Dd6镍基单晶高温合金激光重熔区杂晶的形成机制研究

Abstract

Objective Nickelbased singlecrystal superalloys are widely used in the manufacture of singlecrystal turbine blades in the combustion chambers of aircraft engines owing to their excellent hightemperature mechanical properties. However, these components often suffer from severe damage, such as edge erosion, cracking, and pitting, owing to the harsh operating conditions, including high temperatures and pressures, requiring repairs to extend their service life. Laser additive manufacturing technology has garnered significant attention for repairing nickelbased singlecrystal superalloys owing to its unique advantages, including controllable heat input, the ability to fabricate complex structures, and reparability. However, the appearance of grain defects during the repair process may lead to serious failure phenomena, such as crack propagation and component fracture, during component operation, thereby posing potential risks to the safety and reliability of aircraft engines. Therefore, this study selected a DD6 secondgeneration nickel based singlecrystal superalloy as the substrate material and used lasers with powers of 1200 and 1500 W to remelt the substrate, revealing the mechanisms of stray grain formation at the fusion line, top of the molten pool, and at the intersection of the dendrites, thereby providing a theoretical basis and technical support for the laser additive repair of nickelbased singlecrystal superalloys.Methods This study employed a DD6 nickelbased singlecrystal hightemperature alloy prepared via directional solidification as an experimental substrate material. Subsequently, a laser cladding additive manufacturing device equipped with a 2 kW German Rofin fibercoupled semiconductor laser was utilized. The process parameters included laser powers of 1200 and 1500 W, a scanning rate of 3 mm/s, and a spot diameter of 4 mm for the singletrack remelting experiments on the substrate (001) crystal surface. To prevent sample oxidation during remelting, argon gas was used as a protective gas at a flow rate of 10 L/min. The dendritic morphologies of the substrate and remelted region were observed using an OLYMPUS DSX510 optical microscope. Simultaneously, scanning electron microscopy and Xray energydispersive spectroscopy were employed for detailed analysis of the molten pool morphology and elemental distribution. Electron backscatter diffraction (EBSD) analysis was performed to further investigate the crystallographic properties of the specimens. The sample tilt angle was set to 70°, with a scan step size of 3 μm, using nickel as the calibration phase.HKL Channel 5 postprocessing software was employed for texture and orientation deviation analysis of the samples. Results and DiscussionsThe results show that, after laser remelting, the molten pool could be divided into four regions ([001],[100], [010], and [01 ˉ0]) based on the growth direction of the grains (Fig. 3), and the primary dendrite spacing increased with increasing laser power. From the crystallographic texture characteristics of the molten pool (F...