Effect Of Rare Earth On Microstructure And Properties Of Roller Surface Alloyed By Laser

To improve performance and increase of service life of roller,Based on principle of materials alloying, a kind of coating materials specially used in roller alloyed by laser was designed. The roller which ingredient is 145 CrNiMoTiRe was alloyed by 5kW CO2 laser. The microstructure and properties of roller alloyed by laser were investigated by OM?SEM?XRD?Micro-hardness Testing Machine and MMS-2A screen display friction tester. The experimental results indicate that the optimized laser alloying technological parameters are as follows: P=2.3kW, V=5mm/s, f=320mm, d=30%. The microstructure is consisted of cell-shape crystal, equiaxed crystal and dendrite crystals. From the alloying layer surface to the substrate,it is divided into four areas: alloying area, bonding area, heat-affected zone and substrate In the alloying layer, there are phases such as?Fe,Cr?7C3, MoC, WC, Fe2 Ni and Co2TiO4 besides matrix phase ?-Fe.Addition of CeO₂ into alloying powder can significantly improve the microstructure and properties of alloying layer. When the content of CeO₂ varies from 0 wt.% to 2.0wt.%, the grain size in alloying layer gradually becomes finer. When CeO₂ is up to 2.0wt.%, microstructure in alloying layer becomes finest. However when the content of CeO₂ exceeds 2.0wt.%, the grain size in alloying layer gradually becomes coarser. When CeO₂ is up to 2.0wt.%, hardness,wear resistance and high temperature oxidation in alloying layer are highest. The hardness of alloying layer is up to 1108, It is nearly two times higher than that of substrate, and greater than the hardness without CeO₂ nearly 300. The wear resistance of alloying layer is four times than that of substrate, and which is three times than that of without CeO₂. The high temperature oxidation of alloying layer is three times than that of substrate, and which is two times than that of without CeO₂.The thermal cycle test indicates that with the increase of thermal cycles, the degree of oxidation of microstructure has become increasingly serious. And there are some cracks in microstructure. Those cracks will be appeared firstly at microstructure without CeO₂. When CeO₂ is up to 2.0wt.%, there is no crack in microstructure,in other words, those cracks will be appeared are later at limited number of thermal cycle. There are a large number of residual stress in samples. The residual stress in microstructure with CeO₂ is smaller than that of without CeO₂?With the increase of thermal cycles, the tendency of increase of residual stress is slow when content of CeO₂ is 2.0wt.%, whose residual stress value is much smaller than that of other content of rare earth.