Mechanism Of Ni Based Al₂O₃-TiB₂ Metal Ceramic Powders Mechanical Alloying And The Microstructure And Properties Of The Coatings

Steel is the most widely used industrial materials; the mechanical properties of different steels are very different. Certain steels have been limited in application. The Ni based Al₂O₃-TiB₂ metal ceramic coating was prepared on the surface of Q235 steel substrate by flame spraying, to enlarge its application range in the industrial production. The materials used in the experiment were Al powder, Ti O2 powder and B2O3 powder. The molar ratio is 10: 3: 3. Adding 5%, 10%, 15%, 20%, 25% and 30% of Ni powder, respectively, in the mixed powders. And ball milling under the protection of argon gas to get the Ni based Al₂O₃-TiB₂ metal ceramic powder. Al-Ti O2- B2O3 powder with no Ni powder as control group was tested. Sampled every 2 h in argon atmosphere and analyzed by XRD, SEM and EDS. Differential scanning calorimetry analysis was carried out on the raw mixed powders and milled powders. Ni-based Al₂O₃-TiB₂ cermet powder obtained was screened, dried and pelletized as a raw material for preparing Ni-based Al₂O₃-TiB₂ cermet coating on the surface of Q235 steel by flame-spray. XRD, SEM analysis, micro hardness and friction and wear tests were carried out on the coating. The results show:（1） The mixed powders containing 0%, 5%, 10%, 15%, 20%, 25% and 30% of Ni,got Al₂O₃, TiB₂ multiphase organization when they milled 12 h, 10 h, 8 h, 8 h, 6 h and 4 h. In the ball milling process, in addition to no Ni and 5%Ni mixed powder, other components of the powder were detected in the new phase Ni Al. No Ni powders after mechanical alloying 12 h, according to the chemical equation 10 Al + 3Ti O2 + 3B2O3 = 5Al₂O₃ + 3TiB₂ solid phase reaction, got Al₂O₃, TiB₂ multiphase organization. When Ni is added in Al-Ti O2-B2O3 mixed powders, since the mechanical milling process, Ni preferentially with Al forming the intermediate phase Ni Al, Ni Al easier react with Ti O2 and B2O3 than Al,according to the chemical equation 10 Ni Al + 3Ti O2 + 3B2O3 = 5Al₂O₃ + 3TiB₂ + 10 Ni solid phase reaction, got Al₂O₃, TiB₂ composite organization. In the course of the combustion reaction, milled powder is subjected to severe plastic deformation, the surface energy and lattice distortion energy, high contents of reactive powder particles, the powder required for the reaction temperature to be significantly lower than milled powder.（2） coating hardness test results show that The higher the content of Al₂O₃-TiB₂ ceramic particles in the coating, the higher the micro-hardness of the coating.; friction and wear test results show, 10%（Al₂O₃-TiB₂）-Ni based cermet coating wear resistance is the best. Because of Al₂O₃, TiB₂ crystal structure of Ni larger difference, Al₂O₃-TiB₂ with Ni bonding strength is low. When the coating has high content of Al₂O₃-TiB₂, two-phase interface easy to form micro crack, in the role of cyclic loading for a long time, these micro cracks began to expand, when the crack growth to a certain extent, it will make the crack surrounded area of the micro-particle shedding.