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Kaveh Hajizadeh,Beitallah Eghbali 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.2
The present work investigates the microstructural and mechanical properties of commercial purity titaniumafter processing by a two-step severe plastic deformation procedure entailing warm equal channel angularpressing (ECAP) followed by cold rolling at liquid nitrogen temperature (LNT). The effect of subsequent coldrolling at room temperature is also investigated for comparison. After 10 passes of ECAP, an ultrafine-grainedstructure with average grain size of 213 nm was achieved. Subsequent cold rolling at LNT led to further refinementand decreased the grain size to 114 nm. Under these conditions, the material displayed high tensilestrength of 995 MPa and high elongation to failure of 23%. These promising mechanical properties were interpretedin terms of characteristics of the microstructure: grain refinement, increased dislocation density, and ahigh fraction of high angle grain boundaries.
Mehdi Shaban Ghazani,Beitallah Eghbali,Gholamreza Ebrahimi 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5
Dynamic recrystallization behavior of AISI 321 austenitic stainless steel were studied using hot compressiontests over the range of temperatures from 900 °C to 1200 °C and strain rates from 0.001 s-1to 1 s-1. The criticalstrain and stress for initiation of dynamic recrystallization were determined by plotting strain hardening ratevs. stress curves and a constitutive equation describing the flow stress at strains lower than peak strain. Also, thestrain at maximum flow softening was obtained and the effect of deformation conditions (Z parameter) on thecritical strain and stress were analyzed. Finally, the volume fraction of dynamic recrystallization was calculated atdifferent deformation conditions using these critical values. Results showed that the model used for predictingthe kinetics of dynamic recrystallization has a great consistency with the data, in the form of θ-ε curves,directly acquired from experimental flow curves.