Bionic Repair of Thermal Fatigue Cracks in Ductile Iron by Laser Melting with Different Laser Parameters

Laser Melting of Prefabrication AlOOH-Activated Film on the Surface of Nodular Cast Iron and Its Associated Properties

This study aimed to improve the absorption rate of laser energy on the surface of nodular cast iron and further improve its thermal stability and wear resistance. After a 0.3 mm thick AlOOH activation film was pre-sprayed onto the polished surface of the nodular cast iron, a GWLASER 6 kw fiber laser cladding system was used to prepare a mixed dense oxide layer mainly composed of Al2O3, Fe3O4, and SiO2 using the optimal laser melting parameters of 470 W (laser power) and 5.5 mm/s (scanning speed). By comparing and characterizing the prefabricated laser-melted surface, the laser-remelted surface with the same parameters, and the substrate surface, it was found that there was little difference in the structure, composition, and performance between the laser-remelted surface and the substrate surface except for the morphology. The morphology, structure, and performance of the laser-melted surface underwent significant changes, with a stable surface line roughness of 0.9 μm and a 300-400 μm deep heat-affected zone. It could undergo two 1100 °C thermal shock cycles; its average microhardness increased by more than one compared to the remelted and substrate surfaces of 300 HV, with a maximum hardness of 900 HV; and the average friction coefficient and wear quantity decreased to 0.4370 and 0.001 g, respectively. The prefabricated activated film layer greatly improved the thermal stability and wear resistance of the nodular cast iron surface while reducing the laser melting power.

Advances in Laser Materials Processing

Today, laser processing is becoming more and more relevant due to its fast adaptation to the most critical technological tasks, its ability to provide processing in the most rarefied and aggressive mediums (e [...]

Study on Antifatigue Crack Growth Characteristics of Ball-End Milling Bionic Surface

The surface morphology of parts has an important influence on service performance, such as wear resistance, fatigue resistance, and corrosion resistance. For example, the fatigue fracture resistance of the surface of the automobile cover mold directly determines the quality of the workpiece and the service life of the mold. In nature, the pit-shaped non-smooth form of the surface of certain organisms has good fatigue resistance. Using laser processing and other methods to prepare a pit-shaped bionic non-smooth surface on the surface of the part is an effective method to improve the fatigue resistance of the mold surface. Ball-end milling can form a regularly distributed pit-like surface morphology, and has the advantages of high processing efficiency, wide operating range, and low production cost compared with those of laser processing and preparation technology. It provides a new processing method for efficient milling preparation of bionic surfaces. In this paper, the morphology of the quadrilateral pits on the surface of the dung beetle is used as the prototype of the bionic design, and the mechanism of the antifatigue crack propagation characteristics of the quadrilateral pits of the bionic dung beetle is revealed and analyzed. The fatigue crack growth has a good retarding effect. At the same time, through numerical simulation and experimental research on the fatigue crack growth characteristics of the surface of the bionic pit, the results show that the source of fatigue cracks often starts inside the surface of the processed bionic pit, and the surface of the quadrilateral pit on the surface of the bionic dung beetle has good antifatigue crack growth characteristics.

Effects of Laser Melting Distribution on Wear Resistance and Fatigue Resistance of Gray Cast Iron

The coupling bionic surface is generally prepared by laser melting on the surface of a gray iron brake hub, which can allow the brake hub to achieve excellent wear resistance and fatigue resistance. The designs of most previous experiments have been based on independent units that were uniform in their distribution patterns. Although some progress has been made in the optimization of cell features, there is still room for further improvement with respect to bionics and experimental optimization methods. Here, experiments on units with non-uniform distributions of different distances were used to rearrange and combine the bionic elements. This paper is that the original uniform distribution laser melting strengthening model was designed as a non-uniform distribution model, and the heat preservation and tempering strengthening effect of continuous multiple melting strengthening on the microstructure of the melting zone is discussed. The mechanism of crack initiation and the mode of crack propagation were analyzed. The relationship between the internal stress in the melting zone and the crack initiation resistance was also discussed. In this paper, the mechanism of different spacing distribution on the surface of gray cast iron by laser remelting is put forward innovatively and verified by experiments, which provides a solid theoretical basis for the follow-up industrial application.

Study on Fatigue Characteristics of Bionic Functional Surface of Hardened Steel

In this study, we aimed to process the biomimetic function surface by designing a prototype for modeling the pits on a dung beetle body and the abdomen of a desert viper, and by using high speed milling and controlling the ratio of row spacing to feed rate. Firstly, we conducted three-dimensional parametric modeling and static analysis of the bionic functional surface using 3D modeling software UGNX (12.0, SIEMENS AG, Munich, Germany) and finite element analysis software ABAQUS (2018, Dassault, Providence, RI, USA). Then, the analysis results were imported into the fatigue life analysis software nCode (2018, HBM United Kingdom Ltd., South Yorkshire, UK) to simulate the fatigue characteristics of different bionic pit morphology models. Per the simulated tensile fatigue testing machine, the result shows that the minimum fatigue life value of the quadrilateral pit surface of the simulated dung beetle is one and four times higher than the hexagonal pit morphology and the irregular pit morphology, respectively, whereas the maximum fatigue damage is lower by one and five orders of magnitude, respectively. The quadrilateral pit surface on the biomimetic dung beetle body has better fatigue resistance, which can considerably improve the fatigue damage distribution state and the fatigue life of hardened steel die surfaces. The influential regulation of milling parameters on fatigue performance was studied and the results show that the fatigue resistance of the model is optimal when milling parameters are: row spacing of 0.4 mm, loading space of 0.2 mm, and milling depth of 0.3 mm. The quadrilateral dimensions formed by milling are highly similar to those of a dung beetle body proving that a certain reduction in milling process depth can increase the structural fatigue resistance. From the perspective of fatigue crack growth analysis, the quadrilateral dimples on the surface of the dung beetle improve fatigue crack growth inhibition and fatigue resistance.