| Nowadays,the traditional fossil energy is unable to meet the needs of global population growth and rapid industrialization.Therefore,the application of renewable energy has been closely watched by governments.Compared with other renewable energy power generation technologies,concentrating solar thermal power(CSP)overcomes the mismatch problem of energy supply and demand caused by day and night alternation,climate change and solar radiation instability by combining thermal energy storage systems and conventional generator sets.It is developing towards the goal of high light and heat conversion efficiency,low cost and high service life.While Al-12Si alloy is one of the ideal heat-storage materials,owing to its appropriate phase-transition temperature,excellent heat storage performance and wide application.However,when the system is used in practice,creep failure is easy to occur in the heat exchanger tube in the high-temperature and loading condition,besides,the heat exchanger tube subjected to corrosion of molten Al-Si alloy will accelerate the failure and explosion.Hence,it is important to improve the high-temperature creep and molten Al-Si-alloy corrosion resistance considering failure accidents prevention and long-term,safe and efficient operation of CSP.In this paper,321 austenitic stainless steel is used as the pipe base material,and powder pack aluminizing and laser shock processing(LSP)are applied to comprehensively improve the resistance of high temperature creep deformation and molten Al-Si alloy.The conclusions are as follow:(1)By comparing the surface integrity parameters of 321 stainless steel,aluminized steel and aluminized steel(annealed):The surface of 321 stainless steel sample is complete and smooth.The layer with large surface roughness and hardness of aluminized steel can be divided into three different layers from surface to matrix:Al2O3 film,FeAl outer layer and Fe-Al diffusion layer.After the aluminized steel sample is subjected to diffusion annealing treatment,the crystal grains of matrix are coarsened,and the surface roughness and hardness are increased.Three kinds of samples all exhibited typical creep three stages during high temperature creep,namely deceleration creep stage,steady creep stage and accelerated creep stage.The creep behavior of samples is mainly controlled by dislocation motion and affected by the austenite grains and the second phase precipitation particles.The creep resistance of aluminized steel decreased sharply,but after diffusion annealing treatment,the creep resistance ability of aluminized steel is improved,and its creep rupture life is flat with 321 stainless steel.(2)Through the LSP treatment of different shock times and laser power density on the aluminized steel samples,it is found that the surface of aluminized steel is obviously plastically deformed and the surface roughness increased.The surface of the aluminized steel is remarkably refined,and high-density dislocations and residual compressive stress are introduced,which increase the surface microhardness and strength of impacted samples.The more laser impact times and the higher laser power density,the larger the surface roughness and hardness of the sample,the deeper the hardening effect,and the more significant strengthening effect.When the laser power density is 6.59 GW/cm2,and the number of laser shocks is three times.The surface nucleation and internal crack propagation of the impacted aluminized steel samples retard,the creep void size and density decreased,the steady-state creep rate decreased by an order of magnitude,and the high temperature creep rupture life increased by about 232%compared with the unimpeded aluminized steel samples.(3)By comparing the molten Al-Si alloy corrosion-high temperature creep experiment:The aluminized steel possessed the thinner corrosion layer and the less corrosion-brittle phase(Fe2Al5 and FeA13),showing that better anti-molten Al-Si alloy performance.After laser shock processing,the surface grains of aluminized steel are refined and the layer/substrate bond are tighter.While improving the corrosion resistance of aluminized steel,the surface dislocation density and residual compressive stress are increased,and the creep void nucleation is more difficult,which improves the material's resistance to high temperature creep deformation.On the whole,the aluminized composite three times impact steel has the best performance under molten Al-Si alloy corrosion environment.the creep rupture life reaches 124h,which is 69.8%higher than the untreated sample. |
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