Study On Synthesis Of CBN By Mechanical Activation And Low-pressure Cold Spray Composite Coating Tribological Properties

Wear is one of the main forms of mechanical damage and failure.The use of low-pressure cold spray technology to repair worn parts can effectively prolong the service life of wear parts.The low-pressure cold spray coating technology has the advantages of small size,convenient carrying,simple process and low energy consumption,and has great advantages in repairing the wear parts of large equipment in the construction site.Nickel-based coatings are widely used on the surface of key components of mud pumps due to their good wear resistance and corrosion resistance.However,the hardness of pure nickel coating is low,so it is difficult to meet the harsh conditions of interaction between high load and corrosion environment in mud pump service.The combination of high plastic toughness of metal and high hardness of ceramic particles through structural design is one of the effective means to improve the comprehensive properties of pure nickel coating,and the addition of hard particles can effectively improve the deposition rate and density of low-pressure spraying coating.The Ni-Al₂O₃?Ni-ZrO₂ and Ni-cBN nickel base ceramic composite coatings were prepared by low pressure cold spraying technology.The effect of ceramic hard particles on the wear resistance of the coatings was studied by hardness and dry friction at room temperature.The cubic boron nitride(cBN)was prepared by mechanical activation with hexagonal boron nitride(h BN)at room temperature and atmospheric pressure.The effects of time and rotational speed on morphology,phase structure,grain size and conversion rate were studied.The results were as follows:Adding ceramic particles can obviously improve the comprehensive properties of Ni coatings,and the deposition size of ceramic particles in the coatings directly affects the density of low pressure cold spraying coatings.The Al₂O₃?ZrO₂ ceramic particles with 9-33 vol.%can increase the hardness of Ni metal composite coatings to190.54 Hv_0.1?198.46 Hv_0.1 respectively.In the range of additions,the hardness of composite coating increases first and then decreases with the increase of Al₂O₃content in the range of addition,but ZrO₂ is opposite.The addition of Al₂O₃?ZrO₂?ceramic particles also effectively improves the tribological properties of Ni metal ceramic composite coatings.With the addition 23 vol.%ceramic particles,the wear rate of the Ni-Al₂O₃ composite coating was 3.18×10^-5 mm³/(Nm),The tribological properties of Ni metal ceramic composite coatings showed the opposite variation with the addition Al₂O₃ particles and the addition of ZrO₂ particles.The cBN ceramic particles can increase the hardness of Ni metal composite coatings to 235.03Hv_0.1.The Ni-cBN is 23.35%and 18.43%higher than the Ni-Al₂O₃?Ni-ZrO₂ composite coating.In the range of additions,as the amount of cBN increases,the hardness of composite coating increases first and then decreases.With the addition 23 vol.%cBN ceramic particles,the wear rate of the Ni-cBN composite coating is as low as 4.44×10^-6 mm³/(Nm).Compared with Ni-Al₂O₃?Ni-ZrO₂composite coating,86.04%and 84.42%were reduced respectively.The tribological properties of Ni-cBN composite coatings show the tendency of first decreasing and then increasing with the amount of particle BN.The cubic boron nitride was successfully prepared by using MSK-PCV-300planetary ball mill at a speed of 1200 r/min,with a ball material ratio of 10:1 and vacuum.The rotational speed and time of mechanical activation have different effects on the synthesis of cubic boron nitride.Speed is the key factor of synthesis and plays a decisive role;time is only to promote the synthesis process and play an auxiliary role.With the increase of mechanical activation time,the grain size and disorder of hexagonal boron nitride decrease,the relative volume content of cubic boron nitride increases with time,and the mechanical activation reaches 15.6%at 1200 rpm.The B₂O₃ produced after mechanical activation increases first and then decreases with the increase of mechanical activation time,which is not conducive to the synthesis of cubic boron nitride.