摘要
目的对38CrMoAl进行激光熔覆TC4原位氮化,并研究不同Ni含量对涂层裂纹的影响,进一步提升材料的耐磨性能。方法针对38CrMoAl传统氮化工艺耗时长、能耗高的问题,在38CrMoAl基体上进行激光熔覆TC4,以实现原位氮化。在激光熔覆过程中,快速冷却凝固过程会导致较大的应力,且熔覆材料与基体材料的热物理性质差异较大,使得涂层很容易产生裂纹。通过在熔覆材料中添加Ni来抑制涂层中的裂纹,研究不同Ni含量对38CrMoAl激光熔覆TC4原位氮化裂纹和耐磨性能的影响。结果在TC4中加入Ni元素的质量分数达到30%后,涂层中裂纹的数量将减少,对涂层中的裂纹有明显的抑制作用。加入Ni元素后,涂层中Ti N的尺寸明显减小。由于涂层中存在镍钛化合物和氮化钛组织,因此涂层的硬度可达949.3HV0.3,约为基体的4倍,涂层的硬度会随着Ni元素含量的增加而降低。对加入Ni的涂层的耐磨性能进行分析,发现涂层的磨损量比基体降低了58.74%,与未加Ni涂层相比稍有降低,涂层中的硬质相氮化物会导致磨痕出现较多的剥落坑。涂层的摩擦磨损性能得到提升,其磨损机制主要是磨粒磨损和黏着磨损。结论通过在TC4粉末中添加质量分数为30%的Ni,能够有效抑制38CrMoAl激光熔覆原位氮化涂层中的裂纹,显著提升材料的硬度和耐磨性。
To address the issues of prolonged duration and high energy consumption associated with conventional nitriding processes for 38CrMoAl steel,laser cladding of TC4 alloy is employed on a 38CrMoAl substrate to achieve in-situ nitriding.However,the rapid cooling and solidification during laser cladding induce significant residual stresses,and the substantial differences in thermophysical properties between the cladding material and substrate make the coating highly susceptible to cracking.In this study,nickel was incorporated into the cladding material to mitigate crack formation in the coating.The influence of varying Ni content on both crack suppression behavior and wear resistance performance in laser-clad TC4 coatings with in-situ nitriding on 38CrMoAl substrates was systematically investigated.With a rectangular block of 38CrMoAl with dimensions of 100 mm×50 mm×10 mm as the substrate,the surface was ground smooth with sandpaper and then cleaned with anhydrous ethanol to remove impurities.Prior to the experiment,different mass fractions(20%,30%,and 50%)of Ni powder were added to the TC4 powder to form the cladding powder mixture.The powder was uniformly blended using a planetary ball mill.Subsequently,5%polyvinyl alcohol(PVA)was used as a binder,and the mixed powder was stirred with the binder into a paste,which was then evenly applied onto the substrate.A scanning galvanometer laser system was employed for the cladding process.After laser cladding,the samples were sectioned along the cross section with a wire electrical discharge machining,polished,and then etched with Kroll's reagent(VHF∶VHNO3∶VH2O=1∶2∶17).The microstructure of the coating was examined by optical microscopy(OM)and scanning electron microscopy(SEM),while an energy-dispersive spectroscopy(EDS)was used to analyze elemental distribution.The phase composition of the coating was determined by X-ray diffraction(XRD).A microhardness tester was employed to measure the hardness of both the coating and the substrate.Friction and wear tests were conducted using a tribometer,and the wear track morphology was observed to calculate the wear loss.When the Ni content in TC4 reached 30%,the number of cracks in the coating significantly decreased,demonstrating a remarkable crack-inhibiting effect.The addition of Ni also led to noticeable refinement of TiN particle size in the coating.The simultaneous presence of nickel-titanium intermetallics and titanium nitride(TiN)phases contributed to a coating hardness of 949.3HV0.3,approximately four times that of the substrate.However,the coating hardness exhibited a decreasing trend with increasing Ni content.Tribological analysis revealed that the Ni-modified coating achieved a 58.74%reduction in wear loss compared with the substrate,with marginal improvement over the Ni-free coating.The hard nitride phases in the coating caused pronounced spalling pits along wear tracks.The coating demonstrated enhanced wear resistance,with its dominant wear mechanisms identified as abrasive wear and adhesive wear.In summary,adding 30%Ni to TC4 powder effectively suppresses cracking in the in-situ nitrided coating on 38CrMoAl.The presence of Ni introduces hard nickel-titanium compounds alongside nitrides,enhancing both hardness and wear resistance compared with the substrate.Although the wear resistance improves with Ni addition,the hardness decreases compared with the Ni-free coating.Both hardness and wear resistance decline as the Ni content increases.
作者
张群莉
刘聪
陈智君
杨高林
何锦雯
姚建华
ZHANG Qunli;LIU Cong;CHEN Zhijun;YANG Gaolin;HE Jinwen;YAO Jianhua(College of Mechanical Engineering,Zhejiang University of Technology,Hangzhou 310023,China;Institute of Laser Advanced Manufacturing,Zhejiang University of Technology,Hangzhou 310023,China;Zhejiang Key Laboratory of High-precision and Efficiency Hybrid Processing Technology and Equipment,Hangzhou 310023,China)
出处
《表面技术》
北大核心
2025年第23期165-174,187,共11页
Surface Technology
基金
国家自然科学基金重点项目(52035014)
浙江省高层次人才特殊支持计划(2023R5210)。
