摘要
熔覆过程存在极其复杂的传热及热-弹-塑-流多场耦合变化,将影响对流、传热、传质、凝固和相变,而熔覆中的急冷急热会产生复杂的残余应力与变形,产生熔覆裂纹,影响熔覆层质量。揭示熔覆过程中多场耦合演变机理是控制和避免产生熔覆裂纹的关键。文中以CALPHAD法计算温变物性参数,建立了碟片激光器激光熔覆过程多场耦合模型,综合考虑了光束与粉末间的相互作用,熔池表面张力、浮力对液态金属流动的影响,熔覆带的瞬时变化,计算得出了熔覆过程温度场、速度场、应力场的瞬时变化规律。运用Zeiss-?IGMA HD扫描电镜进行金相实验,验证了所建模型的准确性。计算表明:形成近似2 mm×1.5 mm×1 mm椭球体熔池,最高温度在光斑中心偏后位置;700 ms后,等效热应力稳定在548 MPa左右,熔池底部热应力最大。该研究为减小和消除残余应力提供了有效途径与方法。
Laser cladding exhibits highly complex heat transfer and thermo-elastic-plastic-flow multi-physics field coupling changes. The temperature and flow fields in the melt pool influence the convection, heat transfer, solidification and phase change. The quick cooling and rapid heating of the laser cladding process cause complex residual stress and deformation,producing cladding cracks and affecting the quality of the cladding layer. It has been revealed that the mechanism of multiphysics field coupling in the laser cladding process is the key to control and avoid cladding cracks. The material’s temperaturedependent physical parameters were obtained by the CALPHAD method and a multi-field coupling model for a laser cladding process by disk lasers was established. In the mathematical model, the interactions between the laser beam and the powder flow, the influence of the surface tension and the buoyancy on the liquid metal flow in the melt pool, and the instantaneous change in the shape of the cladding layer were considered. Finally, the laws of instantaneous change for the temperature, flow and stress fields in the cladding process were obtained. The microstructure of the cladding layer was observed by a Zeiss-∑IGMA HD field emission scanning electron microscope, and the accuracy of the model was verified. Results show that an ellipsoid melting pool approximating 2 mm×1.5 mm×1 mm is formed, and the maximum temperature is at the back of the spot center. After 700 ms, the equivalent thermal stress is about 548 MPa, and the maximum thermal stress is at the bottom of the melting pool. This provides an effective way to reduce and eliminate residual stresses.
作者
李昌
于志斌
高敬翔
韩兴
董欣
LI Chang;YU Zhibin;GAO Jingxiang;HAN Xing;DONG Xin(School of Mechanical Engineering and Automation,University of Science and Technology Liaoning,Anshan 114051,China;Anshan Zhengfa Surface Technology Engineering Company Limited by Shares,Anshan 114044,China)
出处
《中国表面工程》
EI
CAS
CSCD
北大核心
2019年第1期124-134,共11页
China Surface Engineering
基金
国家自然科学基金(E050402
51374127)
辽宁省教育厅项目(2017FWDF01)
辽宁科技大学团队项目(6601009830-02)~~
关键词
碟片激光器
激光熔覆
多场耦合
温度场
速度场
应力场
disk laser
laser cladding
multi-field coupling
temperature field
velocity field
stress fied
