ارزيابي تاثير عمليات ترمومكانيكي بر ريز ساختار و خواص حافظه داري آلياژ Ti-50at.% Ni

چكيده انگليسي :

Evaluation of the Effect of Thermomechanical Treatment on Microstructure and Shape Memory Properties of Ti 50 at Ni Ahmad Forouzmehr a foroozmehr@ma iut ac ir Date of submission July 2011 Department of Material Engineerin Isfahan University of Technology Isfahan 84156 83111 Iran Degree MSc Language FarsiSupervisor Asssoc Prof Ahmad Kermanpour ahmad k@cc iut ac ir Prof Fakhreddin Ashrafizadeh ashrafif@cc iut ac irDepartment Graduate Coordinator Assist Prof M PanjepoorAbstractShape memory is an ability of a class of materials to recover the deformation occurred in lowtemperature at high temperature Among shape memory alloys TiNi has attracted researchers interests due to their proper shape memory properties and their ability of changing thetransformation temperature to human body temperature In the current research effect ofthermomechanical treatment including hot rolling cold rolling and annealing on the microstructureand shape memory properties of Ti 50at Ni shape memory alloy was studied The equi atomicTiNi alloy was produced by using vacuum arc melting in water cooled copper crucible The as castmaterial was homogenized at 1000 C for different time up to 8 hours In order to evaluate theactual composition of the material thermal analysis was done The homogenized material was 50 hot rolled at 1000 C followed by annealing at 900 C for 1 hour The hot rolled and annealedspecimens were 10 40 cold rolled at room temperature Post deformation anneal was done at400 500 and 600 C for 1 hour Phase transformation and microstructural evolution was studiedusing X ray diffraction analysis and electron and optical microscopy Tensile and hardness testswere conducted to investigate the mechanical properties of specimens after homogenization andthermomechanical treatments Shape memory effect was measured by using the three point testmethod Results showed that the grain size was reduced about 50 by hot rolling and annealingprocess Additionally martensite percentage was increased with increasing the reduction in coldroll process and decreased by increasing the annealing temperature Specimens annealed even at600 C still contained martensite This remained martensite was increased with increasing thereduction up to 30 but a decrease in remained martensite was observed in the 40 rolledspecimen Microstructures of annealed specimens after cold rolling showed that particle stimulatednucleation at austenite was occurred for 10 40 cold rolled specimens at 500 C andrecrystalization of the matrix was occurred for 20 and higher at 600 C more matrixrecrystalization was occurred for the 40 reduction and 600 C annealed specimen leading to asignificant decrease in dislocation density and consequently hardness and the amount of remainedmartensite Tensile test showed that ductility of material increased with annealing temperature andthe strength on the other hand decreased According to the results of three point bend test due todislocations recovery shape recovery was decreased with increasing the annealing temperature This decrease in shape recovery was intensified by starting recrystallization in matrix of thespecimen 20 rolled followed by annealing at 600 C The annealed specimen at 400 C after20 rolling however showed full shape recovery Key words shape memory alloy Thermomechanical treatment phase transformation recrystallization microstructure

فروزمهر، احمد

ارزيابي تاثير عمليات ترمومكانيكي بر ريز ساختار و خواص حافظه داري آلياژ Ti-50at.% Ni

آلياژ حافظه دار , استحاله فازي , تبلور مجدد