Research On Interfacial Damage Behaviors And Mechanisms Of Mineral Processing Equipment Material Under Multiphase Flow Environment

As a common occurrence in the field of mineral processing that interfacial damage behaviors and mechanisms of mineral processing equipment materials under multiphase flow environment,is one of the key reasons for the failure of mineral processing equipment materials.Every year,an enormous quantity of steel is corroded by cavitation and erosion,causing huge economic losses.In the wet mineral process,the addition of foaming agent makes ore pulp environment more complex,which deteriorates the damage of flow passage components caused by erosion and cavitation.Therefore,it is of great necessity to conduct surface modification of mineral processing equipment materials so as to endow them with excellent abrasive resistance as well as corrosion resistance.Meanwhile,research on interfacial damage behaviors and mechanisms between mineral processing equipment materials and multiphase flow should be conducted to reduce the damage rate of metal material interfacial and prolong the service life of key mineral processing equipment.In this paper,304 austenitic stainless steel?304 SS?,which is a common material of key overcurrent components in mineral processing equipment,is taken as the research object.First,surface modification of 304 SS was performed by surface ultrasonic rolling processing?SURP?;and the microstructure,mechanical properties,surface potential,passivation film state and electrochemical properties of matrix and SURP 304 SS were characterized subsequently.The results show that the SURP specimens display a better abrasive resistance due to the increase of Vickers hardness and residual stress on the surface of the specimens and the transformation of some austenite phase into martensite phase.The increase of Vickers hardness and residual stress helps to reduce the scratch and indentation caused by the collision between specimens and medium flow;and the phase transition of austenite phase into martensite can absorb the impact energy and avoid the crack growth under the effect of cavitation.In addition,the surface of SURP 304SS specimens has the phenomenon of grain refinement,and the surface potential difference between grain boundaries decreases.At the same time,the proportion of O,Cr and Ni in the passivated film increases while the proportion of Fe decreases.The enrichment of Ni is more obvious.Furthermore,the content of high oxide?Cr O₃,Ni₂O₃?and dense oxide?Fe₂O₃,Cr₂O₃,Ni₂O₃?in the passivated film increases.These phenomena endow the SURP specimens with higher open circuit potential and corrosion potential,larger impedance curvature radius and lower corrosion current density.In other words,the corrosion resistance of the sample has been greatly improved.Accordingly,it can be summed up that SURP greatly reduces the mass loss of 304 SS interfacial damage of the specimens in the environment of multiphase flow,prolongs the cavitation incubation period of the material and inhibits the corrosion rate during the growth period.In a word,the mechanism of SURP304 SS resistance to interfacial damage is the combined effects of phase transition,Vickers hardness,residual stress,grain refinement,surface potential,and the composition and thickness of passivation film.Secondly,cavitation,erosion and cavity-erosion coupling experiments were carried out on SURP samples with different SURP parameters and mineral processing parameters.And the effects of SURP parameters and mineral processing parameters on the interfacial damage of 304 SS specimens in multiphase flow environment were revealed.The experiments show that the mineral processing parameters have a significant effect on the interfacial damage behavior of SURP 304 SS:The increase of Ore Pulp Mass reduces the erosion resistance,cavitation erosion and erosion performance of the specimens,for the surface abrasion loss of the specimens increases on the one hand while the electrochemical corrosion resistance is slightly enhanced on the other when the Ore Pulp Mass increases;with the p H of Ore Pulp increasing,the electrochemical corrosion resistance of the specimens increases at first then decreases;the enhancing of erosion speed would accelerate the friction and abrasion between particles and interface,so the erosion resistance of the specimens would reduce.The erosion interfacial damage is mainly caused by cutting wear at low impact angle while controlled by deformation wear and electrochemical corrosion at high impact angle.The mass loss of the specimens witnesses a sharp increase when cavitation is added to erosion process,and the increase of gas content in the corrosive medium would reduce the service life of mineral processing equipment.Increasing of particle size,would reduce the mass loss while improving the electrochemical corrosion resistance.Thereby,the cavitation-erosion corrosion resistance of the specimens can be improved.The characterization and experiments of interfacial damage of 304SS under different SURP times show:when the surface of 304 SS is processed with SURP for 5?10 times,the Vickers hardness and residual stress reach saturation,the grain refinement speed is maximized while the defect generation speed is at a low level;at the same time,the surface potential between the crystals has a minimum difference,and the phase transition between austenite and martensite is in a stable state.In short,304 SS has the best performance of anti-interfacial damage when SURP 5?10 times,and SURP can significantly reduce the interfacial damage of 304 SS in a multiphase flow environment.Finally,the interface between multiphase flow and 304 SS was simulated from the perspectives of molecular dynamics and fluid mechanics at the micro and macro scales respectively,which further enriches interfacial damage behaviors and mechanisms between mineral processing equipment materials and multiphase flow.The binding energy shows that,the?35?E?absolute value of binding energy?of Fe and Cr metal elements is greater than that of oxides in the corrosive solution which contains Cl^-.In the passivated film,Fe and Cr have a strong interaction force with Cl^-and the adsorption is close while Fe₂O₃ and Cr₂O₃ are relatively weak in this aspect;The energy band and state density near the Fermi energy level indicate that O 2p,Cr 3d,2p and Fe 3d,2p are the factors affecting the corrosion current in the passivation film,where O and s orbital electrons of Fe and Cr elements form covalent bonds,so the electrons that generate the current are the electrons bound by the stronger nucleus Nuclear binding force and d orbital electrons in Fe₂O₃ and Cr₂O₃.By contrast,the s orbital electrons of Fe and Cr are free to move,thus being more capable of generating current.The content of high oxide and dense oxide in the passivation film on the surface of SURP specimens is higher than that of the matrix material.Therefore,SURP specimens has a better corrosion resistance.The binding energy,energy band and state density indicate that the change of passivation film composition of 304 SS specimens is one of the mechanisms to improve the interfacial damage performance.Erosion rate is the function that is related to erosion speed,erosion Angle and particle size.The simulated calculation of erosion rate under erosion speed,erosion Angle and particle size is consistent with the rules in the experiment.The thesis contains 100 figures,30 tables and 195 pieces of references.