【作者】 王宁；

【导师】 雷振坤； 李兴民；

【作者基本信息】 大连理工大学 ， 海洋工程， 2025， 硕士

【摘要】 钛合金因高比强度、耐腐蚀性和生物相容性广泛应用于海洋工程、航空航天及生物医学等领域,但硬度低、耐磨性差及高温抗氧化性不足限制了其服役寿命。激光熔覆以能量集中、结合强度高、热影响区小等优势,成为钛合金表面改性和失效部件再制造的有效手段。然而,激光熔覆过程中剧烈的温度梯度变化易诱发内部缺陷和残余应力集中等问题,影响熔覆层质量,尤其在复杂基体形貌条件下,其熔池动力学与应力演化机制尚需深入研究。本文以TC4钛合金激光熔覆为研究对象,围绕工艺参数、扫描路径与基板倾角三个关键因素,结合实验测试与多物理场数值模拟,系统探究激光熔覆过程中温度场、应力场、流场及熔覆层形貌的演变规律。首先,开展单层及多层平面熔覆实验,设计不同激光功率与扫描速度组合,分析工艺参数对熔覆层几何形貌的影响。借助三维数字图像相关(3D-DIC)系统获取基板动态应变场,结合轮廓法测量残余应力分布,为后续数值模拟提供实验依据。结果表明,工艺参数显著影响熔池几何特性:激光功率越高或扫描速度越低,熔池热输入增加,熔覆层宽高比减小;同时,熔覆过程中基板下表面发生翘曲变形。其次,基于Abaqus平台构建瞬态热-力耦合有限元模型,模拟不同工艺参数、单道多层和单层多道扫描策略及不同基板倾角条件下的温度演化与残余应力分布规律。仿真结果显示:残余应力主要集中于熔覆层与基体交界区域;较高功率或较低扫描速度均会导致更高的熔池温度与更大的残余应力;多层熔覆应力呈累积效应,多道熔覆后续熔道的应力低于前道;斜面熔覆中,应力峰值随倾角增加而升高,残余应力分布向倾斜方向偏移。最后,使用COMSOL Multiphysics软件建立三维热-流耦合瞬态模型,综合考虑马兰戈尼效应、浮力、重力及相变潜热等因素,深入分析不同基板倾角下熔池内部温度场与流场的非对称演化特征及其对熔覆层成形的影响。研究发现:基板倾斜会破坏横截面流场原有对称双环流结构,熔池内形成上侧环流和下侧横向流动;随着倾角增大,熔池形状非对称性增强,熔池内部流速逐渐降低,0°至10°变化区间内流速下降最为显著。模拟获得的熔覆层轮廓与实验形貌基本一致,验证了热-流模型的准确性与可靠性。更多还原

【Abstract】 Titanium alloy is widely used in marine engineering,aerospace,and biomedical fields due to its high specific strength,corrosion resistance,and biocompatibility.However,its low hardness,poor wear resistance,and insufficient high-temperature oxidation resistance limit its service life.Laser cladding,with its advantages of concentrated energy input,strong metallurgical bonding,and minimal heat-affected zone,has emerged as an effective technique for surface modification and remanufacturing of failed titanium alloy components.Nevertheless,the rapid thermal gradients during the laser cladding process tend to induce internal defects and concentrated residual stresses,compromising the clad layer’s quality.This issue becomes more pronounced under complex substrate geometries,where the melt pool dynamics and stress evolution mechanisms remain inadequately understood.This study focuses on the laser cladding of TC4 titanium alloy,investigating the effects of three key factors,namely,process parameters,scanning path strategy,and substrate inclination,through a combination of experimental measurements and multiphysics numerical simulations.The evolution of the temperature field,stress field,flow field,and clad morphology during the cladding process is systematically explored.Firstly,single-layer and multi-layer flat surface cladding experiments were conducted using various combinations of laser power and scanning speed to analyze their effects on clad geometry.The three-dimensional digital image correlation(3D-DIC)technique was employed to capture the dynamic strain field of the substrate,while residual stresses were measured using the contour method,providing experimental basis for subsequent numerical simulations.Results show that laser parameters significantly influence the melt pool geometry:higher power or lower scanning speed increases thermal input,leading to a reduced width-to-height ratio of the clad layer.Meanwhile,warping deformation occurred on the underside of the substrate during cladding.Secondly,a transient thermo-mechanical coupled finite element model was developed using Abaqus to simulate the temperature evolution and residual stress distribution under different process parameters,scanning strategies(multi-layer single-track and single-layer multi-track),and substrate inclinations.Simulation results indicate that residual stresses primarily concentrate near the interface between the clad layer and the substrate.Higher laser power or lower scanning speed leads to increased melt pool temperatures and higher residual stresses.A stress accumulation effect is observed in multi-layer cladding,with subsequent tracks exhibiting lower residual stresses than the initial ones.In inclined cladding,the peak residual stress increases with the inclination angle,and the stress distribution shifts toward the inclined direction.Finally,a 3D transient thermo-fluid model was established in COMSOL Multiphysics,considering the Marangoni effect,buoyancy,gravity,and latent heat of phase change to analyze the asymmetrical evolution of temperature and flow fields in the melt pool under various inclination angles and their impact on clad formation.The results reveal that substrate inclination disrupts the original symmetrical double vortex structure of the cross-sectional flow field,resulting in dominant upper-side recirculation and lateral flow at the lower side.As the inclination angle increases,the asymmetry of the melt pool geometry becomes more pronounced,and the flow velocity gradually decreases,most notably within the 0°to 10°range.The simulated clad profiles closely match the experimental morphologies,confirming the accuracy and reliability of the thermal-fluid model.更多还原