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.

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.

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650℃. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400℃ and severe adhesive wear at 650℃ owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to b-Al50(Fe,Cu)50 phase in the coating was higher after test at 400℃ than that at 650℃. The variation of the ratio i/b of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

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.

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.