激光熔覆各向异性对Fe60合金磨损腐蚀性能的影响

Anisotropy Effects on Tribo-Corrosion Performance of Fe60 Prepared by Laser Cladding

目的 提高激光熔覆各向异性材料的抗磨损腐蚀性能。方法 以激光熔覆Fe60合金粉末为研究对象,选取与熔覆方向平行、倾斜45°以及垂直的3个工作表面进行磨损腐蚀测试,重点分析材料构筑方向对磨损腐蚀性能的影响机制。结果 通过对不同工作面摩擦系数、开路电位以及磨损体积的监测,发现与熔覆方向成45°的试样表面具有更好的摩擦稳定性、耐腐蚀性以及磨损抗性。原因在于,工作表面晶粒取向与晶界密度差异引起了试样表面变形抗力的不同。另外,与铸造试样进行对比得出,激光熔覆试样的磨损腐蚀抗性更加优越,主要与凝固过程中高冷却速率引起的组织细化有关。结论 对于激光熔覆各向异性材料,工作表面具有细化的微观组织结构、较高的晶界密度以及良好的变形抗力,有助于提高其磨损腐蚀抗性。

The laser cladding technique has been widely used to improve the tribo-corrosion performance of metal productions.However,the microstructure of materials prepared by laser cladding can present an anisotropy due to the differences of temperature gradient along different directions during solidification.As a result,the performance of tool materials maybe fluctuate greatly with the selection of different working surfaces.Herein,in this paper,the effects of anisotropy on the tribo-corrosion performance were primarily focused on.For that,Fe60 alloy powders manufactured by laser cladding on a stainless steel substrate were selected as the research object.And then three working surfaces,i.e.parallel,incline 45° and vertical to the building direction,were respectively taken for the tribo-corrosion test.Most of efforts were mainly made to analyze the friction coefficient,open circuit potential(OCP),and wear as a function of working surfaces.In order to explore the corresponding reasons,the microstructure,mechanical properties,and worn surfaces morphologies of different testing samples were characterized as well.The results showed that the OCP decreased as wear began at the initial stage.It was ascribed to the destruction of passive film outside the testing surface.Simultaneously,the re-passive behavior also existed,which would reach a balance with the destruction when the friction tended to be stable.The wear rate became slower with the continuous friction.On one hand,it was attributed to the lower contact stress between friction pairs after a running-in stage,which could reduce the complicate mechanical interactions.On the other hand,it was closely related with the re-generated passive film.As compared with other surfaces,the 45° one had the best friction stability,corrosion resistance,and wear resistance.It was resulted from the differences of microstructure.Firstly,the higher density of grain boundaries enhanced the deformation resistance,which was beneficial to the stable contact.Secondly,the corresponding crystal orientation with lower atomic density was also responsible for the deformation resistance.In addition,the selection of 45° sample was compared with an as-casted sample under different loads.It was found that samples prepared by laser cladding had better tribo-corrosion resistance.It was closely related with the refinement of organizations caused by the rapid cooling rate.For instance,the generation of sub-grains could improve the surface hardness,and could reduce the surface activity,so that the materials resistance to mechanical damage and corrosion could be obviously improved.The tribo-corrosion performance was deeply influenced by loads.The increasing load could result in the lower friction coefficient,which was attributed to the disproportionate increase of contact area at tribology interface.Besides,the laser cladding sample had the lower sensitivity to the various load.After test,the worn surfaces of different samples were observed.It was suggested that the load and microstructure could lead to the change of physical mechanisms.Under lower load,the materials damage was dominated by corrosion and abrasive wear.As the load increased,the adhesive mechanism began to play significant roles.The research results could provide reference value in practice.