Under oil lubrication with PAO, the friction behavior is essentially the same for three materials, i.e., baseline, heat treated and FSP treated. This is true for the three loads tested. Fig. 8a and b shows the variation of friction coefficient with time for tests conducted at 25 and 75 N, respectively. The measured friction coefficients are between 0.1 and 0.12 for all the contact pairs. The friction of the baseline material is slightly noisier compared to the hardened surfaces, especially at the low load of 25 N. This may be indicative of more local plasticity at the asperity contacts of the softer annealed material compared to harder surfaces. The average friction coefficient for the entire duration of each of the lubricated tests is shown in Fig. 8c. There was a slight reduction in average friction with load, but little difference between the three conditions of the flat specimen.