Strain rate-dependent high temperature compressive deformation characteristics of ultrafine-grained pure aluminum produced by ECAP

To explore the effect of strain rate ε on the high temperature deformation characteristics of ultrafine-grained materials, the deformation and damage features as well as microstructures of ECAP-treated pure Al at different temperatures T and strain ratesε were systematically studied through compression tests and microscopic observations. The increase in ε eliminates strain softening at T≤473 K, and largely enhances the yield strength and flow stress at 473?573 K. The shear deformation dominates the plastic deformation of ECAP-treated Al. Many cracks along shear bands (SBs) are formed at T≥473 K and secondary SBs basically disappear at 1×10?3 s?1; however, at 1×10?2 s?1, cracks are only observed at temperature below 473 K, and secondary SBs become clearer at T≥473 K. The microstructures of ECAP-treated Al mainly consist of sub-grains (SGs). The increase in ε inhibits the SG growth, thus leading to the increases both in yield strength and flow stress at high temperatures.

Effect of carbon on high temperature compressive and creep properties of β-stabilized TiA l alloy

Carbon is an important alloying element in improving high temperature mechanical properties of various metallic materials.The effects of carbon on high temperature mechanical properties of aβ-stabilized Ti?45Al?3Fe?2Mo(molar fraction,%)alloy were studied through compressive and creep tests.The results show that the carbon addition(0.5%,molar fraction)obviously enhances the high temperature compressive strength and creep resistance of theβ-stabilized Ti?45Al?3Fe?2Mo alloy.A lot of nano-scaled Ti3AlC carbides precipitate in theβ-stabilized alloy and these carbides pin the dislocations,and greatly increase the high temperature properties.At the same time,the carbon addition decreases the amount of?phase,refines the lamellar spacing,and causes solution strengthening,which also contribute to the improvement of the high temperature properties.

Mechanism of High Temperature Deformation in Cast Ti46Al8.5Nb0.2W Alloy

Compression tests A ere conducted in the two phase Ti46Al8.5Nb0.2W alloy with a cast microstructure under the strain rates ranging from 2x10(-5) s(-1) to 10(-2) s(-1) at temperatures ranging front 900degreesC to 1100degreesC. It was found that there exist approximately linear relationships between the flow stress and the logarithm of strain rate at different temperatures. The strain rate dependence was analzed by the thermal activation theory and dislocation climbing is regarded as the controlling mechanism during high temperature compression tests.

Research on testing method of resin sand high temperature compressive strength

High temperature compressive strength is one of the most important performances of resin sand; its value directly concerns the quality of castings. In order to seek the best testing method of resin sand high temperature compressive strength, a self-developed instrument was used to carry out experiments, and the sample shape and size were designed and studied. The results show that a hollow cylinder sample can reflect the strength difference of different resin sands better than a solid cylinder sample, and its data is stable. The experiments selected φ20/5×30 mm as the size of the hollow cylinder samples. The high temperature compressive strengths of phenol-formaldehyde resin coated sand, furan resin self-setting sand, and TEA resin sand were each tested. For the resin sand used for cast steel and cast iron, 1,000 ℃ was selected as the test temperature; for the resin sand used for cast non-ferrous alloy, 800 ℃ was selected as the test temperature; and for all the resin sand samples, 1 min was selected as the holding time. This testing method can truthfully reflect the high temperature performance of three kinds of resin sand; it is reproducible, and the variation coefficients of test values are under 10%.

Lowering the cost of large-scale energy storage:High temperature adiabatic compressed air energy storage

Compressed air energy storage is an energy storage technology with strong potential to play a significant role in balancing energy on transmission networks,owing to its use of mature technologies and low cost per unit of storage capacity.Adiabatic compressed air energy storage(A-CAES)systems typically compress air from ambient temperature in the charge phase and expand the air back to ambient temperature in the discharge phase.This papers explores the use of an innovative operating scheme for an A-CAES system aimed at lowering the total cost of the system for a given exergy storage capacity.The configuration proposed considers preheating of the air before compression which increases the fraction of the total exergy that is stored in the fom of high-grade heat in comparison to existing designs in which the main exergy storage medium is the compressed air itself.Storing a high fraction of the total exergy as heat allows reducing the capacity of costly pressure stores in the system and replacing it with cheaper thermal energy stores.Additionally,a configuration that integrates a system based on the aforementioned concept with solar thermal power or low-medium grade waste heat is introduced and thoroughly discussed.

Hot deformation behavior of a near alpha titanium alloy with/without thermal hydrogen processing

The true stress-true strain curves of Ti-6Al-2Zr-IMO-IV alloy with hydrogen were obtained by hot compression test. The microstructures of the alloy before and after thermo-compression were observed. The apparent activation energies of deformation were calculated for the alloy with and without hydrogen. The behavior and mechanism of deformation for hydrogenated Ti-6A1-2Zr-IMO-IV alloy at high temperature were analyzed. The relationship between hydrogenation time and hydrogen content at 800 ℃ can be expressed as the equation： CH（t）=1.2-1.2exp（-t/120）. The true stress-true strain curves of hot compression for Ti-6Al-2Zr-IMO-IV alloy with hydrogen first move down and then move up as hydrogen content increases. Appropriate hydrogen content can reduce the peak of flow stress to minimal value. The apparent activation energies of deformation of the alloy with 0.47% hydrogen content and without hydrogen were calculated as 140 kJ·mol^-1 and 390 kJ-mol^-1, respectively, at 800 ℃ and at strain rate 8.3×10^4 s^-1. The apparent activation energy of deformation increases when the strain rate enhances from 8.3×10^-4 s^-1 to 8.3×10^-2 s^-1.