Technical Paper: PIM International, Vol.4 No.4 December 2010, pages 68-70, 1263 words

Authors: Hideshi Miura, Hikaru Ikeda, Takanori Iwahashi, and Toshiko Osada

Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.

  

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Abstract

Inconel 718 is a representative Ni-base superalloy. However, it is not easy to produce complex shaped parts at low cost due to the material’s poor workability.

In this study, the Metal Injection Moulding (MIM) process, one of the near net-shape forming methods for such powders, has been applied for fabricating Inconel 718 compacts using both gas and water atomised powders.

By optimising the MIM process, the obtained relative density was near full density (98~99%) and the tensile property of as-sintered compacts had a strength of 1000MPa and elongation of around 10%, properties which are similar to those of wrought materials. High temperature and fatigue properties of heat treated MIM compacts are presented in detail. 

Introduction

Superalloys have been used especially for aerospace and atomic energy applications because of their excellent attributes of high corrosion and oxidation resistance, and high temperature strength. Inconel 718 is one representative Ni-base superalloy. Inconel 718, however, has a high nickel content. It is not easy, therefore, to manufacture complex shaped parts at low cost due to the material’s poor workability.

Powder metallurgy is an effective way to produce the complex shaped parts at low cost. However, with die press moulding of the powder it is also difficult to obtain high density, so it is hoped that metal injection moulding (MIM) will be a suitable processing technique for complex shaped parts even with poor workability materials.

In this paper, MIM of Inconel 718 pre-alloy powders is conducted and the various mechanical properties of the injection moulded compacts are discussed as a function of the type of powders, processing techniques, sintered densities and chemical compositions.
Experimental

Three types of pre-alloyed Inconel 718 powders were used in this study. Table 1 shows the characteristics of the selected powders. Water and gas atomised powders with different particle size and composition were used. In this paper, these powders were designated as W2, W10, and G22 by the differences in atomisation method and particle size. Fig. 1 shows electron micrographs of the selected raw powders. The powders and wax based binders were compounded and pelletised for injection moulding. The solid powder loading was 62 vol.% for the W2 specimen, and 65 vol.% for the W10 and G22 specimens.........

Further sections of this paper include:

• Results & Discussion
  - Relative density, hardness, and grain size
  - Chemical composition
  - Tensile property
  - Fatigue strength
• Conclusion
• References

Figures and Tables:

Fig. 1 Electron micrographs of Inconel 718 alloy raw powders
Fig. 2 Relationship between relative density and sintering temperature for Inconel 718 specimens
Fig. 3 Relationship between hardness and relative density for Inconel 718 specimens
Fig. 4 Optical micrographs of Inconel 718 high density specimens; non-etched (A) and etched (B)
Fig. 5 Relationship between carbon content and relative density for Inconel 718 specimens
Fig. 6 Relationship between oxygen content and relative density for Inconel 718 specimens
Fig. 7 Relationship between tensile strength and elongation for Inconel 718 high density specimens
Fig. 8 Electron micrographs of fractured surfaces, W2 sample on the left, G22 sample on the right
Fig. 9 An S-N curve for high cycle fatigue test at room temperature (G22 specimen)

Table 1 Chemical composition (mass%) of raw powders (Inconel 718)