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A novel method, namely electron beam smelting (EBS) technology was used to prepare the Inconel 740 superalloy. The microstructures, hardness and oxidation behavior were characterized and compared with the traditionally prepared Inconel 740 superalloy. The results imply that the solution treatment gives rise to the coarsening of γ′ precipitates, with further aging treatment, the γ′ precipitates with size of less than 30 nm are distributed dispersively in the matrix, leading to a decreasing of the lattice parameters and an increasing of the misfit. The γ′ precipitates result in shearing mechanism of weakly pair coupling. The EBS 740 superalloy produces better properties than that prepared in the traditional method in both precipitation strengthening effect and oxidation resistance. [ABSTRACT FROM AUTHOR]

More and more attention has been paid to the application of flame retardancy and surface strengthening of titanium alloys in the aerospace field. In this paper, ultrasonic vibration assisted the laser solid formed (LSFed) TF550 flame-retardant titanium alloy was studied, and the influence of ultrasonic vibration on the microstructure and flame-retardant properties of the LSFed TF550 alloy was analyzed. The results showed that the LSFed TF550 alloy after ultrasonic vibration treatment effectively reduced the generation of pores. When the ultrasonic amplitude was 60 μm, the porosity was the lowest. The porosity of the sample was reduced from 3.84 % to 0.53 %, with the reduction of 86 %. The ultrasonic vibration results in the CET transformation of LSFed TF550 alloy specimen, and the average grain length-width ratio decreases from 5.3 to 1.2, and the microstructure of the specimen changes from the average width of 214 μm to the average grain size of 144±12 μm. Especially when the ultrasonic amplitude is 90 μm, the equiaxial grain size and the grain length-width ratio are the lowest. The effect of ultrasonic vibration at different positions was different. The higher the deposition height, the more columnar crystals in the microstructure and the less equiaxed crystals. When the deposition height was 43 mm, equiaxed crystals and columnar crystals began to coexist. Due to the grain refinement effect of ultrasonic vibration, the number of grain boundaries was increased, and the flame-retardant properties of the LSFed TF550 alloy was improved. • After UVA, the porosity of LSFed TF550 alloy reduces from 3.84 % to 0.53 %. • The columnar to equiaxed transition can be achieved by UVA. • UVA refines the grain of the LSFed TF550 alloy from 214 μm to 144±12 μm. • UVA increases ratio of the grain boundary and improves flame-retardant performance. [ABSTRACT FROM AUTHOR]

Effect of solution heat treatment on microstructure and electrochemical behavior was investigated for the electron beam smelted (EBS) 718 superalloy. The results imply that the solution heat treatment has a great influence on the precipitation behavior of EBS 718 superalloys and thus affects the electrochemical behavior. The increase of solution temperature gives rise to the solution of δ phase for both solution treated and aged EBS 718 superalloys. The 980 °C solution treated and aged EBS 718 superalloy exhibits the maximum content of the volume fraction of γʹʹ phase, in parallel with the highest lattice misfits. Further increase of solution temperature results in the precipitation of dispersively distributed γʹ particles. The pitting potential for the solution treated superalloys increases gradually with increase of solution temperature, and a similar behavior is observed for the aged superalloys with an exception of the alloy processed at 980 °C. The effect of solution temperature on the solution treated superalloys can be elucidated by considering the variation of the volume fraction and the size of δ precipitates. For the aged superalloys, the deterioration effect of Nb rich γʹʹ is obvious due to the tetragonal distortion and accompanying strain field in the nearby matrix. Higher solution temperature results in a uniform distribution of the nano-scale γʹ phase and smallest lattice misfits, with the highest apparent activation energy derived to be 52.86 kJ/mol. [ABSTRACT FROM AUTHOR]