بررسي مكانيزم تشكيل نانو كامپوزيت ﴿ Ti6Al4V/(Ti-B و ارزيابي رفتار سايشي آن

چكيده انگليسي :

Determination of Formation Mechanism of Ti6Al4V Ti B Nanocomposite and Evaluation of it s Wearing Behavior Parinaz Salehi Kahrizsangi Email address p salehikahrizsangi@ma iut ac ir Date of submission 04 03 2012 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor s Name Fatollah Karimzadeh Associate Professor karimzadeh f@cc iut ac ir Mohammad Hossein Enayati Associate professor ena78@cc iut ac irAbstractIn the present study synthesis and characterization of Ti6Al4V Ti B nanocomposite by mechanical alloyingwere investigated For this purpose the nanostructured Ti6Al4V matrix was obtained from elementalpowders The nanocomposite was then prepared by mechanical alloying of the Ti Al V B powder mixture Phase transformations structural changes morphological evaluations and hardness measurements of thesamples were studied by means of x ray diffraction XRD scanning electron microscopy SEM energydispersive spectroscopy EDS transmission electron microscopy TEM and microhardness measurements Heat treatment of the powder product was performed for 5 hr at 1100 C in order to study thermal behavior Bulk nanostructured Ti6Al4V alloy and Ti6Al4V 20wt TiB nanocomposite samples were produced throughcold pressing and sintering at 1100 C for 2 and 4 hr respectively Wear tests were performed on bulk samplesat ambient temperature with wearing velocity of 0 03 m s under the applied load of 80 N In the absence of B the nanostructured Ti6Al4V alloy was formed by gradual diffusion mechanism of Al and V atoms in Tilattice to form Ti Al V solid solution after 10 hr milling Prolongation of milling process up to 20 h leads tostabilization of phase in the matrix A nanostructured Ti6Al4V alloy 2vol 98 vol with grainsize of about 20 nm and hardness of about 600 Hv is obtained after 20 hr milling meanwhile the hardness ofthe commercial plate of Ti6Al4V alloy was about 450 Hv Hardness of the heat treated powder increased toabout 950 Hv equal to that of heat treated Ti6Al4V alloy plate in the same condition On the contrary hardness of the pure Ti ball milled for 20 hr with grain size of about 30 nm was about 500 Hv and increase toabout 600 Hv after heat treatment Differences in thermal stabilities of the nanostructured Ti6Al4V alloy andpure nanostructured Ti could be assigned to the favorable effects of alloying elements on hardness TheTi6Al4V 20wt TiB2 nanocomposite was in situ synthesized after 40 hr milling followed by 1 hr heattreatment of Ti Al V B powder mixture at 1100 C Albeit 40 hr milling was previously observed to beenough for the formation of TiB2 reinforcement from Ti 1 67at B powder mixture by gradual diffiusionmechanism Based on TEM observations of the nanocomposite powder the grain size of the matrix andreinforcements were about 15 nm and 20 nm respectively close to what was calculated by Williamson hallformula In search of thermal behavior of the powder product heat treatment was done at 1100 C for 5 hr Hardness increased from about 900 Hv to about 1830 Hv As predicted all TiB2 diffraction peaks had beenreplaced by TiB diffraction peaks due to the insufficient thermal stabilities of TiB2 in Ti matrix Hardness ofthe bulk samples were about 830 Hv and 1030 Hv for Ti6Al4V alloy and nanocomposite respectively Relative density of the bulk nanostructured alloy and nanocomposite was 99 7 and 111 respectively Thebulk nanocomposite and the commercial alloy were the least and the most abrasive respectively Wearbehavior of the bulk nanostructured alloy was inferior to that of nanocomposite due to the absence of TiBreinforcements KeywordsTi6Al4V alloy wear heat treatment solid solution formation mechanism nanostructure

صالحي كهريزسنگي، پريناز

بررسي مكانيزم تشكيل نانو كامپوزيت ﴿ Ti6Al4V/(Ti-B و ارزيابي رفتار سايشي آن

عمليات حرارتي , محلول جامد , نانو ساختار