7418

6924

كارشناسي ارشد

ريخته گري

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1391

سيزده، 81ص.: مصور، جدول، نمودار

ص.ع. به فارسي و انگليسي

احمد كرمانپور

3/10/91

فخرالدين اشرفي زاده، احمد ساعتچي

1396/09/22

كتابنامه

مواد

مهندسي مواد

ID6924

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Evaluating the effect of cooling rate in directional solidification process on structure and mechanical properties of the nickel base superalloy GTD111 Alireza Heydari a heydari@ma iut ac ir Date of Submission April 22 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Language Degree M Sc Farsi Supervisor Dr Ahmad Kermanpur Assoc Prof ahmad k@cc iut ac ir Abstract Directional solidification process of superalloys is one of the advanced technologies to enhance mechanical properties of hot parts in gas turbines such as turbine blades In this work effect of cooling rate on structure and mechanical properties of the directionally solidified DS nickel base superalloy GTD 111 has been evaluated Several polycrystalline bar shaped samples with diameter of 12 mm and height of 200 mm were first prepared The Bridgman directional solidification process was applied under vacuum using ceramic molds and water cooled copper chill plate To investigate the effect of cooling rate the process was conducted under various pulling speeds of 1 3 6 and 9 mm per minute The as cast rods were then solutionized and age hardened under vacuum All cast and heat treated samples were cut along both longitudinal and transverse directions for evaluation of macroscopic and microscopic structures Micro porosity grain structure dendritic structure and microstructure of all specimens were studied by light and electron microscope equipped with EDS DSC test was used to determine temperatures of phase changes in the alloy Hardness tensile properties at room temperature and stress rupture properties of specimens were measured The results showed columnar grain structure for all cooling rates The columnar grains were elongated in the direction of heat transfer along the orientation of 001 The number of grains was decreased with increasing distance to the chill due to the preferential nature of grain growth Increasing the cooling rate resulted in a decrease in both primary and secondary dendrite arm spacings For example the primary arm spacing was 220 and 180 m for the withdrawal rates of 3 and 9 mm min respectively Increasing cooling rate also resulted in an increase in microporosity but a decrease on the size of carbides and eutectic regions Characterizing the heat treated specimens showed a partial dissolution of precipitates during solution treatment Tensile test at room temperature showed higher yield strength and tensile strength but a relatively lower ductility for the DS specimens than the polycrystalline ones Stress rupture test at high temperature low stress condition showed a much higher rupture life for the DS specimens compared to the polycrystalline ones A higher cooling rate resulted in a better creep properties The present work clearly showed an improvement in the mechanical properties of the nickel base superalloy GTD111 possessing directionally solidified microstructure Keywords Bridgman directional solidification Nickel base superalloy GTD 111 Cooling rate Creep

احمد كرمانپور

فخرالدين اشرفي زاده، احمد ساعتچي