com/techdata / hitempHastXdata.php

Finally, the average room temperature tensile data for Hastelloy X are set forth in Table 7 below.

Table 7

Average room temperature tensile data for Hastelloy X

Form

Condition

Ultimate

Tensile

Strength

ksi (MPa)

Yield

Strength at

0.2% offset ksi (MPa)

Elongation

in 2" percent

Sheet, 0.012 to

0.090"

thick

Heat treated at

2150 °F (1177°C)

Rapid Cooled

110.3 (760)

55.1 (380)

44

Sheet,

0.091 to 0.312"

thick

Heat treated at

2150 °F (1177°C)

Rapid Cooled

109.5 (755)

55.9 (385)

45

Plate,

3/8 to 2"

thick

Heat treated at

2150 °F (1177°C)

Rapid Cooled

107.7 (743)

49.1 (339)

51

Source: Hastelloy X technical data (2016) at http://www.hightempmetals.com/techdata / hitempHastXdata.php

Initiatives to expand MIM technologies to facilitate gas turbine manufacturing

There have been a number of initiatives launched in recent years to facilitate the manufacture of gas turbine components using MIM technologies, including innovations in the types of powders that are used. According to Russell (2015), the powders that commonly employed in metal injection molding are obtained through water atomization or gas atomization. In either case, the process involves particle sizes of powders that range from 6µm-40µm. In this regard, Russell advises that, "The average particle size, the particle size distribution and the shape of the metal particles have an influence on the injection viscosity and also the homogeneity of the finished product" (2015, p. 31). At present, there are a number of different powder alloys that can be used for these purposes. Although differing in composition and size, the most commonly used alloy groups include the following:

Stainless steels;

Nickel base superalloys (including 718 Alloy);

Cobalt alloys;

Specialist magnetic alloys; and,

Duplex stainless steels (Russell, 2015, p. 31).

An MIM process developed by Ferri and Ebel (2011) employs titanium alloy components for manufacturing. According to Russell, this innovation holds significant promise for expanding the current applications of metallic powder injection molding that could conceivably be applied to the manufacture of gas turbine engine components. Likewise, in addition to the powder manufacturing methods such as water or gas atomization for creating suitable powders for the MIM process, Voice (2011) identifies an innovative approach to manufacturing powder through the use of liquid jets targeted at the surface of a solid material which results in the ablation of solid material powder particles. According to Russell (2015, "This method for the manufacture of powder is unique in that it is capable of cutting polyhedral grains from a solid material. The solid material could be titanium, a titanium alloy or an intermetallic compound such as gamma titanium aluminide" (p. 32).