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Details for the subject:

Background, Context:

Nodular Graphite Cast Irons (NGCI) are known since the 70th

and actually industrially used to

build some automotive parts mechanically solicited. NGCI present different matrix when

chemical composition and/or the cooling speed vary. We can find a wide range of grades fromthe 100% pearlitic matrix, more mechanically resistant to the 100% ferritic one, with a great

plasticity.

Ferritic NGCI show also good tenacity and are used to built security automotives

parts [1,2,3], where a great absorption of energy during the deformation is needed. Theses

parts are also used in fatigue [4,5]; there are shot penned to put residual compressive stress at

the surface and thus improve the fatigue behavior [6,7].

For answering to economical and ecological considerations, the weight and therefore the

thickness of these parts have to decrease. This is in contradiction with the formation of the

ferritic matrix and the elaboration of such a part need some care. However recent works showthat it is possible to obtain such a matrix in the as cast state, for 5 mm thick samples [8] and

we did it in our laboratory [9].

Although cast irons are not especially vulnerable to atmospheric corrosion, most of

automotive under chassis parts are painted, manly for esthetic considerations. However, the

life length of this coating is very limited and the cost not negligible. The galvanization of cast

iron parts improve the corrosion resistance and guarantee a well surface aspect for a longer

time. This treatment is possible if the surface of the parts is well prepared, namely by 2 shotspenning [10].

During hot dip galvanization, the pieces are immerged in a liquid zinc alloy at around 450C.At this temperature, the material is heat treated like in a tempering treatment and compressive

stress induced by the shot penning can relax. This can modify the fatigue behavior of the

galvanized parts. However a study realized by Els-Botes and Hattingh [11] shows a benefit

effect of galvanization on the number of cycle to failure of cast irons, namely in the case of

ferritic matrix but without specific surface preparation by shot peening.

This study targeted to show how the galvanization process affect the fatigue behavior of shot

penned parts and to optimize the galvanization process (shot penning and galvanization) in the

aim to increase the fatigue length life.

Research subject, work plan:

This study cover wide fields of material science and mechanical engineering, as the

elaboration by casting, the mechanical and thermo chemical surface preparation or the

mechanical testing (roughness and residual stress measurements, fatigue characterization,).

This work started 3 years ago by stages of Master 2 Research Degree [9, 12]. During 3 years,

we developed several technical aspects as the elaboration of cast iron thin pieces with ferritic

matrix, the shot peening and the galvanization of these pieces, the residual stress measurement

by X-ray and the fatigue characterization. Some of these results were presented in recent

symposiums [13,14].

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Under the light of this passed work, we have established a list of parameters which influence

both the quality of the surface and the fatigue behavior. We target now, within the framework

of this PhD thesis, an experimental design to optimize these parameters.

This work needs experimental capacities and offers the opportunity to discover and to practice

a lot of experimental techniques in the mechanical field (fatigue test, X-Ray residual stress

measurement, roughness, hardness,) and in the material science field (cast iron elaboration,surface treatment, microstructure observation by optical microscopy and scanning electronic

microscopy, mico analysis,).

We have the chance to work in a Laboratory with around 70 researchers with complementary

competences (see our web site), also, for each technique used in this study, the work will

follow by a specialist researcher. The team working now on this subject is of 7 associate

professors and 2 researchers.

References:

[1] D. Balloy, J.C. Tissier, Scandinavian Journal of Metallurgy - Steel Research International,

Vol. 78, Issue 2 (2007) 167-172.

[2] Guillemer-Neel C., Bobet V., Clavel M., Material Science Engineering A, Vol. 272 (1999)

431-442.

[3] Labrecque C., Gagn M., Canadian Metallurgical Quarterly, Vol. 37, No. 5 (1998) 343-

378.

[4] Kim J.H., Kim M.G., Key Eng. Mater., Vol. 933, No. 8 (2000) 183-187.

[5] Asi O., Engineering Failure Analysis, Vol.13, Issue 8 (2006) 1260-1267.

[6] Yasuo Ochi, Kiyotaka Masaki, Takashi Matsumara, Takeshi Sekino, International Journal

of fatigue, Vol. 23, Issue 5 (2001) 441-448.

[7] Nadot Y., Denier V., Engineering Failure Analysis 11 (2004) 485-499.[8] www.sorelmetal.com/en/publi/Frset_publi.htm

[9] Stage of Master degree, Richard Coquet, 2008/2009

[10] Dauphin J.Y., Marcy L., Tissier J.C., La galvanisation des fontes, Document de synthse,

Ecole Centrale de Lille, Juillet 1995.

[11] Els-Botes A., Hattingh D.G., Surface Treatment V, 5th

International Conference on

Computer Methods and Experimental Measurements for surface Treatment Effects, Seville,

Spain, 20-22 June 2001, pp 191-200, 2001.

[12] Stage of Master degree, Christophe Grosjean, 2006/2007

[13] Grosjean C., Niclaeys C., Balloy D., Quaegebeur P., Tissier J.C., MECAMAT congress,

Aussois, France, 28 January-1 February 2008

[14] Niclaeys C., Balloy D., Quaegebeur P., Tissier J.C., Grosjean C.; Materiais 2009, 5thinternational materials symposium, Lisbon, Portugal, 5-8 April 2009.