Qi-Nan Han

• Doctor of Philosophy
• Visiting Scholar at National University of Singapore

High-entropy alloys (HEAs) show the potential for high-temperature structural applications, with their superior fatigue properties of particular significance. However, fatigue cracking can be initiated in these materials with phase boundaries (PBs) as a specific source of weakness. In this work, a model eutectic HEA is studied using both in situ an...

The anisotropy of deformation of a single crystal superalloy is studied using a newly designed furnace arrangement which allows for videography from multiple apertures and subsequent digital image correlation (DIC). Thus, for initially cylindrical specimens, the full field of surface strain is measured at a 25 μm spatial resolution. Our approach is...

This paper presents a novel crack size estimation method based on dilated convolution and time series fine tuning using in‐situ Lamb wave. The contributions of this proposed method are twofold: (1) a dilated convolution‐based neural network which is an effective representation learning methods with larger receptive fields for periodic signals and (...

Metallic materials are crucial in engineering applications and often subjected to complex loads and extreme environments, with fatigue being one of the key problems [...]

Turbine blades made of Ni‐based single crystal superalloys (NBSXs) have long‐strip shaped cross sections and rectangular‐sectional structures, where the secondary orientation produces potential effects even the primary orientation is fixed at [001]. Low cycle fatigue behaviors between [010] and [110] transversely oriented rectangular‐sectional NBSX...

High entropy alloys (HEAs) have attracted increasing research because of their excellent material properties and near-infinite design space. Developing effective phase composition prediction method is important for novel HEA design. Machine learning (ML) as an efficient data-driven approach provides a possible method for the phase prediction of HEA...

The fatigue limit of nickel-base single crystal (NBSX) is experimentally studied at an elevated temperature of 980°C. The crack initiation position is revealed as the casting pores in the single crystal under scanning electron microscope (SEM), and distinct “fish-eye” region is observed on the long cycle fatigue fracture surface. The failure mechan...

An experimental method that can quantify relative slip was developed using digital image correlation (DIC) in order to evaluate the sliding portion. The bridge-type test setup was designed to establish the fretting contact condition. The relative displacements between the contact surfaces were determined by DIC methods. Based on the evolution and d...

Fretting fatigue is an important cause of the failure of the turbine blade-disc dovetail joint in aero-engines. In this work in-situ scanning electron microscope (SEM) fretting fatigue experiments using dovetail shape specimens were conducted. The fretting fatigue damage process of Ni-based directionally solidified superalloys including slip trace...

This research focused on evaluating the mechanical properties change of Welding Metals (WMs) at the turbine-end (hot-end, working beyond 500 °C) of a retired CrMoV bainitic gas turbine rotor serving over 14 years, by comparison to those WMs at the compressor-end (cold-end, working below 300 °C). After long-term service, the room-temperature elastic...

The misorientation of nickel-base single crystal (NBSX) superalloy is always ignored in the current research, which in fact has a certain influence on the fatigue life of NBSXs. To investigate this influence, the fatigue tests of NBSX superalloy DD5 with different misorientation angles have been carried out at 980°C, and the failure mechanism has b...

The fatigue behavior of Fe44Mn36Co10Cr10 high entropy alloy (HEA) at room temperature and 300℃ was studied by in-situ SEM observation, electron back-scattered diffraction (EBSD) and crystal plasticity simulation. The microstructure evolution and deformation process was observed by in-situ SEM fatigue experiment. The misorientation and geometrically...

Two metrics Kernel Average Misorientation (KAM) and Image Quality (IQ) widely used in Electron Back-Scatter Diffraction (EBSD) mapping are compared with each other on indicating the dislocations of type 40Cr low alloy steel induced by tensile and cyclic deformations approaching failure limits respectively. The tensile deformation up to 12% just bef...

The fatigue behavior of Fe44Mn36Co10Cr10 high entropy alloy (HEA) at room temperature and 300℃ was studied by in-situ SEM observation, EBSD and crystal plasticity simulation. The microstructure evolution and deformation process was observed by in-situ SEM fatigue experiment. The misorientation and geometrically necessary dislocation (GND) density w...

The crystal orientation effect on the fretting fatigue behavior in Ni-based single crystal superalloys (NBSX) was studied in this paper using crystal plasticity finite element (CPFE) simulation. The crystal plasticity constitutive model considering back stress was applied in the CPFE simulation, and four different crystal orientations were calculat...

In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis. in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack formation and propagation process. The fretting fatigue tests under different load conditions are carried out, then the lifetime and...

The effects of temperature and load on fretting fatigue induced geometrically necessary dislocation (GND) distribution in titanium alloy are studied by electron back-scattered diffraction (EBSD) in this paper. Fretting fatigue experiments under different temperature and load in TC11 titanium alloy are carried out and samples with small cracks are o...

Pure iron wires were obtained by a two-step process involving torsion and cold drawing. A steep change in grain size through the cross-section of wires was produced during the torsion stage. The Vickers hardness increased from 193 HV to 252 HV when measured from the inner to the outer layer. The microstructure of the outer region underwent more sev...

Slip deformation is the predominant fatigue damage form of nickel-based single crystals at intermediate temperature range (near 760℃). Under different crystal orientations, the dominant slip system may be an octahedral or cubic slip system. This paper explores the dominant slip systems under different crystal orientations through crystal plastic fi...

The influence of orientation and temperature on fatigue short crack propagation behavior of Inconel 718 alloy was studied at both 25 oC and 650 oC by in-situ fatigue testing under scanning electron microscope. The fatigue crack growth rates (FCGR) showed evident dependence on orientation at both temperatures, following: XZ < X < Z. The FCGR differe...

The fretting fatigue behavior of Ni-based single crystal (NBSX) superalloy specimens with different crystal orientations ([110] and [010]) was investigated by in-situ scanning electron microscopy at 400 °C. The slip lines on the surface of the specimens were captured during the test, and crack paths were recorded. These results show that the domina...

The indentation behaviours of Ni-based single crystal (NBSX) superalloy in different crystal orientations are studied by indentation tests and Electron Backscattered Diffraction (EBSD) analysis. The effects of crystal orientations on pile-up modes, dominant slip system distribution and geometrically necessary dislocation (GND) density distribution...

The crystal orientation effect on fretting fatigue induced crack initiation and geometrically necessary dislocation (GND) distribution in Ni-based single-crystal (NBSX) is studied by in-situ SEM observation and electron back-scattered diffraction (EBSD) analysis in this paper. Slip lines and crack initiation are observed in the fretting contact are...

The effect of crystal orientation on fretting fatigue induced crack initiation and dislocation distribution is studied by in-situ SEM observation and electron back-scattered diffraction (EBSD) in this paper. Cracks and slip lines are observed in the fretting contact area of Ni-based single-crystal (NBSX) superalloys. The in-situ SEM observation cap...

Material failure of runway centerline lights was observed in Beijing Capital International Airport after a period of service. In the present paper, visual inspection indicated that cracks initiated from the threaded surface of the lamp, and propagated until fracture. The mechanical properties of three typical lamps were evaluated by tensile, fatigu...

To understand the influence of recrystallization on the low-cycle fatigue behavior of directionally solidified nickel-based DZ4 superalloy, crystal plasticity-based finite element (CPFE) analysis was carried out to study the cyclic plastic behaviors. Using the design of experiments (DOE) technique, a series of CPFE simulations were designed and per...

A dovetail fixture for fretting fatigue test was designed. Fretting fatigue experiments were performed for Ni-based single crystal (NBSX) superalloys at 600 and 700 °C in two secondary orientations, [110] and [010]. The influence of secondary orientation and temperature on fretting fatigue behavior was investigated. The crystal plasticity finite el...

Creep damage of austenitic stainless steels was evaluated by Electron Back-Scattered Diffraction (EBSD) analysis of creep deformation induced grain lattice distortion in this research. Based on the existing work of plasticity characterization by EBSD misorientation parameters, we used the grain lattice distortion parameter “Grain Reference Orientat...

The effect of crystal orientation on fretting fatigue crack formation behaviors of Ni-based single crystal (NBSX) superalloys is investigated in this paper. Differences of slip lines and crack formation patterns between two crystal orientations are revealed by in-situ fretting fatigue experiments. The cracks are found to initiate along the directio...