Yuanjing Chen

Preliminary investigation of directionally solidified NiAl–28Cr–5.5Mo–0.5Hf composite

An in-situ NiAl/Cr(Mo)-Hf eutectic composite has been successfully fabricated using the Bridgman technique. The microstructure was analyzed using scanning electron microscopy (SEM) with energy disperse spectroscopy and transmission electron microscopy (TEM). The mechanical behavior of the composite, including compressive and tensile properties at room and elevated temperature, was studied. It was found that the strengths of the composite are higher than that of NiAl alloys. Subsequently, the mechanism of improving the strength was analyzed

Brittle-to-ductile transition in multiphase NiAl alloy

The microstructure of a directionally solidified (DS) NiAl/Cr(Mo,Hf) alloy was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). This alloy was composed of NiAl, Cr(Mo) and Ni2AlHf phases. Tensile testing of this multiphase NiAl alloy was performed from room temperature to 1323 K at various strain rates from 1.04×10−4 s−1 to 1.04×10−2 s−1. It was found that the brittle-to-ductile transition temperature (BDTT) of this alloy was higher than values reported for many of NiAl-based alloys and dependent on the strain rate. Regardless of strain rate, at temperatures just above the BDTT, the fracture morphology changed from NiAls cleavage and debonding along the NiAl/Cr(Mo) interface to completely ductile in nature. It was also found that the apparent activation energy responsible for BDT is 463 kJ mol−1, which may be responsible for the higher BDTT.

Fabrication of nanopillar forests with high infrared absorptance based on rough poly-Si and spacer technology

Nanopillar forests with high infrared (IR) absorptance are fabricated based on a highly flexible, controllable and micro-fabrication compatible parallel approach. The key technique of the approach is using rough surfaces of poly-Si films as support structures in spacer technology. In a wavelength region of 1.5–5 μm, IR absorptance of the large-area nanopillar forests reaches a minimum of 95%, which is much higher than that of poly-Si films and Si3N4-based IR absorbers. As the approach is compatible with conventional micro-fabrication process, the nanopillar forests can be photo-patterned and generated on microstructures or devices. It is expected that the nanopillar forests can be employed as absorbers in micro-electro-mechanical system IR sensors to improve performance. (Some figures may appear in colour only in the online journal)

Microstructural studies of in-situ formed MgB2 phases in a Mg alloy matrix composite

Abstract The microstructure of in-situ formed MgB2 phases in a Mg alloy matrix composite was studied by means of transmission electron microscopy and high-resolution electron microscopy. The MgB2 phases have hexagonal plate-like morphology with a remarkable interfacial energy anisotropy. The interfaces between MgB2 and Mg are sharp without any intermediate layer. The interfaces are semi-coherent with a regular arrangement of misfit dislocations. Dislocation loop and 60° dislocation are observed in the MgB2 phases. A phase transformation from MgB2 to Mg is observed and a structural model is proposed to describe the phase transformation process.

Theoretical and experimental studies of the dislocation structure at the NiAl-Cr(Mo) interfaces

The dislocation structure at the NiAl/Cr(Mo) interfaces has been studied by high resolution electron microscopy (HREM). The (110) and (111) cube-on-cube interfaces were examined. Both of the interfaces have been found to be partially coherent. Theoretical calculation of the expected dislocation structure at the interfaces was made based on the CSL/DSC lattice model. The experimental observations and theoretical prediction were shown to be in generally good agreement, with some differences with respect to the detailed structure.

Fabrication of polyimide sacrificial layers with inclined sidewalls based on reactive ion etching

Polyimide is used as a sacrificial material because of its low stress, its removable ability and its compatibility with standard micromachining processes. In this work, polyimide structures with inclined sidewalls are fabricated with a reactive ion etching process, where SiO2 is used as the hard-mask material. The structures can be further used as sacrificial layers in micro-electro-mechanical systems infrared (IR) sensors to support IR absorbers, to realize the thermal connections between the absorbers and the thermopiles, and to scale down the size of the sensors. As a result, IR sensors with low-residual-stress absorption, high structural stability, low heat loss and small dimensions can be achieved.

Equilibrium position of misfit dislocations at the NiAl-Cr(Mo) interface

chinese acad sci, inst met res, atom imaging solids lab, shenyang 110015, peoples r china.;chen, yx (reprint author), chinese acad sci, inst met res, atom imaging solids lab, shenyang 110015, peoples r china

Orientation relationships and interfaces between NiAl and G-phase Ni16Hf6Si7

Besides cube-on-cube orientation relationship, a new kind of orientation relationship between NiAl and G-phase Ni16Hf6Si7 was observed, i.e. [111](NiAl) parallel to [552](G) and (1(1) over bar 1)(NiAl) parallel to (2(2) over bar 0)(G), which showed a good agreement with the prediction from a recently proposed geometric method. The interfaces between NiAl and G-phase in both cases were also studied

Out-of-plane easy-axis in thin films of diluted magnetic semiconductor Ba1−xKx(Zn1−yMny)2As2

Single-phased, single-oriented thin films of Mn-doped ZnAs-based diluted magnetic semiconductor (DMS) Ba1−xKx(Zn1−yMny)2As2 (x = 0.03, 0.08; y = 0.15) have been deposited on Si, SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, and MgAl2O4 substrates, respectively. Utilizing a combined synthesis and characterization system excluding the air and further optimizing the deposition parameters, high-quality thin films could be obtained and be measured showing that they can keep inactive-in-air up to more than 90 hours characterized by electrical transport measurements. In comparison with films of x = 0.03 which possess relatively higher resistivity, weaker magnetic performances, and larger energy gap, thin films of x = 0.08 show better electrical and magnetic performances. Strong magnetic anisotropy was found in films of x = 0.08 grown on (La,Sr)(Al,Ta)O3 substrate with their magnetic polarization aligned almost solely on the film growth direction.