热喷涂3D打印制备孤立纳米YSZ厚热障涂层的内应力演化特性的模拟计算研究

Study of Evolution Characteristics of Inner Stress of Thermal Spray 3D Printing Standing Nanostructured YSZ Thick Thermal Barrier Coatings via Modeling and Simulation

孤立厚涂层通常被用来测试涂层的热物理性能,如热膨胀系数、热扩散系数、比热容等.不同形状的孤立厚陶瓷涂层通常通过在不同形状的石墨模具上采用等离子体喷涂增材制造的方法制备.采用有限元“生死单元”模拟技术对3D打印增材制造过程中的纳米结构YSZ热障涂层的残余应力进行了有限元模拟.考虑了方形、圆柱形、六棱柱及星柱形四种结构的石墨模具,系统计算并比较了四种石墨模具制备的厚涂层的应力分布特征.研究结果表明:在厚涂层的侧面存在较大的压应力集中,最大压应力往往分布在柱的边角或边缘处.对于热喷涂3D打印圆柱状厚涂层,压应力连续分布在厚涂层侧面的环形面上.对于四种类型的厚涂层,热喷涂3D打印圆柱状厚涂层在x,y,z三个方向上最大压应力值最小,分别为-19.574 MPa,-19.565 MPa和-56.569 MPa.且x,y,z三个方向上应力梯度变化最小(分别为0.169 MPa/mm,0.173 MPa/mm,0.0218×10-3 MPa/mm),而星柱型厚涂层x,y,z三个方向上应力变化梯度最大(分别为2.344 MPa/mm,14.092 MPa/mm,2.171 MPa/mm).涂层的应力随着涂层厚度的增大而增大,且纳米结构涂层的应力低于传统结构涂层的应力.通过应力状态及应力大小的调控,将会促进YSZ涂层的铁弹性相变,进一步提高涂层的断裂韧性,从而有望进一步提高涂层的抗热震性能.

Standing thick coatings are usually used to test the thermal-physical properties of coatings,such as coefficient of thermal expansion(CTE),thermal diffusion coefficient,specific heat capacity,etc.Standing thick ceramic coatings with different shapes are usually prepared by plasma spraying additive manufacturing on graphite moulds with different shapes.The stress distribution of nanostructured YSZ thermal barrier coatings in thermal spray 3D printing process was simulated via finite element life-and-death element simulation technology.Four kinds of graphite moulds with square,cylindrical,hexagonal and star-shaped structures were considered.The stress distribution characteristics of thick coatings prepared on four kinds of graphite moulds were systematically calculated and compared.The results show that:there will be a large compressive stress concentration on the profile of the coating.The maximum compressive stress is located near the edge of the column,while for the thermal spray 3D printing(TS3DP)cylindrical coating,the compressive stress is continuously distributed on the circumferential surface of the profile.As for the four types of thermal spray 3D printing coatings,the TS3DP coating with cylinder shape has the minimum value of the maximum of the compressive stress in the x,y,z directions.The corresponding values are-19.574 MPa,-19.565 MPa and-56.569 MPa,respectively.The stress gradient with cylinder shape is the least for the four types of TS3DP coatings in x,y and z directions(the corresponding values are 0.169 MPa/mm,0.173 MPa/mm and 0.0218e-3 MPa/mm,respectively).While the stress gradient with star type is the highest for the four types of TS3DP coatings in x,y and z directions(the corresponding values are 2.344 MPa/mm,14.092 MPa/mm and 2.171 MPa/mm,respectively).The surface residual stress will increase with the increasing of the coating thickness.The nanostructured coatings have lower residual stress compared with the conventional TBCs.To induce the occurrence of the ferroelalstic phase transformation will improve the fracture toughness of the TS3DP coating via the control of the stress state and magnitude.