WC对激光熔覆层组织及耐磨耐冲击性的影响

激光熔覆Ni基合金涂层具有良好的综合性能,但耐磨与耐冲击性能仍有待提高。分别采用含微米与纳米WC颗粒的Ni基粉末激光熔覆制备WC/Ni涂层,研究两种WC颗粒对Ni基涂层组织及耐磨耐冲击性的影响。利用SEM与XRD对涂层进行微观组织分析,利用高速摄像机分析熔覆过程中的熔池形态。采用磨损试验机、夏比冲击试验机对涂层进行耐磨性与耐冲击性测试。纳米WC对熔池流动的促进作用强于微米WC,并使涂层组织得到更显著的细化。由于微米WC与Ni45涂层结合紧密,磨损试验中能有效抵抗配磨件微凸体的切削,最终显著增强涂层耐磨性,磨损率较Ni45涂层降低88.38%。但微米WC的高脆性不利于涂层耐冲击性的提高,冲击韧性仅为Ni45涂层的91.28%。由于纳米WC在细化晶粒的同时会弥散分布于晶界与共晶区,在磨损过程中阻碍位错运动,抑制晶粒塑性变形,进而减弱配磨件对涂层的切削,提高涂层耐磨性,磨损率较Ni45涂层降低53.43%。由于在晶界与共晶区的纳米WC会阻碍裂纹扩展并改变扩展方向,进而提高形成贯穿裂纹的能量,增加涂层断裂所需的冲击功,使涂层耐冲击性得到显著提高,冲击韧性较Ni45涂层提高13.37%。通过有限元分析可知,在冲击过程中涂层中的高脆性微米WC会形成高应力集中,证明其对涂层耐冲击性具有不利影响。而纳米WC能降低位错的不均匀滑移,缓解位错堆积,进而有效分散涂层在冲击过程中形成的应力集中,证明其能显著提高复合涂层的耐冲击性能。研究证明,纳米WC能实现涂层耐磨性与耐冲击性的同步提升。

Effect of WC on Microstructure, Wear Resistance and Impact Resistance of Laser Cladding La

Laser cladding Ni based alloy coating has good comprehensive properties, but the wear resistance and impact resistance still need to be improved. Therefore, WC/ Ni coatings were prepared by laser cladding of Ni based powders containing micro and nano WC particles respectively, and the effects of WC particles on the microstructure, wear resistance and impact resistance of Ni based coatings were studied. The SEM and XRD were used to analyze the microstructure of the composite coating. The high-speed camera was used to analyze the shape of the molten pool during the cladding process. Wear tester and charpy impact tester were used to test the wear resist- ance and impact resistance of the composite coatings. The effect of nano WC on the molten pool flow is stronger than that of micro WC, and the microstructure of the coating is more refined. Due to the close combination of micro-WC and Ni45 coating, it can effectively re- sist the cutting of asperity in wear test, and finally significantly enhance the wear resistance of the coating, and the wear rate is 88. 38% lower than that of the Ni45 coating. However, the high brittleness of micro-WC is not conducive to the improvement of impact resistance, the impact toughness is only 91. 28% of the Ni45 coating. the wear rate of the nano-WC coating is 53. 43% lower than that of the Ni45 coating because the nano WC particles are dispersed in the grain boundary and eutectic region while refining the grain,which hinders the movement of dislocations and inhibits the plastic deformation of the grain. Due to the nano WC in the grain boundaryand eutectic region will hinder the crack propagation and change the propagation direction, thus increasing the energy of forming through cracks and the impact energy required for coating fracture, and significantly improving the impact toughness of the coating. The impact toughness of the coating is 13. 37% higher than that of Ni45 coating. Through the finite element analysis, it can be seen that the micro-WC in the coating will form high stress concentration during the impact process, which proves that it has adverse effects on the impact resistance of the coating. However, nano WC can reduce the uneven slip of dislocations, alleviate the accumulation of disloca- tions, and effectively disperse the stress concentration formed in the impact process of the coating, which proves that it can significantly improve the impact resistance of the composite coating. The results show that nano WC can improve the wear resistance and impact re- sistance simultaneously.