Abstract
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.
Highlights
Nickel superalloys stand out for their high corrosion, abrasion, and mechanical resistance at high temperatures, competing in the market with other materials, namely austenitic stainless steels
Ni-Si-B alloys have the potential for use in the glass industry due to their high resistance to wear, impact, corrosion, and oxidation at high temperatures
These results indicate that the reduction of the eutectic constituent (Ni-γ-Ni3Si) to values below the X-ray diffraction (XRD) detection limit and the consequent enrichment of austenite in silicon are certainly due to atomic diffusion
Summary
Nickel superalloys stand out for their high corrosion, abrasion, and mechanical resistance at high temperatures, competing in the market with other materials, namely austenitic stainless steels. These alloys are attractive for many applications: aerospace, chemical, oil and gas, nuclear, automotive, as well as tool and mold industries, since they with-stand severe wear conditions, corrosive environments, and thermal fatigue [1,2]. The alloys for molds for the glass industry must exhibit inert behavior, ensuring that there are no reactions at the interface between the liquid glass and the mold surface These alloys must show superior toughness and thermal fatigue resistance to withstand a large number of thermal cycles at high temperatures. Another important property is the thermal conductivity, as it determines the efficiency of heat transfer, allowing the glass to cool quickly and reducing the production cycle time [3,4,5].
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