Microstructure and Microhardness of Ni/Al-TiB₂ Composite Coatings Prepared by Cold Spraying Combined with Postannealing Treatment

• Main Authors: Xiao Chen, Chengdi Li, Shunjian Xu, Yao Hu, Gangchang Ji, Hongtao Wang
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Coatings
• Subjects: cold spraying; NiAl intermetallic compounds; TiB₂; microstructure; porosity
• Online Access: https://www.mdpi.com/2079-6412/9/9/565

Ni/Al-TiB₂ composite powders were deposited on the surface of 316L stainless-steel substrates by cold spraying at gas temperatures of 250 and 450 °C, respectively. Then, the as-sprayed coatings were annealed at 650 °C for 10, 20, and 30 h. The experimental results showed that the average porosity of as-sprayed coating dropped from about 0.68% to 0.054% as the cold spraying gas temperature increased. The contents of Ni, Al, and TiB₂ in the as-sprayed coatings were different from that of the Ni/Al-TiB₂ composite powders. The main phase compositions of the as-sprayed Ni/Al-TiB₂ coatings were the same as those of composite powder, consisting only of pure Ni, Al, and TiB₂ phases. TiB₂ as a reinforced particle in the as-sprayed coating could obviously increase the microhardness of the coatings. NiAl₃ and Ni₂Al₃ intermetallic compounds were synthesized in situ in all of the annealed coatings, and the average contents of NiAl₃ and Ni₂Al₃ intermetallic compounds increased as the cold spraying gas temperature increased. The distribution of TiB₂ particle was changed as the annealing times increased, which changed from more comparative uniform distribution to accumulation. The average porosity of the annealed coatings increased as the annealing time increased. The microhardness of Ni/Al-TiB₂ coatings annealed at 650 °C for 10 h was increased remarkably due to the reinforcement role of TiB₂ particles and NiAl₃ and Ni₂Al₃ intermetallic compounds.