Residual stress of thin diamond films deposited by chemical vapor deposition (CVD) method was measured using a new method for residual stress measurement we developed. Compressive residual stresses of CVD diamond films were determined from the height and diameter of protuberance of film delaminated by pulse laser spallation technique. We produced the protuberance with different diameter and height by changing the laser energy. Compressive stresses were calculated from the momentum balance of atmospheric pressure and internal compressive force of the film. The residual stress of the well-faceted diamond film was measured as K338G22 MPa and agreed well with the stress (K348G 17 MPa) measured by the X-ray diffraction method. In three other polycrystalline diamond films with different grain structure, the compressive stresses decreased from 300 to 147 MPa with decreasing the grain size from a few microns to tens of nanometers. Small compressive stresses of fine grain films are correlated with the grain boundary structure according to visible Raman spectra study conducted. q

Water cavitation technique can be applied to modify the surface strength of materials as an attractive new peening route. By inducing cavitation of ultrahigh speed water due to water-jet, the numerous impacts induced by the cavitation bubbles impact can produce compressive residual stress on material surface in the similar way as that by shot peening. In the present paper, an automobile part of steel gear shaft with complex shape is processed by water peening process. Compressive residual stress induced by water peening was measured to investigate the surface strengthening effect as a quantitative factor. The residual stresses on the tooth surface of the gear are measured by X-ray diffraction method. The effect of process conditions such as water outlet pressure, standoff distance of the nozzle, and peening time are discussed. To investigate the effect of heat treatment, carburizing-quenching is implemented to the gear shaft. By comparing the residual stresses of the tooth before and after water peening, the effectiveness of water peening process on surface strengthening is verified for a quenched gear shaft.

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