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.
Cracks generated by a wire electric discharge machining on compact tension specimens are first repaired by high powered laser beam with different weight fractions of nano‐WC added at the crack tip. Digital image correlation method combined with J‐integral theory is used to measure and calculate J‐integrals of the repaired specimens. Fracture properties of the repaired specimens are compared and studied. The residual stress of specimens after being repaired by laser was also studied to analyze the feasibility of J‐integral to evaluate the fracture properties of the repaired parts. It is found that the influence of residual stress can be neglected when calculating J‐integral in a certain region in case of when the residual stress is small. The J‐integral obtained by the digital image correlation measurement is accurate and can effectively evaluate repairing effects. The paper provides guidance for laser repaired cracks with nanomaterial addition and an effective method for the evaluation of repairing effect.
Compact tension specimens with prefabricated cracks are repaired by laser with micro/nano materials added at the crack tip. Different combinations of laser parameters, i.e., laser power, laser spot diameter and heating time, were applied to investigate their effects on the microstructures and fracture properties of repaired specimens. J-integrals were calculated according to the digital image correlation (DIC) measurements, and microstructures were examined using scanning electron microscopy (SEM). When suitable laser parameters were used, homogeneous and compact equiaxed grains with no cracks, pores, and agglomeration are observed in the repaired layer, and the J-integral of repaired specimens is approximately 20% less than that of unrepaired specimen. The paper reveals relations among laser parameters, J-integrals, and microstructures, and provides a guideline for the selection of laser repair parameters.
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