High Temperature Deformation Characteristics of Al-Zn-Mg Alloy Modified with CaO-Added Mg.

Hot torsion tests were performed on an Al-Zn-Mg alloy modified with CaO-added Mg to investigate the effects of the Mg additive on the high temperature deformation characteristics. Effective stress- strain curves and processing maps were established from the experimental results under a range of deformation conditions. The fracture strain of the CaO-added Al-Zn-Mg alloy was higher than that of the Al-Zn-Mg alloy. The CaO-added Al-Zn-Mg alloy did not show an instability region in the processing map but the commercial Al-Zn-Mg alloy exhibited adiabatic shear bands at low temperatures and at a high strain rate. The results shown in this study were attributed to the reduction of the second phase by the addition of CaO-added Mg.

Brazing Characteristics and Bonding Strength of Pure Titanium Joints Brazed with Low-Melting Temperature Zi-17Ti-22Ni Filler Metal.

The brazing characteristics and bonding strengths of pure titanium joints are evaluated for joints brazed with Zr-17Ti-22Ni filler. Vacuum brazing was conducted at temperatures between the melting temperatures of the filler metals and the beta-transition temperature of pure titanium at 3 MPa of pressure for 5 min. Fracturing of the pure titanium joint brazed at 1,093 K occurred before yielding during the tensile tests owing to the presence of a serious segregation region containing harder and more brittle [Ti, Zr]2Ni intermetallic compounds. In contrast, in pure titanium joints brazed at and above 1,113 K, fracturing occurred at the base metal. The yield strengths of the samples brazed at 1,113 K-1,133 K were estimated to be in the range of 320-350 MPa and the ultimate tensile strengths likewise ranged from 350 to 380 MPa. The strength of pure titanium brazed at 1,153 K decreased rapidly. The results of this study show that the optimum temperature to ensure good performance after the brazing of pure titanium with Zr-17Ti-22Ni as a filler metal ranges from 1,113 K to 1,133 K.

Microstructural and Mechanical Characteristics of A356 Alloys as a Function of Mn Content and Cast Thickness.

In this study, the changes in the microstructural characteristics and mechanical properties of A356 alloys as a function of Mn content and cast thickness were evaluated using structural analysis and tensile tests. Five different A356+x%Mn alloys were prepared by casting in molds of different thicknesses followed by solid solution treatment at 813 K for 195 min and aging treatment at 423 K for 120 min. It was confirmed that the secondary dendrite arm spacing (SDAS) increased with increasing thickness of the cast sample, whilst, for a given thickness, the addition of small amounts of Mn resulted in a decrease of the SDAS. Mn contents of 0.05-0.15% resulted in ~7-9% improvements in the spheroid ratio of the primary Si particles compared to that of the commercial A356 alloy. Further, the spheroid ratio of the primary Si particles obtained in the thin cast samples were higher than that obtained in the thick cast samples. In particular, the addition of small amounts of Mn was also effective in suppressing the formation of the needle-like beta Al-Fe-Si intermetallic compound. The yield and tensile strengths of the thinner cast samples were higher than those of the thicker cast samples. Finally, Mn contents of 0.05-0.15% resulted in enhanced yield and tensile strengths, but Mn content ≥0.1% resulted in decreased elongation.

Pore Characteristics of Lotus-Type Porous Cu-Fe and Cu-Cr Alloys Fabricated by Unidirectional Solidification.

Lotus-type porous Cu-Fe and Cu-Cr with long cylindrical pores was fabricated by centrifugal casting under hydrogen atmosphere and the effect of alloying elements on pore characteristics of lotus-type porous Cu was investigated. For the lotus type porous Cu-Fe alloy, the porosity slightly decreased and the average pore diameter slightly increased with increasing Fe content. For the lotus-type porous Cu-Cr alloy, the porosity sharply decreased and the average pore diameter drastically increased with an increase in the Cr content. From these results, it was found that the pore evolution and growth are affected by alloying element and this leads to the change in the pore characteristics of lotus-type porous Cu-Fe and Cu-Cr alloys.

Effect of the Spray Distance on the Properties of High Velocity Oxygen-Fuel (HVOF) Sprayed WC-12Co Coatings.

In this study influence of spray distance on the properties of WC-12Co coatings deposited by HVOF was investigated. WC-12Co coating was sprayed at spray distance of 300, 385 and 450 mm. From microstructure observation, it is confirmed that the porosity of coatings increases with increasing the spray distance. The X-ray diffraction patterns indicate that the coatings consist of pure WC, W, and Co as well as W2C and Co6W6C phases. The increase of the spray distance accelerated the decarburization of coatings. From micro hardness tests, it was found that the hardness and the fracture toughness decreased with increasing spray distance. These mechanical properties would be related with not only porosity but also the degree of decarburization.

Preparation and Properties of WC-Based Alloy Coatings with Controlled Co and Cr via High Velocity Oxy-Fuel Spray Technique.

WC based alloy coatings included different mass percent of Co and Cr have been synthesized on high carbon steel by using a facile high velocity oxy-fuel spray method. The mechanical nature of the coating films has been investigated by micro vickers hardness and fracture toughness. X-ray diffraction (XRD) and EDX analyses indicate that the three different samples (WC-10Co-4Cr, WC-17Co, and WC-12Co) consist of pure WC, W, Cr, and Co constituents as well as W2C and Co6W6C phases. The SEM and image analysis results show that WC-10Co-4Cr condition has higher porosity than those of WC-17Co, and WC-12Co coatings. WC-17Co coating showed the highest value in the hardness and fracture toughness test among three different samples. The obtained results revealed that the mechanical properties of WC based alloy coatings synthesized by a facile high velocity oxy-fuel spray method is very sensitive to Co content.

Hot Deformation Behavior of Hot-Extruded AA7175 Through Hot Torsion Tests.

The hot deformation behavior of hot-extruded AA7175 was investigated with flow curves and processing maps through hot torsion tests. The flow curves and the deformed microstructures revealed that dynamic recrystallization (DRX) occurred in the hot-extruded AA7175 during hot working. The failure strain was highest at medium temperature. This was mainly influenced by the dynamic precipitation of fine rod-shaped MgZn2. The processing map determined the optimal deformation condition for the alloy during hot working.

Effect of Zn on Pore Characteristics in Lotus-Type Porous Cu.

The effect of Zn on pore characteristics in lotus-type porous Cu alloy was investigated. The lotustype porous Cu-Zn alloys were fabricated with Zn content from 0.01 to 0.1 at% by the centrifugal casting method. The results demonstrated that the porosity was rarely affected by Zn content. However, the average pore diameter and pore number density of the lotus type porous Cu-Zn alloys were significantly affected by the Zn content. The average pore diameter decreased as the Zn content increased up to 0.01 at%, and then increased as the Zn content increased up to 0.1 at%. In contrast, the variations in the pore number density of the lotus-type porous Cu-Zn alloys showed the reversed tendency with respect to that of the average pore diameter. The increase in heterogeneous nucleation sites for pores attributed to the decreased average pore diameter and the increased pore number density.

Effects of Heat Treatment on Interfacial Behavior and Bonding Strength of Surface Activated Bonding Ti-Al Laminate.

The surface activated bonding (SAB) method generally has the advantage of high bonding strength, low contact resistance, and high microstructural stability at room temperature. In this study, Ti-Al laminates were produced by surface activated bonding with aluminum and titanium foils. Heat treatment was conducted at the temperature range from 200 to 550 °C in vacuum. The bonding strength Ti-Al laminates was measured by a peel test, and the interfacial characteristics were investigated microstructural observation. The results showed that the bonding strength was the highest with heat treatment at 400 °C, microstructure observation revealed that the bonding strength of the Ti-Al laminate was influenced by the interfacial characteristics.

Synthesis of nanoparticles using electrical explosion of Ni wire in Pt solution.

The structure, size and morphology of nanoparticles produced by electrical explosion of Ni wire in Pt(NH3)2(NO2)2 solution were investigated. TEM results showed the formation of Ni and Pt nanoparticles as a result of the procedure. Ni nanoparticles were formed by the explosion of the Ni wire due to the passage of high current, evaporation, ionization, and cooling in the liquid medium. Ni nanoparticles were near spherical and showed particle sizes ranging from a few nanometers up to 50 nm. Pt nanoparticles were possible formed by the dissolution of OH- in Pt(NH3)2(NO2)2 solution during the electrical explosion of the Ni wire resulting in a plasma reaction. The formed Pt nanoparticles were ellipsoidal and showed particle sizes ranging to less than 5 nm. The lattice parameter of the Pt nanoparticles almost corresponded to the standard values reported. The obtained results indicate that Pt nanoparticles can be formed from a Pt solution without a reducing agent by electrical explosion of a metallic wire resulting in a plasma reaction.

Microstructure and Mechanical Properties of Commercially Pure Ti/Steel Joint Brazed by Zr-Ti-Ni Amorphous Filler Metal.

In this study, the characteristics of commercially pure titanium (hereinafter referred as CP-Ti)/Steel joints, brazed with Zr-Ti-Ni amorphous filler metal were analyzed. The effects of brazing temperature and time on the microstructure and joining strength of the CP-Ti/Steel joints were investigated. It was observed that Ti diffused into stainless steel substrate formed a brittle reaction zone, which contained intermetallic compounds, such as τ (Ti5Cr7Fe17), (Fe, -Ni)Ti, and FeTi, observed at the joint interface. As the brazing temperature and time increased, the width of the reaction layer in the joint was observed to increase. To suppress the oxidation of the substrates, the experiment was conducted at a cooling and heating speed of 100 °C/min, under a vacuum of 5×10-5 torr. The joining strength was observed to be significantly affected by the brazing conditions, such as temperature and duration time. The shear strength test showed that the strength increased for 15 min and then sharply decreased. This was attributed to the formation of brittle intermetallic compounds, like (Fe, Ni)Ti. The joint brazed at 880 °C for 15 min showed the maximum joining strength, of 216 MPa.

Dislocation Structure in Hot Deformed Al-Zn-Mg Alloy by X-ray Line Profile Analysis.

The microstructure of extruded Cu-free Al-Zn-Mg alloy is studied. Hot torsion tests are performed on a Cu-free Al-Zn-Mg alloy to investigate the effect of large strain deformation on the dislocation behavior. The dislocation structure is characterized by X-ray diffraction profile analysis, and the effective stress-strain curves are obtained by hot torsion tests. The dislocation density at low deformation temperature is found to be higher than that at high deformation temperature. The dislocation density of the alloy increases gradually up to ε = 1 with increasing strain and does not change significantly during further deformation.

Effect of Radio Frequency Plasma Treatment on Evaporation Behavior and Characteristics of RuCr Alloy Powder.

The evaporation behavior and characteristics of jet milled RuCr alloy powders processed by radio-frequency (RF) plasma treatment were evaluated during this study. RF plasma treatment was found to be effective in eliminating internal pores and in manufacturing spherical powder. However, the RF plasma treatment resulted in the evaporation of Cr. The degree of evaporation of Cr was significantly affected by the powder feeding rate. As a result, it was found that controlling the torch power was more effective than controlling the powder feeding rate for obtaining desirable RuCr alloy powders.

Improved Sensing Behaviors in Reduced Graphene Oxide Functionalized with Ni(OH)2 Nanoparticles.

In this paper, we detail improvements in the sensing properties of reduced graphene oxide (RGO), which were achieved through functionalization. The functionalization process utilizes graphene oxide suspensions, generating nanoparticles on the RGO surface mainly comprised of Ni(OH)2 phase. Raman spectra indicate that functionalization increases the degree of disorder in RGOs. NO2 gas sensing tests reveal an approximate increase of 154% in the sensor response of the RGOs after functionalization. Possible mechanisms for improving sensing responses via functionalization are discussed. The enhancement is due to the spillover effect, to the increase of the sensor surface by the catalytic particles, to the reduction of RGO conduction volume through the generation of depletion region, and to the resistance modulation of the heterojunctions.

Fabrication of a high-performance hip prosthetic stem using ß Ti-33.6Nb-4Sn.

This study used severe cold rolling followed by cold swaging of ß Ti-33.6% Nb-4% Sn rods to form a characteristic fiber structure composed of stress-induced α″ martensite with <010> texture and a ß phase with <101> texture, resulting in a material with a low Young's modulus of 40GPa. The material's tensile strength of 1270MPa and fatigue strength of 850MPa were attained by heat treatment at 673K for 5h through fine α precipitation in the fiber structure. A new method of fabricating a high-performance hip prosthetic stem was investigated based on the low Young's modulus and high strength obtained. After fabricating the stem by cold rolling, cold swaging, cold die-forging and machining, its neck region was given higher strength through local heat treatment, while the low Young's modulus remained almost unchanged in a distal portion of the stem. When a stem tip in the distal part was heat treated at 423K, reverse αâ€³â†’ß transformation occurred and the tangent modulus decreased to less than 30GPa, accompanied by stress-induced ß→α″. It was concluded that the method presented herein provided a low Young's modulus of approximately 40GPa in the distal part and high fatigue strength of approximately 850MPa in the neck region of a high-performance hip prosthetic stem.

Effect of swaging on Young׳s modulus of ß Ti-33.6Nb-4Sn alloy.

The effect of swaging on the Young's modulus of ß Ti-33.6Nb-4Sn rods was investigated by X-ray diffraction, thermography, microstructural observations, deformation simulator analysis and cyclic tensile deformation. Stress-induced α″ martensite was stabilized by swaging, dependent on the diameter reduction rate during swaging. Thermography and deformation simulator analysis revealed that swaged rods were adiabatically heated, and consequently, stress-induced α″ underwent reverse transformation. Young's modulus, which was measured by the slope of the initial portion of the stress-strain curve, decreased from 56GPa in the hot-forged/quenched rod to 44GPa in the rapidly swaged rod with a high reduction rate and to 45GPa in the gradually swaged rod with a low reduction rate. The tangent modulus, which was measured by the slope of the tangent to any point on the stress-strain curve, decreased with strain even in the linear range of the stress-strain curve of the hot-forged/quenched rod and the rapidly swaged rod, while the tangent modulus remained unchanged for the gradually swaged rod. It was found that Young's moduli in swaged ß Ti-33.6Nb-4Sn rods were affected by stabilized α″ martensite. Low Young's modulus of 45GPa and high strength over 800MPa were obtained when the reverse transformation by adiabatic heating was suppressed and the stress-induced α″ was sufficiently stabilized by gradual swaging to a 75% reduction in cross section area.

Microstructure and properties of cross-roll rolled and heat treated metastable TiNbSn alloy.

A (Ti-35mass%Nb)-4mass%Sn alloy was cross-roll rolled with a reduction ratio of 70% in which the roll axes are tilted by ± 5 degrees away from the transverse direction of the rolled sample and then aged at 250 degrees C for 2 h. Cross-roll rolling was found to increase yield strength and Young's modulus, simultaneously. Yield strength was higher in cross-roll rolled than in conventionally rolled at same reduction ratio. Yield and tensile strength further increased by a low temperature ageing by ψ precipitation hardening and microstructure refinement. Yield and tensile strength of the aged 70% cross-roll rolled sample were higher than those of the aged 70% conventionally rolled one.

Mechanical properties and microstructures of ß Ti-25Nb-11Sn ternary alloy for biomedical applications.

The mechanical properties and microstructures of ß Ti-25%Nb-11%Sn ternary alloy rods were investigated for biomedical applications as a function of heat treatment temperature after swaging by an 86% reduction in cross-section area. An as-swaged rod consisting of a ß (bcc) single phase shows a low Young's modulus of 53 GPa, which is interpreted in terms of both the metastable composition of the ß alloy undergoing neither an athermal ω transformation nor a deformation-induced ω transformation and <110>texture development during swaging. Heat treatment at 673 K (400 °C) for 2h leads to a high strength of approximately 1330 MPa and a high spring-back ratio of yield stress to Young's modulus over 15×10(-3), with acceptable elongation. This high strength is attributable to needle-like α precipitates, which are identified by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high-resolution electron microscopy (HREM).

The bone tissue compatibility of a new Ti-Nb-Sn alloy with a low Young's modulus.

A Ti-Nb-Sn alloy was developed as a new ß-type titanium alloy which had a low Young's modulus and high strength. The Young's modulus of the Ti-Nb-Sn alloy was reduced to about 45 GPa by cold rolling, much closer to human cortical bone (10-30 GPa) than that of Ti-6Al-4V alloy (110 GPa) and other ß-type titanium alloys developed for biomedical applications. The tensile strength of the Ti-Nb-Sn alloy was increased to a level greater than that of Ti-6Al-4V alloy by heat treatment after severe cold rolling. In this study the cytotoxicity of Ti-25Nb-11Sn alloy was evaluated in direct contact cell culture tests using metal disks and the bone tissue compatibility - examined using metal rods inserted into the medullary canal of rabbit femurs. The remarkable findings were that: (1) there were no significant differences in the relative growth ratio and relative absorbance ratio between cells grown with the Ti-Nb-Sn alloy, Ti-6Al-4V alloy and CP-Ti in direct contact cell culture tests; (2) there were no significant differences in the load at failure between the Ti-Nb-Sn alloy and Ti-6Al-4V alloy in pull-out metal rods tests; (3) there were no significant differences in new bone formation around metal rods between the Ti-Nb-Sn alloy and Ti-6Al-4V alloy in histological evaluations. The new Ti-Nb-Sn alloy with an elasticity closer to that of human bone is thus considered to be bioinert while also having a high degree of bone compatibility similar to that of Ti-6Al-4V alloy.