Microstructure And Performance Of Multi-component Alloying Layer On M50 Steel Induced By High Current Pulsed Electron Beam

In this paper,surface alloying treatment induced by high current pulsed electron beam is proposed to improve comprehensive performance of M50 steel under extreme conditions.The effects of different process parameters on the microstructure and properties of 0Cr25Ni20 alloying layer were studied by means of changing the parameters of pre-plating layer thickness,irradiation voltage and irradiation times.There are three parts in this paper,the first part is the microstructure of 0Cr25Ni20 pre-plating layer deposited by magnetron sputtering;the second part is the microstructure of 0Cr25Ni20 alloying layer irradiated by electron beam and the last part is the properties of the 0Cr25Ni20 alloying layer.The microstructure of 0Cr25Ni20 pre-plating layer and alloying layer was analyzed by SEM and XRD.The results show that the surface of 0Cr25Ni20 pre-plating layer deposited by magnetron sputtering is uniform and dense,with no obvious cracks and other defects.And it was observed to be cellular under high magnification electron microscope.The main phase of the coating was(Cr-Ni-Fe-C)austenite phase with face-centered cubic structure.When the pre-plating layer is irradiated with an electron beam,more craters will be generated.As the irradiation voltage increases,the density of the craters decreases,and the surface tends to be smooth and flat.When the substrate M50 is pre-irradiated with a lower energy electron beam,the amount of carbides in the center of craters decrease but not completely disappeared.When the experiment is performed with a lower irradiation voltage and irradiation times,the alloying layer remains partially.When the irradiation voltage or the irradiation times are too high,the alloying layer on the surface will be splashed.The main phases of 0Cr25Ni20 alloying layer irradiated by the electron beam are austenite phase and Fe-Cr solid solution phase with body-centered cubic structure.With the increase of the irradiation voltage,the content of austenite phase increases significantly.The surface hardness,friction and wear behavior and corrosion resistance changed a lot after surface alloying,and the process parameters have a great impact on the performance.The surface elastic modulus after electron beam irradiation are all about 9GPa,as well as the surface microhardness is between 7-12 GPa.When the thickness of pre-plating layer is 700 nm and the irradiation voltage is 25 k V,the surface microhardness peaked at about 12 GPa.According to the microstructure analysis,the alloying layer mainly consists of Fe-Cr solid solution phase and residual austenite phase.Because the main strengthening mechanism is solution strengthening,all specimens have reduced hardness.The alloying layer has the highest self-lubricating life when the irradiation voltage is 10 k V and only irradiate for 5 times.The main wear mechanisms of alloying layer are oxidation wear and adhesive wear.After surface alloying treatment,the corrosion potential is significantly higher than that of the original M50 steel sample,and the self-corrosion current has significantly decreased.According to the results of salt spray corrosion and brine immersion tests,after corrosion,the surface quality of alloying layer is better than that of the original M50 steel,and the alloying layer has lower corrosion weight loss.In a word,alloying layer has better corrosion resistance.It can be concluded that surface alloying treatment induced by high-current pulsed electron beam improves the comprehensive performance of M50 steel to some extent,and the corrosion resistance has been improved.