Papers by Keyword: Microstructural Characteristics

Abstract: The ability to plasticize Hydroxypropyl Methyl Cellulose/Beeswax (HPMC/BW) composites depends on plasticizers and their concentration. This paper conducted studying on the impacts of plasticizers to HPMC/BW properties. The plasticizers were used in this research included Glycerol (G), Propylene Glycol (PG), and Polyethylene Glycol 400 (PEG 400) which had the concentration changed in range of 1-3%. HPMC/BW composite films incorporated with 2% of plasticizers formed films with the best characteristics among three tested concentration. Tensile strength and elastic modulus of films were decreased when adding plasticizers, whereas elongation at break were increased. Therefore, it caused an increase in oxygen permeability of HPMC/BW films in comparison with the control film. However, Glycerol showed the lowest Oxygen Permeability (OP) values compared to other composite films. The films were evaluated its microstructural quality using method of scanning electron microscopy (SEM) which had the effects of plasticizers and their efficiencies of plasticizing polymer networks.

Abstract: Ultra-fine filler or mineral powder is the main mineral component responsible for structure formation in the bitumen-mineral system, therefore mineral and chemical composition, chemical reactivity, surface area, fineness, particle shape, porosity and density are the crucial parameters for structure formation of the composite. This work studied the effect of fineness and chemical and mineral composition of fillers on the structure of asphalt binder. It was demonstrated that an increase in surface area boosts porosity, and void content of the filler, but reduces the porous size. For carbonate fillers such as limestone and chalk with high fineness it was investigated that compaction applied to asphalt binder specimens showed very low water saturation. This can be explained by the film effect of water impermeable bitumen in the matrix and by small porous size with mostly close pores. An increase in surface area of silicate fillers improves the compaction of structure but cannot reach the same level of compaction degree demonstrated by the specimens with carbonate fillers. SEM analysis of microstructural characteristics for the asphalt binder showed that the incorporation of fine-fractioned chalk filler resulted in the formation of asphalt binder with high density and micro-and nanoporous matrix.

Abstract: A metallurgical examination of surface defects of pipes made of steel of strength category X70 was carried out. The characteristic microstructural features of defects were determined. The causes of the formation of surface defects of the pipe were established. Comparison of the actual and calculated compositions of the detected satellite inclusions was conducted.

Abstract: With the development of aircraft engine, higher requirement was put forward on turbine disk materials. In the present work, new thoughts on improving high temperature properties of superalloys have been proposed and a newly developed candidate turbine disk material for 850°C-900°C application with a composition of Ni-Co-Cr-W superalloy has been investigated. The results show that W is beneficial for mechanical properties. Microstructural characteristics and hot deformation of this new alloy were studied by optical microscope (OM), field emission scanning electric microscope (FESEM) and energy dispersive X-ray spectrometer (EDX) and differential scanning calorimetry (DSC). The results show that the main precipitates in the as-cast condition are γ’ phase, primary MC carbides and eutectic phase. The incipient melting temperature, γ’ solvus and MC solvus are 1312°C, 1220°C and 1356°C respectively. Cracks are observed in the tested samples after hot deformed at 1160°C to 1220°C with 30% strain. They initiated at the surface of the samples and propagated along the grain boundaries and also initiated at the interface of carbides and matrix.

Abstract: This paper presents a summary of a preliminary research aimed at producing ultrafine-grained (UFG) and heterogeneous microstructure in microalloyed steel and testing these materials under dynamic loading conditions (strain rates 800 s^-1 and 1800s^-1). The UFG and bimodal-structures, due to grain size, structural composition or morphology of structural components, were produced by an advanced thermomechanical processing, namely rolling in: hot, two-phase and cold-hot combined conditions. The advantage of bimodal microstructures is their maximization of mechanical behavior under extreme loading conditions due to promoted accumulation and interactions of geometrically necessary dislocations. The dynamic work-hardening behavior has been studied as a function of solute atoms and fine-scale, second-phase particles in the UFG and bimodal-structures. The substantial complexity of the phenomena, which occur through the evolution of microstructure and texture in response to dynamic loading, presents formidable challenges to theoretical model development of plastic deformation of UFG and bimodal-structures. Such an extraordinary work hardening provides an attractive strategy to develop optimal combination of mechanical properties i.e. strength/ductility ratio. A multi-scale analysis capable of including material behavior in different scales should be applied to discuss mechanical response of mentioned above microstructures and to help to analyze their influence on mechanical behavior under dynamic loading. The investigation was performed for a material of common application: high strength microalloyed steel X70. The experimental results show that strain rate sensitivity of the heterogeneous microstructures obtained by various thermomechanical rolling routes are significant, but not by a similar magnitude with the microstructure compositions and increasing strain rate.

Abstract: The effect of aging temperature on microstructure and mechanical properties of Fe-16Mn-1.3C-0.3V steel was investigated. After a series of heat treatment experimental processes, including solution treatment at 1080 oC for 1 h then aging treatment at 350 oC, 400 oC, 450 oC, 500 oC and 550 oC for 1 h respectively, the microstructure of V alloyed high manganese austenitic steels were studied using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental steel had the best comprehensive performance after aging treated at 450 oC for 1 h. It presented hardness of 249HB, impact toughness of 215 J·cm^-2, tensile strength of 707 MPa, yield strength of 421 MPa and elongation of 30.8%. With the aging temperature increased, the amount of precipitates increased and precipitates gradually transformed from globularity to needle. EDS analysis showed the most striking difference between two types carbides. That the globular carbide had a lot of vanadium element, which could cause the hardness of globular carbide higher than needle-like carbide. TEM showed the size of these globular carbide particles were 10~100 nm. SADP demonstrated that the fine globular precipitate was vanadium carbide (VC).