Effect of ultrasonic frequency on the microstructure and properties of laser cladding chromium carbide reinforced nickel-based coatings

Using ultrasound-assisted laser cladding technology, researchers prepared nickel-based chromium carbide coatings on H13 hot-work tool steel substrates. The present study investigated the effects of ultrasound frequency on the microstructure, mechanical properties, and wear characteristics of nickel-based chromium carbide coatings. The results demonstrated that the phase composition of nickel-based chromium carbide coatings prepared by laser cladding after ultrasonic treatment remained unchanged. Ultrasonic interference disrupted the Marangoni flow, leading to cavitation degassing and a subsequent decrease in porosity. The dilution rate increased from 11.2% to 16.3%, with surface flatness and defect suppression attaining optimal levels at 34 and 36 kHz, respectively. Microscopically, at frequencies of 26 and 28 kHz, columnar grains were refined to 13~15μm; at 32 and 34 kHz, cavitation and acoustic flow synergized to form equiaxed grains of 3~5μm at the top; at 36 kHz, the cavitation bubble radius and dendrite spacing were optimally matched, with columnar crystals refined to 3.5μm and equiaxed crystals reaching 2.1μm, accounting for 65% of the total. The high-frequency attenuation effect intensifies at frequencies above 38 kHz, leading to a decline in refinement efficiency. The average microhardness of the coating increases with increasing ultrasonic frequency, from 597.9 HV_0.5 to 738.1 HV_0.5. Following the application of 36 kHz ultrasonic waves, the coating grains underwent refinement, the interface bonding experienced reinforcement, and the cavitation impact and acoustic flow effects diminished the martensitic flow and adhesion effects, thereby reducing pores and cracks. The grinding marks transformed deep and wide plow grooves to shallow and narrow plow marks, with the depth exhibiting a decrease from 99.3μm to 95.4μm and the width demonstrating a reduction from 1570.2μm to 1466.3μm. The phenomena of pile-up and peeling were almost eliminated. Ultrasonic processing achieves a transition from severe plastic deformation to mild plowing through a three-in-one mechanism of "carbide refinement-interface metallurgical transformation-matrix strengthening," which significantly enhances the wear resistance and stability of the coating. Furthermore, ultrasonic vibration has been demonstrated to effectively reduce the formation of cracks in the cladding layer, enhancing its quality and extending the service life of components.