The evaluation of hot-working characteristics of cobalt-based implant alloys

The hot-working characteristics of wrought Co-Ni-Cr-Mo implant alloy during ingot-to-billet conversion were evaluated using a Gleeble-2000A simulator. The hot tensile test at 700–1 320 °C was used to determine the optimum hot-working parameters at a strain rate equivalent to that of conventional press forging to ensure acceptable hot workability. Hot ductility and deformation resistance as a function of temperature can be clearly established. The fracture surfaces of the tensile specimens were examined to correlate them with the hot tensile ductility values at various temperatures. The poor ductility at temperatures above 1300 °C was attributed to the incipient melting of grain boundaries. The effect of temperature and strain rate on the flow-stress behaviour and microstructures were investigated by uniaxial compression testing in the temperature range 900–1200 °C and strain rate, , range of 0.01–10s^–1. The strain-hardening and steady-state behaviour were described from the measured true stress-true strain curves.     

Possible ways of enhancing high temperature ductility in CuO doped cubic zirconia (8Y–CSZ)

Abstract

The effect of initial density and rapid prestraining on superplastic ductility of 1 wt-%CuO doped cubic zirconia (8Y–CSZ) was investigated. To obtain a range of initial densities, the tensile test specimens were slip cast to net shape and pressureless sintered over a range of temperatures in air. The specimens were then superplastically tested at a temperature of 1500 K and at a constant strain rate of 1×10^-4 s^-1. The results showed that specimens with low initial densities had lower flow stresses and higher superplastic elongations to failure than higher density specimens. The reasons for the ductility change were discussed with reference to the presence of porosity and grain growth. For the prestraining test, a specimen with an initial density of 95% was prestrained to 30% at a temperature of 1550 K and at a prestrain rate ? · ₁ of 1×10^-3 s^-1, followed by elongation to failure at a slower test strain rate ? · ₂ of 1×10^-4 s^-1. It was seen that prestraining at the above test conditions considerably improved superplastic ductility. The reasons for this ductility enhancement were explained in terms of suppression of grain growth.     

High-strain-rate superplasticity in oxide ceramics

Factors limiting the strain rate of superplastic deformation in ceramic materials are discussed on the basis of existing models and experimental results concerning high-temperature plastic deformation, intergranular cavitation and dynamic grain growth. From the discussion, it is indicated that simultaneously fulfilling the following conditions is essential for attaining high-strain-rate superplasticity (HSRS) in ceramic materials: reduction in the initial grain size, enhanced diffusivity, suppressed dynamic grain growth, a homogeneous microstructure and a reduced number of residual defects. In the light of these conditions, explanations are given for HSRS attained in earlier studies on some oxide materials. It is also shown that HSRS can be intentionally attained in doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and composites synthesized from ZrO₂, Al₂O₃ and MgO₂; the tensile ductility of these composites reached 300–2500% at a strain rate of 0.01–1.0 s⁻¹. The postdeformation microstructure indicates that some secondary phases may suppress cavitation damage and thereby enhance HSRS.     

Cavitation and fracture of mechanically alloyed aluminium at high homologous temperatures

The tensile behaviour of mechanically alloyed (dispersion strengthened) IN90211 was characterized at strain rates between 0.0001 and 340 sec^–1 at temperatures between 425 and 475 ° C, At strain rates above 0.1 sec^–1, superplastic elongations were obtained (maximum elongation 525% at 475 ° C, 2.5sec^–1. Large elongations were possible due to the lack of cavitation, even though the strain-rate sensitivity was lower (m 0.25) than usually found in superplasticity. Cavitation was precluded by the morphology of the platelet-shaped grains in which low-angle subgrain boundaries were predominantly perpendicular to the tensile axis. Grain-boundary sliding was observed along high-angle grain boundaries which were generally parallel to the tensile axis. At the high homologous testing temperatures (0.76 to 0.81), concurrent grain-boundary sliding and lattice slip was made possible by the rapid lattice diffusivity and easy climb of lattice dislocations over dispersions in the matrix and grain boundaries.     

Effect of superplastic deformation on the grain size and tensile properties of Al-6.2Zn-2.5Mg-1.7Cu (7010) alloy sheet

An Al-Zn-Mg alloy (7010) was cold-rolled and annealed to produce a small recrystallized grain size, and superplastically deformed in the temperature range 475 to 520° C at strain rates to 2.8×10^–3 sec^–1. At 500° C and sec^–1 superplastic elongations up to 350% were obtained, but above about 60% elongation the residual room-temperature tensile properties after heat treatment decreased due to increasing grain-boundary cavitation. Grain growth rates were increased by superplastic strain.     

Poly(3-nonylthiophene-co-methylthiophene)s: New soluble conductive copolymers

New conductive soluble copolymers of 3-nonylthiophene (3NT) and 3-methylthiophene (3MT) were chemically synthetized using FeCl₃ in chloroform solution as a catalyst at room temperature and a N₂ atmosphere. The structural properties of the undoped and iodine doped 3NT-co-3MT have been studied by UV-Vis, FTIR, 1H- and ¹³C-NMR, GPC, DSC, TGA, WAXD, magnetic susceptibility and charge transfer measurements. The results show that copolymers (3NT-co-3MT) have a random arrangement. These copolymers have good thermal stability dependent on the 3NT. 3MT content and low magnetic susceptibility (typical for compounds of this class) which decreases with increasing temperature. The conductivity of the iodine doped copolymer (3NT-co-3MT) (measured in the dark at room temperature) increases distinctly in comparison to the undoped samples (2–8×10^–9 Sm^–1).     

The effect of CuO on the grain growth of ZnO

The grain growth kinetics in the 1, 2, 3 and 4 wt.% CuO doped ZnO was studied using the simplified phenomenological grain growth kinetics equation Gⁿ – G₀ⁿ = K₀ t exp (– Q/RT) together with microstructure properties of the sintered samples. The grain growth exponent value (n) was found to be 3 for 1, 2 and 3 wt.% CuO doped ZnO and 5.5 for 4 wt.% CuO doped ZnO. The apparent activation energy was decreased with CuO doping up to 3 wt.% from 250 kJ/mol to 150 kJ/mol but it was not changed significantly (155 kJ/mol) by 4 wt.% CuO doping. CuO doping up to 3 wt.% promoted the grain growth of ZnO whereas 4 wt.% CuO doping inhibited the grain growth of ZnO because of formation of Cu-rich secondary phase in the grain boundaries.     

Effect of atmosphere on superplastic deformation behavior in nanocrystalline liquid-phase-sintered silicon carbide with Al2O3-Y2O3 additions

Nanocrystalline -SiC with additions of 5.135 wt% Al₂O₃ and 3.867 wt% Y₂O₃ was subjected to tensile deformation in order to study its microstructural behavior under the dynamic process. The liquid-phase-sintered body had a relative density of >95% and an average grain size of 190 nm. Tension tests were conducted at initial strain rates range from 3 × 10^–4 to 2 × 10^–5 s^–1, in the temperature range 1873–2048 K, in both argon and N₂ atmospheres. Although grain-boundary liquids formed by the additions vaporized concurrently with the decomposition of SiC and grain growth, the maximum tensile elongation of 60% was achieved in argon. The grain-boundary amorphous phase formed a crystalline phase during testing in an N₂ atmosphere and fracture occurred at <8% elongation. Grain-boundary sliding was still the dominant mechanism for deformation.     

Mechanical properties of the Ni3(Si,Ti) alloys doped with carbon and beryllium

The Ni₃(Si, Ti) alloys doped with small amounts of carbon and beryllium were tensile tested in two environments, vacuum and air, over a wide range of test temperatures. The yield stresses of the carbon-doped alloys were almost identical to the undoped alloys while those of the beryllium-doped alloys were slightly higher than the undoped Ni₃(Si, Ti) alloys. The doping with carbon enhanced the elongation and ultimate tensile strength (UTS) whereas doping with beryllium reduced the elongation over the entire temperature range tested. The fracture patterns were primarily associated with the ductility behaviour. As the elongation (or UTS) increased, the fracture pattern changed from the intergranular to the transgranular fracture patterns. No environmental embrittlement of the ductility of the carbon-doped alloys was found at ambient temperatures but it was evident at elevated temperatures. Ductilities were reduced at high temperatures when the carbon-doped alloys were tensile tested in air. At high temperatures the environmental embrittlement observed is suggested to be due to the penetration of (free) oxygen into the grain boundaries causing the ductility loss in the carbondoped alloys.     

Properties of GaN grown on sapphire substrates

Epitaxial growth of GaN on sapphire substrates using an open-tube growth furnace has been carried out to study the effects of substrate orientation and transfer gas upon the properties of the layers. It has been found that for the (0001) substrates, surface appearance was virtually independent of carrier gas and of doping levels. For the (1 ¯102) substrates surface faceting was greatly reduced when He was used as a transfer gas as opposed to H₂. Faceting was also reduced when the GaN was doped with Zn and the best surfaces for the (1 ¯102) substrates were obtained in a Zn-doped run using He as the transfer gas. The best sample in terms of electrical properties for the (1¯102) substrate had a mobility greater than 400 cm² V^–1 sec^–1 and a carrier concentration of about 2 × 10¹⁷ cm^–3. This sample was undoped and used He as the transfer gas. The best (0001) sample was also grown undoped with He as the transfer gas and had a mobility of 300cm²V^–1 sec^–1 and a carrier concentration of 1 × 10¹⁸ cm^–3.     

Superplastic properties of a TiAl based alloy with a duplex microstructure

The superplastic properties of a engineering TiAl based alloy with a duplex microstructure were investigated with respect to the effect of testing temperatures ranging from 950°C to 1075°C and strain rates ranging from 8 × 10^–5 s^–1 to 2 × 10^–3 s^–1. A maximum elongation of 467% was achieved at 1050°C and at a strain rate of 8 × 10^–5 s^–1. The apparent activation energy was calculated to be 345 kJ/mol. Also, the dependence of the strain rate sensitivity values on strain during superplastic deformation was examined through the jump strain rate tests, and microstructural analysis was performed after superplastic deformation. It is concluded that superplasticity of the alloy at relatively low temperature and relatively high strain rate results from dynamic recrystallization, and grain boundary sliding and associated accommodation mechanism is related to superplasticity at higher temperature and lower strain rate.     

Microstructure and superplasticity of Mg–Al–Ca electromagnetic casting alloys after hot extrusion

Microstructure and superplastic properties of the plates extruded from the Ca containing Mg alloy (1 wt.% Ca–AZ31) billets fabricated by electromagnetic casting (EMC) without and with electromagnetic stirring (EMS) were examined. The linear intercept grain sizes of the extruded materials were 3.7 μm and 2.1 μm, respectively. The material extruded from the EMC + EMS billet exhibited good superplasticity at low temperatures as well as at high strain rates, including the tensile elongations of 370% at 1 × 10⁻³ s⁻¹, −523 K and 550% at 1 × 10⁻² s⁻¹, −673 K. These values largely exceeded those of the AZ31 alloys with the similar grain sizes. The superior superplasticity of the extruded EMC + EMS billet could be attributed to fine grains and high grain stability at elevated temperatures by the presence of finely dispersed particles of thermally stable (Al,Mg)₂Ca phase. The constitutive equations were developed for describing the high-temperature deformation behavior of the fine-grained 1 wt.% Ca–AZ31 alloys with different grain sizes in wide range of temperature and strain rate.     

Synthesis,defect characterization and photocatalytic degradation efficiency of Tb doped CuO nanoparticles

Monoclinic undoped and Tb doped CuO are prepared by solution combustion method and annealed at different temperatures. The effect of annealing and doping on their structural and optical properties of CuO are examined using XRD, FTIR and DRS. The surface and lattice defects in CuO and Tb doped CuO is analyzed qualitatively and quantitatively using positron lifetime and Doppler broadening spectroscopy. The average positron lifetime and electron momentum (energy) S parameter increases owing to the number of vacancies in the CuO lattice upon doping and decreases with increasing temperature. The migration of vacancies from grain to grain boundary region is observed at 600 °C annealed samples. At 800 °C, the overall behavior of lifetime value denotes that the vacancy type defect is recovered, cluster vacancy and microvoids exists with reducing size. The photocatalytic performance of undoped and Tb doped CuO on degradation of methylene blue (MB) and methyl orange (MO) is investigated under visible light for two different lamp power and dye concentration. The influence of annealing temperature and dopant ion on the efficiency is also elaborated. Enhanced photocatalytic efficiency in Tb doped CuO is observed upon annealing. X-ray photoelectron spectroscopy (XPS) result indicates that the valence states of Cu, O and Tb ions exist at the surface of the particles. Brunauer–Emmett–Teller N₂ adsorption–desorption analyses were employed to characterize specific surface area and porosity of Tb doped CuO. The doped CuO with pore size of about ～34 nm have a surface area of 16–28 m²/g. The surface area effect plays an important role in the enhanced catalytic performance on Tb doped catalysts.     

Optical and electrical properties of soluble copolymers of pyrrole-thiophene-3-decylthiophene

Three novel soluble copolymers of pyrrole(P)-thiophene(T)-3-decylthiophene (D) at different molar ratio of comonomers 4 : 1 : 5, 1 : 4 : 5 and 1 : 1 : 2 have been synthesized. NMR, FTIR, UV, emission spectroscopy, GPC, DSC, TGA and conductivity measurements were used to characterize these copolymers. The dark electrical conductivity increases from 3–7 × 10^–6 S/m for undoped samples to 10^–1–10^–2 S/m for samples doped with 4% of iodine, and to 10–10² S/m for 16% of iodine in a form of I₃ ^–.     

High-temperature deformation and fracture behaviour of Cu-SiO2 bicrystals

Bicrystals of CU-SiO₂ dispersion-hardened alloys and of pure copper were tensile tested at various temperatures between 450 and 1050 K at a strain rate of 1.5 x 10^–4 sec^–1. In the case of pure copper bicrystals, elongation to fracture did not depend significantly on temperature and the fracture mode was invariably transgranular up to 850 K. On the other hand, the ductility of CU-SiO₂ bicrystals decreased with increase in temperature and the transition in the fracture mode from transgranular to intergranular occurred at around 450 K. SiO₂ particles on grain boundaries play an important role on intergranular fracture by suppressing grain-boundary sliding and also on the retardation of recrystallization during deformation. Two types of Cu-SiO₂ bicrystals having different crystal orientation relationships show quite different deformation and fracture behaviour. This can be explained in terms of the contribution of lattice dislocations to the grain-boundary sliding.     

Effect of cooling rate in overageing and other thermomechanical process parameters on grain refinement in an AA7475 aluminium alloy

Fine-grained AA7475 aluminium alloy sheets were produced in this study by a thermomechanical treatment involving solution anneal, overageing, rolling and recrystallization steps. It has been found that the cooling rate after the intermediate overageing treatment should be fast to obtain the finest grain size. The fast cooling rate ensured the presence of relatively large particles of MgZn₂ and some supersaturation prior to cold rolling. Generally, the final grain structure was heterogeneous, with bands of fine grains lying parallel to the rolling direction. In material rapidly cooled after overageing, bands of fine grains were also observed in the transverse direction and these bands were associated with shear bands formed during rolling. The fine-grained AA7475 alloy sheets with an average grain size of about 9 m showed large tensile elongations of about 800% when deformed at 516 °C and with an initial strain rate of 5×10^–4s^–1.     

Superplastic deformation of Al-Li-Cu-Mg alloy sheet

Al-2.5 Li-1.2 Cu-0.6 Mg-0.12 Zr (wt%) alloy sheet was cold-rolled, solution heat-treated for 20 min at 510° C, prestrained by 3% and superplastically deformed at 450 to 540° C at strain rates between 1×10^–4 and 2.8×10^–1 sec^–1. The maximum elongation obtained was 300%. Significant cavitation occurred above about 0.5 strain at a rate (void volume/unit strain) of 4% at 540° C and 6% at 500° C. The onset of cavitation coincided with a reduction in the room-temperature tensile properties after reheat-treatment. During annealing at 500 to 540° C, grain coarsening near the sheet surface was associated with magnesium and lithium depletion. Superplastic deformation produced a fine equiaxed microstructure by dynamic recrystallization.     

High-temperature deformation behaviour of YBa2Cu3O7−x

High-temperature compression tests were performed in air for YBa₂Cu₃O_7–x polycrystals with grain sizes of 3 and 7 m at various strain rates between 1.3×10^–5 and 4×10^–4s^–1 and at temperatures between 1136 and 1253 K. Steady state deformation appeared above 1203 K for both samples. A stress exponent of 1.3 and an activation energy of 150 kJ mol^–1 were evaluated. The compression tests and microstructural observations revealed that there was a difference in deformation mechanism above and below 1203 K. The dominant mechanism was diffusional creep associated with grain-boundary sliding above 1203 K, and dislocation glide accompanied with grain-boundary sliding below 1203 K. The growth of anisotropic grains and their preferred arrangement were enhanced by deformation.     

Recrystallization behaviour and electrical properties of germanium ion implanted polycrystalline silicon films

The recrystallization behaviour of undoped and phosphorus-doped polycrystalline silicon films amorphized by germanium ion implantation at doses ranging from 1 × 10¹⁵ to 1 × 10¹⁶cm^-2 are investigated, and the electrical properties of phosphorus-doped films after recrystallization are studied. The phosphorus doping concentration ranges from 3 × 10¹⁸ to 1 × 10²⁰cm^-3. It is found that the nucleation rate decreases for undoped films and increases for phosphorus-doped films with increasing germanium dose; the growth rates decrease for both doped and undoped films. The decrease in nucleation rate is caused by the increase in implantation damage. The decrease in growth rate is considered to be due to the increase in lattice strain. The grain size increases with germanium dose for undoped films, but decreases for phosphorus-doped films. The dependence of the electrical properties of the recrystallized films as a function of phosphorus doping concentration with different germanium doses can be explained in terms of the grain size, crystallinity and grain boundary barrier height.     

Enhancement of the diffusional creep of polycrystalline Al2O3 by simultaneous doping with manganese and titanium

The effect of simultaneous doping with manganese and titanium on diffusional creep was studied in dense, polycrystalline alumina over a range of grain sizes (4–80m) and temperatures (1175–1250° C). At a total dopant concentration of 0.32–0.37 cation %, diffusional creep rates were enhanced considerably such that the temperature at which cation mass transport was significant was suppressed by at least 200° C compared to that observed in undoped material. The Mn-Ti (and Cu-Ti) dopant couple was far more effective in enhancing creep rates and suppressing sintering temperatures than the Fe-Ti couple. The enhanced mass transport kinetics are believed to be caused by significant increases in both aluminium lattice and grain-boundary diffusion. When aluminium grain-boundary diffusion is enhanced by increasing the concentration of divalent impurity (Mn²⁺, Fe²⁺) or by creep testing at low temperatures, creep deformation is Newtonian viscous.