A comparative study is made on root bending fatigue performance of spur gears and plane bending fatigue performance of notched test bars. R = 0 root bending fatigue tests are made on small spur gears with critical root radius 1.0 mm. The results are compared to plane bending fatigue tests of 0.9 mm radius notched specimens. Results are presented for tests on 4%Ni/2%Cu/1.5%Mo prealloyed PM steel with addition of about 0.6% graphite. Predicted values from the test bars coincide well with the results obtained from the gear root fatigue tests.

The solubility of Cr in cubic carbides in the systems WC-Co-TaC and WC-Co-ZrC has been determined using equilibrium samples. Thermodynamic calculations were used to design the alloys through extrapolations of Gibbs energy expressions. The alloys were designed to have a microstructure containing the following phases: WC, liquid, , graphite and cubic carbide. The alloys were investigated using scanning electron microscopy and analyzed using energy-dispersive X-ray spectrometry. The present work shows how the Cr solubility depends on which cubic carbide former that is present. The WC-Co-Cr-Zr alloy has no detectable amount of Cr whereas the WC-Co-Cr-Ta alloy has 12% Cr in the cubic carbide.

Sintered steels are materials characterized by residual porosity, whose dimension and morphology strongly affect the fatigue crack growth behaviour of the material. Prismatic specimens were pressed at from Astaloy CrM powder and sintered varying the sintering temperature and the cooling rate. Optical observations allowed to evaluate the dimensions and the morphology of the porosity and the microstructural characteristics. Fatigue tests were performed to investigate the threshold zone and to calculate the Paris law. Moreover tests were performed to complete the investigation. Both on fatigue and samples a fractographic analysis was carried out to investigate the crack path and the fracture surface features. The results show that the Paris law crack growth exponent is around 6.0 for sintered and around 4.7 for sintered materials. The same dependence to process parameters is not found for .

Optimized choice of material for two principally different types of PM components is presented. The first is characterized by high stresses in areas with high stress concentrations (for example synchronizer hubs with very sharp notches, typically <0.25mm in the pre-synchronizer slot and the inner splines). The second type has slightly larger notch radii (small spur gears and sprockets with typically notch radii between 1- 3mm). Diffusion alloyed materials are well suited for sharp notch components. Pre-alloyed materials are also well suited for applications with sharp notches if compressive residual stresses in the notch roots are created by appropriate process control. A free choice of material is available for components with the larger notch radii.