Preparation Of Aluminum Based Quasicrystal Coating And Its Thermal Insulation-Friction-Corrosion Properties

Metal-based thermal protection coatings have been applied in the early 20th century,but their further development was limited because of the poor thermal insulation performance in most cases.In 1984,quasicrystal material was discovered as a solid ordered phase with a structure between crystal and amorphous.It combines long-range quasi periodic translation order with amorphous rotational symmetry.And the special structure makes it outstanding in mechanics,tribology and heat insulation,and shows good prospects for application in the field of medium temperature thermal protection.In the study of quasicrystal materials,Al-based quasicrystal types account for a substantial part,it is relatively in-depth.Compared with other quasicrystalline materials,Al-based quasicrystal materials perform well in terms of friction and wear reduction and thermal insulation.At present,the preparation methods of Al-based quasicrystal thermal spraying coatings are mainly plasma spraying,supersonic flame spraying.However,the coatings prepared by explosive spraying has the characteristics of high bonding strength,which has a good effect on improving the performance of coatings.The thesis made the study of both Al-Cu-Fe and Al-Cu-Fe-Sc coatings prepared by explosive spraying.Al-Cu-Fe and Al-Cu-Fe-Sc powders were annealed and the performance of them was characterized.Subsequently,the preparation process parameters were optimized for Al-Cu-Fe and Al-Cu-Fe-Sc coatings.The thermal insulation performance of the two coatings prepared by the optimal process parameters was studied.The effect of heat treatment on the hardness,bond strength and corrosion resistance of the two coatings was analyzed.Finally,the tribological properties of the two coatings at room temperature and high temperature were investigated.The results show that:1.The quasicrystal content of the powder was increased significantly after annealing.The quasicrystal content in powder was more than 95%after annealing at 800℃.The optimized parameters of Al-Cu-Fe coating were 56%oxygen fuel ratio,150mm spraying distance and4guns/s spraying frequency;and the optimized parameters of Al-Cu-Fe-Sc coating were56%oxygen fuel charge gun ratio,210mm spraying distance and 1gun/s spraying frequency.2.The Al-Cu-Fe coating and Al-Cu-Fe-Sc coating prepared by the optimal parameters showed excellent thermal insulation properties.At 700℃,the specific heat capacity of the two kinds of coatings were 0.749J/（g·K）and 0.719J/（g·K）,and the thermal conductivity were5.913W/（m·K）and 8.747W/（m·K）,respectively.3.The surface hardness of heat-treated Al-Cu-Fe coating increased from 569.4HV_0.3 to658.33HV_0.3,and the bonding strength increased from 33.25MPa to 58.75MPa.After heat treatment,the surface hardness of Al-Cu-Fe-Sc coating increased from 566.01HV_0.3 to643.68HV_0.3.The bonding strength increased from 53MPa to 69.75MPa,indicating that the addition of Sc element improved the bond strength of the coatings.4.The friction coefficients of Al-Cu-Fe coating at room temperature and high temperature were 0.526～0.635 and 0.512～0.768 respectively under 5N,15N and 25N loads,and0.511～0.656 and 0.500～0.578 for Al-Cu-Fe-Sc coatings,respectively.The wear rates of the two coatings were one order of magnitude lower than that of the substrate under 15N and 25N loads.At room temperature,the wear mechanisms of the two coatings were gradually changed from abrasive wear to adhesive wear with the increase of load.At high temperature,the wear were mainly adhesive wear,and delamination wear existed under partial load.5.The corrosion resistances of Al-Cu-Fe coating and Al-Cu-Fe-Sc coating were not much different from that of the substrate before annealing,but the corrosion resistances were significantly enhanced after annealing.The self corrosion current density of Al-Cu-Fe coating and Al-Cu-Fe-Sc coating reduced to 1/4 and 1/5 of that before annealing respectively when the self corrosion potentials were similar.