Papers by Keyword: High Temperature Properties

Abstract: This paper conducted extensive review of extant literature on fusion-based technique for surface modification of austenitic stainless steel AISI 304 grade (304SS) for high temperature self-lubricating application using refractory carbides. Careful systematic review of available literature indicates that among the families of refractory carbides, only silicon carbide (SiC) and titanium carbide (TiC) were successfully adsorbed on the surface of 304SS via fusion melting techniques with TiC having more documentation. Yet, this information was limited to ambient temperature properties of the TiC coatings as such high temperature properties as creep-fatigue, thermal stability, hot corrosion and oxidation were not reported. Additionally, information on the incorporation of hexagonal boron nitride (hBN) into TiC coatings to address the high temperature self-lubricating challenges associated with the alloy was not available. Further, literature is scarce on multi-layer longitudinal and transverse coatings to address the challenges inherent with single layer coating. The review established that there is a wide gap in both knowledge and practice in the deposition of self-lubricating high temperature properties in 304SS substrate material using fusion-based technique which offers a window for research exploration.

Abstract: In order to improve the rutting resistance of the asphalt pavement, the base asphalt needs to be modified. Two kinds of nano-organic montmorillonite (nano-OMMT) with different interlayer spacing were used as the modifier. The content of the two OMMTs in asphalt is the same, being 3wt%. The high temperature properties of the modified asphalts were compared. The effect of interlayer spacing of nano-OMMT was discussed. Results have shown that different nano-OMMT interlayer spacing leads to different high temperature properties. The asphalt modified by 3wt% of the OMMT with the interlayer spacing of 2.8nm shows better high temperature resistance that modified by the OMMT with the interlayer spacing of 3.8nm. More nano-OMMTs with other interlayer spacings should be used to explore the effect of interlayer spacings on the properties of asphalt.

Abstract: To evaluate the high temperature properties and rheological behavior of Iranian Rock Asphalt(IRA), convectional test and temperature scanning test over modified asphalt containing A-70 asphalt as base asphalt and IRA as different amount were conducted. The results show 1) an increase in asphalt binder’s capability of deformation resistance under high temperature, decreases both in asphalt binder’s temperature sensitivity and low-temperature performance; 2)an increase in anti-rutting factor, a decrease on loss tangent value, an improvement of dynamic viscosity. Thus the asphalt binder’s high temperature performance is greatly improved and anti-rutting capability strengthened.

Abstract: High temperature tensile test was conducted to study high temperature properties of the magnesium based composites reinforced with SiC particulates and monolithic magnesium as well. It was found that tensile strength of monolithic magnesium and Mg-SiC composites decreased with an increase in testing temperature. While the elongation to failure both samples were increased when increasing temperature. At all testing temperature, the tensile strength of the composite sample was found to be superior compared to monolithic magnesium due to presence of SiC particulates and efficiency of spark plasma sintering process in fabrication of the composites.

Abstract: The FeMnCrNi/Cr₃C₂ inter metallic composite coatings are prepared by high velocity arc spraying (HVAS) technology on 20G steel. The properties, such as the microstructure, micro hardness, binding strength, high temperature oxidation, thermal shock resistance, and erosion in high temperature, are studied based on methods such as analysis of optical microscope, micro hardness, field emission scanning electron microscope (FESEM), and spectrum analysis. The result shows that FeMnCrNiAl/Cr₃ C₂ coatings, compared with 20G steel substrate, present higher micro hardness, binding strength and more excellent high temperature properties, which will be improved if added with rare-earth Alloy.

Abstract: This research effort aims to evaluate the mechanical properties of concrete with two aggregate type, light weight and normal weight at elevated temperatures. To understand the mechanical properties at elevated temperature, normal and light weight concrete of 60 MPa grade was exposed to temperature range 20 to 700°C under 0%, 20%, 40% load conditions and compressive strength, elastic modulus, thermal strain and transient creep at target temperature were inspected. Experimental results show that light weight concrete has higher compressive strength, although the strength of normal weight concrete degenerated more sharply than the light weight concrete at elevated temperature. Moreover, the thermal strain (0% unstressed) and total strain (20%, 40% stressed) of normal weight concrete was higher than that of light weight concrete. Loading conditions significantly influenced the mechanical properties of normal weight concrete compared to that of light weight concrete at high temperature.

Abstract: The possibilities to improve the properties of steels for tubes exposed at high temperatures are explored. The mechanical properties and forming behavior of an experimental casting of type 9Cr-ferritic steels, P92, containing 2%W, are studied. The hardenability was determined by means of continuous cooling diagrams associated with hardness measurements and microstructure observations. Tensile tests from room temperature to 650°C were carried out to determine the variation of the strength and ductility in this temperature range. In addition, Charpy impact tests were conducted to characterize the toughness of the steel and the ductile-brittle transition temperature. Finally, hot torsion tests at various temperatures and strain rates were carried out and the generalized stresses and strains to rupture for each test are determined. With these data forming stability maps were generated to characterize the best forming conditions.

Abstract: Silicon nitride samples were formed by pressureless sintering process, using neodymium oxide as sintering aid. The short term compressive creep behavior was evaluated over a stress range of 50-300 MPa and temperature range 1200-1350 0C. Post sintering heat treatments in nitrogen with a stepwise decremental variation of temperature were performed in some samples and microstructural analysis by X-ray diffractometry and Transmission Electron Microscopy showed that the secondary crystalline phases which form from the remnant glass is dependent upon heat treatment. For the non heat treated samples, glassy regions were revealed, by centered dark field images, using diffuse scattered electrons, to be located at three and four point grain junctions. No direct evidence of microstructural changes involving dislocation generation or motion was detected in the stress and temperature range studied. Stress exponents near unity, related to grain boundary accommodation processes were obtained for low temperatures and for heat treated samples. The behaviors for the heat treated samples were correlated in terms of depletion of metallic rareearth ions and impurities from grain boundaries and triple junctions, with subsequent crystallization of the primary glass. The non heat treated samples showed higher creep rates at higher stresses and temperatures. The deformation processes in these cases were correlated to stress concentrations at grain boundary and triple point junctions, caused by grains rotation and sliding, accommodated by cavitation.

Abstract: With fly ash, metakaolin, slag and alkaline activator as raw materials, the geopolymeric ceramic was synthesized and the properties, such as the weight loss, compressive strength and the structures, at high temperatures of 400~1200°C were measured. The weight loss is in the range of 8~13% from 400°C to 800°C. Comparing with the strength at room temperature, the compressive strength of samples is mostly increased at 400°C and all of them increased at 800°C. 9.65~28.32% strength declines at 1200°C. The variation of the compressive strength with temperature is explained based on the analyses of the phases constitutes and the thermal properties of samples.

Abstract: The role of alloying elements in the improvement of the high temperature strength of Al-12Si(CuNiMg) cast alloys used for automotive piston applications was investigated. The addition of alloying elements such as Mn, Cr, Ti and Ge was studied and the detailed characterization of the composition and morphology of the constituent phases after over aging at 350
 for 1000 hrs was performed. The compositions and volume fractions of the equilibrium phases determined by thermodynamic calculation were compared with the experimental results. The addition of transition elements, including Mn, Cr and Ti, increased the volume fraction of the intermetallic phases, which effectively enhanced the high temperature strength of the alloys. Among these transition elements, Mn turned out to be the most effective alloying element. After adding up to 0.5wt% of Mn, a large number of intermetallic phases, α-Al(Mn,Fe)Si as well as fine Al6(Mn,Fe) particles were precipitated and a significant improvement in the elevated temperature properties was achieved. The addition of Ge promoted the precipitation of the θphase (metastable phase, θ-Al2Cu), due to the formation of GeSi precipitates, thereby improved the mechanical properties of the alloy after T6 heat treatment. However, the presence of these GeSi precipitates did not affect the coarsening of the θ phase to form Qphase( Al5Cu2Mg8Si6) during aging and, thus, the elevated temperature properties were not improved by the addition of Ge.