Effect of Heat Treatment on the As-Cast Microstructure and Hardness of NiSi3B2 Alloy

• Published in: Metals (Basel ) Vol. 11; no. 4; p. 539
• Main Authors: Gorito, Gonçalo M., Moreira, Aida B., Lacerda, Pedro, Vieira, Manuel F., Ribeiro, Laura M. M.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.04.2021
• Subjects: Alloys; Backscattering; Borides; cast Ni-Si-B alloys; Cooling; Corrosion resistance; Corrosive wear; Hardness; Heat treating; High resistance; High temperature; high temperature alloys; Impact resistance; Investment casting; Machinability; Machining; Metal fatigue; Microstructure; Nickel; Nickel base alloys; Oxidation resistance; Phases; Quantitative analysis; Scanning electron microscopy; Solidification; Solution heat treatment; Temperature; Wear resistance; United States > US; Germany
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met11040539

Cast Ni-Si-B alloys have the potential for high-temperature applications because of their high resistance to wear, impact, corrosion, and oxidation at elevated temperatures due to an appropriate balance of hard phases and austenite that ensures a good compromise between toughness and hardness. In this work, NiSi3B2 specimens, fabricated by the lost-wax casting process, were investigated. Given the complex multiphase cast microstructure, a differential scanning calorimeter (DSC-TGA) analysis was employed to characterize the reactions that occur during solidification and the resulting phases were characterized using scanning electron microscopy (SEM), with energy-dispersive microanalysis (EDS) and backscattered electron (BSE) image and X-ray diffraction (XRD). Due to the presence of hard phases, machining of the Ni-Si-B components can pose additional difficulties. Therefore, the conditions of the solution heat treatment, which might lead to the homogenization of the microstructure, consequently improving its machinability, were also investigated. The results of the heat-treated samples indicated that the dissolution of the eutectic constituent is accompanied by a significant decrease in the hardness (approximately 17%). It is important to emphasize that the solution heat treatments carried out reduced the hardness without affecting the percentage of borides, which will allow improving the machinability without adversely affecting the alloy performance in service.