Amporn Wiengmoon

Magnesium Ferrite (MgFe2O4) Nanostructures Fabricated by Electrospinning

Magnesium ferrite (MgFe2O4) nanostructures were successfully fabricated by electrospinning method. X-ray diffraction, FT-IR, scanning electron microscopy, and transmission electron microscopy revealed that calcination of the as-spun MgFe2O4/poly(vinyl pyrrolidone) (PVP) composite nanofibers at 500–800 °C in air for 2 h resulted in well-developed spinel MgFe2O4nanostuctures. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature. Crystallite size of the nanoparticles contained in nanofibers increased from 15 ± 4 to 24 ± 3 nm when calcination temperature was increased from 500 to 800 °C. Room temperature magnetization results showed a ferromagnetic behavior of the calcined MgFe2O4/PVP composite nanofibers, having their specific saturation magnetization (Ms) values of 17.0, 20.7, 25.7, and 31.1 emu/g at 10 Oe for the samples calcined at 500, 600, 700, and 800 °C, respectively. It is found that the increase in the tendency ofMsis consistent with the enhancement of crystallinity, and the values ofMsfor the MgFe2O4samples were observed to increase with increasing crystallite size.

Effects of Destabilisation Heat Treatment on Microstructure, Hardness and Corrosion Behaviour of 18wt.%Cr and 25wt.%Cr Cast Irons

Effects of destabilisation heat treatment on microstructure, hardness and corrosion resistance of 18wt.%Cr and 25wt.%Cr irons have been investigated. The as-cast samples were heat-treated by destabilisation at 1000°C for 4 hour and then air cooling. The microstructure was investigated by light microscopy and scanning electron microscopy. The results show that the as-cast microstructure in 18wt.%Cr iron consists of pearlite, formed by decomposition of primary dendritic austenite, plus eutectic structure. In the 25wt.%Cr iron with lower hardness, the microstructure consists of primary dendritic austenite plus eutectic structure. The austenite had partly transformed to martensite, especially at areas adjacent to eutectic carbides. After destabilisation, the microstructure of both irons consists of eutectic and secondary carbides in a martensite matrix giving increased hardness. It was found that corrosion resistance of the irons was improved after destabilisation. The 25wt.%Cr showed superior corrosion resistance than the 18wt.%Cr iron due to greater residual Cr in the matrix to encourage passivity.

Microstructure, Hardness and Wear Properties of Sintered Fe-Mo-Si-C Steels with Spheroidal Graphite Iron/Compacted Graphite Iron-Like

Sintered Fe-Mo-Si-C steels were prepared from pre-alloyed Fe-0.85Mo powder added with fixed 4wt.% silicon carbide powder and varied graphite powder contents. It was found that the graphite powder addition caused morphological change from black nodular to black vermicular particles and resulted in decrease of black nodular/vermicular particle fraction, increase of pearlite fraction and slight change of ferrite fraction. The black nodular particles were either graphite or Fe-Mo-Si-C/graphite core-shell particles whereas vermicular particles were totally composed of carbon. The microstructural features showed influence on mechanical property of the sintered Fe-Mo-Si-C alloys. Wear properties of the sintered steels were strongly affected by their microstructural components. The sintered Fe-0.85Mo+4wt.%SiC steels showed highest friction coefficient and volume loss. Addition of graphite to the sintered Fe-0.85Mo+4wt.%SiC steels, not only changed morphology and chemistry of black particles but also reduced friction coefficient and volume loss. The reduction of both determined wear properties were attributed to the presence of vermicular graphite particles.

Oxidation Behavior of 30wt.%Cr-3.75wt.%V High Chromium Cast Iron

This work focuses on the oxidation behavior of 2.4wt.%C-30wt.%Cr-3.75wt.%V cast iron in air at 1000 °C for 1-48 h with weight gain measurements taken at different times. The oxidized surfaces and cross sections were characterized by XRD, OM, SEM and EDS. It was found that the as-cast microstructure consisted of a ferritic matrix and M7C3 carbide. The surface oxide scale consisted of multi-oxides and the grain size of the oxides increased with increasing holding times. XRD and SEM-EDS results revealed that the multi-oxide layer can be Cr2O3, (Fe,Cr,V)2O3 and SiO2. After about 48 h, a continuous SiO2 inner-layer was observed and the oxide scale tended to swell, contained pores, and became detached from the surface because of its poor adherence.

Effects of T6 Age Hardening on Microstructure and Mechanical Properties of Al-Si-Cu Cast Aluminium Alloy

Effects of T6 artificial aging heat treatment on microstructure, microhardness and ultimate tensile strength of Al-4.93 wt% Si-3.47 wt% Cu alloy were investigated. The T6 age hardening treatment consists of solution treatment at 500±5°C for 8 hours followed by quenching into hot water at 80°C and artificial aging at 150, 170, 200 and 230°C for 1-48 hours followed by quenching into hot water. Microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and SEM revealed that the microstructure in the as-cast condition consists of primary dendritic α-Al, acicular-plate and globular forms of eutectic Si and intermetallic phases including globular Al2Cu and a flake-shape Al5FeSi. By T6 aging hardening, some intermetallics were dissolved and spheroidized. The volume fraction of eutectic phases in the as-cast, solution-treated, and solution-treated plus aging at 170°C for 24 hours is 17%, 12% and 10%, respectively. TEM results showed that precipitates in under-aging condition at 170° C for 6 hours are in the form of disc shape with the diameter in the range of 7-20 nm. At peak aging at 170°C for 24 hours, thin-plate precipitates with about 3-10 nm in thickness and 20-100 nm in length were found, lengthening to about 30-200 nm at longer aging time. The microhardness and ultimate tensile strength were increased from 71 HV0.05 and 227 MPa in the as-cast condition up to 140 HV0.05 and 400 MPa after solution treatment plus aging at 170°C for 24 hours, and decreased at prolong aging time.

Microstructure, hardness, corrosion and dry wear of 17wt%Cr-3wt%C-7wt%Mo cast iron

Abstract The microstructure of a 17wt%Cr-3wt%C white cast iron with relatively high Mo addition (7 wt.-% Mo) has been investigated by X-ray diffraction, light microscopy, scanning electron microscopy and transmission electron microscopy together with energy dispersive X-ray spectroscopy. Mo dissolves partly in the matrix and partly in the typical Cr-rich M7C3 eutectic carbide and also leads to microstructural modification by forming a fine Mo-rich lamellar structure at interdendritic regions with a volume fraction of 11 %. The Mo-rich phase in this lamellar structure may also be a carbide of the M6C type and is believed to form at the later stage of solidification by a subsequent eutectic reaction. Destabilization heat treatment at 1000°C for 4 hours followed by air hardening results in precipitation of M7C3 and M23C6 secondary carbides, transformation of dendritic and eutectic austenite to martensite with some austenite being retained, and modification of local chemical composition, importantly an increase in the Mo and C content in the matrix. This causes a significant improvement in hardness, corrosion and dry wear properties. Tempering at 450°C for 4 hours leads to more temper-carbide precipitation and formation of ferrite, possibly by decomposition of retained austenite. However, an improvement in properties was not observed.