Jianxin Dong

Interfacial segregation and cosegregation behaviour in a nickel-base alloy 718

Abstract The Auger analyses provided clear evidence of sulfur and phosphorus segregation to grain boundaries and carbide/matrix interfaces. The degree of segregation was different for the two elements. Sulfur was preferentially segregated at the carbide/matrix interface while phosphorus was mainly distributed on grain boundaries. It was also found that metal elements, such as Mo and Nb also segregated to grain boundaries, these grain boundary segregation results show the existence of the attractive interactions of phosphorus with metal elements of Mo and Nb at grain boundaries, especially the co-segregation of Mo–P. It did not find any interaction of sulphur with metal elements at grain boundaries.

Investigation of the abnormal effects of phosphorus on mechanical properties of INCONEL718 superalloy

Abstract The effects of phosphorus on mechanical properties of the world’s most widely used superalloy INCONEL718 was examined. The results indicate that P has little effect on the tensile properties of INCONEL718 at room temperature, 500 or 650°C, but it increases stress rupture life and ductility. Phosphorus also improves the creep property and crack propagation resistance of INCONEL718. Further microstructure analysis by means of optical, SEM and TEM does not reveal the obvious effect of P on grain size and precipitation of INCONEL718. Some theoretical discussions were held aiming at further understanding the role of P in INCONEL718. It was suggested that the interaction of P–GB–M (metal element) complex might be responsible for this.

Molecular dynamics simulation on phosphorus behavior at Ni grain boundary

Phosphorus is commonly regarded as a common impurity and detrimental element in most Fe-base and Ni-base alloys. To study the problem in detail, it is feasible to use computer simulation techniques, which can investigate events on a much finer space and time scale than can be reached with presently available experimental techniques. The study of fracture and embrittlement at the atomic scale often used molecular dynamics (MD) and quantum-chemical methods. The most important and difficult step of molecular dynamics simulation is the determination of interatomic potential. As the first step of studying on the behavior of phosphorus in Ni-Cr-Fe system, the goal of this paper is to study the behavior of phosphorus in Ni grain boundary.

Relationship Between Grain Boundary Segregation of Antimony and Temper Embrittlement in Titanium-Doped Nickel-Chromium Steel

The antimony segregation at grain boundary was observed and the temper embrittlement in titanium-doped nickel-chromium steel was analyzed. It is concluded that the antimony segregation at grain boundary is nonequilibium and the kinetics of temper embrittlement agrees well with those of nonequilibrium antimony segregation at grain boundary. Besides. the mechanism of nonequilibrium antimony segregation at grain boundary proved to be the most satisfactory one among the existing mechanisms to interpret the antimony-induced embrittlement kinetics in the nickel-chromium steel. Based on these, the activation energy and frequency factor of diffusion of antimony-vacancy complexes were obtained according to the concept of critical time in nonequilibrium grain boundary segregation theory.

The appearance of magnesium and its effect on the mechanical properties of Inconel 718 with low sulfur content

The appearance of magnesium and its effect on the mechanical properties of Inconel 718 with low sulfur content were investigated. The results show that magnesium has almost no effect on the tensile properties of Inconel 718 at room temperature, 500°C and 650°C. When the content of sulfur is lower than 10 ppm, magnesium can decrease the stress rupture life of Inconel 718 at 650°C, 686 MPa. The fractography and microstructure analysis by means of scanning electron microscopy (SEM) reveal that magnesium has little effect on the rupture method and microstructure of Inconel 718, i.e. grain size and δ-phase, etc. The Auger research shows that there is no segregation of magnesium at grain boundaries. The main appearance method of magnesium is Mg(O,S).

Nucleation mechanisms of dynamic recrystallization for G3 alloy during hot compression

Dynamic recrystallization (DRX) mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200xa0°C and strain rates from 0.1 to 5.0xa0s−1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dislocations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate.

Influence of Chloride Ion and Temperature on the Corrosion Behavior of Ni‐Fe‐Cr Alloy 028

Recently, the working condition of tubing systems used in oil and natural gas industries are severer than before with the increasing exploitation of acidic gas fields. The corrosion problems induced from the corrosive environment with chloride ion medium and high temperature have been much more concerned. The presence of chloride ion can accelerate the dissolution of metals. The corrosion performance is also sensitive to the operating temperature. Classic localized corrosions such as the pitting or the crevice type due to environmental temperature and chloride ion.

The Effect of Primary γ' Distribution on Grain Growth Behavior of GH720Li Alloy

In this paper, a series of hot compression tests were carried out under different hot deformation parameters, covering the temperature range of 1000oC to 1170oC, strain rate range of 0.01s -1 to 1s -1 and compression reduction of 30%, 50%, and 70%. After that, all specimens were heat treated under the standard heat treatment schedule of GH720Li to investigate its hot deformation characteristics, especially the grain growth behaviors. The further OM and SEM observations were adopted to investigate the interaction mechanism of the primary γ′ distribution and grain growth for GH720Li alloy. The results show that for GH720Li alloy, when hot deformed below γ′ solvus, the banded or bi-model structure always occurs; while hot deformed near or over γ′ solvus, the uniform grain size distribution can be obtained. Further microstructure analysis shows that the bi-model or banded grain size distribution in GH720Li alloy is mainly due to the nonuniform re-dissolving of primary γ′ during heating process; while the uniformity of primary γ′ phase is determined by the uniformity of elements in this alloy. In other word, the homogenizing process for ingot is the key reason for later grain size control. Introduction GH720Li (UDIMET 720Li) is a high strength nickel-based superalloy being considered for applications for modern gas turbines and aero-engines. The chemical composition of this alloy is related to that of GH720 (UDIMET 720) from which it is derived, but differs from it with respect to the chromium, carbon and boron levels. Till now, a lot of studies [1-6] have been done for GH720Li alloy including the solutioning and precipitating of γ prime phase, the ingot to billet conversion process control, the heat treatment schedule optimizing, the mechanical behavior under service conditions, etc. However, the microstructure of GH720Li consists of primary, secondary and tertiary γ′ due to its special heat treatment schedule. Primary γ′ lies at the γ-grain boundaries and