Powder Metallurgy Ni-cr/bn Preparation Process And Its Performance Study

Ni-20Cr/BN was fabricated by powder metallurgy. The microstructure and properties of Ni-20Cr/BN were investigated by DTA,XRD,SEM,OM,hardness and the three point bending test .The effect of BN content on sintering properties of Ni-based abradable seal alloy was investigated.The sintering process and model with BN and without BN were studied.To establish model to reseach the process of Ni-20Cr/BN sintering expansion. Effect of the content of BN on oxidation of Ni-20Cr/BN at 900℃ and carburization and dusting of Ni-20Cr/BN during sintering at 1250℃ were reviewed, reasons and mechanism of oxidation and carburization are discussed.The study shows:The strength density and hardness of Ni-20Cr/BN are all increasing with the improving sintering temperature.The reasonable sintering tempetature is between 1150℃ and 1200℃. the hardness of Ni-20Cr/BN changes little and the three point bending strength of Ni-20Cr/BN improves slightly with the first-sintering temperature increasing.BN powders hinder sintering between powders,and sintering expansion and density falling were discovered.The oxidation layer of Ni-Cr consists of α -Cr₂O₃, NiCr₂O₄ and NiO but the oxidation layer of Ni-20Cr/BN consists of α - Cr₂O₃ and CrBO₃ during at 900 ℃.The oxidation kinetics curves of Ni-20Cr/BN obey the parabolic law.The oxidation velocity is increasing then falling with the content of BN more.Ni-20Cr/BN was carburization and dusting when contacting with graphite ,so Ni-20Cr/BN should be protected with inertia materials to avoid carburization and dusting.The friction coefficient of Ni-20Cr/BN is lower than without BN additive.