Effects of electric current on solid state phase transformations in metals

2016

Materials & Design

Abstractκ-carbide () in high aluminium (Al) steels is grown from austenite () via + or α+ ( represents ferrite), and is a lamellar structure. This work demonstrates that the formability of high Al lightweight steels is affected by the lattice misfit and interface shape between  and matrix. The cold workability can be improved by either to change the steel chemical constitution or to implement an electro-thermo-mechanical process. For ferrite-matrix-based high Al steel, electric-current promotes the spheroidization and refinement of  structure and reduces volume fraction of  phase. This retards the crack nucleation and propagation, and hence improves the materials formability. The observation is caused by a direct effect of electric-current rather than side effects.

Section: Discussionmentioning

confidence: 99%

Influence of κ-carbide interface structure on the formability of lightweight steels

2016

Materials & Design

“…The treatment has also been applied to various aspects of materials processing, e.g. to generate plasticity [3], to refine microstructure [4] and to expedite structural relaxation [5,6].…”

Section: Introductionmentioning

confidence: 99%

“…Studies have shown that the effect of electropulsing on both substitutional and interstitial precipitations is complex and depends on various factors such as the alloy system, the solutionizing time and temperature, the aging time and temperature, the magnitude of the current density and its frequency [5]. Since precipitation is a diffusion-controlled phase transformation, it is expected that electromigration may play a significant role when considering the effect of electric current pulses.…”

Section: Introductionmentioning

confidence: 99%

Effect of electric current pulses on the microstructure and niobium carbide precipitates in a ferritic-pearlitic steel at an elevated temperature

Rahnama

2015

J. Mater. Res.

Niobium is an important alloying element in steels. In the present work an effort has been made to investigate the effect of electropulsing on the niobium carbide (NbC) at an elevated temperature (800 ºC). The results show that the electropulsing treatment can generate an evenly distributed NbC by decreasing the kinetics barriers for precipitation. It has been also found that a semi-transformed pearlite structure forms in such a way that the grains are oriented towards a direction parallel to that of the electric current flow. Furthermore, the electropulsed sample benefits from refined grain size. This is thought to be due to the electropulse-enhanced nucleation rate. Tensile testing has been carried out in order to compare the properties of electropulsed sample with that of without electropulsing. The results show that the sample with treatment has greater yield strength and ultimate tensile stress (UTS) while its elongation is only 1% less that of the unelectropulsed samples. The improved mechanical properties of the sample with pulsing are attributed to its finer grain sizes as well as the elimination of precipitation free zones (PFZs) caused by the electropulsing treatment.

“…Basically, the segregation is closely related to the process of diffusion, in particular the thermal diffusion segregation is most concerned due to the enhanced diffusion at high temperatures [1][2][3][4]. In the application of pulsed electric current, the atomic diffusion can be enhanced [5,6] and the thermodynamic barrier for phase transformations can be decreased [7,8]. These suggest that segregation in materials would be greatly exacerbated when passing a pulsed electric current.…”

Section: Introductionmentioning

confidence: 99%

“…In the application of electric current, the atomic diffusion can be enhanced [5,6]. Possibilities for enhancing the diffusion by pulsed electric current include an increase in the diffusion pre-exponential factor and/or a reduction in the diffusion activation energy [6].…”

mentioning

confidence: 99%

Segregation of copper in an Fe–Cu alloy under pulsed electric current

Zhang

Philosophical Magazine Letters

2015

Effect of electric current on the segregation of copper precipitates in the Fe-13.6Cu alloy is evaluated. Results of this approach present two stages of segregation, namely, grain-boundary segregation during the solidification and interphase segregation during the decomposition of a solid solution. The segregation becomes apparent not only because the thermodynamic barrier for segregation is decreased, but also because the diffusion is greatly enhanced. Based on the thermodynamic and kinetic aspects, the segregation process under electric current would be of great interest and of physical importance because this kind of electric currentinduced segregation was much stronger than the thermal diffusion segregation.