Papers by Author: Chang Chen

Abstract: The self-propagating combustion reaction 0.741Mg + 0.247Fe2O3 + 0.188Ni + 0.318Cr → 0.741MgO + Fe0.494Ni0.188Cr0.318 was applied to prepare a nano-MgO reinforced Fe-Cr-Ni composite, by reactive hot pressing (RHP) under a condition of 700°C/30MPa/2h. The densification was enabled by the low temperatures produced by the exothermic reaction. According to TG-DTA and X-ray diffractometry (XRD), the highly-exothermic thermite reaction began at about 600°C and the in-situ formation of composites comprised predominantly of (FCC) Cr0.19Fe0.7Ni0.11, (FCC) Fe-Cr, (BCC) MgO and a small quantity of (BCC) MgFe2O4. The Vickers hardness was 3.67GPa, the three-point bending strength was 112.5±10MPa, and the fracture toughness was 3.28 MPa•m1/2. The microstructure of the composite was observed via scanning electron microscopy. This indicated that the distributions of in-situ-formed (BCC) MgO phases (~800 nanometers) were homogeneous into in a matrix of a fine-grained metallic alloy phases that gather together to form agglomerates in the composite.

Abstract: The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. The model is used to investigate the influence of sound incidence angle and the inclination angle between facesheet and core sheet on the sound transmission loss (STL) of the sandwich structure. The results show that the inclination angle has a significant effect on STL, and sandwich panels with corrugated cores are more suitable for the insulation of sound having small incidence angle.

Abstract: Based on low-temperature hot-press sintering and rapid thermit reaction, heat-resistant metal matrix composites with nano-ceramic reinforcement were prepared via reactive hot pressing. According to XRD, the composites comprised predominantly of (fcc) Cr0.19Fe0.7Ni0.11, (fcc) Fe-Cr and alumina at 700°C through the highly-exothermic thermit reaction between the starting powders. Three-point bending strength, fracture toughness, Vickers hardness and relative density increased with the increase of hot-press sintering temperature and holding time. The improving mechanical properties may be explained by increasing of content of (fcc) Cr0.19Fe0.7Ni0.11. SEM analysis showed a microstructure consisting of equiaxial granules at 700°C for 1 h and a uniformly dispersed network of very fine grains at 700°C for 2 h. It is considered that, in the reactive hot-pressing process, Al atoms diffused into the metal matrix (Fe2O3, Cr, Ni) sites and formed Al2O3 and Fe-Cr-Ni matrix. Such a technique offers the possibility of synthesizing heat-resistant metal matrix composites with nano-ceramic reinforcement materials at considerably lower temperature.