Influence of Rhenium on the Grain Boundary Strength, Phase Evolution, and High Temperature Mechanical Properties of a Fine-Grain Nickel-Base Superalloy at 982°C

Abstract

The influence of Re on the grain boundary (GB) strength, phase evolution, and 982 C mechanical properties of fine-grain Mar-M247 superalloy was investigated. Quantitative statistical analysis showed that an increase of Re content in Mar-M247 resulted in a decrease of the size, and an increase in the number of GB carbides. The results of tensile and 982 C/200 MPa creep tests showed that tensile properties and creep life both increase with an increase in Re up to a maximum at 3 mass%. The tensile and GB strength increased with increasing the number of fine GB carbides. The addition of 1$3 mass% Re reduced steady-state creep rates and postponed the onset of the acceleration stage in three ways: (1) by increasing the amount of primary cuboidal 0 phase; (2) by increasing the strength of matrix; and (3) by increasing the development of 0 raft. It also prolonged the duration of the accelerating creep stage by refinement and an increase in the number of GB carbides. The above mentioned factors resulted in a prolongation of creep life. It is noted that the GB carbide evolution and GB strengthening effect by addition of Re have not been reported in the nickel-base superalloy before. However, addition of greater amounts of Re, such as 5 mass% Re, causes deterioration of the tensile and creep properties due to the formation of P phases.

Electrochemical corrosion characterization of nickel aluminides in acid rain

“…According to table 3, the minor corrosion current density was presented by Ni 3 Al as compared with that of NiAl, probably due to the concentrations of H 2 SO 4 (3.25x10 -4 M) and HNO 3 (2.5x10 -4 M), in this sense, NiAl has a higher corrosion current density by the presence of HNO 3 for equal concentrations of H 2 SO 4 and HNO 3 [9]. The anodic dissolution of both alloys may proceed via the kinetics of the anodic dissolution of Ni in acid solutions following the reaction path [25]: (8 This reaction mechanism considers the water adsorption process in the mechanism of electrooxidation: The variation of the corr value with respect to time observed in figure 5, is a typical behavior of these alloys immersed into NaCl solution. RYBALKA K.V.…”

“…Nickel aluminides such as NiAl and Ni 3 Al have received considerable attention for high temperature structural and coating applications in aerospace field [1][2][3], and due to high temperature strength, high corrosion resistance, high thermal and electrical conductivity, high melting temperature (1638°C), high Young's module (240GPa) have been regarded as a promising candidate for the high temperature applications [4,5]. Ni-base superalloys, Co alloys and steels are widely used in applications such as aircraft turbine blades and power plants due to present good corrosion resistance at elevated temperatures, however, the lower density (5.86g/cm 3 ) than superalloys and excellent high temperature oxidation resistance, allowed nickel aluminides being extensively studied in the past decades to replace superalloys [6][7][8]. As the nickel aluminides also has good properties for low temperature applications, studies of corrosion resistance at low temperature in aqueous media is interesting, because these materials will not always be at the operating temperatures, and corrosion damage during manufacture or maintenance may result in catastrophic failure during service [9].…”