Sharif Digital Repository

The hot workability of a wrought 49.8 Ni-50.2 Ti (at pct) alloy was assessed using the hot compression tests in temperature range of 700-1000°C, strain rate of 0.001-1s-1, and the total strain of 0.7. The constitutive equations of Arrhenius-type hyperbolic-sine function was used to describe the flow stress as a function of strain rate and temperature. The preferable regions for hot workability of the alloy were achieved at Z (Zener-Holloman parameter) values of about 109-1013 corresponding to the peak efficiency of 20-30% in the processing map. However, a narrow area in the processing map including the deformation temperature of 1000°C and strain rate of 1s-1 is inconsistent with the related... 

In the present work, high-energy mechanical alloying (MA) was employed to synthesize a nanostructured magnesium-based composite for hydrogen storage. The preparation of the composite material with composition of MgH2-5 at% (TiCr1.2Fe0.6) was performed by co-milling of commercial available MgH2 powder with the body-centered cubic (bcc) alloy either in the form of Ti-Cr-Fe powder mixture with the proper mass fraction (sample A) or prealloyed TiCr1.2Fe0.6 powder (sample B). The prealloyed powder with an average crystallite size of 14 nm and particle size of 384 nm was prepared by the mechanical alloying process. It is shown that the addition of the Ti-based bcc alloy to magnesium hydride yields... 

To improve the hydrogen kinetics of magnesium hydride, TiCr 1.2Fe0.6 alloy was prepared by vacuum arc remelting (VAR) and the alloy was co-milled with MgH2 to process nanostructured MgH2-5 at.% TiCr1.2Fe0.6 powder. The hydrogen desorption properties of the composite powder were studied and compared with pure magnesium hydride. X-ray diffraction (XRD) analysis showed that the composite powder prepared by VAR/mechanical alloying (MA) procedure consisted of β-MgH2, γ-MgH2, bcc Ti-Cr-Fe alloy, and small amount of MgO. The average size of particles and their grain structure after 4 h MA were determined by a laser particle size analyzer and XRD method and found to be 194 nm and 11 nm,... 

A fine-grained Al-Mg/Al3Ti nanocomposite was fabricated by friction stir processing (FSP) of an aluminum-magnesium (AA5052) alloy with pre-placed titanium powder in the stirred zone. Microstructural evolutions and formation of intermetallic phases were analyzed by optical and electron microscopic techniques across the thickness section of the processed sheets. The microstructure of the nanocomposite consisted of a fine-grained aluminum matrix (1.5 μm), un-reacted titanium particles (<40 μm) and reinforcement particles of Al3Ti (<100 nm) and Mg2Si (<100 nm). Detailed microstructural analysis indicated solid-state interfacial reactions between the aluminum... 

Friction stir welding (FSW) parameters, such as tool material, tool geometry, tilt angle, tool rotational speed, welding speed, and axial force play a major role in the weld quality of titanium alloys. Because of excessive erosion, tool material and geometry play the main roles in FSW of titanium alloys. Therefore, in the present work for the first time, tool material and geometry, tool tilt angle, cooling system and shielding gas effects on macrostructure, microstructure, and mechanical properties of pure titanium weld joint were investigated. Result of this research shows that Ti can be joined by the FSW, using a tool with a shoulder made of tungsten (W) and simple pin made of tungsten... 

The present paper deals with different effects of homogenization time and cooling environment on Ni-42.5wt%Ti-7.5wt%Cu alloy. The alloy was prepared by vacuum arc melting. Afterwards, three homogenization times (half, one and two hour) and three cooling environments (water, air and furnace) at 1373 K were selected. Optical and Scanning Electron Microscopic methods, EDX, DSC and hardness tests have been used to evaluate the microstructure, transformation temperatures and hardness. Results indicate that specimens that were cooled in air are super-saturated. Also, the microstructure from furnace cooling has many disparities with the other cooling environments' microstructure and two types of... 

Abstract: Nickel–titanium (NiTi) nanoparticles are ultrafine smart materials manifesting shape memory effect at very small scales. We have produced NiTi nanoparticles surrounded by an amorphous carbon shell using an innovative spark discharge system. The resulting nanoparticles were studied using various characterization methods to systematically study their size, morphology, size distribution, composition, structure, and thermal behavior. Field-emission scanning electron microscopy and dynamic light-scattering results indicated that the average size of the produced nanoparticles was about 13 nm. High-resolution transmission electron microscopy, energy-dispersive spectroscopy (EDS), and... 

The demands for high-performance biomaterials are driving the development of new metallic alloys with improved mechanical and biological responses. In this study, a nanocrystalline Ti-Cu intermetallic alloy was prepared by a powder metallurgy route, and its application as an orthopedic material was evaluated by the microstructural, mechanical, corrosion, antibacterial, cytotoxicity and osseointegration examinations. Microstructural characterization revealed the formation of TiCu and Ti2Cu3 as major phases with 23 nm grain size in the structure of the alloy. The synthesized alloy exhibited ultra-high hardness of 10 GPa, acceptable toughness of 8.14 MPam1/2, a ∼98 % anti-bacterial rate against... 

Ti64/CaP nanocomposite powder was fabricated and characterized for use in powder-bed 3D printing. The microstructure and phase composition, morphology, particle size distribution, sphericity, flow behavior and dispersion of the as-fabricated particles on the building plate of the 3D printer were investigated. The results confirmed a uniform distribution of nanostructured calcium phosphate particles on the surface of primary Ti64 ones. Calcium phosphate appears as an octa-calcium phosphate phase. The morphology of the particles was shown as spherical, and their sphericity was better than the as-received Ti64 particles. The particle size distribution of nanocomposite powder indicated a smaller... 

Bipolar Plates (BPPs) are the most crucial component of the Polymer Electrolyte Membrane (PEM) fuel cell system. To improve fuel cell stack performance and lifetime, corrosion resistance and Interfacial Contact Resistance (ICR) enhancement are two essential factors for metallic BPPs. One of the most effective methods to achieve this purpose is adding a thin solid film of conductive coating on the surfaces of these plates. In the present study, 410 Stainless Steel (SS) was selected as a metallic bipolar plate. The coating process was performed using titanium nitride and chromium nitride by the Cathodic Arc Evaporation (CAE) method. The main focus of this study was to select the best coating... 

We produced bifurcated bone-like shape memory implant (BL-SMI) with desirable tooth-root fixation capability by compact-sintering of TiH2–Ni-urea mixture. The primary constituents of the porous product were Ni and Ti. We could adjust the pores' shape, size, and interconnectivity for favorite bone ingrowth by using urea as a space holder. Without urea, we obtained an average porosity of 0.30, and a mean void size of 100 μm. With 70 vol % urea, we got 62% interconnected pores of 400 μm average size. Aging allowed us to tune the austenite-martensite transformation temperatures towards the needed body tissue arouse. Differential scanning calorimetry measured the transformation temperatures.... 

The most common reasons for hard-tissue implant failure are structural loosening and prosthetic infections. Hence, in this study, to overcome the first problem, different bioinspired coatings, including dual acid-etched, anodic TiO2 nanotubes array, anodic hierarchical titanium oxide (HO), micro- and nanostructured hydroxyapatite (HA) layers, and HA/chitosan (HA/CS) nanocomposite, were applied to the titanium alloy surfaces. X-ray diffraction and FTIR analysis demonstrated that the in situ HA/CS nanocomposite formed successfully. The MTT assay showed that all samples had excellent cell viability, with cell proliferation rates ranging from 120% to 150% after 10 days. The HO coating...