Metal injection moulding of a new Fe-8Ni micron-size pre-alloyed powder

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Metal injection moulding of a new Fe-8Ni micron-size pre-alloyed powder

Technical Paper: PIM International, Vol.3 No. 4 December 2009, pages 54-59, 2107 words

Authors: A. Nouveau, H. Senillou & M. Bonneau

Eurotungstene, 9 rue André Sibellas, BP 152X, 38042


Metal injection moulding of a new Fe-8Ni micron-size pre-alloyed powderAbstract

With more than 60 years of international experience in powder metallurgy, Eurotungstene operates in business sectors such as cemented carbides, high-density materials, diamond tools and recently also in the metal injection moulding (MIM) industry as a manufacturer of micron-size metal powders.

Eurotungstene’s ability to innovate in the diamond tools industry has allowed the company to be considered as a technological leader: the company was the first to develop a new concept in binders for diamond tools applications (1997), and to produce, on an industrial scale, an extensive range of pre-alloyed powders by hydrogen reduction. This innovative solution [1] aims to replace the use of cobalt in binders for diamond tools: the more competitive pre-alloyed powders are now largely consumed by tool manufacturers.

Today, Eurotungstene offers its know-how and its experience to the MIM industry. By making a pre-alloyed Fe-8Ni powder, PA-FN08, with enhanced sintered part properties, Eurotungstene’s manufacturing process allows us to consider an alternative to the atomised or blended carbonyl powders [2-5]. PA-FN08 belongs to Microneex®, a range of micron-size metal powders, specially designed for MIM applications. PA-FN08 is the first pre-alloyed powder developed for the MIM industry by this manufacturing process that Eurotungstene is extending to other grades (Fe-36Ni, Fe-50Ni, Fe-29Ni-17Co…).

Part I. Development of a micron-size MIM powder

Considering the MIM market requirements and the µ-MIM developments, the aim of this research was to tailor a micron-size Fe-8Ni powder, suitable for the MIM process [6] and providing good mechanical properties [7-11]. A description of the study and key parameters of the Fe-8Ni powder are provided, followed by the characterisation of the final commercial PA-FN08 powder and mechanical properties of a sintered specimen in Part II.

Experimental material and procedure

Powder characterisation 
Eurotungstene produced four micron-size pre-alloyed Fe-8Ni powders through different processes. Powder properties displayed in Table 1 show different tap densities. Powder aspects are illustrated in the SEM pictures (Fig. 1). Oxygen levels were quite high but linked to a non-industrial process.

Binder system and mixing
In order to evaluate the compounding ability of the powders, four feedstocks were prepared: the four references of powders were mixed in a standard polymer-wax feedstock. Its composition was 54wt% polypropylene (PP), 43wt% paraffin wax (PW), 3wt% stearic acid (SA).

The mixing operations were conducted in a Brabender Plastograph W50EHT mixer with a pair of roller rotor cylinders, which is giving torque as a function of time. Homogeneity and maximum solid loading of each feedstock were evaluated by torque measurements [12-13] .

The same procedure was repeated for four tests: a small amount of powder was added, about 10g, all within two minutes, in order to wait for feedstock homogenisation. Depending on the powder and the binder, stabilisation sometimes proved difficult to obtain. However, a clear progressive increase trend of the torque was observed. A steady state value of the torque between two additions is a representation of homogeneity of the feedstock. The critical solid loading (in vol%) was considered to be reached when the torque curve displayed a drastic increase with the addition of a small amount of powder. In a second step, several tests were conducted with different ratios of paraffin wax. Stearic acid content was fixed for all four experiments, at a constant temperature of 180°C....

Further sections of this paper include:

- Part I. Development of a micron-size MIM powder
- Experimental material and procedure
- Powder characterisation
- Binder system and mixing
- Results and discussion
- Behaviour of powders in the feedstocks
- Tap density as criterion for MIM powders
- Ability of Powder 3 to be held in different binder systems
- Part II. Complete evaluation of PA-FN08
- Introduction
- Experimental
- PA-FN08 technical characteristics
- F-FN08 feedstock preparation and injection moulding
- Debinding and sintering conditions
- Results and discussion
- Green parts
- Sintered parts
- Mechanical properties
- Microstructure evaluation
- Conclusion
- Acknowledgement

Figures and Tables:

Fig. 1 SEM pictures of powders: Powder 0 top left, Powder 1 top right, Powder 2 lower left, Powder 3 lower right

Fig. 2 Evolution of critical solid loading for the four powders

Fig. 3 Torque as a function of solid loading for four different powders

Fig. 4 Link between critical solid loading and tap density

Fig. 5 Critical solid loading as a function of paraffin wt%, for Powder 3

Fig. 6 SEM of the PA-FN08 powder

Fig. 7 Particule size distribution (laser diffraction) of PA-FN08 powder

Fig. 8 Viscosity versus shear for F-FN08

Fig. 9 MIM tensile bar dimensions (ISO2740)

Fig. 10 Optimised sintering cycle for F-FN08

Fig. 11 Weight and density of the sintered parts

Fig. 12 Linear shrinkage rate from green to sintered state

Fig. 13 Porosity evaluation: top row, PA-FN08 (left 100µm, right 20µm). Bottom row Iron-Nickel 8% mix, (left 100µm, right 20µm)

Fig. 14 Microstructures after nital etching. Top row PA-FN08 after nital etching (left 100µm, right 20µm). Bottom row Iron-Nickel 8% mix after nital etching (left 100µm, right 20µm)

Table 1 Physical analysis of the four powders

Table 2 Chemical and physical characteristics of PA-FN08 powder

Table 3 Moulding parameters

Table 4 Weight and dimensions of green parts

Table 5 Chemical composition of the sintered parts after sintering

Table 6 Dimensions of the sintered parts

Table 7 Mechanical properties of the sintered parts

Table 8 Comparison of porosity

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