The failure of sintered steels differs from the behaviour of wrought steels because of factors such as porosity, remnants of previous particle surfaces and generally more complex microstructures. A...

A review of failure of sintered steels: fractography of static and dynamic crack nucleation, coalescence, growth and propagation

The present paper is aimed at investigating the effect of the sinter-hardening treatment in improving the tooth root fatigue resistance of gears obtained by Powder Metallurgy. The gears were produc...

Tooth root bending fatigue strength of small-module sinter-hardened spur gears

Fatigue and Fracture Control for Powder Metallurgy Components

Powder-metal-processed bearings and gears are finding increasing application because of their economical and technical advantages. The residual pores from the sintering operatives act as lubricant pockets and dampen sound and vibration. However, porosity also decreases the mechanical strength and reduces the life of components fabricated by powder processing relative to similar wrought components. The rolling contact fatigue behavior of sintered and heat treated steel rollers was investigated using a fatigue test machine designed and fabricated for that purpose. The powder-metal-processed and the wrought steel rollers that were tested had similar composition and hardness and were mated against wrought steel rollers of high hardness. The contact stress versus number of cycles to failure data showed that the wrought steel had a very high endurance limit under rolling contact fatigue compared to the sintered steels investigated. Rolling contact fatigue behavior was found to depend on the porosity present in the material. Large surface peeling failures and pitting type fatigue failures were observed in the sintered and hardened steels, while only pitting type failures were observed in the wrought steels

Rolling Contact Fatigue Behavior of Sintered and Hardened Steels

The method of studying processes of deformation and failure of powder materials in the column of a scanning electron microscope in situ is quite promising, and it is suitable for the further study of processes of failure. The specifies of the processes of deformation and failure of sintered iron manifests itself mostly at the structural level. Upon nucleation of a crack that is able to grow under the effect of applied stresses, the stage of formation of micropores and merger of microcracks does not play a substantial role. Cracks nucleate at places containing defects such as pores and particle boundaries. Primary cracks can nucleate independently of each other at places of increased stress concentration that is due to the inhomogeneity of the structure of sintered iron. A crack nucleated at the preceding stage of loading can be arrested, forming a stable defect during subsequent loading. This shows that porous iron is able to effect relaxational rearrangements in large volumes of material. The authors detected experimentally the rotation of individual particles during deformation, and that is direct proof of the substantial role of rotational modes in the deformation of porous bodies. The previously voiced assumption that the length of the slipmore » plane in sintered iron is limited by the dimension of the element of the structure bounded by intraparticular pores was experimentally confirmed.« less

Investigation of the special traits of failure of sintered iron by the in situ method

Crack development has been investigated in sintered iron with porosities between 10 and 20%. The ductility of the samples was changed by O2 or N2 annealing and low temperature deformation. Depending on the work hardening ratio, various characteristic fracture modes have been observed by means of tensile experiments combined with analyses of acoustic emission within the scanning electron microscope (SEM). Corresponding to these fracture modes, the fracture toughness (J c values) showed a strong dependence on porosity and thermal treatment. The behaviour is discussed on the basis of a fracture model for a single sintered neck. PM/0204

G. Leitner

Papers

Crack Propagation and Processes Near Crack Tip of Metallic Sintered Materials