Effects of Double-Stage Annealing Parameters on Tensile Mechanical Properties of Initial Aging Deformed GH4169 Superalloy

This study takes large size samples after hot-upsetting as research objects and aims to investigate the optimization double-stage annealing parameters for improving the mechanical properties of hot-upsetting samples. The double-stage annealing treatments and uniaxial tensile tests for hot-upsetting GH4169 superalloy were finished firstly. Then, the fracture mode was also studied. The results show that the strength of hot-upsetting GH4169 superalloy can be improved by the double-stage annealing treatment, but the effect of annealing parameters on the elongation of GH4169 alloy at high temperature and room temperature is not significant. The fracture mode of annealed samples at high-temperature and room-temperature tensile tests is a mixture of shear fracture and quasi-cleavage fracture while that of hot-upsetting sample is a shear fracture. The macroscopic expressions for the two fracture modes belong to ductile fracture. Moreover, it is also found that the improvement of strength by the double-stage annealing treatment is greater than the single-stage annealing treatment. This is because the homogeneity of grains plays an important role in the improvement of strength for GH4169 superalloy when the average grain size is similar. Based on a comprehensive consideration, the optimal annealing route is determined as 900 °C × 9–12 h(water cooling) + 980 °C × 60 min(water cooling).

Behavior of Nitrogen in GH4169 Superalloy Melt during Vacuum Induction Melting Using Returned Materials

The nitrogen behavior of superalloy melt GH4169 during the vacuum induction melting (VIM) process was clarified by using different proportions of returned materials including block-shaped returned material, chip-shaped returned material, and pure materials to produce a high–purity superalloy melt and provide guidance for the purification of the superalloy melt. For the nitrogen removal during the VIM process, the denitrification rate in the refining period reached 10 ppm per hour on average, which is significantly higher than 1 ppm per hour on average in the melting period. The denitrification reaction of superalloy melt GH4169 under extremely low vacuum pressure is controlled by both the mass transfer of nitrogen in the melt and the chemical reaction of the liquid–gas interface. The nitrogen removal of superalloy melts during VIM occurs through the two methods of gasification denitrification and nitride floatation because the nitrides begin to precipitate in the liquid phase at 1550 °C. A higher nitrogen removal rate can be obtained by increasing the proportion of chip-shaped material or decreasing the proportion of block-shaped material.

Sustainable and Efficient Processing of Gh4169 Superalloy With Rotating Short Arc Milling Method

High processing efficiency and low environmental pollution have been recognized as important goals of sustainable electrical discharge machining (EDM). This paper proposed a sustainable and efficient EDM method called rotating short arc milling. In order to improve the processing efficiency and reduce pollutant emissions, the principles of this method to achieve high material removal rate (MRR), low tool electrode wear rate (TEWR) and environmentally friendly dielectric are described separately. The rotating short arcs generated by the compound field can improve the machining efficiency. The action of the magnetic field and the internal high-pressure dielectric can quickly remove the debris avoiding irregular discharge, thereby improving the machining quality. Due to the attraction effect of the magnetic field on the debris, several debris adhere to the processing end of the tool electrode to form a protective layer and participates in the processing as a part of the tool electrode, which can reduce the tool electrode wear. Tap water is used as the working fluid to reduce pollutants generated during processing. Then, a series of experiments are conducted to study the influence of process parameters on the processing of GH4169 superalloy. The results show that the machining voltage, machining depth and magnetic field strength are the three most important factors that affect the efficiency and sustainability of rotating short arc milling. Furthermore, the optimal process parameters are obtained by using gray relational analysis method to optimize the machining process in terms of high efficiency and environmental protection.