Nanostructure and phase instability of the topmost surface layer of Inconel-718 superalloy processed in low-temperature (LT) gas carburization atmosphere

2021 ◽  
Author(s):  
CORNELIU SARBU ◽  
Keyword(s):  
Surface Layer ◽  
Low Temperature ◽  
Inconel 718 ◽  
Phase Instability ◽  
Inconel 718 Superalloy

scholarly journals Phase instability of the topmost surface layer of Inconel-718 superalloy in low-temperature gas carburization atmosphere, revealed by means of (HR)(S)TEM

2019 ◽  
Vol 1 (1) ◽  
pp. 11-12
Keyword(s):  
Surface Layer ◽  
Low Temperature ◽  
Inconel 718 ◽  
Engineering Properties ◽  
Surface Microstructure ◽  
Phase Instability ◽  
General Validity ◽  
New Findings ◽  
Gas Atmosphere ◽  
Inconel 718 Superalloy

The surface microstructure modifications induced by the industrial treatments with the effect of enhancement of the surface engineering parameters in metallic alloys (hardness, wear, corrosion resistance) are utterly important. The recently invented, industrially successful surface hardening by carburization of 316L stainless steel (SS) in gas atmosphere at low-temperature (LT) [1] was extended with similar results to the Ni-Fe base Inconel-718 superalloy (IN-718) [3] and to several other alloys. The accepted model of surface microstructure modification due to processing is not based on full data about the modified topmost layer microstructure. It is missing the visualization of the new microstructure by means of (HR)(S)TEM and analysis. The effect of LT gas carburization is currently explained by a model of surface grains lattice dilatation due to the so called colossal carbon supersaturation (LTCSS) [2] that is not conform to the classical phase diagrams and is claimed to be valid in all alloys including IN-718 [4]. Our work reports new findings that reveal the up to now unknown nanostructure of the topmost carburized (at 570ºC) layer ~5 µm thick of IN-718 and cast doubts on the general validity of the LTCSS. The (HR)(S)TEM and nanoscale analysis were used to reveal the nanostructure of samples prepared in a special way by ion beam milling. We got no evidence of a classical crystalline microstructure of the carburized IN-718 upper-most layer that can match the requests of the LTCSS model. Instead, we put into evidence the nano-structure of the topmost ~ 5 µm thick layer of the carburized surface showing that it consists both (i) in nanocrystalline austenite and carbides and (ii) in an amorphous phase that contains the main alloy elements, with or without carbon (Fig-1). Segregated Ni nanoclusters (Fig-2) are occurring at large areas, apparently not including other main alloy elements. A fragmentation mechanism of the topmost surface layer (consisting initially of µm-sized grains) can be figured out by starting from the observed segregation in the initial alloy grains of the main alloy elements, agglomerated both inside grains close to grain boundaries (GBs) and at the GBs (Fig-3) and by the segregation of carbon both inside grains along GBs (Fig-4) and outside grains at GBs. Those chemical segregates can be considered as precursors in the process of fragmentation and are proving the phase instability of the surface alloy grains in the LT carburizing gas atmosphere, thereby revealing the chemical reactivity of the IN-718 surface grains with the LT carburization gas mixture. The surface reactivity can be valorized industrially through developing new research for finding novel compositions of LT gaseous mixtures able to modify the engineering properties of the alloys surfaces.

scholarly journals Phase Transformations during Low Temperature Nitrided Inconel 718 Superalloy

2016 ◽  
Vol 56 (6) ◽  
pp. 1076-1082 ◽  
Author(s):  
Yan Jing ◽  
Wang Jun ◽  
Gu Tan ◽  
Xiong Ji ◽  
Fan Hongyuan
Keyword(s):  
Low Temperature ◽  
Phase Transformations ◽  
Inconel 718 ◽  
Inconel 718 Superalloy

scholarly journals Study of ultrasonic vibration–assisted thread turning of Inconel 718 superalloy

2019 ◽  
Vol 11 (10) ◽  
pp. 168781401988377
Author(s):  
Yu He ◽  
Zhongming Zhou ◽  
Ping Zou ◽  
Xiaogang Gao ◽  
Kornel F Ehmann
Keyword(s):  
Surface Quality ◽  
Ultrasonic Vibration ◽  
Inconel 718 ◽  
Gas Turbines ◽  
Tool Path ◽  
Machining Parameters ◽  
Thread Cutting ◽  
Workpiece Surface ◽  
Inconel 718 Superalloy ◽  
The Relationship

With excellent properties, high-temperature superalloys have become the main application materials for aircraft engines, gas turbines, and many other devices. However, superalloys are typically difficult to machine, especially for the thread cutting. In this article, an ultrasonic vibration–assisted turning system is proposed for thread cutting operations in superalloys. A theoretical analysis of ultrasonic vibration–assisted thread cutting is carried out. An ultrasonic vibration–assisted system was integrated into a standard lathe to demonstrate thread turning in Inconel 718 superalloy. The influence of ultrasonic vibration–assisted machining on workpiece surface quality, chip shape, and tool wear was analyzed. The relationship between machining parameters and ultrasonic vibration–assisted processing performance was also explored. By analyzing the motion relationship between tool path and workpiece surface, the reasons for improved workpiece surface quality by ultrasonic vibration–assisted machining were explained.

Enhancing the wear and oxidation behaviors of the Inconel 718 by low temperature aluminizing

2021 ◽  
Vol 412 ◽  
pp. 127069
Author(s):  
Kadir Mert Döleker ◽  
Azmi Erdogan ◽  
Tuba Yener ◽  
Abdullah Cahit Karaoglanlı ◽  
Orhan Uzun ◽  
...  
Keyword(s):  
Low Temperature ◽  
Inconel 718 ◽  
Oxidation Behaviors

Nonlinear surface wave measurements on aged and laser shock surface-treated Inconel 718 superalloy

2021 ◽  
Vol 121 ◽  
pp. 102457
Author(s):  
Vania M. Rodríguez-Herrejón ◽  
Alberto Ruiz ◽  
Carlos Rubio-González ◽  
Víctor H. López-Morelos ◽  
Jin-Yeon Kim ◽  
...  
Keyword(s):  
Surface Wave ◽  
Inconel 718 ◽  
Laser Shock ◽  
Shock Surface ◽  
Wave Measurements ◽  
Inconel 718 Superalloy ◽  
Nonlinear Surface

scholarly journals Microstructure and Corrosion Properties of La2Zr2O7/NiCoAlY Thermal Barrier Coatings Deposited on Inconel 718 Superalloy by Laser Cladding

Coatings ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 101
Author(s):  
Kaijin Huang ◽  
Wei Li ◽  
Kai Pan ◽  
Xin Lin ◽  
Aihua Wang
Keyword(s):  
Corrosion Resistance ◽  
Thermal Barrier Coating ◽  
Laser Cladding ◽  
Inconel 718 ◽  
Electrochemical Techniques ◽  
Thermal Barrier ◽  
Nacl Solution ◽  
Corrosion Performance ◽  
Barrier Coating ◽  
Inconel 718 Superalloy

In order to improve the seawater corrosion resistance of Inconel 718 superalloy, a La2Zr2O7/NiCoCrAlY thermal barrier coating corrosion resistant to 3.5 wt.% NaCl aqueous solution was prepared by laser cladding on Inconel 718 superalloy. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and electrochemical techniques were used to study the microstructure and the corrosion performance of the coating in 3.5 wt.% NaCl solution. The results show that the thermal barrier coating is mainly composed of primary La2Zr2O7 phase and γ + laves/δ phase eutectic structure. The corrosion potential and corrosion current of the coating in 3.5 wt.% NaCl solution are higher and lower than that of the Inconel 718 substrate, respectively, indicating that the corrosion performance of the coating is better than that of the Inconel 718 substrate. The presence of La2Zr2O7 phase in the thermal barrier coating is the main reason for its corrosion resistance to 3.5 wt.% NaCl solution.

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