Fabrication of niobium carbide coating on niobium by interstitial carburization. (April 2020)

• Record Type: Journal Article
• Authors: Zhao, Ziyuan; Hui, Pengfei; Liu, Fuyuan; Xu, Yunhua; Zhong, Lisheng; Zhao, Mingxuan
• Is Part Of: International journal of refractory metals & hard materials. Volume 88(2020)
• Publication Date: 2020-04
• Subjects: Hard coating -- Refractory metal -- Diffusion -- Hot pressing -- Carburizing; Heat resistant alloys -- Periodicals; Refractory materials -- Periodicals; Metallography -- Periodicals; Alliages réfractaires -- Périodiques; Matériaux réfractaires -- Périodiques; Métallographie -- Périodiques; Heat resistant alloys; Metallography; Refractory materials; Periodicals; Electronic journals; 669.73
• DOI: 10.1016/j.ijrmhm.2020.105187
• Languages: English
• ISSNs: 0263-4368

Abstract

Abstract: Ceramic coatings on niobium substrates are fabricated by hot-pressing the niobium with cast iron at 1100 °C. The interstitial carbon atoms diffuse into the niobium, and NbC and Nb2 C precipitate in the surface, forming a ceramic coating. The total volume fraction of the ceramic phases in the coating reaches 92%, and the grain size is in the range of 170–1000 nm. Both the volume fraction and the grain size of the ceramic phases decrease with increasing depth with respect to the coating surface, displaying a gradient microstructure. In the coating, the crystallographic orientations of NbC and Nb2 C are randomly distributed. In the substrate, some isolated NbC and Nb2 C nuclei exhibit the Kurdjumov–Sachs orientation relationship and the Porter orientation relationship with the matrix respectively, namely 1 1 ¯ 1 10 1 ¯ NbC // 1 1 ¯ 0 11 1 ¯ Nb and 10 1 ¯ 0 0001 Nb2C // 110 1 1 ¯ 5 Nb . The coating remarkably improves the surface hardness of the niobium from 110 HV to 1600 HV, and it is strongly bonded with the substrate. Highlights: Interstitial carbon atoms in cast iron diffuse into niobium forming a cermet coating. The coating is completely dense, the volume fraction of carbides reaches 92%. The coating has a gradient microstructure with ultrafine carbide grains. NbC and Nb2 C exhibit the K-S OR and the Porter OR with the matrix respectively. The surface hardness reaches 1600 HV and the adhesion strength of the coating is high.