Musa Yıldırım

The tribological properties of A356-SiCp metal-matrix composites fabricated by thixomoulding technique

Abstract In this study, A356-SiCp metal-matrix composites were produced through thixomoulding process, and these composites were subjected to wear tests. The composites containing various volume fractions of SiCp particles (5%, 10%, 15% and 20%) as the reinforcement were produced at two different temperatures of 590°C and 600°C. The influences of processing temperatures and reinforcement ratio on the properties and wear behaviour of the composites were investigated. Prior to the wear tests, microstructural properties and hardness of the composites were determined. For the wear tests, a pin-on-disc-type wear apparatus was employed to carry out the wear tests. The wear tests were carried out at 2.0 m/s sliding speed under 15 N load and for four different sliding distances. A scanning electron microscope (SEM) was used to examine the wear mechanisms on the worn surfaces of the composites. The results indicated that sphericity rate and hardness of the composites produced at 590°C were higher than those of the composites produced at 600°C. In addition, the composites produced at 590°C exhibited lower weight loss and friction coefficient.

Investigation of microstructure and wear behaviors of al matrix composites reinforced by carbon nanotube

ABSTRACT In this study, the effect of CNT amount in Al-CNT composites produced by adding carbon nanotube (CNT) to 7075 Al alloy in various amounts on microstructure and wear behaviors of aluminum matrix composites was investigated. CNT was added to 7075 Al alloy powder at five different amounts. The powders were mechanically milled for 2 hours. Mechanical milled powders were cold pressed and then pre-shaped by hot pressing. Pre-shaped samples were sintered for 1 hour under 10−6 millibar in 580°C. Microstructure examinations, hardness measurements, and wear tests were carried out. The results show that CNTs in the microstructure were agglomerated as nanotube amount increases and there was no uniform distribution. The highest hardness value was obtained in AMC reinforced with 1% CNT while it is seen that hardness of the composite decreases and weight loss increases as CNT amount increases.

An Investigation of Wear Behaviors of AA7075 Al Hybrid Composites

Abstract This study investigates the wear behavior of Al hybrid composites produced by adding 4 % Ti and different amounts of B4C (ex situ) to the AA7075 alloy produced by powder metallurgy method in order to obtain TiAl3 (in situ) reinforcement phase. Different amounts of B4C (3 %, 6 % and 9 %) were added to the 4 % Ti added AA7075 alloy. Preformed parts were sintered in controlled atmosphere (argon) heat treatment furnace at 580 °C for 4 hours and then cooled. After the sintering process, the samples were characterized with scanning electron microscopy, X-ray diffraction and density and hardness measurements. Wear tests of the samples were conducted at 1ms-1 sliding speed, under 30N load for 6 different sliding distances (500–3000 m). As a result of the study, the density of the AA7075 alloys, added 4 % Ti and different amounts of B4C, was observed to decrease by the increasing amount of reinforcement elements. Also, the highest hardness value was measured for the 9 % B4C added AA7075 alloy. Wear test results showed that the weight loss of the aluminum hybrid composites increased with the increasing sliding distance. On the other hand, it was observed that weight losses of composites decreased with increasing amount of B4C.

Yaşlandırılmış AA7075 Alaşımında Solüsyona Alma Sıcaklığının Aşınma Performansına Etkisinin İncelenmesi

Bu calismada, yaslandirma isil islem oncesi farkli solusyona alma sicakliklarinin (465 °C, 470 °C, 475 °C, 480 °C ve 485 °C) AA7075 alasiminin mikro yapi ve asinma davranislari uzerine etkisi arastirilmistir. Yaslandirilan alasimlarin mikro yapi incelemelerinde taramali elektron mikroskobu kullanilmistir. Asinma testleri pin-on-disk tipi asinma cihazinda 1,5 ms-1 kayma hizi, 30 N yuk ve dort farkli (500 m, 1000 m, 1500 m ve 2000 m) kayma mesafesi kullanilarak yapilmistir. Yapilan calismalar sonucunda, solusyona alma sicakligindaki artisa paralel olarak alasimlarin sertliklerinin arttigi ve 30 N yuk uygulanarak yapilan asinma testlerinde en dusuk agirlik kaybinin 485 °C’de solusyona alinan ve 120 °C’de 24 saat yaslandirilan AA7075 alasiminda elde edildigi belirlenmistir. Genel olarak asinma yuzeyi SEM goruntulerinden, hem adhesiv asinma mekanizmasinin hem de abrasif asinma mekanizmasinin aktif oldugu belirlenmistir.

Toz Metalurjisi Yöntemiyle Üretilen 7075 Al Alaşımlarında Mn Miktarının Aşınma Davranışlarına Etkisinin İncelenmesi

Bu calismada, toz metalurjisi yontemiyle AA7075 alasimina Mn ilave edilerek uretilen alasimlarin mikro yapi, sertlik ve asinma davranislari incelenmistir. Alasimlar, gaz atomize 7075 Al alasim tozlarina 4 farkli oranda (%0,5, %1, %2 ve % 3) Mn ilave edilerek mekanik alasimlama yontemi ile uretilmistir. Uretilen alasim tozlari soguk preslenerek on sekillendirildikten sonra atmosfer kontrollu ortamda sinterlenmistir. Farkli miktarda Mn ilave edilerek uretilen numunelerin mikro yapi incelemeleri taramali elektron mikroskobuyla yapilmistir. Sertlik olcumleri mikro sertlik cihazinda, asinma testleri pin-on-disk tipi asinma cihazinda 15 N yuk altinda dort farkli kayma mesafesinde test edilmistir. Yapilan calismalar sonucunda alasima ilave edilen Mn miktari arttikca sertligin arttigi bunun yaninda asinma testleri sonucu agirlik kaybinin azaldigi belirlenmistir.

The Effects of Molding Materials on Microstructure and Wear Behavior of A356 Alloy

Abstract In this study, the effect of molding materials on microstructure and wear behavior of A356 alloy was investigated. Different microstructures were obtained by casting A356 alloy into the molds made from three different materials. Homogenization and aging heat treatments were applied as cast blocks. The aged samples were tested by pin-on-disk-type standard wear equipment. The results showed that casting into different mold materials resulted in different microstructures of A356 alloy. Microstructures of the Al–Si–Mg alloy differ depending on the mold materials. Secondary dendrite arm space (SDAS) decreased proportionally with increasing cooling rate. Based on the cooling rate, hardness values of the alloy also differ. As the cooling rate increased, hardness of the alloy increased. The SDAS increased due to the decreasing cooling rate. In wear tests, increasing weight loss was observed with decreasing cooling rate.