Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

Physical Hardening of Asphalt Binders Relative to Their Glass Transition Temperatures

Abstract: Physical hardening (physical aging) is a process that occurs below room temperature in asphalt binders. Physical hardening causes time-dependent isothermal changes in the rheological behavior and specific volume of asphalt binders. The process is reversible: when the asphalt binder is heated to room temperature or above, the effect of physical hardening is completely removed. Physical hardening for amorphous materials is generally reported as occurring below the glass transition temperature (Tg), but this is not the case for asphalt binders, in which physical hardening is observed both above and below Tg. The glass transition temperature of asphalt binders is measured by using three different techniques: dilatometry, differential scanning calorimetry, and rheological considerations (peak in the loss modulus versus temperature). These three techniques give roughly equivalent estimates of the glass transition temperature. The behavior of physical hardening in asphalt binders is somewhat different than that ...

On the strain hardening behaviour of magnesium at room temperature

Abstract: The strain hardening behaviour of randomly oriented polycrystals deformed in tension and compression is analysed using the Kocks-Mecking phenomenological approach. At low stresses, an extended regime of linear hardening consistent with an athermal forest hardening mechanism, akin to that observed in face-centered cubic metals, is observed. The increase in yield strength with decreasing grain size can also be accounted for by relating the mean free path of dislocations to the grain size. Profuse twinning in compression seems to have little or no effects on the overall strain hardening behaviour.

Improvements of strength and ductility in aluminum alloy joints via rapid cooling during friction stir welding

Abstract: Microstructures, tensile properties and strain hardening behavior of a friction stir welded (FSWed) thick AA2219 aluminum alloy under optimized welding parameters and varying cooling conditions (air cooling and water cooling) were investigated with three slices (top, middle and bottom) through the plate thickness. While the yield strength was lower in the FSWed joints than in the base metal, the ultimate tensile strength of the FSWed joints with water cooling reached nearly that of the base metal. In particular, FSW resulted in a significant improvement in the ductility of the alloy due to the presence of recrystallized fine grains with fragmented and uniformly dispersed second-phase particles in the weld nugget zone. Water cooling resulted in both higher strength and ductility, but lower strain hardening capacity than that with air cooling during FSW. Compared with the middle and bottom slices, the top slice had a higher strength, but lower ductility and strain hardening capacity. While stages III and IV hardening occurred after yielding in both base metal and FSWed samples, the FSW led to higher hardening capacity and strain hardening rate and exponent mainly in the middle and bottom slices. The fracture surfaces after FSW exhibited more obvious ductile fracture characteristics with dimples and tearing ridges along with micropores.

A micromechanical model of hardening, rate sensitivity and thermal softening in BCC single crystals

Abstract: The present paper is concerned with the development of a micromechanical model of the hardening, rate-sensitivity and thermal softening of bcc crystals. In formulating the model, we specifically consider the following unit processes: double-kink formation and thermally activated motion of kinks; the close-range interactions between primary and forest dislocations, leading to the formation of jogs; the percolation motion of dislocations through a random array of forest dislocations introducing short-range obstacles of different strengths; dislocation multiplication due to breeding by double cross-slip; and dislocation pair annihilation. The model is found to capture salient features of the behavior of Ta crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate.