ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets

This article presents an investigation of the effect of serrated grain boundaries on the high temperature creep behaviour of IN718 superalloy. XRD, DSC, SEM and TEM have been conducted to study the microstructures; experimental results have shown that the morphology of grain boundaries can be a function of heat treatment conditions. In addition, creep tests have been performed on samples with and without serrated grain boundaries under 650 °C/625 MPa. In conclusions, the formation of δ phase during the heat treatment can influence the morphology of grain boundaries, and an improvement of 400 h creep rupture life has been attributed to the serrated grain boundaries.

Effect of serrated grain boundaries on the creep property of Inconel 718 superalloy

Hot working characteristics and dynamic recrystallization of delta-processed superalloy 718

Flow stress behavior and microstructures during hot compression of delta-processed superalloy 718 at temperatures from 950 to 1100 °C with strain rates of 10−3 to 1 s−1 were investigated by optical microscopy (OM), electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM). The relationship between the peak stress and the deformation conditions can be expressed by a hyperbolic-sine type equation. The activation energy for the delta-processed superalloy 718 is determined to be 467 kJ/mol. The change of the dominant deformation mechanisms leads to the decrease of stress exponent and the increase of activation energy with increasing temperature. The dynamically recrystallized grain size is inversely proportional to the Zener–Hollomon (Z) parameter. It is found that the dissolution rate of δ phases under hot deformation conditions is much faster than that under static conditions. Dislocation, vacancy and curvature play important roles in the dissolution of δ phases. The main nucleation mechanisms of dynamic recrystallization (DRX) for the delta-processed superalloy 718 include the bulging of original grain boundaries and the δ phase stimulated DRX nucleation, which is closely related to the dissolution behavior of δ phases under certain deformation conditions.

Hot deformation behavior of delta-processed superalloy 718

The commissioning and the initial operation for the first plasma in the KSTAR device have been accomplished successfully without any severe failure preventing the device operation and plasma experiments. The commissioning is classified into four steps: vacuum commissioning, cryogenic cool-down commissioning, magnet system commissioning, and plasma discharge.Vacuum commissioning commenced after completion of the tokamak and basic ancillary systems construction. Base pressure of the vacuum vessel was about 3 × 10−6 Pa and that of the cryostat about 2.7 × 10−4 Pa, and both levels meet the KSTAR requirements to start the cool-down operation. All the SC magnets were cooled down by a 9 kW rated cryogenic helium facility and reached the base temperature of 4.5 K in a month. The performance test of the superconducting magnet showed that the joint resistances were below 3 nΩ and the resistance to ground after cool-down was over 1 GΩ. An ac loss test of each PF coil made by applying a dc biased sinusoidal current showed that the coupling loss was within the KSTAR requirement with the coupling loss time constant less than 35 ms for both Nb3Sn and NbTi magnets. All the superconducting magnets operated in stable without quench for long-time dc operation and with synchronized pulse operation by the plasma control system (PCS). By using an 84 GHz ECH system, second harmonic ECH assisted plasma discharges were produced successfully with loop voltage of less than 3 V. By the real-time feedback control, operation of 100 kA plasma current with pulse length up to 865 ms was achieved, which also meet the first plasma target of 100 kA and 100 ms. The KSTAR device will be operated to meet the missions of steady-state and high-beta achievement by system upgrades and collaborative researches.

Commissioning and initial operation of KSTAR superconducting tokamak

To evaluate the accelerated creep phenomena for ramjet combustor, the stress rupture tests for Inconel 718 alloy were performed at a temperature range of 649–760 °C and a stress range of 381–1093 MPa. The stress exponent, n , under the given conditions was obtained. Also, the activation energy, Δ H , was calculated from the experimental results. An empirical formula of accelerated creep rate for Inconel 718 alloy was calculated by computer simulation. The accelerated creep life of Inconel 718 alloy was evaluated by using Larson–Miller parameter.

Stress rupture characteristics of Inconel 718 alloy for ramjet combustor

Status of the ITER vacuum vessel construction

Qualification of phased array ultrasonic examination on T-joint weld of austenitic stainless steel for ITER vacuum vessel

https://www.telegrid.enea.it/Conferenze/SOFE05/DATA/01_06.PDF

J.W. Sa

Papers

Stress rupture characteristics of Inconel 718 alloy for ramjet combustor

Status of the ITER vacuum vessel construction

Qualification of phased array ultrasonic examination on T-joint weld of austenitic stainless steel for ITER vacuum vessel

Status of the KSTAR Tokamak Construction

Progress of ITER vacuum vessel