Pre-cracked 304 stainless steel compact tension specimens were repaired by a CO2 laser at the crack tips with the addition of different weight fractions of nano-Al2O3. Crack opening displacements were measured by a digital image correlation system for the evaluation of fracture performance. Microstructures of the repaired areas were examined by scanning electron microscopy equipped with an energy dispersive spectrometer. Results indicated that laser repair with the addition of 1.0 wt.-% nano-Al2O3 resulted in metallurgical bonding at the interface and fine columnar crystal in the repair layer. The addition of nano-Al2O3 increases sites of heterogeneous nucleation, which acts as a fine-grain strengthener. In addition, the uniform distribution of nano-Al2O3 plays a role in dispersion strengthening, resulting in improved fracture performance by approximately 10 % to 30 % as applied loads varied from 1 to 20 kN. However, the excessive addition of nano-Al2O3 gives rise to the agglomeration and micro-cracks in the repair layers and clear detachment are observed at the interface.
The optimization of process parameters is usually essential for achieving improved properties at efficient and cost-effective process conditions. The influence of laser parameters, i.e. laser power, spot diameter, and laser heating time, on the fracture property of repaired specimens was investigated by Taguchi experiment. Cracks were first fabricated on 304 stainless steel compact tension specimens by wire cutting and then repaired by adding nanocomposites at crack tips under different combinations of laser parameters. The repairing effects were evaluated by crack opening displacement measured by digital image correlation and microstructure characterized by scanning electron microscope. The analysis of variance was used to investigate the contribution of factor variables to the fracture parameter of crack opening displacements. The fracture property was improved most at the optimal repair process parameters of laser power of 1800 W, spot diameter of 3 mm, and heating time of 0.5 s within the selected range of experiments. The influence of laser parameters on the fracture properties of repaired specimens is found in the sequence of spot diameter, laser power, and heating time. This paper reveals the relationship of process–microstructure–fracture property in laser repair and provides a guideline for the selection of laser parameters to improve the quality of crack repair.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.