Contributions a l'amelioration de l'usinabilite de pieces fabriquees par metallurgie des poudres (French text)

The first chapter of this thesis presents an exhaustive literature review on machining in general, and on the main differences that exist between the machining of wrought and sintered steels. The second chapter consists of a critical review of the techniques available for the complete characterization (stereological parameters and chemical composition) of second phase particles.; The third chapter synthesizes three articles presented at the end of the document (appendix) that discuss the characterization of second phase particles. This chapter presents the techniques developed based on the size of the second phase particles to be characterized.; The second section of chapter 3 focuses on the characterization of second phase particles with a diameter inferior to one micrometer. To develop a robust technique, we studied the quantitative characterization of multi-phase inclusions. More specifically, we discuss the advantages and disadvantages of selected characterization techniques in electron microscopy as well as different techniques of sample preparation.; Finally, the last section of chapter 3 focuses on the characterization of wear on tools used to machine P/M parts. Thus, to characterize flank wear on drill bits, we present a method based on image analysis to superimpose the image of the new tool on the image of the same tool after it has been used to drill a given number of holes.; The fourth chapter presents a summary of the work done to improve the machinability of parts made via the P/M process. The first section presents some results which demonstrate that, for drilling operations, the evolution of the axial force as a function of the quantity of material removed is directly proportional to the width of flank wear on the tool. The second section of this chapter focuses on the advantages of using sinter-hardenable powder grades pre-alloyed with manganese sulfide particles. The last section of this chapter discusses the effect of furnace atmosphere during elaboration of and sintering of powders pre-alloyed with manganese sulfide particles. Finally, a model of the transformation of the MnS particles during the elaboration and sintering of resulfurized P/M steels is presented. The latter indicates that when the partial pressure of oxygen is high, internal oxidation of the manganese sulfide particles takes place along the grain boundaries in contact with the surface. (Abstract shortened by UMI.)...