The Research Of Surface Modification Of Alloy DZ4 Irradiated By High-intensity Pulsed Ion Beam

Surface irradiation of refractory alloy DZ4 is realized by using High intensity pulsed ionbeam (HIPIB) containing Cⁿ⁺(30mol%) and H⁺(70mol%), where the accelerating voltage andpulse duration are fixed at 250kV and 70ns respectively. The modification mechanism ofHIPIB irradiating on the surface of DZ4 alloy is studied by analyzing the microstructures andproperties of original and irradiated samples, in the purpose of further understanding theappropriate application fields of HIPIB method.Scanning electron microscopy (SEM) demonstrates that after radiations craters appear onthe surface of DZ4 alloy and there exist plenty of Cr, Mo, and C on the surface of the craters.The appearance of craters is due to uneven physical and chemical properties of materials.Craters trend to disappear after irradiated for many times. Transmission electron microscopy(TEM) demonstrates that the original sample is mostly composed ofγ' andγ' phases.Compared with the original sample, a 10nm-deep nanocrystal layer appears after irradiation,which is composed of Ni, Cr, Al, Ti, W, Mo and Co elemental crystal with a grain size of 5～10nm.γ' does not exist under the nanocrystal layer, andγ' content increases gradually to bethe same as the base with depth increasing. There exists a region with plenty of dislocations atthe position 20μm-deep under the surface of sample 100-15. X-ray diffraction (XRD)demonstrates that there exists stress in irradiated samples.The electrochemical corrosion test shows that the corrosion resistances of samples aregreatly improved after irradiated by HIPIB, corrosion rates decline, and passivations happenmore easily than the original one. The isothermal oxidation test shows that the hightemperature oxidation resistances of irradiated samples are also improved, because it's mucheasier to form a continuous compact Al₂O₃ layer on the surface of irradiated samples than ofthe original one. Nanohardness test demonstrates that a maximum of hardness first appears onthe top surface of irradiated samples, and hardness decreases to a minimum one with thedepth increasing, and then finally increases to the same hardness value as the base. It is theharder irradiated surface layer that results in the decrease of the friction coefficients. Knoopmicrohardness (H_k) test also demonstrates that the hardness of the base is improved by HIPIBirradiation and the wear resistance is also improved accordingly, which can be attributed tothe appearance of a lot of dislocations.