Effect of intermediate heat treatment temperature on microstructure and notch sensitivity of laser solid formed Inconel 718 superalloy

Abstract

Inconel 718 superalloys deposited by laser solid forming (LSF) were heat treated with solution treatment, intermediate heat treatment (IHT) and two-stage aging treatment in sequence (SITA heat treatment). The effect of IHT temperature on microstructure, tensile property and notch sensitivity of LSFed Inconel 718 superalloy at 500 ℃ were investigated. As-deposited columnar grains have transformed to equiaxed grains and the grains were refi ned due to the recrystallization during the SITA heat treatment. It is found that the size and amount of δ phase dispersed at grain boundaries decreased with the increasing of IHT temperature, and δ phase disappeared when the IHT temperature reached 1 020 ℃. The ultimate tensile strength (UTS) and yield strength (YS) of smooth samples increased to a maximum when the IHT temperature reached 980 ℃ and then decreased slightly to a minimum when the IHT temperature was 1 000 ℃, and followed by slight increasing again till the IHT temperature reached 1 020 ℃, resulted from the competition of precipitation strengthening effect of γ″ and γ′ phase and the grain boundary weakening effect caused by the gradual disappearance of δ phase with increasing the IHT temperature. The notch sensitivity factor (q e ) decreased but still greater than 1 as the IHT temperature increased, which is attributed to the decrease of the size and amount of δ precipitation.

Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures

“…Secondly, the formation of the δ phase will deplete the strengthening γ＂phase [18], thus J o u r n a l P r e -p r o o f decreasing the strength of the material. In addition, a moderate fraction of δ phase plays a positive role in eliminating notch sensitivity and stress concentration [42]. The excessive δ phase is more likely to promote crack initiation and propagation [43][44].…”

Study on the microstructure, mechanical property and residual stress of SLM Inconel-718 alloy manufactured by differing island scanning strategy

“…Inconel-718 is characterized by high yield strength, high-strength, and corrosion resistance, which has been used in a wide range of applications at elevated temperature ∼700°C, such as gas turbines, liquid fueled rockets, aircraft, nuclear reactors, pumps and mold [1,2]. Recently, Inconel-718 based parts have been fabricated by selective laser melting (SLM), a rapid prototyping manufacturing technique, which can directly process complex shape 3-dimensional parts that cannot usually be obtained using conventional processes from metallic powder layer by layer [3,4].…”

Alloy design for laser powder bed fusion additive manufacturing: a critical review

“…As a comparison, the cooling rate in conventional casting is approximately 0.5 • C • s −1 [43]. Consequently, the additively manufactured (AM'ed) microstructure is one or two orders of magnitude smaller than the as-cast materials [50]. The repeated ultrafast heating and cooling cycles during L-PBF also gives rise to a higher dislocation density comparing to their cast counterparts [12].…”