We report a method for surface status assessment, which is based on spectrum analysis of impact response frequency. Impact behavior of 2Cr13 (AISI-420) stainless steel bulk material, plasma-sprayed Cr2O3 ceramic coating and flame-sprayed NiCrBSi alloy coatings were investigated. By using a specifically designed impact tester and its attached measuring system, time domain signals and frequency signals in the course of impact were recorded and analyzed. Both single impact mode with different energies and repetitive impact mode were applied. Surface morphologies after impact were observed. The results showed a significant interrelationship between the impact effect and the characteristics of the response frequency spectrum. Changes occurring in the material surface during impact were represented by the modification of response frequency spectrum. Discussions were made from energy point of view. We defined "attribute energy" in the form of frequency character to indicate surface status.

Impact assessment for laser hardened hypoeutectoid 2Cr13 martensite stainless steel was carried out on a specifically developed ball-on-flat impact tester. Results showed better impact behavior of 2Cr13 surfaces treated by a continuous wave CO2 laser than those under conventional heat treatment. Micro-hardness measurement demonstrated that the surface hardness of the laser treated specimens varied with the operation parameters of laser hardening. Scanning electron microscope (SEM) analysis and surface profile measurement suggested that the size of the impact wear scars of 2Cr13 specimens decreases with the increase of the surface hardness. EDX analysis showed that the oxidation resistance of the laser-hardened surfaces was relatively superior to their conventionally heat-treated counterparts. Compared with conventionally-treated 2Cr13 steel, the superior impact wear resistance of laser surface-processed steel was attributed both to grain refinement and to the higher martensite content near the surface that resulted from rapid cooling.

Based on heat transfer analysis and the consideration of the evaporation of surface asperities, a simplified model for laser surface polishing was established. As the dimension of asperities is usually in the scale of sub-micron, the model thus assumed uniform temperature over and in an asperity entity and the heat transfer could thus be treated as a point unit problem. The model aimed at preliminary prediction of the adequate setting of the processing parameters (typically the laser irradiation time) for laser polishing of a metal with known geometric surface consisting of micro-asperities and material properties. Prediction for polishing metallic materials of Fe, Al, Ti, and the 304 stainless steel showed the temperature rise in asperity varying significantly with the original surface topography of the substrates. Results indicate that, for the polishing of most metals with pulsed laser, laser with short pulse duration normally in the range of nano-second or less is required. Laser polishing of steel using a KF excimer laser with the pulse duration of 30 ns was subsequently performed. Characterizing the irradiated surface morphology by scanning electron microscope (SEM) and atomic force microscope (AFM) showed evident improvement in surface finish of the tested specimens.

A YAG pulsed laser with different pulse durations in the millisecond range was used to spot-irradiate ASSAB DF-2 (AISI-01) cold work steel. The influence of the pulse duration on the surface morphologies of the irradiated spots was studied by scanning electron microscopy (SEM), energy dispersion spectrometry (EDX) and three-dimensional surface profilometry. Results showed that the changes of the surface morphology were not uniform, especially for relatively shorter pulse durations. Surface roughness and morphology of the irradiated DF-2 cold work steel varied with the pulse duration depending on whether melting of the surface material occurred. Relevant mechanisms were discussed. Schematic map was also introduced to describe the change of the surface morphology.

This paper presents the results of the study on the effect of laser melting-solidification processing on the structure and tribological properties of plasma spray Al-Cu-Fe quasicrystalline alloy coatings. Dense and hard coatings were obtained by the laser post-treatment processing and the volume fraction of the icosahedral (i) phase was found to be dependent on the laser power and scanning velocity conditions. Using a parameter d, defined as the ratio of the laser power P, to the scanning velocity v, i-phase was observed to form for low values of d as a consequence of the high cooling rates. Furthermore, a correlation was worked out between the microhardness and the parameter d. Owing to the microstructure modification, the laser post-treatment provided significant improvement to the tribological properties of the plasma sprayed Al-Cu-Fe QC coatings. The frictional behavior was found to be dependent on the constituent phases formed in the laser post-treated coatings. In particular, low values of the friction coefficient were recorded in the early stage of the test for coatings containing a high volume fraction of i-phase. However, owing to the brittleness of the i-phase, the difference of the frictional behavior was reduced after 150 cycles, and the friction coefficient for all laser post-treated coatings stabilized at a value which was approximately half that of the as-received plasma sprayed coatings. After laser post-treatment, the wear rate was significantly improved only for the coatings containing a high content of i-phase.