Effect Of Heat Treatment On The Microstructural Evolution And Mechanical Properties Of Carbonyl Iron Absorbing Coatings

With the rapid development of radar detection technology today,the development and use of stealth materials is a key means to improve the survival rate of weapons and enhance national defence strength,and the development of radar absorbing coatings has become a hotspot for research by the military forces of various countries.Traditional wave-absorbing coatings can no longer meet the requirements of weapon survival and surprise defence,so the development of high-temperature resistant wave-absorbing layers is imperative.The evaluation and characterisation of the mechanical properties of high temperature resistant absorbing coatings is the key to process optimisation.In this project,a heat treatment experiment was carried out at 550 ℃ for 4-500 h.By analysing the microstructure,porosity,adhensive strength and Vickers hardness of the coating,the relationship between the mechanical parameters of the absorbing coating and the long heat treatment time was established,and the electromagnetic parameters and reflection loss of the coating were tested at different times after the heat treatment at 550 ℃.（1）The high-temperature resistant wave-absorbing coatings were prepared and the changes in structural organization,microscopic morphology and porosity after heat treatment were investigated.The experimental results show that the carbonyl-iron polysilazane absorbent coating prepared by the spraying method is cured at 450 ℃,and the carbon-carbon double bond in the coating breaks and polymerises,forming a spherical structure with a homogeneous structure.The coating is mainly composed of Fe,C,N,Si and O.The porosity of the original coating is 6.30 %.Fe,Fe₂O₃ appears in the coating after heat treatment at 550 ℃ for 20 h.This is due to the oxidation of the carbonyl iron during the heat treatment process.By observing the physical phase,morphology and porosity of the coating,it is possible to provide a theoretical basis for analysing the pattern of change in the properties of the coating under different temperature and process conditions.（2）The mechanical properties of the heat-treated wave-absorbing coatings were tested,and the electromagnetic parameters obtained were used to simulate the waveabsorbing properties of the coatings.The results show that the maximum adhensive strength at 80 h of heat treatment is 11.88 MPa,and the modulus of elasticity of the pure coating at room temperature is 28.64 GPa which is much lower than that of the titanium alloy at 135.19 GPa.The modulus of elasticity of the pure coating does not vary significantly with heat treatment time,while that of the TC4 titanium alloy decreases with increasing test temperature.At 550 ℃,the hardness of the coating showed an "M" pattern of variation with increasing heat treatment time,reaching a maximum value of 95.47 HV at 200 h.The electromagnetic parameters of the coating at different times of heat treatment were lower than those of the original coating.The minimum reflection loss of-13.95 dB at 16.39 GHz was achieved for the 20 h heattreated absorbers.These test data reflect the changes in the mechanical and wave absorbing properties of the coating at high temperatures,laying the foundation for future research into the high temperature absorbing coatings of carbonyl iron.