Papers by Keyword: Low Temperature Superplasticity

Abstract: It is shown that formation of ultrafine-grained structure in EK61 superalloy up to grain sizes less than 1 μm provides to realize superplastic properties. The influence of deformation in the temperature range 600-1100 °C and strain rate range 10^-4s^-1– 10^-3s^-1 on the microstructure and properties of ultrafine-grained nickel-based alloy EK61 is studied. It is established that in temperature range 750-900 °C the alloy demonstrates superplasticity (SP) characteristics: strain rate sensitivity factor “m” correspond to 0.39-0.59, stable structure and low changes in the form and size of grains. The maximum SP is displayed at temperatures of 800 °C, wherein the elongation is 1431 %. It has been experimentally confirmed that the use of low-temperature superplasticity is a promising for processing sound solid phase joints by pressure welding of similar and dissimilar Ni-based superalloys.

Abstract: 5083 aluminum alloy was processed with combined process of warm rolling and annealing. Elongation and tensile strength of samples were measured to analyze the influences of annealing temperature and annealing time on its mechanical properties.Results show that low temperature superplasticity is very sensitive to temperature. The maximum elongation for 5083 aluminum alloy reaches 443% at 250°C and a strain rate of 1×10^-3s^-1, which means that 5083 aluminum alloy exhibits excellent low temperature superplasticity. Low temperature annealing before drawing could not effectively improve the elongation.

Abstract: Superplastic behavior was investigated using an extruded Mg-Zn-Y alloy with the dispersion of the quasicrystal phase particle in fine-grained matrix. Tensile tests showed that the low temperature superplasticity was behaved at a temperature of 473 K and maximum elongation was 462 % at 573 K in 1  10-5 s-1. The deformed microstructure observation showed that the dominant deformation process was grain boundary sliding. The present alloy also demonstrated a high possibility for secondary forming, such as superplastic forge forming. Furthermore, the forged alloy had a homogeneous microstructures, no mechanical anisotropy and uniform micro-hardness properties in any portion of a forged product.

Abstract: The low-temperature superplastic flow behavior of two lots of Ti-6Al-4V sheet with an ultrafine microstructure was modeled. One lot (Sheet A) had an equiaxed-alpha starting microstructure; the flow stress/flow hardening exhibited by this material was explained on the basis of the Bird-Mukherjee-Dorn constitutive equation. The other material (Sheet B), having a mixed equiaxed- and remnant-lamellar alpha microstructure, underwent flow softening, flow hardening, or steady-state flow depending on test temperature and strain rate. These behaviors were interpreted in the context of a dynamic spheroidization model. The apparent flow softening at the end of all of the flow curves was explained using a simple flow-localization model.

Abstract: Effects of hydrogen on superplastic deformation behavior were investigated through high temperature tensile experiment in this paper. It is found that reasonable hydrogen contents can improve the superplastic behavior such as lowering flow stress and temperature and increasing m value. While addition of 0.1wt% hydrogen in Ti-6Al-4V alloy, peak flow stress decrease to 53%, deformation temperature decrease 60°C. The influence of hydrogen on microstructure transition by means of optic microscope, SEM, TEM and XRD was also researched. The results show that β phase amounts in the hydrogenated alloy increase with hydrogen contents, while hydrogen contents reach to 0.2wt%, martensite becoming coarser with the increase of hydrogen contents. Moreover, dislocations density of hydrogenated alloy after deformation is lower than that of unhydrogenated alloy because of hydrogen action.