Development Of High-strength Materials Research Articles

Properties study of artificial aggregate with high-content recycled concrete powder

With the need for urban development, there is a trend towards constructing large-span and super high-rise buildings. People have placed higher performance requirements on building materials. Therefore, the development of high-strength materials has become one of the current research focuses. Recycled concrete powder (RCP) is the residual powder generated while crushing waste concrete into a recycled aggregate. In order to achieve the low energy consumption resource utilization of RCP solid waste, a large amount of RCP with slag (a by-product of the blast furnace ironmaking process) addition was activated under an alkaline environment to prepare a cementitious material. The effects of RCP/Slag, liquid-solid ratio, Na2O content, and Na2SiO3 modulus on the setting time, compressive strength, and microstructure of alkali-activated high-content RCP-slag cementitious materials (AARCPS) were determined. The results showed that AARCPS had good compressive strength and microstructure; as the RCP content increased, the setting time of the cementitious material gradually prolonged. Based on the research of AARCPS, the mixing ratio was improved, and alkali-activated high-content RCP-slag aggregates (AARCPSA) were prepared. The results showed that with the increase in RCP content, the material fast setting speed and the sticky surface of material balls phenomenon during the aggregate preparation process was improved, and increasing the RCP content from 0% to 50% increased the ball-forming rate by about 14.36%. AARCPSA has good early strength performance, with the compressive strength at 3d reaching 75.18%–90.15% of that at 28d and the compressive strength at 7d reaching 93.85%–99.51% at 28d. The maximum compressive strength at 28d was 8.2 MPa. Increasing the slag and Na2O content in AARCPSA increased aggregate strength and density and decreased water absorption. The increase in RCP content and the decrease in Na2O content increased the peak strain of single particle compression of the aggregate and improved the deformation performance of the aggregate.

Microstructural Characterization of Excel Zirconium Alloy

Excel zirconium alloy (Zr-3.5Sn-0.8Mo-0.8Nb) was manufactured in the 80's within the research programs for the development of high strength materials for CANDU (CANada Deuterium Uranium) pressure tubes. Excel test results showed a better dimensional stability, a higher creep resistance andits hydrides are less susceptible to reorientation during service, compared with the current material in use, Zr-2.5Nb. These factors extend the useful life of the tubes and make Excel a good option for the production of pressure tubes. The aim of the present work is to characterize the microstructure of this alloy analyzing specimens with different contents of hydrogen. The phases were studied using optical microscopy, SEM, TEM and X-ray diffraction. The quantitative chemical analysis was performed using EDS technique.

General relation between tensile strength and fatigue strength of metallic materials

With the development of high-strength materials, the existing fatigue strength formulae cannot satisfactorily describe the relation between fatigue strength σw and tensile strength σb of metallic materials with a wide range of strength. For a simple but more precise prediction, the tensile and fatigue properties of SAE 4340 steel with the tensile strengths ranging from 1290MPa to 2130MPa obtained in virtue of different tempering temperatures were studied in this paper. Based on the experimental results of SAE 4340 steel and numerous other data available (conventional and newly developed materials), through introducing a sensitive factor of defects P, a new universal fatigue strength formula σw=σb(C−Pσb) was established for the first time. Combining the variation tendency of fatigue crack initiation sites and the competition of defects, the fatigue damage mechanisms associated with different tensile strengths and cracking sites are explained well. The decrease in the fatigue strength at high-strength level can be explained by fracture mechanics and attributed to the transition of fatigue cracking sites from surface to the inner inclusions, resulting in the maximum fatigue strength σwmax at an appropriate tensile strength level. Therefore, the universal fatigue strength formula cannot only explain why many metallic materials with excessively high strength do not display high fatigue strength, but also provide a new clue for designing the materials or eliminating the processing defects of the materials.

High-strength Al 94(V, Ti) 4Fe 2 alloys consisting of nanogranular amorphous and fcc-Al phases

Nanogranular amorphous (Am) phase with a grain size of 7 nm was formed in coexistence with fcc-Al phase in melt-spun Al 94V 4-xTi xFe 2 (x=0 to 3 at%) alloys. The formation of the Am phase is due to the solidification process of liquid(L) → primary Am + remaining L → Am + Al resulting from the suppression of the precipitation from liquid to icosahedral (I) phase. The Am + Al alloys exhibit high tensile strength (σ f) of 1400 MPa. The nanogranular Am phase is important for the development of high strength materials through the formation of nonequilibrium phases.

Development of ultra high strength steels based on spinodal decomposition

A new idea for the development of ultra high strength steels by utilizing the spinodal decomposition of the Fe-Mo binary system is proposed. The idea comprises the restraint of the brittleness of the Fe-Mo alloy by reducing the Mo-content necessary to spinodal decomposition and by microstructure refining such as grain refining, subgrain refining etc; the former is realized by the alloying with some elements which, in general, have a tendency towards ordering (i.e., negative interchange energy between the nearest neighbour atoms) when combined with iron, and the latter by thermomechanical treatment and/or cold rolling. On the basis of the idea, that hidden properties indispensable to high strength materials are successfully drawn from the Fe-Mo alloy; we have obtained a 4GPa grade high tensile steel of Fe-Mo-Co-V. This idea is sure to contribute new suggestions to the development of high strength materials.

高強度機械部品材料の開発

高強度機械部品材料の開発