THERMOPHYSICAL CHARACTERISTICS OF THE HVAF COATING FROM QUASICRYSTALLINE ALLOY OF THE Al-Cu-Fe SYSTEM

Abstract

The article deals with the results of determining the thermal conductivity coefficient from quasicrystalline coatings of the Al-Cu-Fe system in the temperature range up to 900 °C. The Al-Cu-Fe quasicrystalline alloy acquires a great interest for practical use as a material for protective coatings. The Al-Cu-Fe alloy is used to produce thermal barrier coatings in internal combustion engines, non-stick coatings on chemical synthesis equipment and in the food industry and to prevent the icing in aviation. The Al-Cu-Fe quasicrystals have low density, high hardness, high elasticity modulus, high values of corrosion resistance and wear resistance, low coefficient of friction, lowered adhesion, low thermal conductivity in combination with the coefficient of thermal expansion, which is close by its value to some metals. The water atomized Al63Cu25Fe12 powder with a dispersion of +40/-63 μm that has a content of the quasicrystalline phase of about 60 wt. % was used for spraying. The coating was sprayed to the butt of a cylindrical substrate from steel 45 (diameter – 25 mm, height – 10 mm), which before spraying was subjected to jet-abrasive treatment by corundum powder with a determining particle size of 1 mm at air pressure of spraying of 0.5 MPa. The Al-Cu-Fe coating with a thickness of more than 0.8 mm was made by high-speed air-fuel (HVAF) spraying using a burner GVO-RV12 with the following spraying mode: the pressure in the combustion chamber of the burner is 1.0 MPa; the oxidant excess coefficient a ≈ 1.2, the spraying distance is 270 mm. The samples were installed on the side surface of the drum (diameter 120 mm), which rotates at a speed of 2.0 rev/s (the speed of movement of the sputtering spot is 0.8 m/s). Spraying was done in three steps of 10 seconds each with a 30 second cooling time between them. Determination of the temperature dependence of the thermal conductivity of the coating was carried out by solving the inverse problem of thermal conductivity by one-dimensional temperature fields in samples obtained by single-sided jet heating with an industrial hot air torch (at surface temperatures up to 450 °C) and an oxygen-propane welding torch (at temperatures above 450 °C). It is shown that the values of the thermal conductivity coefficient of Al-Cu-Fe quasicrystalline coatings in the range of 20 °С…900 °С vary within λ = 1.9 – 2.31 W/(m×K).