【摘要】 采用激光定向能量沉积技术制备了第二代单晶高温合金DD405薄壁结构，通过试验和理论相结合的手段对单晶高温合金在激光定向能量沉积过程中的热裂纹形成机制进行分析和探究。结果表明，热裂纹的形成是由应力集中、液膜稳定性和碳化物析出相3个因素所决定的。由于激光定向能量沉积过程的逐层叠加，残余应力随着沉积高度递增，因此沉积区存在高水平的残余拉应力。沉积区的晶界处会出现显著的应力集中，液膜在两侧拉应力作用下发生撕裂导致裂纹萌生。液膜稳定性与相邻晶粒间的晶界角度密切相关，当大角晶界大于40°时，会在拉应力的驱动下形成热裂纹。MC型碳化物析出相通过“钉扎作用”抑制液相补缩及弱化与基体之间结合强度等作用进一步促进了热裂纹形成。更多还原

【Abstract】 The thin-wall structure of the second generation single-crystal superalloy DD405 was fabricated by laser directed energy deposition technology. The mechanism of hot crack formation in the process of laser directed energy deposition was analyzed and explored by combining experiment and theory. The formation of hot cracking was determined by stress concentration, liquid film stability and carbide precipitated phase. The residual stress in deposition region increased with the deposition height due to the layer-by-layer stacking of the laser directed energy deposition process, so there is a high-level tensile stress in the deposition region. Significant stress concentration occurred at the grain boundary of the deposition region, and the liquid film was teared under the tensile stress on both sides, leading to crack initiation.The stability of liquid film was closely related to the angle of grain boundary between adjacent grains. When the high angle grain boundary is larger than 40°, thermal cracks will be formed under the drive of tensile stress. MC-type carbide precipitates promoted crack initiation by a pinning effect on the liquid feed and weakening interface bonding strength with the substrate.更多还原