Technical Paper: PIM International, Vol.4 No.1 March 2010, pages 67-70, 1907 words

Authors: J.M. Contreras [1], A. Jiménez-Morales [1] and J.M. Torralba [2]

[1] Dept. of Materials Science and Engineering, Universidad Carlos III de Madrid , Avda. de la Universidad 30, 28911, Leganés (Madrid), Spain
[2] IMDEA Materials, Universidad Carlos III de Madrid , Avda. de la Universidad 30, 28911, Leganés (Madrid), Spain

Abstract

Inconel 718 is one of the most common Ni-base superalloys due to its large number of engineering applications in automotive, chemical, aerospace and energy generation industries. The aim of this work is to study the influence of the particle size distribution along with the chemical composition of different Inconel 718 powders on the final properties of components fabricated by Metal Injection Moulding (MIM).

In order to carry out this study, five feedstocks have been prepared with monomodal, bimodal, narrow and wide particle size distributions mixing four raw Inconel 718 powders in different proportions. Next, all of the feedstocks are injection moulded to fabricate green parts that are subjected to debinding and sintering processes using different atmospheres and temperature cycles. Finally, the relative density, porosity and hardness of the sintered materials are determined relating the particle size and chemical characteristics of the powder with the results.

There are not too many papers that provide information about MIM of Inconel, making this technology highly suitable for reducing production costs in many applications. This article sheds light on what are the most convenient Inconel 718 powders to be processed by MIM

Introduction

Metal injection moulding represents an alternative process to manufacture powder metallurgy components. It is inspired by the polymer injection process allowing the fabrication of small, complex, near-net-shaped parts in a profitable way. This technology has been successfully applied in the last two decades to a great number of ceramic and metallic engineering materials, growing in numbers every year. Among all of them, nickel base superalloys seem to be good candidates to be processed by this technique, allowing cost savings when compared to other techniques such as investment casting. Inconel 718 is the superalloy most extensively used in the industry for applications that require high temperatures. This material can be hardened by precipitation of different phases containing Nb, Al and Ti and it combines high strength with a good corrosion resistance. Many applications of Inconel 718 are found in aerospace, energy generation, chemical, medical and tooling industries [1]. One important disadvantage is the careful analysis and control of the processing of this material, since different elements such as carbon, oxygen and nitrogen cause a deterioration of its mechanical properties [2].

The aim of this work is to investigate the influence of different powder characteristics, such as the particle size distribution and the chemical phases present in the raw powder, on the processing of the superalloy Inconel 718 by MIM.......

Further sections of this paper include:

Experimental
Results and Discussion
Conclusions
Acknowledgement
References

Figures and Tables:

Fig. 1 SEM images of the Inconel powders: (a) Inco 1 (<22 m), b) Inco 2 (16-45 m), c) Inco 3 (45-63 m) and d) Inco 4 (95-212 m)

Fig. 2 SEM image of Inco 3 under higher magnification

Fig. 3 Particle size distribution of the four Inconel powders (Inco 1 to Inco 4) that are used in this work

Fig. 4 Carbon and oxygen contents after thermal debinding using different atmospheres

Fig. 5 Relative density and shrinkage of Inconel components after sintering in a vacuum

Fig. 6 TGA-DTA analysis of Inconel 718 powder Inco2

Fig. 7 Hardness of Inconel parts sintered at 1280ºC for 360 minutes (cycle STR-3)

Table 1 The characteristics of the four Inconel 718 powders that are used in this work: pycnometer density, apparent density, tap density and particle size distribution

Table 2 Chemical composition of Inconel 718 powders

Table 3 The proportions (% by volume) of the Inconel 718 powders that are used to fabricate the powder blends 1 to 5

Table 4 The critical and optimal solids loading of the Inconel feedstocks that are determined by torque rheometry

Table 5 The thermal debinding cycles to remove the binder system from the green parts

Table 6 The sintering cycles: atmospheres, thermal cycle and duration.