Short Period Of Annealing Research Articles

High strength and toughness of Ti–6Al–4V sheets via cryorolling and short-period annealing

The trade-off between strength and toughness has always been a key problem hindering the application prospect of titanium alloys. In this study, Ti–6Al–4V titanium alloy was processed by cryorolling combined with short-period vacuum annealing to overcome the problem. Results show that after annealing at 973 K, its yield strength and ultimate tensile strength were as high as 1020 MPa and 1126 MPa, respectively, and the elongation reached 10.9%. The static toughness of Ti–6Al–4V titanium alloy reached more than 12,000 MPa·%, which is the highest value compared with the rolled other kinds of titanium alloys reported in recent years. During short-period annealing of cryorolled Ti–6Al–4V sheets, the pinning effect of fine β phase particles and the competition mechanism between α and β grains inhibited the coarsening of grains. Meanwhile, partial recrystallization and recovery make the combination of micro-grains and ultrafine-grains. The shear band structure was weakened after annealing, which provides more favorable conditions for homogeneous deformation before fracture, which contributed to the enhanced toughness. The methods adopted here are suitable for large-scale industrial manufacturing the high strength and toughness Ti–6Al–4V alloys and might be applied to other kinds of Ti alloys.

The mechanism of grain refinement and plasticity enhancement by an improved thermomechanical treatment of 7055 Al alloy

An improved double step hot rolling (DTR) processing was proposed to manufacture fine grained Al–Zn–Mg–Cu alloys based on pre-deformation, short-period annealing and final hot rolling. The DTR processing can produce high-quality rolling sheets with much finer recrystallized structures and significantly improved mechanical properties when compared with the conventional hot rolling (CTR). The main differences between the two TMTs (thermomechanical treatments) were investigated and the specific grain refining procedure of DTR was carefully characterized. The results show that the grain refinement is mainly proceeded via dislocation rearrangement and low angle grain boundaries transition, which can be attributed to the pinning effect of deformation induced precipitates (DIPs). Pre-deformation can accelerate the formation and spheroidization of fine DIPs which prohibit the migration of grain boundaries and the movement of dislocations. As a result, high density dislocation cells are formed and turn into polygon sub-grains after short-period intermediate annealing. During the final hot rolling, low angle grain boundaries gradually transferred into high angle grain boundaries which contributes to the final fine grained structures. The initiation and propagation of cracks were also delayed by grain refinement.

Impact of high temperature and short period annealing on SnS films deposited by E-beam evaporation

Thin films of SnS were deposited on Mo-substrate using electron beam evaporation at room temperature. As-deposited SnS films were annealed at a constant high temperaure of 860K for different short period of times, 1min, 3min, and 5min. The impact of heat treatment period on the physical properties of SnS films was investigated using appropriate characterization tools. XRD analysis revealed that the films were highly oriented along (111) plane with orthorhombic crystal structure. Surface morphology of as-deposited SnS films showed an identical leaf texture where as the annealed films showed large orthorombic slab shape grains in adidition to the leaf shape grains, which indicates the significance of short period annealing at high temperature. The transmission electron microscopy confirmed that those large orthorombic slabs had single-crystalline nature. The results emphasized that the short period annealing treatment at high temperature stimulated the growth of film towards the single crystallinity.

Improved thermo-mechanical processing for effective grain refinement of high-strength AA 7050 Al alloy

An improved thermo-mechanical processing (N-ITMT) was proposed for manufacturing fine-grained precipitation-hardening Al–Zn–Mg–Cu alloy based on cold rolling, short-period annealing and continuous rolling, and the corresponding microstructure evolution and mechanical properties were investigated. The N-ITMT processing can produce high-quality rolling sheets without edge cracks compared with the traditional RI-ITMT. The recrystallized fine-grained structures of N-ITMT samples are similar to those of RI-ITMT when the total reduction of N-ITMT reached 85% and exhibited high stability during long-period solution treatment. Moreover, the mechanical properties of N-ITMT samples are almost the same as those of RI-ITMT after peak aging (T6). It shows that cold deformation plus short-period annealing can acquire large quantities of MgZn2 particles with diameter ≥0.2μm, which can perform as nucleation sites for new recrystallized grains during subsequent solution treatment. It is greatly indicated that the static long-period overaging used by RI-ITMT can be replaced by cold deformation plus shot-period annealing, and the continuous rolling after short-period annealing would benefit the crack-free rolling sheets. Thus, N-ITMT would be a good alternative to RI-ITMT for efficient commercial production of different heat-treatable Al alloys to acquire fine grains.

Formation Mechanism of CuAlO2 Prepared by Rapid Thermal Annealing of Al2O3/Cu2O/Sapphire Sandwich Structure

Abstract Single-phase CuAlO2 films were successfully prepared by thin-film reaction of an Al2O3/Cu2O/sapphire sandwich structure. We found that the processing parameters, such as heating rate, holding temperature and annealing ambient, were all crucial to form CuAlO2 without second phases. Thermal annealing in pure oxygen ambient with a lower temperature ramp rate might result in the formation of CuAl2O4 in addition to CuAlO2, since part of Cu2O was oxidized to form CuO and caused the change in reaction path, i.e. CuO + Al2O3 → CuAl2O4. Typical annealing conditions successful to prepare single-phase CuAlO2 would be to heat the sample with a temperature rampt rate higher than 7.3 °C/sec and hold the temperature at 1100 °C in air ambient. The formation mechanism of CuAlO2 has also been studied by interrupting the reaction after a short period of annealing. TEM observations showed that the top Al2O3 layer with amorphous structure reacted immediately with Cu2O to form CuAlO2 in the early stage and then the remaining Cu2O reacted with the sapphire substrate.

Supramolecular morphology of two-step melt-spun poly(dioxanone) fibers

Structure of poly(dioxanone) (PPDX) fibers produced through a two-step melt-spinning process with an additional short-period annealing above the melting temperature of PPDX was investigated and the effect of annealing on the degradation behavior was discussed. The morphological study carried out by etching the fibers using a phosphate or permanganate solution suggested that the fibers take a skin–core structure, and both the skin layer and the core region consist of a bundle of microfibrils. The micro-beam X-ray diffraction analysis revealed that the short-period annealing in the production process only slightly promotes the crystallization in the skin layer but contributes to increasing the packing of amorphous chains near the skin, which seems to be the controlling factor of the hydrolytic degradation behavior of the fibers.

Silicon nanoparticle synthesis by short-period thermal anneals at atmospheric pressure in argon

Silicon nanoparticles have been studied for a wide variety of applications including nanoelectronic, photovoltaic, and optoelectronic devices. In this work, silicon nanoparticles were synthesized by short-period annealing of silicon-on-insulator substrates to temperatures ranging between 600 and 900 °C in argon gas at atmospheric pressure. Two different top silicon layers were deposited by ion-beam sputtering onto oxidized substrates. The thinner 6 nm top layer samples were annealed to temperatures for 30 s periods while thicker 15 nm top layer samples were annealed for 60 s periods. For both sets of samples, nanoparticles were observed to form at all the anneal temperatures through imaging by AFM. One long-period UHV anneal study, with 30-min anneal times, observed nanoparticle formation at temperatures similar to the current work while another similar long-period UHV anneal reported nanoparticle formation only above well-defined formation temperatures that depended upon the starting top layer thickness. In the current work, the average nanoparticle radius was found to increase both with the final anneal temperature and anneal period. For the highest anneal temperatures of the 6 nm top layer samples, a changing surface topography indicated that the thinner Si source layer was becoming depleted and the nanoparticle formation process was nearing completion. No such changes were observed for the thicker 15 nm samples at the same temperatures.

Fabrication of interconnected microporous biomaterials with high hydroxyapatite nanoparticle loading

Hydroxyapatite (HA) is known to promote osteogenicity and enhance the mechanical properties of biopolymers. However, incorporating a large amount of HA into a porous biopolymer still remains a challenge. In the present work, a new method was developed to produce interconnected microporous poly(glycolic-co-lactic acid) (PLGA) with high HA nanoparticle loading. First, a ternary blend comprising PLGA/PS (polystyrene)/HA (40/40/20 wt%) was prepared by melt blending under conditions for formation of a co-continuous phase structure. Next, a dynamic annealing stage under small-strain oscillation was applied to the blend to facilitate nanoparticle redistribution. Finally, the PS phase was sacrificially extracted, leaving a porous matrix. The results from different characterizations suggested that the applied small-strain oscillation substantially accelerated the migration of HA nanoparticles during annealing from the PS phase to the PLGA phase; nearly all HA particles were uniformly presented in the PLGA phase after a short period of annealing. After dissolution of the PS phase, a PLGA material with interconnected microporous structure was successfully produced, with a high HA loading above 30 wt%. The mechanisms beneath the experimental observations, particularly on the enhanced particle migration process, were discussed, and strategies for producing highly particle loaded biopolymers with interconnected microporous structures were proposed.

Intermetallic ordering and structure in Fe–Pd alloy nanoparticles

We report an in situ study of epitaxial island formation and alloying of FePd nanoparticles using reflection high-energy electron diffraction (RHEED) followed by ex situ atomic structure characterization. We used aberration corrected (AC) scanning transmission electron microscopy (STEM) with a high-angle annular dark field (HAADF) detector for the study of chemical ordering. The FePd nanoparticles were formed by sequential deposition of Pd and Fe onto NaCl substrates, which was then followed by heating to high temperatures to promote chemical ordering during a short period of annealing. We show that the epitaxial island growth and subsequent alloying of Fe into Pd can be clearly detected by RHEED. The high resolution and the atomic number (Z) contrast of AC HAADF-STEM allow a clear observation of nanometer-sized local chemical order in very small nanoparticles. The results revealed complex chemical structures at an intermediate stage of the ordering process with ordered regions of both L10 and L12 phases.

Diffusion behavior of Cu in Cu/electroless Ni and Cu/electroless Ni/Sn-37Pb solder joints in flip chip technology

For Cu pads used as under bump metallization (UBM) in flip chip technology, the diffusion behavior of Cu in the metallization layer is an important issue. In this study, isothermal interdiffusion experiments were performed at 240°C for different times with solid-solid and liquid-solid diffusion couples assembled in Cu/electroless-Ni (Ni-10 wt.% P) and Cu/electroless Ni (Ni-10 wt.% P)/ Sn-37Pb joints. The diffusion structure and concentration profiles were examined by scanning electron microscopy and electron microprobe analysis. The interdiffusion fluxes of Cu, Ni and P were calculated from the concentration profiles with the aid of Matano plane evaluation. The values of JCu, JNi, and JP decreased with increasing annealing time. The average effective interdiffusion coefficients on the order of 10−14 cm2/s were also evaluated within the diffusion zone. The amounts of Cu dissolved in the intermetallic compounds (IMCs) Ni3Sn4 and Ni3P that precipitate after annealing the Cu/electroless Ni/Sn-37Pb joints were about 0.25 at.% and 0.5 at.%, respectively. For the short period of annealing, it appears that the presence of electroless Ni (EN) with the Sn-Pb soldering reaction assisted the diffusion of Cu through the EN layer.

The Microstructure and Chemical State of W-Si-N Layers Formed in W / WN x / Poly ­ Si Systems during Postannealing

The microstructure and the chemical binding state of the interfacial layer in Si was investigated by using high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). After a short period of annealing, the Si-N layer and island-type precipitation formed between and poly Si as a result of the thermodynamic instability of films at 900°C. HR-TEM imaging and XPS analysis indicated that the island-type precipitation is composed of W, Si, and N. With increasing annealing time, the Si-N layer became thinner and the island-type precipitation became a continuous layer having an amorphous phase about 3 nm thick. However, above a critical annealing time, the interfacial layer thickness remained constant due to the formation of a stable W-Si-N layer. © 2004 The Electrochemical Society. All rights reserved.

Interfacial reactions between WNx and poly Si1−xGex films

The interfacial reactions at the WNx/poly Si interface and at the WNx/poly Si0.4Ge0.6 interface with the annealing conditions were investigated using high resolution transmission electron microscope (HR-TEM) and x-ray photoelectron spectroscopy (XPS). In the WNx/poly Si system, after a short period of annealing, an island-type precipitation was clearly observed under the Si–N layer, which was formed between WNx and poly Si. HR-TEM image and XPS analysis indicated that the island-type precipitation is composed of W, Si, and N. With increasing annealing time, the Si–N layer became thinner and island-type precipitation became continuous layer. However, in the WNx/poly Si0.4Ge0.6 system, the formation of precipitation was obviously prevented after annealing and the island-type precipitation remained between the WNx films and the poly Si1−xGex films in spite of long time annealing. These results are attributed to the fact that the Si in poly Si0.4Ge0.6 reacts preferentially with N, produced in the decomposition of WNx films, due to lower Gibbs free energy of the Si compound than the Ge compound and unreacted Ge atoms accumulate at the WNx/poly Si1−xGex interface.

Effect of annealing on PbTiO 3 thin-film quality improvement

The significant finding of this experiment was that annealing improves the quality of PbTiO 3 thin film. Moreover, following a short period of annealing, a high-quality perovskite-type PbTiO 3 thin film was constructed on a Pt/SiO 2/Si (100) substrate at a depositing temperature of 350°C, and supports IC fabrication processes to produce PbTiO 3 thin film devices. Under experimental conditions, the annealing process decreased the full width at half maximum (FWHM) of the perovskite phase (111) peak, bringing the 2 θ closer to the standard 2 θ of the PbTiO 3 perovskite phase (111) peak defined by the Joint Committee on Powder Diffraction Standards (JCPDS). The experiment herein involved good quality perovskite-phase PbTiO 3 thin film on a Pt/SiO 2/Si substrate deposited at 350°C and exposure to 5.93 W/cm 2 of RF power, which was then annealed at 700°C for 5 min and then allowed to return to room temperature for more than 15 min. The perovskite structure of the PbTiO 3 thin film constructed under the above conditions reached an FWHM (111) peak of 0.259° and a grain size of 341 Å.

Formation of GaAs Ohmic Contacts by Using Ion Beam Mixing

ABSTRACTIon beam mixing effects on metals and highly doped semiconductors on GaAs for formation of ohmic contacts have been studied. In this study, we have principally selected Pt as metal and Ge as semiconductors electrodes for GaAs. In Pt/GaAs system, we observed alloying phenomena induced by Si+, Ar+, Ge+ ion mixing effects. The amount of GaAs reacted with Pt was found to be proportional to the mass of the incident ions for constant dose. Concernig with the formation of ohmic contacts, only in the case of Si implantation through Pt films, the conversion from Schottky- to ohmic-contact was observed due to ion beam mixing effects. In Ge/GaAs system, we observad the solid state epitaxy for implanted Ge layer by the first annealing at 450°C in the two step annealing, but no activation of the implanted species. For activating implanted species, the second annealing at 800°C was effective. Concerning with the formation of ohmic contacts, we observed that the ohmic I-V characteristics for Ge/GaAs system could be obtainable when the following conditions were satisfied at the same time: 1) high dose implantation of As+ into Ge layer, 2) low dose implantation of Si into Ge/GaAs boundary and 3) relatively short period annealing in the second annealing step. From such study, it is concluded that ion beam mixing in conjunction with rapid annealing would be most promising for forming stable and reproducible ohmic contacts.

内部酸化したAu-Sn合金のメスバウアー効果

Mössbauer spectra of 119Sn nuclei have been measured for an Au-2.0 at%Sn alloy annealed in air at temperatures between 673 K and 1073 K. An internally oxidized phase was observed and determined to be SnO2. The internal oxidation process was discussed by the changes in Mössbauer spectra and their parameters. The results are summarized as follows:(1) The oxide phases formed during the internal oxidation process were found to be only SnO2, in which the 119Sn isomer shift ΔSI=0.02±0.04 mm/s relative to BaSnO3, and the magnitude of quadrupole splitting ΔEQ=0.49±0.02 mm/s.(2) By annealing in H2 gas flow for 1.8 ks at 1123 K, the oxide was completely reduced and Sn atoms dissolved into Au matrix.(3) The oxide phase was localized near the specimen surface within the depth of 0.8 μm. No preferential oxidation along grain boundary was observed.(4) During a short-period annealing, the formation of oxide proceeded with the internal oxidation, the rate of which was controlled by the diffusion of oxygen in Au matrix. Dependence of the oxidation process on the annealing temperature was of the Arrhenius type, and its activation energy was obtained to be 0.49±0.07 eV. After annealing at 973 K for 0.6 ks, transition from the internal to the external oxidation occurred, and the oxidation rate was sharply diminished.(5) Using Wagner’s theory for the internal oxidation, the sum of EOS, the heat of solution for oxygen in Au and EOD, the activation energy of diffusion for oxygen in Au, were determined. The obtained value of EOS+EOD, 1.2±0.1 eV, suggests that the mechanism of diffusion of oxygen in Au is the same as in Cu and Ag.