Objective Laser process parameters have a significant effect on surface texture morphology. Existing research has focused on the influence of laser process parameters on the morphology of micropits and the processing mechanism. However, in the laser ablation of metal materials, the geometry and size of the surface texture are not stable with changes in the laser process parameters. To solve this problem, based on a laser ablation test, this study systematically investigates the influence of laser energy density on the evolution process of the surface texture geometry of GCr15 steel, analyzes the formation mechanisms of different morphologies, and describes the geometric size and shape stability of the surface texture of GCr15 steel, which provides a theoretical basis for the processing and size control of the surface texture of GCr15 steel.Methods In this study, GCr15 steel is used. First, the samples are ground and polished to avoid the additional influence of surface roughness and flatness on the laser ablation test. Second, a laser ablation test is performed on the pretreated samples. The laser energy density is increased from 54.585 W/mm2to 473.968 W/mm2, spot diameter is 350 p.m, pulse number is 1, and laser incident angle is 90 degrees . After the ablation test, the surface texture of the ablated sample is analyzed and measured by a three-dimensional confocal microscope.Results and Discussions The point texture of the laser ablation surface is mainly divided into four stages (Figs. 2 and 3). With an increase in the laser energy density, the central region of the point texture changes from a pit to a bulge, gradually becoming a pit again, and finally becoming an irregular pit. The bulge structure of the edge region of the point texture becomes increasingly obvious with an increase in the laser energy density. The variation in the geometric size of the point texture differs at different stages (Fig. 4 and Table 2). In the first stage, the laser ablation point texture forms a pit shape. When the laser energy density increases from 54.585 W/mm2 to 129.992 W/mm2, the diameter and depth of the point texture increase. The maximum pit diameter and depth are 342 p.m and 73 p.m, respectively. When the laser energy density increases from 129.992 W/mm2to 151.113 W/mm2, the pit depth gradually decreases to zero. In the second stage, the laser ablation point texture has a bulge shape. When the laser energy density increases from 151.113 W/mm2to 181.988 W/mm2, the height and diameter of the bulge gradually increase, and the maximum diameter and height are 513 p.m and 97 p.m, respectively. As the laser energy density continues to increase, the height and diameter of the bulge gradually decrease. In the third stage, the diameter and depth of the point texture are smaller than those in the first two stages, while the depth of the point texture changes significantly compared with that of the first two stages. The diameter of the point texture first decreases and then increases. The maximum diameter and depth of point texture are 220 p.m and 127 p.m, respectively. In the fourth stage, due to plasma shielding, the diameter and depth of the point texture change slowly with increasing laser energy density, and the diameter and depth of the pit remain stable at 216 p.m and 156 p.m, respectively. The average structure error of the point texture morphology first decreases and then increases with increasing laser energy density (Fig. 10). When the laser energy density is 54.585 W/mm2, the average structure error of the point texture morphology is 3.16%. When the laser energy density reaches 181.988 W/mm2, the average structure error of the point texture morphology reaches its minimum value of 2.08%. When the laser energy density continues to increase from 233.985 W/mm2to 363.977 W/mm2, the average structure error of the point texture morphology also increases from 5.03% to 8.03%. Conclusions When the laser energy density is 181.988 W/mm2, the melt flow increases significantly with increasing laser energy density, the surface texture morphology changes from pit to bulge, the texture diameter and height reach their maximum values with increasing laser energy density, the average structure error of the morphology is minimized, and the single point morphology becomes stable. As the laser energy density increases to 223.985 W/mm2, the melt flow effect is strong, surface texture morphology changes from bulge to pit, texture depth increases sharply with increasing laser energy density, texture diameter decreases first and then increases, and the average structure error of the morphology reaches 5.03%. When the laser energy density exceeds 311.980 W/mm2, the geometric size of the pit changes slowly, average structure error of the morphology increases, and texture morphology structure becomes unstable.
