E. Sabri Kayali

Residual stress estimation of ceramic thin films by X-ray diffraction and indentation techniques

Abstract The residual stresses in ceramic thin films obtained by the indentation method have been found to be three times higher than those of the X-ray diffraction method. This discrepancy can be eliminated by setting the geometrical factor for the Vickers pyramid indenter to 1 in the relevant equation of the indentation method.

High Cycle Fatigue Behavior of Thermally Oxidized Ti6Al4V Alloy

In this study, the effect of thermal oxidation on the high cycle rotating bending fatigue behavior of Ti6Al4V alloy was investigated. Oxidation, which was performed at 600°C for 60 h in air, considerably improved the surface hardness and particularly the yield strength of the alloy without scarifying the tensile ductility. Unfortunately, the rotating bending fatigue strength at 5x106 cycles decreased from about 610 MPa to about 400 MPa upon oxidation. Thus, thermal oxidation leaded a reduction in the fatigue strength of around 34%, while improving the surface hardness (HV0.1) and yield strength 85 % and 36 %, respectively.

The effect of Cu and Al on the mechanical properties of gravity-cast hyper-eutectic Zn–Al-based alloys

A series of Zn – Al-based alloys, one group with 1 % Cu and the other without Cu, was produced by using gravity casting. The effect of Al content on hardness, ultimate tensile strength (UTS), impact strength, and tensile creep behaviour at 120 °C and an applied stress of 40 MPa has been investigated. It has been found that the hardness and UTS of the alloys considerably increased with increasing Al content, but the creep strength decreased. The impact strength of the alloys improved with increasing Al content up to 7.5 % and then reduced gradually with further increase in Al content. In addition, the effect of 1 % Cu addition on the mentioned properties has been determined. While the addition of 1 % Cu had a profound effect on increasing the hardness, UTS, and creep strength, it did not have a significant effect on the impact strength of the alloys. Metallographic examinations showed that an increasing Al content of the alloys increased the volume fraction of the Al-rich b dendrites in expense of a decreased volume fraction of the eutectic, which is in principle responsible for the change in mechanical properties of the alloys depending on the Al content

Influence of retrogression and re-ageing on the mechanical and corrosion properties of 7039 aluminium alloy

The effect of T6 and retrogression and re-ageing (RRA) treatments on the corrosion and mechanical properties of a 7039 Al alloy was examined. T6- and RRA-tempered alloys exhibited a similar intergranular corrosion resistance for a retrogression time of 3 min at 220 °C. The results revealed that an RRA-tempered alloy (3 min retrogression at 220 °C followed by re-ageing) exhibited a higher hardness and strength and a lower ductility and toughness than a T6-tempered alloy with a significant improvement in the stress corrosion cracking resistance.

The effect of Ti alloying on the mechanical properties and microstructure of a Zn–Al–Cu–Mg alloy

Abstract The effect of Ti additions (0.01–0.20 wt.%) on the hardness, ultimate tensile strength, impact strength and creep properties of the gravity-cast Zn–Al–Cu–Mg alloy ZA-8 has been investigated. The Ti additions have no significant effect on the hardness. The ultimate tensile strength of the standard ZA-8 alloy has not been changed significantly with Ti additions up to 0.15 wt.% and then decreased with further increase in Ti content. The impact strength shows a maximum around 0.05–0.15 wt.% Ti. The lowest creep resistance is obtained at 0.01 wt.% Ti, and the highest value of creep resistance is reached for 0.20 wt.% Ti. Metallographic studies indicated that the addition of Ti has a profound effect on the microstructure. Also, Ti forms a complex-shaped intermetallic compound which was identified as TiZn15 by X-ray diffraction. It is suggested that the TiZn15 particles cause the increase in creep resistance and decrease in tensile strength.

Conventional sintering of diamond cutting tool used in natural stone cutting

Diamond Tools, used in natural stone cutting, is produced commonly by powder metallurgy with Spark Plasma Sintering (SPS) and/or Conventional Sintering (CS). Co is generally used as metal matrices because of their bonding strength and optimum wear rate. However, because of cobalt’s high prices, other alloying elements are also used to decrease the cost of diamond tools. Aim of this study is to compare mechanical, physical, microstructural properties of diamond cutting tools made of Co-Ni-Cu-Sn matrix, produced by Spark Plasma Sintering and Conventional Sintering. Spark Plasma Sintering performed at 850 °C and Conventional Sintering performed at various temperatures (between 950 and 1150 °C) and times (1 to 4 hours). Then various properties (density, hardness, compression strength) of Conventional Sintered and Spark Plasma Sintered tools were investigated and compared. The experimental results showed that SPS tools have much better properties than CS tools.

Numerical and Experimental Investigation of Friction Effect in Limiting Dome Height Test

In this study, the effect of friction in limiting dome height test was investigated numerically and experimentally. Ultra-low-carbon galvanized steel sheets were used as a test material. The thickness of the material was 1.2 mm. Limiting dome height tests were carried out by using three different lubricants, and the test was modeled with the finite-element method. Simulations were done using various friction coefficients to show the effect of friction on the limiting dome height test. It has been observed that necking/fracture area is decreasing and necking/fracture location moves toward the pole side of the material with the decline of the friction coefficient. Similar results were also obtained in the experiments.

Hot Extruded Carbon Nanotube Reinforced Magnesium Matrix Composites and its Microstructure, Mechanical and Corrosion Properties

Carbon nanotube (CNT) reinforced magnesium (Mg) matrix composite rod was successfully fabricated by mechanical ball milling followed by hot extrusion processes. CNTs used were multi-wall carbon nanotubes (MWCNTs). The starting Mg chips were ball-milled under argon atmosphere for 3 h to coat the surface of Mg chips with the pretreated MWCNTs. The CNT-coated Mg chips were then mixed with aluminum (Al) powder at the compositions of Mg-6 wt.% Al-x wt.% CNT (x = 0.5, 1, 2 and 4). The mixture was cold compacted and finally hot extruded.

The Effect of Matrix on the Mechanical Properties of Squeeze Cast Al - 50 % SiCp Composites

This study has been conducted to investigate the mechanical properties of aluminum matrix 50 vol.% SiC particle (SiCp) reinforced composites produced by a squeeze casting technique. Commercial 2618, 6082, and 7012 aluminum alloys were utilized as the matrix material. Composites were tested in as-cast and T6-tempered states. Mechanical properties of the composites were determined by hardness measurements and impact tests. As-cast composites exhibited lower hardness along with a better impact resistance than their T6-tempered states. After T6-tempering the hardness of 7012 matrix composite reached to a value of 324 HV2, which is comparable with the hardness of quenched and tempered steels.

An Investigation of Fretting Wear Behaviour of a Ternary (Zr,Hf)N Coating

In this study, the wear behaviors of ZrN and (Zr, 21wt.% Hf)N coatings, deposited on hardened AISI D2 cold work tool steel by a arc-physical vapor deposition (PVD) technique were examined by a fretting wear tester. Wear tests were conducted by rubbing Al2 O3 and steel balls on the surfaces of the coatings under dry sliding condition. Characterization tests showed that, the hardness and the surface roughness of the examined coatings were almost the same. However, addition of 21wt.% Hf to ZrN improved the adhesion between the coating and the substrate. Fretting wear tests conducted by rubbing both Al2 O3 and steels balls revealed that, addition of 21wt.% Hf achieved an increment in the wear resistance of the ZrN coating. Steel ball encouraged oxidative wear, while wear of the coatings by Al2 O3 ball progressed by coating removal.© 2005 ASME