单道激光熔覆高熵合金工艺优化及复合涂层耐冲蚀性能研究

Process Optimization of Single Pass Laser Cladding High Entropy Alloy and Study on Erosion Resistance of Its Composite Coatings

采用激光熔覆技术在0Cr13Ni5Mo水电用不锈钢表面制备了陶瓷增强高熵合金涂层。以显微硬度和稀释率作为指标,设计了三因素三水平正交实验,确定了单道最佳熔覆工艺为激光功率2500 W、扫描速度200 mm/min、送粉速度9.5 g/min。采用上述最佳工艺参数,并选择50%搭接率,制备了AlCoCrFeNi-1%Ni(质量分数,下同)包Al_(2)O_(3)复合涂层,采用X射线衍射仪、扫描电镜、显微硬度仪等分析表征复合涂层的微观组织、物相和显微硬度。通过射流式冲蚀试验装置研究850℃、保温2 h热处理对复合涂层耐冲蚀性能的影响。结果表明,热处理后复合涂层微观组织未发生相变,复合涂层依然由体心立方结构(BCC)的单相固溶体相所组成,但晶粒尺寸显著细化。高熵合金-1%Ni包Al_(2)O_(3)复合涂层的显微硬度从热处理前的504HV 0.3提高到545HV 0.3。当冲蚀时间为30 min时,热处理前后涂层的质量损失分别为63.5 mg和50.5 mg,当冲蚀时间为120 min时,热处理前后涂层的质量损失分别为178.5 mg和146.9 mg,热处理后的复合涂层表现出更好的耐冲蚀性。热处理后,涂层在低冲蚀角度下由液、固双相流微切削作用的“犁沟”形貌为主,随着冲蚀角度的提高,涂层表面从单一“犁沟”形貌渐变为微切削和冲击破碎协同作用的“犁沟”“唇片”“凹坑”的复合形貌。

Ceramic-reinforced high entropy alloy coating was prepared on the surface of stainless steel used in 0Cr13Ni5Mo turbines by laser cladding technology.Using microhardness and dilution rate as indexes,an orthogonal experiment with three factors and three levels were performed,and the optimal single-channel cladding technology was determined as follows:laser power 2500 W,scanning speed 200 mm/min,powder feeding speed 9.5 g/min.AlCoCrFeNi-1wt%Ni-coated Al_(2)O_(3)composite coating was prepared with the optimum process parameters and 50%bonding rate.The microstructure,phase and microhardness of the composite coating were analyzed and characterized by X-ray diffractometer,scanning electron microscope and microhardness tester.The influence of heat treatment at 850℃for 2 h on the erosion resistance of the composite coating was studied by an injection-flow erosion test device.The results show that the microstructure of the composite coating does not undergo phase transformation after heat treatment,and the composite coating is still composed of single-phase solid solution with body-centered cubic structure(BCC),but the grain size is significantly refined.The microhardness of AlCoCrFeNi-1wt%Ni-coated Al_(2)O_(3)composite coating increased from 504HV 0.3 before heat treatment to 545HV 0.3.Before and after heat treatment,the mass loss of the coating is 63.5 mg and 50.5 mg when the coating is eroded for 30 min.The mass loss was 178.5 mg and 146.9 mg after 120 min of erosion.The composite coating showed better erosion resistance after heat treatment.After annealing treatment,the surface morphology of the coating showed a‘furrow’dominated by the micro-cutting effect of liquid and solid two-phase flow at low erosion angle.With the increase of erosion angle,the coating surface gradually changes from a single‘furrow’morphology to a composite morphology of‘furrow’‘lip piece’and‘pit’under the synergic effect of micro-cutting and impact crushing.