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Effect of Annealing on Strain-Temperature Response under Constant Tensile Stress in Cold-Worked NiTi Thin Wire  [PDF]
Xiaojun Yan,Jan Van Humbeeck
Smart Materials Research , 2011, DOI: 10.1155/2011/160927
Abstract: The present paper aims to understand the influence of annealing on the strain-temperature response of a cold-worked NiTi wire under constant tensile stress. It was found that transformation behavior, stress-strain relationship, and strain-temperature response of the cold-worked NiTi wire are strongly affected by the annealing temperature. Large martensitic strains can be reached even though the applied stress is below the plateau stress of the martensite phase. At all stress levels transformation strain increases with increasing annealing temperature in the range of 350°–450°C and decreases with increasing annealing temperature in the range of 450°–650°C. The martensitic strain at lower stress levels exhibits the same tendency. At higher stress levels the martensitic strain increases with increasing annealing temperature. 1. Introduction Among many shape memory alloys (SMAs), NiTi has been widely used in many technological and engineering applications due to its excellent shape memory effect, superelasticity, high damping capacity, and others [1, 2]. Its remarkable properties result from a reversible martensitic phase transformation between austenite and martensite phases, which can be either stress induced or temperature driven. The transformation is sensitive to factors such as material composition, deformation processing, and heat treatments. Therefore, a mix of cold work followed by a specific annealing process has been comprehensively considered to optimize the physical and mechanical properties of a NiTi product and achieve shape memory and/or superelasticity. Significant efforts have been made to address the effects of heat treatment on transformation behavior [3–5], microstructure [6–8], recovery stress [9, 10], damping [11, 12], plateau stress and strain [13, 14], as well as lifetime of NiTi SMAs [15, 16]. To open new applications of NiTi SMAs, including smart structures, intelligent controllers, and memory devices, the understanding of strain and phase transformation behavior under constant applied stress is essential. In the present paper the influence of annealing on martensitic transformation and residual strains of cold-worked NiTi wire developed during cooling/heating under constant tensile stress has been investigated. 2. Experimental Procedure The experiments were performed on a commercial NiTi wire provided by SAES Getters (Italy) with a diameter of 0.076?mm and a normal composition of 50.2 at % Ni. As-received wires (35% cold-worked) with a length of 100?mm were annealed in an argon atmosphere for 10?min at 350°, 450°, 550°, and
Microstructural Evolution in Cold-Rolled Squeeze-Cast SiCw/Al Composites during Annealing
Microstructural Evolution in Cold-Rolled Squeeze-Cast SiC_w/Al Composites during Annealing

Wenlong ZHANG,Dezun WANG,Zhongkai YAO,Mingyuan GU,
Wenlong ZHANG
,Dezun WANG,Zhongka YAO,Mingyuan GU State Key Lab of MMCs,Shanghai Jiao Tong University Shanghai,China School of Materials Science and Engineering,Harbin Institute of Technology,P.O. Box,Harbin,China

材料科学技术学报 , 2004,
Abstract: A 15 vol. Pct SiCw/Al composite was fabricated by a squeeze cast route followed by hot extrusion in the extrusion ratio of 18:1 and cold rolling to 50%. Microstructural evolution in the cold rolled composite during annealing was studied using macrohardness measurement and transmission electron microscopy (TEM). It was found that, during cold rolling the plastic flow of the matrix was restricted by the whiskers around them along the rolling direction, which resulted in different microstructure from near whiskers to far away. The cold rolled composite exhibited different microstructural development on 1 h annealing at different temperatures. Under annealing at about 100℃, recovery reaction occurred obviously and the introduction of SiC whiskers resulted in enhanced recovery reaction. Under annealing above about 200℃, recrystallization (growth of nuclei by high-angle grain boundary migration) and extended recovery took place simultaneously. When annealing temperature was increased up to 500℃, recrystallization fully took place in the cold rolled microstructure. The starting temperature of recrystallization was about 200℃. Whiskers played a role in stimulating the nucleation of recrystallization.
Microstructural Characteristics of Underwater Shock Consolidated Aluminum Composites

材料科学技术学报 , 2003,
Abstract: Metal matrix composites (MMCs) offer extra strength and high temperature capabilities in comparison with unrein-forced metals. Aluminum composites possess higher stiffness, strength, fatigue properties and low weight advantages. Carbon fiber reinforced Al composites (Al-Cf) and silicon carbide particulate reinforced Al composites (AI-SiCp) were shock densified using axisymmetric assemblies for underwater explosions. Unidirectional planar shock waves were applied to obtain uniform consolidation of the composites. The energy generator was a high explosive of 6.9 km/s detonation velocity. Irregular morphological powders of Al were the base material. The reinforcement ratio was 15 Vol. pet for Al-Cf composites and 30 Vol. pet for AI-SiCp composites. The microstructural and the strength characteristics of the shock consolidated Al composites are reported.
The effect of alloy powder morphology on microstructural evolution of hot worked P/M FeAl  [PDF]
T. ?leboda,K. Doniec
Archives of Materials Science and Engineering , 2007,
Abstract: Purpose: This paper presents the results of the research focused on the influence of both the starting FeAl alloy powder particle characteristics and the thermomechanical processing parameters on the microstructural evolution of these materials.Design/methodology/approach: Fully-dense FeAl alloy powder compacts were tested in compression on servo-hydraulic Gleeble testing machine, at the temperature range of 700°C to 1100°C, and at strain rates of 0.1 s-1 and 10 s-1. After processing, the microstructure of each deformed specimen was examined using optical microscopy.Findings: Considerable strain rate sensitivity of the investigated alloy was observed, especially with reference to microstructural development. The use of alloy powders in thermomechanical processing of FeAl alloys can substantially enhance the possibility to control both the microstructure and mechanical behavior of these alloys.Research limitations/implications: The influence of starting FeAl alloy powder particle morphology and processing strain rate on the microstructural evolution of investigated alloy was discussed.Practical implications: The results of this research could be directly employed in the design of deformation schedules for the industrial processing of FeAl alloys.Originality/value: FeAl alloy powder morphology influences the thermomechanical processing of P/M FeAl alloys, what was proved in this paper.
Exogenous inoculation of pure aluminum structure  [PDF]
T. Wróbel,J. Szajnar
Archives of Foundry Engineering , 2011,
Abstract: In paper is presented problem concerning inoculation of pure aluminum 99,5% structure, which is realized mainly by intensification of liquid metal movement in mould. In aim of realization of forced movement during the crystallization of liquid metal was used rotateelectromagnetic field, which is generated by induction coil fed with frequency of supply current from 5 to 100Hz. Effect of structure refinement obtained by influence of electromagnetic field was compared with refinement obtained by use of traditional inoculation, which f[Hz] consists in introducing of additions in form of titanium and boron to metal bath.
Effect of High Pressure Annealing on Microstructure and Thermal Conductivity of Aluminum Nitride Ceramics  [PDF]
LI Xiao-Lei-1, 2 , LI De-You-3, WANG Li-YIng-1, LI Chang-Sheng-1, SU Tai-Chao-1, MA Hong-An-2, JIA Xiao-Feng-1, 2
无机材料学报 , 2010, DOI: 10.3724/sp.j.1077.2010.00537
Abstract: The thermal annealing is an effective means of structural adjustment and performance improvement for AlN ceramics. AlN ceramics prepared at high pressure with Y2O3 as sintering additive, were annealed at high-pressure (5.0GPa) in a chinese cubic anvil ultra high-pressure and hightemperature device. The effects of high pressure annealing on microstructure and thermal conductivity of aluminum nitride ceramics were studied. The results show that the grain size of the AlN ceramics annealed at 5.0GPa and 970℃ for 2h is significantly increased, the actual crystal morphology is realistic and the second phases are almost present at the grain boundaries or triple pockets compared with the samples before annealing at high pressure. Its thermal conductivity reaches 173.2W/(m·K), which is 2.2 times of the samples without heat annealing at high pressure. However, while the annealing time is extended to the 4h, the pore size of AlN ceramics is increased with anti -densification. And the thermal conductivity of AlN ceramics annealed at 5.0GPa and 970℃ for 4h is reduced to 80.9W/(m·K).
Microstructural and Mechanical Characterization after Thermomechanical Treatments in 6063 Aluminum Alloy  [PDF]
Waldemar A. Monteiro, Iara M. Espósito, Ricardo B. Ferrari, Sidnei J. Buso
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.211206
Abstract: The aim of this work is the mechanical and microstructural characterization by optical and electron microscopy as well as microhardness of Al 6063 alloy after mechanical and thermal treatment. Al-Mg based alloys have special attention due to the lightness of the material and certain mechanical properties and recyclability. Such alloys produce good mechanical properties in moderate mechanical efforts (up to 700 MPa) and good resistance to the corrosion. Cold rolling steps (30%, 60% and 90% in area reduction) in Al 6063 alloy were employed for the recrystallization studies, followed by thermal treatment using four isothermal heating (423K, 523K, 623K and 723K) during 1800, 3600, 5400 and 7200s. The direct observation and chemical microanalysis were made in a JEOL200C and JEOL2010 transmission electron microscopes combined with mechanical characterization utilizing Vickers microhardness measurements. Normally classified as non-heat-treatable these alloys obtain higher strength either by strain-hardening or by solid solution. The nucleation of new grains is a non stability of the deformed microstructure, depending on subgrain size heterogeneities present as potential embryos in the deformed state adjacent to high local misorientation. The results indicate a significant effect of second-phase particles on recrystallization and how to control the resulting microstructure and texture by the use of particles. It may be a preferential growth in the early stage due to their local environment or a selection of certain orientations from among those produced by particles stimulated nucleation or a preferential nucleation at particles in favored sites such as grain boundaries.
Effect of vanadium carbide on commercial pure aluminum  [PDF]
Hua-ping Sun,Jun Wu,Tian Tang,Bo Fan,Zheng-hua Tang
- , 2017, DOI: https://doi.org/10.1007/s12613-017-1467-5
Abstract: The effect of vanadium carbide (VC) on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of VC and Al5Ti1B were also compared. The refined samples of commercial pure aluminum were examined using optical microscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results suggest that VC is a good refiner of commercial pure aluminum. The addition of only 0.3wt% VC can decrease the grain size of aluminum to 102 μm, whereas the casting temperature and holding time have little effect on the grain size. The refining efficiency of VC is better than that of Al5Ti1B. The VC particles in molten aluminum act as nuclei and the grain refinement of aluminum alloys by VC particles is achieved via heterogeneous nucleation.
Powder Metallurgical Fabrication and Microstructural Investigations of Aluminum/Steel Functionally Graded Material  [PDF]
Mahmoud M. Nemat-Alla, Moataz H. Ata, Mohamed R. Bayoumi, Wael Khair-Eldeen
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.212228
Abstract: Aluminum/steel electric transition joints (ETJs) are used in aluminum reduction cell for the purpose of welding aluminum rod and steel bracket components. Solid state welding process used for joining aluminum and steel at the electric transition joints have the drawbacks of cracking and separation at the interface surfaces. Cracking and separation at the electric transition joints are caused by the stress singularities that developed due to the mismatch in thermal and mechanical properties of each material. To overcome the drawback of electric transition joints, aluminum/steel functionally graded may be used as electric transition joints or proposed. Therefore manufacturing and investigation of aluminum/steel functionally graded materials fabricated by powder metallurgy process were carried out through the current work. Different samples with different layers of aluminum/steel functionally graded materials were compacted using steel die and punch at the same compacted pressure and sintered temperature. After investigating the different samples of aluminum/steel functionally graded materials under different fabrication conditions, the suitable fabrication regime was determined with the aid of microscopic observations.
On Nucleation Temperature of Pure Aluminum in Magnetic Fields
Chuanjun Li;Hui Yang;Zhongming Ren;Weili Ren;Yuqin Wu
PIER Letters , 2010, DOI: 10.2528/PIERL10041412
Abstract: Solidification of pure aluminum without and with a magnetic field has been investigated by differential thermal analysis (DTA). DTA curves showed that the nucleation temperature of pure aluminum was decreased as a magnetic field strength increased although its melting process was almost not influenced. The nucleation suppression could be attributed to the increase of the solid-liquid interfacial energy which might originate from more orderly arrangement of atoms on the solid-liquid interface upon applying a magnetic field.
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