Precipitates formation and its impact in friction stir welded and post-heat-treated Inconel 718 alloy

  • PDF / 1,048,705 Bytes
  • 6 Pages / 595 x 842 pts (A4) Page_size
  • 97 Downloads / 198 Views

DOWNLOAD

REPORT


Precipitates formation and its impact in friction stir welded and post-heat-treated Inconel 718 alloy Kuk Hyun Song, Han Sol Kim and Won Yong Kim Korea Institute of Industrial Technology, 7-47, Songdo-Dong, Yeonsu-gu, Incheon, 406-840, Korea

ABSTRACT In order to investigate the formation of precipitates such as MC carbides and intermetallic compounds in the friction stir welded and post-heat-treated Inconel 718 alloy, this work was carried out. Furthermore, the microstructural and mechanical properties of welds and post-heat-treated material were evaluated to identify the effect on precipitates formed during post-heat-treatment. Friction stir welding (FSW) was performed at a rotation speed of 200 rpm and welding speed of 150 mm/min; heat treatment was performed after welding at 720 °C for 8 hours in vacuum. As a result, the grain size due to FSW was notably refined from 5–20 µm in the base material to 1–3 µm in the stir zone; this was accompanied by dynamic recrystallization, which resulted in enhancements in the mechanical properties as compared to the base material. In particular, applying heat treatment after FSW led to improvements in the mechanical properties of the welds—the microhardness and tensile strength increased by more than 50% and 40% in fraction, respectively, as compared to FSW alone.

INTRODUCTION Inconel 718, age-hardenable alloy, is widely used in aircraft engines, power plants and gas turbines due to its good properties such as creep and corrosion resistance, and high strength at high temperature [1-2]. In general, to manufacture these parts, the fusion welding such as CO2 laser, Nd-YAG laser and electron beam welding have been applied lately [3-5]. However, in case of applying the fusion welding on Inconel 718 alloy, there are some problems such as Boron / Niobium segregation, Laves phase and liquation cracking in weld zone or heat affected zone (HAZ) due to its higher heat input [6-7]. Therefore, to complement these weak points, the application of FSW that is possible to be welded at solid state, resulting in lower heat input than that of the fusion welding, is requested. The precipitation on Ni-base superalloys plays an important role in increase of mechanical properties, such as hardness, strength and creep rupture life [4-6]. Especially, the precipitation of gamma double prime (γ″) in the grains and M23C6 carbides in the grain boundaries has been reported to be effective for the increase of mechanical properties [4]. However, the researches on the precipitation of the friction stir welded Ni-base superalloys have rarely been reported until now [8]. Therefore, in this study, FSW of Inconel 718, age hardenable alloy, was carried out to investigate the microstructural and mechanical properties of friction stir welds and to evaluate the relationship between the precipitation and the mechanical properties by the heat treatment after the FSW.

EXPERIMENTAL DETAILS The material used in this study was Inconel 718 alloy. To carry out the FSW, samples were prepared by 150 mm × 32.5 mm × 2 mm sheet

Data Loading...