مجله مواد نوین
سال سوم شماره 4 (پیاپی 12، تابستان 1392)

NiTiCu intermetallic compound with nanocrystalline structure was successfully synthesized through mechanical alloying and subsequent annealing process. The X-ray diffraction (XRD) analysis revealed that after 60 h milling of high purity elemental powders mixture of Ni، Ti and Cu via a planetary high energy ball milling، the Cu dissolved into B2 structure and NiTiCu phase was obtained. Annealing of as-milled powders at 1173 K for 15 min leads to formation of nanometric NiTiCu (B19'') phase، grain growth and release of internal strain. Structural characterization was examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results demonstrated that this route result in preparation compounds with suitable morphology and homogeneous structure. Formation of nanometric structure enhances thermoelasticity and shape memory behavior in this compound by narrowing the thermal hysteresis.

In the present research، the effects of continuous zirconia reinforcement and Mg content of the matrix alloy on the tribological properties of aluminum matrix composites produced via pressureless infiltration was investigated. The zirconia foam used as reinforcement was synthesized by replacement method according to the following steps: plunging polymeric (polyurethane) foam in to a ceramic slush، removing the additional slush and pyrolyzing and sintering at elevated temperature. The pure Al and Al alloys with2، 6 and 10wt% Mg content penetrated to the zirconia foam under nitrogen atmosphere. Specimens in the form of discs were thereby used for the wear test with a pin-on-disk apparatus using 52100 steel pins. The weight loss and wear rate of specimens were measured under 6. 5، 26 and 52 N loads and a sliding distance of 900 m. Sliding surface and debris of each specimen was examined by a Scanning Electron Microscope (SEM). Results indicated that reinforced materials have better wear resistance in comparison with unreinforced matrix alloys. Under the low load the weight loss was low due to the formation of protective MML (mechanically mixed layer) layer on the surface which prevented the direct contact of metallic and steel surfaces. Under the high load، the oxide layer was not stable and severe wear occurred due to the adhesive wear mechanism. Increasing the Mg content of the alloys decreased the wear rate because of the better wetting of the matrix alloys and the stronger bonding in the matrix-reinforcement interface.

In this work the effect of preheat and post weld heat treatment on the properties of AISI 4140 steel was evaluated. TheExperements were carred out on three different conditions: 1-without preheat and without post weld heat treatment. 2-with preheat and without post weld heat treatment. 3-with pre heat and with post weld heat treatment. Welding process was SMAW. The effect of preheat and post weld heat treatment on mechanical properties was evaluated by mechanical testes such as impact test، tensile test، hardness test and bend test. The changing of microstructure was studied by optical microscope. With preheat and post weld heat treatment the mechanical properties of weld area should be controlled. The post weld heat treatment can improve the fracture toughness.

In present study effects of Zn content on microstructural changes، physical and mechanical properties of prealloyed brass sintered powder were investigated. Two kinds of brass prealloyed powder with composition of Cu-20Zn and Cu-28Zn were produced via water atomization technology، and compacted to obtain samples with green densities of 6. 63 and 6. 74 g/cm3، respectively. The Sintering process was carried out at 930 °C and 45 min in Ar atmosphere. According to obtained results of sintered density، the densification parameter of Cu-20Zn and Cu-28Zn samples were calculated 52. 6% and 5% respectively، which indicated more densification in Cu-20Zn. Moreover hardness and impact energy showed that mechanical properties changed by varying Zn content. Metallographic and fractographic studies showed that Zn caused the formation of spherical and coarser pores and dezincification in Cu-28Zn. It is concluded that by controlling of sintering parameters in the of brass alloys، which have higher Zn content، desired properties can be reached.

The barreling that occurs in compression test is very sensitive to frictional conditions which put it as a simple test method in determining friction factor. Moreover، knowing the effect of other parameters such as the material properties on barreling can increase the accuracy of the experiment in evaluating the friction condition. Therefore، in the present study، the effect of strain hardening exponent، n، strength coefficient، k، and yield stress، σ0، on barreling in uniaxial compression test are evaluated using Finite Element Method (FEM). For this purpose، the distributions of stress and strain obtained from FEM are considered.

Titanium dioxide and Hydroxyapatite were simultaneously added to plasma electrolyte nitrocarburizing bath of 316L stainless steel in order to improve the corrosion behavior of steel. Then the samples were placed in the electrolyte and biased with a negative voltage of 145 volt. Cross section and surface morphology were studied using a scanning electron microscope (SEM). The results of EDX and XRD analysis reveal the presence of Titanium، Calcium، Phosphorus، Nitrogen and Carbon. Corrosion behavior of the coating was investigated by tafel polarization tests in Ringer solution. The composite coating exhibits an improvement in corrosion behavior.

Elastomer nanocomposites based on natural rubber (NR) and ethylene propylene diene monomer (EPDM) reinforced with different content of modified nanoclay (cloisite ISA)، i. e. 1،3،5،7 wt% were produced using two roll - mill. Also to educated the effect of matrix composition on microstructure and mecanical properties of the nanocomposites. NR/EPDM ratio was varied (50/50، 75/25، 100/0، 0/100 and 25/75). X- ray diffraction was performed to evaluate the silicate layers. The results of XRD showed that the distance between silicate layers increased and the polymer chains peneterated in to the layers. TEM micrographs proved the formation of intercalated and exfoliated nanocomposites. Also the results showed that compression setting and heat distorsion of Elastomer nanocomposites promoted as nanoclay content added to the matrix. Increase in EDPM/NR ratio cansed to decrease tensile and tear strengths unlike compression setting of the nanocomposites. Furthermore addition of nanoclay and increasing EPDM content of matrix to increased the aging of Elastomer.

Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. Among these، accumulative roll bonding has been extensively used to produce multi-layered composites. In the present study، a new manufacturing process for Cu/Ni composites was developed by using Copper and Nickel sheets as starting materials. It was observed that as passes of ARB proceeded Nickel layers were necked and fractured. After seven ARB passes، a multi-layer Cu/Ni composite including homogeneously distributed fragmented Ni layers in the Cu matrix was achieved. Structure and mechanical properties of these composites were studied within different stages of ARB process. With increasing strain during ARB passes strength of these composites increased but elongation decreased. Also، scanning electron microscopy (SEM) was used to study the microstructure of the layers. Finally the magnetic behavior by magnetic device detector (VSM) was investigated and tensile tests were performed to investigate the mechanical behavior of ARB products.