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Transformation Temperature (transformation + temperature)
Selected AbstractsCruciform fillet welded joint fatigue strength improvements by weld metal phase transformationsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2008PH. P. DARCIS ABSTRACT Arc welding typically generates residual tensile stresses in welded joints, leading to deteriorated fatigue performance of these joints. Volume expansion of the weld metal at high temperatures followed by contraction during cooling induces a local tensile residual stress state. A new type of welding wire capable of inducing a local compressive residual stress state by means of controlled martensitic transformation at relatively low temperatures has been studied, and the effects of the transformation temperature and residual stresses on fatigue strength are discussed. In this study, several LTTW (Low Transformation-Temperature Welding) wires have been developed and investigated to better characterize the effect of phase transformation on residual stress management in welded joints. Non-load-carrying cruciform fillet welded joints were prepared for measurement of residual stresses and fatigue testing. The measurement of the residual stresses of the three designed wires reveals a compressive residual stress near the weld toe. The fatigue properties of the new wires are enhanced compared to a commercially available wire. [source] Phase Evolution During Formation of SrAl2O4 from SrCO3 and ,-Al2O3/AlOOHJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Yu-Lun Chang Through the execution of experimental investigation, thermogravimetry, X-ray diffractometry, Fourier transform-infrared spectrometry, transmission electron microscopy, and energy-dispersive spectrometry, a variant reaction mechanism model was proposed for the solid-state reaction between SrCO3 and Al2O3/AlOOH for formation of SrAl2O4 material. The solid-state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO3 from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO3 and alumina. Conversely, at temperatures higher than that, the solid-state reaction is dominated by the diffusion of Al3+ ions into the SrCO3 lattice. In this mechanism, two metastable species, hexagonal SrCO3 and hexagonal SrAl2O4, were observed. The activation energies of SrCO3 decomposition in the solid-state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ,130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO3 decomposition decreases to 34 kJ/mol. [source] Crystallite and Grain-Size-Dependent Phase Transformations in Yttria-Doped ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Arun Suresh In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the "equilibrium" monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal , monoclinic phase transformation is examined more broadly across the yttria,zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal , monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases. [source] Properties of Ionic-Conducting ,-Bi2O3 Containing Mixed DopantsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2002Stephen D. Nunn ,-Bi2O3 compositions were prepared to evaluate the effect on properties of using mixed dopants. Baseline compositions containing 28 mol% of the alkaline-earth oxides CaO, SrO, or BaO were used for comparison. When the alkaline earths were combined in pairs to dope the bismuth oxide, the resulting properties were intermediate between the baseline end members. The data suggest that the transformation temperature for forming the high-conductivity ,1 phase can be varied continuously over a temperature range of about 565° to 750°C. Utilization of additional additives having different ionic size or valence charge compared with the alkaline earths resulted in no observed property changes that could be attributed to the additive alone. The most important variables influencing the conductivity level and phase transformation temperature of ,-Bi2O3 were the type and the amount of the alkaline-earth dopant in the composition. [source] Fabrication and properties of nano-ZnO/glass-fiber-reinforced polypropylene compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2010Yi-Hua Cui Polypropylene (PP) is widely used in many fields, such as automobiles, medical devices, office equipment, pipe, and architecture. However, its high brittle transformation temperature, low mechanical strength, dyeing properties, antistatic properties, and poor impact resistance, considerably limit its further applications. Nano-ZnO treated by KH550 coupling agent and glass fibers (GFs) were introduced in order to improve the mechanical performance and flowability of PP in this research. The crystallization behavior and microstructure of nano-ZnO/GFs/PP hybrid composites were analyzed by differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy. The effect of crystallization behavior on the mechanical properties of the nanocomposites was investigated and analyzed. The results indicated that nano-ZnO surface-coupled by KH550 could be uniformly dispersed in the PP matrix. The incorporation of nano-ZnO and GFs resulted in increases of the crystallization temperature and crystallization rate of PP and a decrease of the crystallization degree. The introduction of nano-ZnO and GFs also enhanced the tensile strength and impact toughness of the hybrid composites and improved their fluidity. Composites containing 2% of nano-ZnO and 40% of GFs possessed the optimum mechanical properties. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] The way composition affects martensitic transformation temperatures of Ni,Mn,Ga Heusler alloysPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2007X. Q. Chen Abstract A systematic substitution of Ge, Si, C and Co for Ga in the non-stoichiometric Ni,Mn,Ga alloys was performed. The relationship between the compositions of different elements including Ni, Mn, Ga, Ge, Si, C, Co, In and martensitic transformation temperature (Ms) was studied in detail for the present alloys together with data collected from a variety of sources. It is found that Ms is a sensitive parameter to the composition. The size factor and electron concentration are usually thought to be the way the composition influences Ms in the Ni,Mn,Ga alloys. Here, analyzing by linear regression, the electron density maybe a most appropriate parameter to describe the way the composition influences Ms when compared with size factor and electron concentration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modelling of Shape Memory Alloys and Experimental VerificationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003M. Schleich Prestrained shape memory alloys change their length when heated above their transformation temperature. This effect can be used to generate high forces in a small workspace, which has particular advantages in actuator design. The optimization and control of the shape memory actuator requires a comprehensive simulation of the material behavior. However, many of the existing models are limited to specific load cases or offer rough approximations only. A material model for shape memory alloys from Seelecke [1] is examined in this paper. This model describes the behavior of a shape memory wire, which is heated by electric current. It is implemented in a simulation program to investigate the actuator output and to improve the performance. Finally, the parameters of the simulation are adapted to experimental results. [source] Cast NiTi Shape-Memory Alloys,ADVANCED ENGINEERING MATERIALS, Issue 6 2005M. Ortega The purpose of this study is to build a fundamental understanding of the relationship between the structure and properties of cast nickel-titanium (NiTi). The structure of the cast material will be analyzed at various scales and will be related to the properties of the cast material such as transformation temperatures, stress-strain behavior, and recovery properties. This study demonstrates that cast NiTi can possess excellent shape-memory properties. [source] Magnetic Field-Induced Phase Transformation in NiMnCoIn Magnetic Shape-Memory Alloys,A New Actuation Mechanism with Large Work OutputADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Haluk E. Karaca Abstract Magnetic shape memory alloys (MSMAs) have recently been developed into a new class of functional materials that are capable of magnetic-field-induced actuation, mechanical sensing, magnetic refrigeration, and energy harvesting. In the present work, the magnetic &!hyphen;field-induced martensitic phase transformation (FIPT) in Ni45Mn36.5Co5In13.5 MSMA single crystals is characterized as a new actuation mechanism with potential to result in ultra-high actuation work outputs. The effects of the applied magnetic field on the transformation temperatures, magnetization, and superelastic response are investigated. The magnetic work output of NiMnCoIn alloys is determined to be more than 1,MJ m,3 per Tesla, which is one order of magnitude higher than that of the most well-known MSMAs, i.e., NiMnGa alloys. In addition, the work output of NiMnCoIn alloys is orientation independent, potentially surpassing the need for single crystals, and not limited by a saturation magnetic field, as opposed to NiMnGa MSMAs. Experimental and theoretical transformation strains and magnetostress levels are determined as a function of crystal orientation. It is found that [111]-oriented crystals can demonstrate a magnetostress level of 140,MPa T,1 with 1.2% axial strain under compression. These field-induced stress and strain levels are significantly higher than those from existing piezoelectric and magnetostrictive actuators. A thermodynamical framework is introduced to comprehend the magnetic energy contributions during FIPT. The present work reveals that the magnetic FIPT mechanism is promising for magnetic actuation applications and provides new opportunities for applications requiring high actuation work-outputs with relatively large actuation frequencies. One potential issue is the requirement for relatively high critical magnetic fields and field intervals (1.5,3,T) for the onset of FIPT and for reversible FIPT, respectively. [source] Phase transformation behaviour and bending properties of hybrid nickel,titanium rotary endodontic instrumentsINTERNATIONAL ENDODONTIC JOURNAL, Issue 4 2007Y. Hayashi Abstract Aim, To investigate the bending properties of hybrid rotary nickel,titanium endodontic instruments in relation to their transformation behaviour. Methodology, Four types of nickel,titanium rotary endodontic instruments with different cross-sectional shapes (triangular-based and rectangular-based) and different heat treatment conditions (super-elastic type and hybrid type with shape memory effect) were selected to investigate bending properties and phase transformation behaviour. Bending load of the instruments was measured in a cantilever-bending test at 37 °C with the maximum deflection of 3.0 mm. A commercial rotary instrument, ProFile (PF; Dentsply Maillefer, Ballaigues, Switzerland) was used as a reference for the bending test. Phase transformation temperatures were calculated from the diagrams obtained from differential scanning calorimetry. Data were analysed by anova and Scheffe's test. Results, The bending load values of the hybrid type that had undergone additional heat treatment at the tip were significantly lower (P < 0.05) than those of the super-elastic type with no additional heat treatment. The bending load values of rectangular-based cross-sectional shaped instruments were significantly lower (P < 0.05) than those of triangular-based cross-sectional shaped instruments. Phase transformation temperatures (Ms and Af points) of the hybrid type were significantly higher (P < 0.05) than the super-elastic type. The Mf and As points of the tip part were significantly higher (P < 0.05) than those of the whole part of the hybrid instrument. Conclusions, Additional heat treatment of hybrid nickel,titanium instruments may be effective in increasing the flexibility of nickel,titanium rotary instruments. [source] Physical and mechanical characterization and the influence of cyclic loading on the behaviour of nickel-titanium wires employed in the manufacture of rotary endodontic instrumentsINTERNATIONAL ENDODONTIC JOURNAL, Issue 11 2005M. G. A. Bahia Abstract Aim, To analyse the influence of cyclic loading on the mechanical behaviour of nickel-titanium (NiTi) wires employed in the manufacture of ProFile rotary endodontic instruments. Methodology, Nickel-titanium wires, 1.2 mm in diameter, taken from the production line of ProFile rotary endodontic instruments before the final machining step, were tensile-tested to rupture in the as-received condition and after 100 load,unload cycles in the superelastic plateau (4% elongation). The wires were characterized by X-ray energy-dispersive spectroscopy, X-ray diffraction and by differential scanning calorimetry and compared with new size 30, .06 taper ProFile instruments. The fracture surfaces of the wires were observed by scanning electron microscopy. Results, The mechanical properties of the as-received wires, their chemical composition, the phases present and their transformation temperatures were consistent with their final application. Only small changes, which decreased after the first few cycles, took place in the mechanical properties of the cycled wires. The stress at maximum load and the plastic strain at breakage remained the same, while the critical stress for inducing the superelastic behaviour, which is related to the restoring force of the endodontic instruments, decreased by approximately 27%. Conclusions, The mechanical behaviour of the NiTi wires was modified slightly by cyclic tensile loading in the superelastic plateau. As the changes tended towards stabilization, the clinical use of rotary NiTi ProFile instruments does not compromise their superelastic properties until they fracture by fatigue or torsional overload, or are otherwise discarded. [source] Crystallite and Grain-Size-Dependent Phase Transformations in Yttria-Doped ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Arun Suresh In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the "equilibrium" monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal , monoclinic phase transformation is examined more broadly across the yttria,zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal , monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases. [source] The way composition affects martensitic transformation temperatures of Ni,Mn,Ga Heusler alloysPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2007X. Q. Chen Abstract A systematic substitution of Ge, Si, C and Co for Ga in the non-stoichiometric Ni,Mn,Ga alloys was performed. The relationship between the compositions of different elements including Ni, Mn, Ga, Ge, Si, C, Co, In and martensitic transformation temperature (Ms) was studied in detail for the present alloys together with data collected from a variety of sources. It is found that Ms is a sensitive parameter to the composition. The size factor and electron concentration are usually thought to be the way the composition influences Ms in the Ni,Mn,Ga alloys. Here, analyzing by linear regression, the electron density maybe a most appropriate parameter to describe the way the composition influences Ms when compared with size factor and electron concentration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||