بررسي ترموديناميكي فرايند رشد دانه در فلزات نانو ساختار با حضور عناصر افزودني بوسيله شبيه سازي ديناميك مولكولي

چكيده انگليسي :

The thermodynamical study of grain growth in nanostructure metals in presence of additional elements by molecular dynamic simulation Samira Sahebgharani Email address s sahebgharani@ma iut ac ir Date of Submission on May 6 2013 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Masoud Panjehpour Assistant Professor pnjepour@cc iut ac ir Mahdi Ahmadian Assistant Professor ahmadian@cc iut ac irAbstractNowadays there is a great interest in nano crystalline materials due to their unique properties Sincegrain boundaries have very high energy there is a huge tendency to grain growth for nano materialswhich will deteriorate their desirable properties There are several types of models for describingthermodynamic behavior of nano crystalline materials These models including Song QAD and EOSmodels are used to investigate about grain growth of nano materials finding methods to prevent furthergrain growth These models indicate that under a critical grain size grain growth tendency is stopped Therefore decreasing the grain size below critical size is one of the methods for preventing from graingrowth of nano materials As a result particular properties of nano materials are preserved for practicalgoals However finding a way to increase critical grain size is necessary due to its very small size Oneof these methods is utilizing secondary element atoms in the pure metal structure and decreasing thegrain boundaries energy Among all proposed models only Song s model claims that by applyingsome changing it can predict thermodynamic behaviour of metal alloys in nanometer scale On theother hand no precise investigation has been done to evaluate capability of this model for predictingthermodynamic behaviour of metal alloys in nano scale still now Thus the aim of this project was toevaluate the capability of Song s model for predicting critical grain size of Al Mg alloy by usingmolecular dynamic simulation In addition penetration behaviour of Mg and Al was investigated byusing this simulation Moreover effect of entering Mg atoms on Al grain growth was studied byconsidering energy changing of the nano structure Al and critical grain size was calculated The resultsindicated that Mg atoms move to grain boundaries after entering Al structure As a result of decreasinggrain boundaries energy grain stability against growing was provided Furthermore Mg atoms controlgrain growth phenomena by creating strong bonds in Al structure and decreasing diffusion coefficientof Al atoms Comparing molecular dynamic simulation results and its calculated critical grain size withthose calculated by Song s model it can be seen that this model do not show good ability in predictionof alloy behaviour in nano scale Simulation of Cu Zr alloy system showed that results werecompatible with Al Mg simulation results In general molecular dynamic simulation results indicatedthat proper selection of secondary element could help to increase critical grain size at differenttemperature Keywords nano structure materials grain growth additive element molecular dynamic simulation Song s model

صاحبقراني، سميرا

بررسي ترموديناميكي فرايند رشد دانه در فلزات نانو ساختار با حضور عناصر افزودني بوسيله شبيه سازي ديناميك مولكولي

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