不同基面角度对激光熔覆Ni_(2)5/WC涂层耐磨性的影响

Effect of Different Substrate Angles on Wear Resistance of Laser Cladding Ni_(2)5/WC Coating

目的为实现模具曲面或斜面区域修复,研究不同基面角度对激光熔覆Ni_(2)5/WC涂层形貌和耐磨性的影响。方法采用激光熔覆技术在不同角度的基体表面制备了Ni_(2)5/WC修复涂层,利用X射线衍射仪(XRD)、维氏硬度计、扫描电镜(SEM)和摩擦磨损试验机,分析和研究了不同角度对涂层截面形貌、物相组成、微观组织、显微硬度和摩擦磨损性能的影响及机理。结果熔覆过程中,基体表面为90°时,在重力作用下,粉末流向下偏移,部分粉末无法进入熔池,使得单道涂层厚度降低,熔池内的金属熔液受重力影响向下滑落,激光熔覆快速凝固的特点使得熔液在滑落前凝固,导致涂层形心向下侧偏移。在重力、运载气体及空气阻力的作用下,混合粉末中密度更大的WC颗粒向下偏移量更大,未进入熔池的大尺寸的WC颗粒更多,使得涂层中WC颗粒含量降低。WC颗粒含量影响涂层的磨损形式,0°涂层主要磨损形式为犁削作用和黏着磨损,90°涂层主要发生了磨粒磨损。结论不同角度单道涂层的截面形状和厚度不同,0°涂层呈现两侧较为对称的半圆或半椭圆,涂层厚度更大,90°涂层的形心随重力向下侧偏移,涂层厚度明显减小;涂层的物相种类相同,均由FeNi_(3)、Ni_(2)B及WC等相组成;0°涂层显微硬度平均值为446.67HV0.2,90°涂层显微硬度平均值为456.13HV0.2。0°涂层磨损率为0.0026 mg/m,90°涂层磨损率为0.008 mg/m,0°涂层耐磨性优于90°涂层,磨损机制不同是耐磨性产生差异的主要原因。

It is an excellent surface repair technology by laser cladding,which has the advantages of small heat input,high bonding strength with substrate and high repair efficiency.To realize the repair of the inclined mold surface area and obtain stable quality repair coating,the influence of different substrate surface angles on the morphology and wear resistance of the laser cladding coating was studied.Ni_(2)5/WC composite coating was prepared by laser cladding with different angles.Q235 steel is selected as the base materials and the surface is derusted and decontaminated until smooth and clean.Cladding experiments are carried out with RFL-C1000 laser at two different substrate angles,the laser power is 850 W,the scanning speed of single track cladding layer is 4,8,12 mm/s,respectively;The multi-pass cladding speed is 12 mm/s and the overlap between the two adjacent is 50%.Samples are prepared by wire cutting and polishing machine,and corrode the cross sections of samples with aqua regia.Then,observe the microstructure of single track cladding layers and multi-pass cladding layers by scanning electron microscope(ZEISS Sigma 300).Analyze the phase composition of the coating by an X-ray diffractometer(D/MAX-2500)and measure the microhardness distribution from the composite coating to substrate by microhardness tester(THV-1MDT).The friction test is performed on wear tester(M-2000).Calculate the weight loss of the friction mill and observe the morphology by a three-dimensional profilometer and scanning electron microscope after the friction surface.When the inclination angle of the substrate surface to the ground was 90°,under the action of gravity,the powder flows downward,and some powders cannot enter the molten pool,resulting in the reduction of the thinkness of the single coating.The metal melt in the molten pool slides downward under the influence of gravity.The rapid solidification of laser cladding makes the melt solidify before sliding,resulting in the downward deviation of the coating centroid.Under the action of gravity,carrier gas and air resistance,the downward displacement of WC particles with higher density in the mixed powder is greater,resulting in more WC particles can’t enter the molten pool,which reduces the content of WC particles in the coating.WC particles content affect the wear form of the coating.The main wear forms of the 0°coating are ploughing and adhesive wear,and the 90°coating is mainly abrasive wear.The section shape and thinkness of a single coating at different substrate surface angles are different.The 0°coating presents a semicircle or semi ellipse with more symmetrical sides and greater thinkness,and the centroid of the 90°coating shifts downward with gravity.The phases of the coating are the same,which are composed of FeNi_(3),Ni_(2)B and WC.The microhardness of 0°coating is 446.67HV0.2 and 90°coating is 456.13HV0.2.The wear rate of 0°coating is 0.0026 mg/m and 90°coating is 0.008 mg/m.The wear resistance of 0°coating is better than that of 90°coating.Different wear mechanism is the main reason for the difference of wear resistance.