البحث — المستودع الرقمي العراقي

نتائج البحث: 25 من أصل 272

دراسة سلوك البلى الانزلاقي الجاف لسبائك المنيوم - 7% سليكون عمليا وباستخدام تقنية تصميم التجارب == Studying Dry Sliding Wear Behavior of Al - 7% Si Alloys Using Experimental And DOE Techniques

اسم المؤلف: قاسم سعد عبد الواحد

اسم المشرف: عقيل ظاهر صبحي | علي عبار خليف

الموضوع العام: هندسة الانتاج والمعادن والمواد

السنة: 2014

الموضوع الدقيق: هندسة المعادن

الدرجة: ماجستير

الجامعة: الجامعة التكنولوجية

اللغة: الانكليزية

مكان الجامعة: بغداد

الصفحات الاولى:

المستخلص: تعد سبائك الالمنيوم - سليكون والتي تحتوي على التيتانيوم احدى المواد التي تتميز بمقاومتها للبلى كما بينت الدراسات والابحاث العلمية ذلك.في هذا البحث تم صب سبيكة المنيوم - 7% سليكون وبنسب مختلفة من التيتانيوم (0.5 , 1 , 1.5%) وتحت معدلات تبريد مختلفة في قال | Aluminum - silicon alloys that contain Titanium can be considered one of the wear resistant materials and attract several researchers recently.In this work ,Al - 7%Si alloy with different percentages of Ti ( 0.5 , 1 , 1.5% ) was poured under different solidification conditions into the metal mould.All prepared alloys were dry slided under different bearing pressures ( 5 , 10 , 15 , 20 , 25 N ) on the steel counterface surface using pin on disk wear apparatus. Optical microscope and scanning electron microscope (SEM) were used to study the microstructure and determine wear mechanism of Al - Si alloys respectively. On the other hand , X - ray diffraction technique (XRD) was used to determine the phases that were present in the matrix of Al - Si alloys.Microstructural analysis and X - ray diffraction showed that two phases are presented in the matrix of Al - 7%Si alloys.These phases are ? - aluminum and eutectic and three phases are present in the matrix of Al - Si alloys that contains Ti. These phases are ? - aluminum ,eutectic and titanium aluminide Ti9Al23.Significant refinement occurred for ? - aluminum, eutectic and titanium aluminide Ti9Al23 phases when using metallic mould cooled with cold water in comparison with heated and unheated metallic moulds Hardness was increased with increasing Ti percentage and with increasing the severity of solidification condition used.Remarkable changes in the wear rate occurred for Al - Si alloys during dry sliding in which the magnitude of wear rate was dependent on the Ti percentage ,load and solidification condition used.Design of experiment (DOE) was used to optimize the effect of process variables ( load and Ti percentage) on the wear rate under different solidification conditions using computational statistical software (Mintab 16).

تاثير التشكيل على البنية المجهرية وسلوك البلى للمواد المعدنية المتراكبة النانوية Al2O3 / A356 == The Role of Forming On Microstructure And Wear Behavior of Metal Nano Composite Al2O3 / A356

اسم المؤلف: مروان باسل حسين

اسم المشرف: نوال عزت عبد اللطيف | عقيل ظاهر صبحي

الموضوع العام: هندسة الانتاج والمعادن والمواد

السنة: 2014

الموضوع الدقيق: هندسة المعادن

الدرجة: ماجستير

الجامعة: الجامعة التكنولوجية

اللغة: الانكليزية

مكان الجامعة: بغداد

الصفحات الاولى:

المستخلص: في هذا البحث تم تحضير المواد المركبة النانوية اساس معدني (A356/Al2O3) باستخدام تقنية (rheocasting) ومن ثم تم اجراء عملية التشويه على الساخن عند درجة حرارة °250 م.في البداية تم صهر السبيكة A356 في درجة حرارة °730 م بعدها تم تبريدها الى درجة حرارة الشبه ص | In the present work Al2O3/A356 nano composites have been prepared using rheocasting technique, the nano composites were then processed using hot deformation at 250 °C.Firstly A356 matrix alloy was melted at about 730 °C, the superheated molten alloy was allowed to cool to the semi - solid temperature at 600 °C, then Al2O3 nano - particles with different size (10,20) nm and different weight percentages (1 and 2)%wt were added inside the vortex formed due to stirring , hot deformation carried out with different ratio 30% and 40% at the temperatures of 250 °C and strain rates 0.1 s?1. The produced nano composites samples were characterized using optical and scanning electron microscopy ,X - ray diffraction , hardness test and wear test using pin on disc apparatus. The results of microstructural observations showed that the Al2O3 nano particles cluster mostly near the grain boundaries and form a band surrounding the grain boundaries. The dendritic structure of ? - Al phase is fragmented and the ? grains became more uniform and smaller than their corresponding as - cast 356 alloy. On other hand the microstructures of nano - Al2O3/A356 composites after casting and hot deformation at 250°C, showed modification of ? - Al and Si eutectic. The columnar dendrites ? - Al phase changed to the nearly equiaxed grains or globular morphology. The results of hardness test showed that the nano Al2O3/A356 composite were exhibited higher hardness than the as - cast A356 alloy The nano - composites hardness, increase with increases the size and increases in weight percentage of the Al2O3 nano - particles, and with increasing percentage deformation. The result of wear test showed that the hot deformed nano Al2O3 /A356 composites have greater wear resistance compared with hot deformed A356 alloy. Furthermore, with increasing the particle size and the percentage of Al2O3 nano particles, wear rate will decrease. The results also revealed that the optimal results was achieved at the nano - composites containing 20nm Al2O3 particles after hot deformation with 40%. SEM studies of the worn surface of nano composites showed that the main wear mechanism was oxidative in conjunction with metallic wear.

كلال الدورات المنخفضة في سبيكة المنيوم قابلة للتصليد بالترسيب == Low Cycle Fatigue of Precipitation Hardened Aluminum Alloy

اسم المؤلف: سيف خالد محمود

اسم المشرف: ظافر صادق الفتال

الموضوع العام: هندسة الميكانيك

السنة: 2014

الموضوع الدقيق: ميكانيك تطبيقي

الدرجة: ماجستير

الجامعة: الجامعة التكنولوجية - قسم الهندسة الميكانيكية

اللغة: الانكليزية

مكان الجامعة: بغداد

الصفحات الاولى:

المستخلص: لسبائك الالمنيوم عالية المقاومة طيف واسع من التطبيقات من صناعة السيا ا رت الى الصناعات الفضائية.ان السبب الرئيسي وراء النمو السريع للطلب على هذة السبائك هو مزيج من الخواص الفريدة التي جعلت منها واحدة من اكثر الت ا ركيب والمواد الهندسية استعمالا، ولذلك ل | High strength AL - alloys have a wide spectrum of applications from automobile to aerospace industries. The demand for these aluminum alloys grows rapidly because of the unique combination of properties which make them the most versatile of engineering and construction materials. Hence, development of high strength Al - alloys continues to be an important area of research.In this work, the influence of different heat treatments on the mechanical properties and fatigue life under low cycles of wrought 7075 aluminum alloy was experimentally investigated. The heat treatments included peak ageing (T6), over ageing (T73) and annealing (O).The effect of heat treatments on the alloy was explained in terms of their influence on the mechanical properties. The results showed that T73 temper has an ultimate strength of 504.7 MPa and elongation of 12.5%. Peak ageing treatment enhanced the strength by 10.9% and reduced the elongation by 7.2%, while in the annealed condition, the strength was reduced and the elongation was improved by 51.33% and 31.2%, respectively. T6 had the highest hardness followed by T73 and O tempers.The flat fatigue specimens were subjected to constant reverse bending load. The tests were performed at the laboratory environment with a frequency of 23.3 Hz and at a stress ratio (R) of - 1. For each temper, strain - life graphs were obtained for specimens with notches in the form of central cylindrical holes made by drilling. The fatigue resistance of specimens with notches was compared to the results for notch - free specimens. It was observed that the presence of a stress raiser, such as a drilled hole, lowers the fatigue life for all tempers. However, the notch sensitivity of the fatigue life was different for each temper.The fatigue crack growth rate of T73 and annealed temper was investigated, the results showed that T73 treated sample exhibits higher crack growth resistance. Paris` equation was derived for each temper Keywords : LCF. precipitation hardening. 7075 aluminum alloy. fatigue crack growth.