Microstructural Evolution of a High W Content Ni-Based Superalloy at γ′ Sub-Solvus Temperatures

Sigeng Zhou,Naicheng Sheng,Shijie Sun,Shigang Fan,Jinjiang Yu,Guichen Hou,Jinguo Li,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1

The evolution of γ′ phase and γ/γ′ eutectic during short-time heat treatment of the Ni-based superalloy with high W content,K416B are investigated. In this study, high temperature Differential Scanning Calorimetry (DSC) is employed to designthe heat treatment experiments and the precipitate temperature of secondary γ′ is found in the cooling curve. The standardcoarsening model is applied to figure out the coarsening rate constant of γ′ precipitate. On this basis, a novel method isproposed to predict the globularization time of γ phase in γ/γ′ eutectic during the heat treatment process. As holding temperatureincreases, more γ lamellae convert to platelets before reaching thermodynamic equilibrium. Electron microscopyobservations exhibit the boundary splitting and necking formation on the γ plate surface. Moreover, the dissolution kineticsof γ phase is quantitatively assessed by JMAK model. The volume fraction descends rapidly in the initial stage, and thenreach to a threshold. Above proposed approaches are validated via various heat treatment experiments.

Thermal Stability of GH4065A Superalloy Based on Microstructural and Performance Evolution Following Long-Term Aging

Yingbo Bai,Rui Zhang,Chuanyong Cui,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.2

This study investigates the thermal stability of a GH4065A superalloy at intermediate temperatures by conducting long-termaging treatments for 100–6000 h at 700–800 °C. Secondary γ′-phase coarsening and intergranular M6Ccarbide precipitationoccurred during aging. The activation energy for secondary γ′-phase coarsening was 259.89 ± 25.45 kJ mol−1, suggestingthat this process was predominantly controlled by elemental diffusion. The tensile strength at a testing temperature of 700 °Cwas stably above 1200 MPa for the alloys aged at 700 °C but continuously declined as the aging temperature increased, witha direct correlation identified between the secondary γ′-phase coarsening and strength reduction upon aging. Increasing theaging temperature transitioned the deformation mechanism from Orowan bowing around the γ′ phase to dislocation slipthrough the broadened matrix channels, leading to decreased strength. Long-term aging effectively eliminated intermediatetemperatureintergranular brittle fracture. The elongation to failure at a testing temperature of 700 °C increased by approximately35% after aging at 800 °C for 6000 h, attributed to grain-boundary diffusion of W and Mo and intragranular softening,which improved the deformation coordination ability at the grain boundaries. Finally, the precipitation of intergranular M6Cparticles after prolonged aging promoted plastic deformation via micropore aggregation.

Creep Properties of a Nickel-Based Single Crystal Superalloy with Low Density

Yuling Du,Zihao Tan,Yanhong Yang,Xinguang Wang,Yizhou Zhou,Jingguo Li,Xiaofeng Sun 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

A novel nickel-based single crystal superalloy with low density had been designed and the creep deformation mechanismsof the experiment alloy under two conditions (1050 °C/200 MPa and 1100 °C/137 MPa) had been systematically discussed. The topological inversion had been observed after fracture under the above two conditions. The effects of temperature andstress on creep life of the experiment alloy had been found no significant difference under the two conditions. It was indicatedthat the small decrease in temperature exerted limited influence on the creep behaviors of single crystal superalloys in therange of high temperature.

On Synergistic Effects of Hierarchical γ′ Precipitates and Discontinuous Plastic Flow in a Ni-based Single Crystal Superalloy with an [001] Orientation

Yunling Du,Yanhong Yang,Shuai Guan,Xinguang Wang,Chuanyong Cui,Jinguo Li,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.1

A discontinuous plastic flow is detected in a single-crystal superalloy with an [001] orientation during tensile tests over a wide temperature range. Results reveals that the synergistic impact of normal γ′ precipitates and nanoscale γ′ precipitates in γ matrix on the dislocations motion is the root of the serrated flow.

Effect of Sulfur on Microstructures and Solidification Characteristics of a Nickel-Base Single Crystal Superalloy

Shaofeng Chen,Naicheng Sheng,Shigang Fan,Shijie Sun,Guichen Hou,Jinguo Li,Lirong Liu,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12

The effects of sulfur on the microstructures and solidification characteristics of a second-generation single crystal superalloywere clarified through optical microscope (OM), scanning electron microscope (SEM), differential scanning calorimetry(DSC) and electron probe microanalysis (EPMA). When sulfur was added to the alloy, the area fraction of theeutectic and microporosity decreased with the area fraction of MC carbides increasing. The γ / γ’ eutectic morphologychanged from mosaic + fan + coarse γ’ to mosaic + fan as the sulfur content increased, and very few γ / γ’ eutectic wasfound in the alloy with the highest sulfur content. Moreover, sulfur tended to segregate at the interdendritic regions andform Hf / Cr- rich sulfides, which were adjacent to the carbides or eutectic. This work not only uncovers some sulfideswrapped by eutectic or carbides, but also presents the solidification sequence of the interdendritic regions in high sulfurcontent alloy was discussed.

Mechanisms of thermally induced deflection of a long-span cable-stayed bridge

Yi Zhou,Limin Sun,Zhijian Peng 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.3

Variation of temperature is a primary environmental factor that affects the behavior of structures. Therefore, understanding the mechanisms of normal temperature-induced variations of structural behavior wouldhelp in distinguishing them from anomalies. In this study, we used the structural health monitoring data of theShanghai Yangtze River Bridge, a steel girder cable-stayed bridge, to investigate the mechanisms of thermallyinduced vertical deflection ( DT ) at mid-span of such bridges. The DT results from a multisource combination ofthermal expansion effects of the cable temperature (TCab ), girder temperature (TGir ), girder differential temperature(TDif ), and tower temperature (TTow ). It could be approximated by multiple linear superpositions under operationalconditions. The sensitivities of DT of the Shanghai Yangtze River Bridge to the above temperatures were in thefollowing order: TCab > TGir > TTow > TDif . However, the direction of the effect of TCab was observed to beopposite to that of the other three temperatures, and the magnitudes of the effects of TCab and TGir were found tobe almost one order greater than those of TDif and TTow . The mechanisms of the thermally induced verticaldeflection variation at mid-span of a cable-stayed bridge as well as the analytical methodology adoptedin this study could be applicable for other long-span cable-stayed bridges.

A Large-Scale, Stratified Genetic Analysis of the Major Histocompatibility Complex Region in Early- and Late- Onset Psoriasis in China

( Yi Zhou ),( Minglong Cai ),( Yujun Sheng ),( Xuejun Zhang ) 대한피부과학회 2021 Annals of Dermatology Vol.33 No.1

Background: Psoriasis vulgaris is a chronic inflammatory skin disease which occur at any age. It can be clinically classified into two age-onset subtypes: early-onset psoriasis (EOP; <40 years) and late-onset psoriasis (LOP; ≥40 years). More evidence showed EOP and LOP have different genetic architecture, notably the risk allele human leukocyte antigen (HLA)-C*06:02 located within the major histocompatibility complex (MHC) region, which was reported to be the outstanding variant associated with EOP. However, genetic structure of EOP and LOP have not been fully elucidated. Objective: To investigated HLA genetic heterogeneity between EOP and LOP in China. Methods: We first calculated the MHC-based heritability of EOP and LOP respectively. Then, we conducted a large-scale, stratified analysis including 7,097 EOP, 1,337 LOP patients, and 9,906 healthy controls by using MHC target sequencing data from a previous study. Results: We observed that HLA alleles collectively explained a larger heritability of EOP (27.4%) than LOP (11.3%). Further association analysis identified three independent loci (HLA-C*01:02, p=6.70×10^-8; HLA-A amino acid position 9, p=3.27×10^-17; and HLA-A amino acid position 161, p=5.75×10^-10) that confer specific susceptibility to EOP. Our data also confirmed HLA-C*06:02 as an independent psoriasis-associated variant, contributing a higher degree of risk to EOP than LOP. Moreover, case-case analysis confirmed that HLA-C*06:02-positive psoriasis patients have earlier onset. Conclusion: Our analysis indicating that different genetic background underlie the EOP and LOP. We believe these findings will serve to predict psoriasis risk in the future and facilitate clinical decision. (Ann Dermatol 33(1) 61∼67, 2021)

Roles of the complement system in alcohol-induced liver disease

Yi Zhou,Guandou Yuan,Fudi Zhong,Songqing He 대한간학회 2020 Clinical and Molecular Hepatology(대한간학회지) Vol.26 No.4

Alcohol-induced liver disease (ALD) is a complex disorder, with a disease spectrum ranging from steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Although the pathogenesis of ALD is incompletely understood and currently no effective drugs are available for ALD, several lines of evidence suggest that complement activation and oxidative stress play crucial roles in the pathogenesis of ALD. Complement activation can regulate the production of ROS and influence oxidative stress in ALD. Precise regulation of the complement system in ALD may be a rational and novel avenue to postpone and even reverse the progression of disease and simultaneously promote the repair of liver injury. In this mini-review, we briefly summarize the recent research progress, especially focusing on the role of complement and oxidative stress-induced transfer RNA-derived fragments, which might help us to better understand the pathogenesis of ALD and provide aid in the development of novel therapeutic strategies for ALD.