The microstructure, tensile, and axial fatigue behavior of Fe-Mo-Cu-Ni alloys made by binder-treated processing were investigated and the attendant mechanical behavior compared to that of an analogous alloy processed by diffusion alloying. Binder treatment can provide a variety of advantages in manufacturing over diffusion alloyed powders, including faster and more consistent flow into the die cavity, increased green strength, and reduction of fine particle dusting. In addition to conventional porosity, smaller, "copper diffusion" pores were observed where copper particles were present prior to forming a liquid phase during sintering and diffusion into the iron particles. The heterogeneous microstructure in both alloys was typical of P/M alloy steels, consisting of areas of "divorced pearlite," martensite, and nickel-rich ferrite. Tensile and fatigue resistance were enhanced by an increase in the molybdenum content in the alloys. The tensile strength of both types of alloys was similar and fatigue life was essentially identical for the two systems. Fractographic observations showed that fracture initiated primarily at pore clusters in the surface region. Investigation of small cracks by a surface replication technique showed that fatigue cracks nucleated at pores or pore clusters, and that crack propagation exhibited a significant amount of deflection and branching, attributed to local obstacles in the microstructure, such as Ni-rich areas. Fracture surfaces showed ductile fracture in the interparticle bridge regions, cleavage facets in pearlitic regions, and striations due to cyclic loading.
|Original language||English (US)|
|Number of pages||9|
|Journal||International Journal of Powder Metallurgy (Princeton, New Jersey)|
|State||Published - Apr 1 2001|
ASJC Scopus subject areas
- Metals and Alloys
- Industrial and Manufacturing Engineering