316L不锈钢激光快速成形的微观组织模拟

NUMERICAL MICROSTRUCTURE SIMULATION OF LASER RAPID FORMING 316L STAINLESS STEEL

针对316L不锈钢激光快速成形(LRF)薄壁试样的凝固组织形态分布,从凝固理论出发,建立了激光快速成形柱状晶/等轴晶转变(CET)及一次枝距λ_1与有限元温度场耦合数值模型,模拟了成形高度为2.8 mm的LRF薄壁试样凝固组织形态及分布。结果表明:316L不锈钢LRF组织由致密、均匀、外延生长的细长柱状晶组成,一般不发生CET转变,组织中λ_1在6.5—17μm范围内,且随熔覆高度的增加而逐渐增大,模拟结果与实验符合很好。在此基础上,对成形高度为40 mm薄壁件的凝固组织形态及分布进行了预测。

The laser rapid forming（LRF） as an advanced solid freedom fabrication technology, has been developed rapidly in recent decade.By rapid prototyping with laser cladding,LRF realizes the direct net shaping of the components with irregular shapes and fine inner structures,and gives a short route,low cost and high flexibility fabrication of aero components,aero-engine parts and biomedical implants.In the LRF,melting and solidification are happened in a dynamic non-equilibrium,high temperature gradient and rapid solidification manner,so that the microstructure of the laser rapid formed part is finer than that of ordinary cast or forge part and presents a characteristic of typical epitaxial growth.Therefore,to achieve the predict and control of the microstructure evolution is a key problem.Much efforts have been devoted to narrating the solidification and crystallization in melting pool,but little attention has been paid to study the microstructure of LRF part.In this paper,the evolution of temperture field and solidification of LRF part were concerned,the relationships between as-deposited microstructure and the local solidification conditions such as solidification velocity and temperature gradient of moving melting pool were also investigeted.A coupled 2D transient finite element LRF epitaxial growth model was developed.The morphology evolution and first order dendrite arm spaceλ1 distribution in 2.8 mm high LRF 316L stainless steel wall were simulated.The results show that the microstructure of LRF 316L stainless steel wall is mainly columnar austenitic dendrites, and theλ1 gradually becomes larger from the bottom about 6.5μm to the top about 17μm which is in good agreement with the experimental.Further more,on the basis of the validated model,morphology evolution andλ1 distribution in 40 mm high LRF 316L stainless steel wall are also predicted.