Dursun Özyürek

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.

An investigation into the wear behaviour of TiB2 particle reinforced aluminium composites produced by mechanical alloying

Abstract In this study, wear behaviour of TiB2 particle reinforced aluminium (Al) composites produced by the mechanical alloying method was investigated. TiB2 ceramic particles of four different volume fractions were mechanically alloyed with Al and A356 alloy matrix materials. The mechanically alloyed particles were cold presses and then sintered at 550°C. After the sintering process, the composites were characterised through hardness measurements, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Wear tests were also carried out on a pin-on-disc type wear apparatus under 10, 25 and 50 N loads. Wear loss of the composites were found to decrease with increasing hardness which increased with increasing TiB2 particle volume fraction. However, increasing the applied load and sliding distance increased the wear loss. Wear surface examinations showed that various wear mechanisms were effective in wear of the composites.

Effects of Different Heat Treatment Conditions on Fatigue Behavior of AA7075 Alloy

Abstract In this study, the effect of different heat treatment processes applied to AA7075 alloys on the fatigue behavior was examined. The processes applied to AA7075 aluminum included annealing (O), high temperature pre-precipitating (HTPP), artificial aging (T6), retrogression and re-aging (RRA). The annealing heat treatment was performed for 2 hours at 500°C and samples were cooled in the furnace. In the artificial aging (T6) process, after the samples were solution treated for 2 hours at 500°C, they were quenched at room temperature and aged for 24 hours at 120°C. In the retrogression and re-aging process, samples were solution treated for 1 hour at 220°C after the T6 process and then re-aged for 24 hours at 120°C. In the high temperature pre-precipitating, pre-precipitates were formed for 30 minutes at 450°C and then, it was aged for 24 hours at 120°C. All samples were characterized through the scanning electron microscope (SEM + EDS), hardness measurements and X-ray difraction (XRD) techniques. At the end of experimental studies, SEM and EDS examinations XRD results revealed that η (MgZn2) phase formed in the microstructure following the HTTP, RRA and T6 heat treatment processes. As a result of the fatigue tests, the highest fatigue strength was measured in samples treated with artificial aging (T6), the lowest fatigue strength was measured in the annealed (O) samples.

Exchange of experience the effect of synthesis time on the wear behavior of Al–8%Ti alloy produced by mechanical alloying

In this study, Al–8%Ti alloy was produced by mechanical alloying. The produced powders were cold pressed at 630 MPa and synthesized at 600°C for 12 and 24 h under argon gas atmosphere. After synthesis processes, the specimens were examined by SEM, XRD, and hardness tests. Wear tests were carried out under dry sliding conditions using a pin-on-disk type machine at a constant load of 30 N and a sliding speed of 1 m/sec. Total sliding distances were selected as 500, 1000, 1500, and 2000 m. The experimental results showed that the hardness and density of Al–%8Ti alloy increased with increasing synthesis time. It was also observed that volume reduction increased with increasing sliding distance and decreased with increasing synthesis time.

Wear Properties of Titanium and Ti6Al4V Titanium Alloy by Mechanical Milling

Abstract In this study, wear characteristics of titanium and titanium alloyed materials produced with mechanical alloying/milling (MA/MM) method were studied. In production of titanium and titanium alloyed materials, sponge titanium, gas atomised titanium powder and pre-alloyed Ti6Al4V alloy powder were used. The produced materials were characterised by scanning electron microscope, optical microscope, X-rays diffractometer (XRD) and EDS. The wear tests were carried out on a pin-on-disc type wear device under three different loads (15–30–45 N), four different sliding distances (500–1000–1500–2000 m) and a sliding speed of 1 ms–1. The results showed that no porosity was found on the gas atomised titanium and the Ti6Al4V alloy while very low amounts of micro porosity were formed on the sponge titanium samples. EDS analysis, on the other hand, revealed some Fe contamination on the materials, arising from the milling environment. It was seen that the hardness values of the samples produced from the gas atomised titanium powder were higher either than the samples produced from the sponge titanium, or the samples produced from the Ti6Al4V alloy. The fact that the wear losses obtained for the samples produced from the TiAl4V and gas atomised titanium powders were lower when compared to the sponge titanium. This was considered as the result of porous structure of sponge titanium.

An Investigation on Wear Resistance of SiCp-Reinforced Aluminium Composites Produced by Mechanical Alloying Method

In this study, AI-SiCp composites were produced by a mechanical alloying method using SiCp powders up to 20 vol% as a reinforcement. The produced compositions were cold pressed at 630 MPa with a single action and sintered at 560°C for minutes under Ar gas atmosphere. The experimental result showed that the reinforcement phase SiCp was homogeneously dispersed in the Al matrix and the interface between Al matrix and SiCp was well formed. Wear tests were carried out under dry sliding conditions using a pin-on-disk type testing machine at three different loads of ION, 25N and SON and at a sliding speed of 2.08 m/s. Total sliding distance was selected as 400, 800, 1200 and 1600 m. After wear tests, the wear amount was determined by measuring the weight and dimension of specimens. It was seen that the wear rate increased with increasing the applied load from ION to 50N, sliding distance and decreased with increasing SiCp amount. Microstructures and worn surface of Al-SiCp composites were investigated by SEM.

Microstructure–bifilm interaction and its relation with mechanical properties in A356

Cooling conditions and inclusions are of the most important factors that affect mechanical properties of cast aluminium alloys. This study investigated the effect of secondary dendrite arm spacing (SDAS) on the shape of pores (i.e. bifilm unravelling) and the mechanical properties of cast A356 alloy. Different cooling conditions were established by electrolytic copper chill, H13 steel chill and insulated ceramic that was placed in the mould cavity. SDAS and shape of pores were investigated by optical microscopy. The fracture surfaces of tensile test samples were analysed by SEM and EDX. Weibull two-parameter statistical method was used to assess the tensile properties. Results show that mechanical properties were dominantly affected by pore morphology that was formed by bifilms. Increasing the cooling rate (i.e. decreasing SDAS), the unravelling of bifilms delayed which decreased porosity formation significantly.

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.

Effects of Re-Aging on the Fatigue Properties of Aluminum Alloy AA7075

Abstract In this study, 7075 aluminum alloy was subjected to triple-aging of retrogression and re-aging (RRA) treatments. The alloy was retrogressed at 220 °C for 60 minutes following the T6 heat treatment and later re-aged at temperatures between 100 °C and 140 °C for 24 hours and at 120 °C for various durations in the range of 15–35 hours. The effects of temperature and duration of re-aging on hardness and the fatigue behaviors of RRA tempered 7075 aluminum alloys were investigated. The results show that temperature and duration of re-aging have an influence on both hardness and fatigue resistances. An increment of the hardness values depends on increasing of re-aging temperature and times until 120 °C and 24 hours and reaches to the maximum value. However, those values decrease with higher re-aging temperatures and longer duration than 120 °C and 24 hours, respectively. On the other hand, in the fatigue tests, the highest fatigue resistance was observed for the sample re-aged at 120 °C for 24 hours, while the sample re-aged at 140 °C for 24 hours showed the longest fatigue life under lower fatigue stress.

The Effects of T5 and T6 Heat Treatments on Wear Behaviour of AA6063 Alloy

Abstract In this study, T5 heat treatment was applied to AA6063 alloy aged at 455 K for 2 hours after extrusion at 686 K. T6 heat treatment was also carried out by ageing at 455 K for 2 hours after solution heat treatment at 794 K for 1 hour. Heat treated T5 and T6 specimens were tested by pin-on-disc type wear equipment. Wear test was carried out by using 10, 20, 30 N loads and 400, 800, 1200 and 1600 m wear distance. T5 and T6 heat treated specimens were characterized with scanning electron microscope, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and hardness measurements. Worn surfaces of the specimens was also characterised with SEM. The results indicated that small and homogenously dispersed Mg2Si precipitates formed in AA6063 aluminium alloy with T6 heat treatment were compared to the T5 heat treatment. As a result of increment precipitate size, wear resistance decreased. T6 heat treated specimens showed higher hardness compared to the T5 heat treated specimens. In addition wear resistance and friction coefficient of both T5 and T6 heat treated specimens decreased with increasing applied load.