Effect of Extrusion Pass on Microstructure and Transformation Temperature of NiTiNb Alloy

2014 ◽  
Vol 687-691 ◽  
pp. 4347-4350
Author(s):  
Jun Wei Liu ◽  
Zi Peng Ouyang ◽  
Shi Qiang Lu ◽  
Jian Bao Hou ◽  
Yuan Zhi Huang
Keyword(s):  
Free Energy ◽  
Interfacial Energy ◽  
Transformation Temperature ◽  
Energy Transformation ◽  
Transformation Temperatures ◽  
Chemical Free Energy

In this research, the Effect of extrusion pass on microstructure and transformation temperature of NiTiNb alloy was researched. The results shows that ECAP can efficiently break the hard and brittle (Ti, Nb)2Ni phase. At the same time, β-Nb phase particles were precipitated and grow up after ECAP process.Due to enhancement of interfacial energy, train energy and non-chemical free energy, transformation temperatures including: As, Af, Ms and Mf increases with extrusion pass.

In Situ Observation of Phase Transformations during Welding of Low Transformation Temperature Filler Material

2010 ◽  
Vol 638-642 ◽  
pp. 3769-3774 ◽  
Author(s):  
Arne Kromm ◽  
Thomas Kannengiesser ◽  
Jens Gibmeier
Keyword(s):  
Residual Stresses ◽  
Phase Transformations ◽  
Volume Change ◽  
Transformation Temperature ◽  
High Energy ◽  
Filler Materials ◽  
Transformation Temperatures ◽  
Welding Processes ◽  
Compressive Residual Stresses

Tensile residual stresses introduced by conventional welding processes diminish the crack resistance and the fatigue lifetime of welded components. In order to generate beneficial compressive residual stresses at the surface of a welded component, various post-weld treatment procedures are available, like shot peening, hammering, etc. These post-weld treatments are, however time and cost extensive. An attractive alternative is to generate compressive stresses over the complete weld joint in the course of the welding procedure by means of so-called Low Transformation Temperature (LTT) filler materials. The volume change induced by the transformation affects the residual stresses in the weld and its vicinity. LTT fillers exhibit a relatively low transformation temperature and a positive volume change, resulting in compressive residual stresses in the weld area. In-situ measurements of diffraction profiles during real welding experiments using Gas Tungsten Arc (GTA)-welding process were realized successfully for the first time. Transformation temperatures during heating and subsequent cooling of LTT welding material could be assessed by means of energy dispersive diffraction using high energy synchrotron radiation. The results show that the temperature of martensite start (Ms) is strongly dependent on the content of alloying elements. In addition the results indicate that different phase transformation temperatures are present depending on the welding depth. Additional determination of residual stresses allowed it to pull together time and temperature resolved phase transformations and the resulting phase specific residual stresses. It was shown, that for the evaluation of the residual stress state of LTT welds the coexisting martensitic and austenitic phases have to be taken into account when describing the global stress condition of the respective material in detail.

The Effects of Si on the Nucleation Kinetics of Ferrite in Dual Phase Steels

2007 ◽  
Vol 26-28 ◽  
pp. 1307-1310 ◽  
Author(s):  
Sang Hwan Lee ◽  
Kyung Jong Lee
Keyword(s):  
Free Energy ◽  
Interfacial Energy ◽  
Free Energy Change ◽  
Nucleation Theory ◽  
Energy Change ◽  
Classical Nucleation Theory ◽  
Nucleation Kinetics ◽  
Kinetics Of ◽  
Volume Free Energy Change ◽  
Thermodynamic Factors

It is generally accepted that Si promotes kinetics of polygonal ferrite due to thermodynamic factors such as Ae3 and maximum amount of ferrite formed. However, in this study, it was found that the difference between the measured rates of ferrite formation in C-Mn steel and Si added steel was much larger than that expected considering only thermodynamic factors. The classical nucleation theory with pillbox model was adopted to figure out what is the most controlling factor in formation of ferrite. The volume free energy change was calculated by use of the dilute solution model. The diffusivity of carbon (DC) was formulated as functions of C, Mn and Si by using experimental data. It was found that the volume free energy change was still predominant but the kinetic factors such as interfacial energy and the diffusivity of carbon by addition of Si were not negligible at lower undercooling. However, with increasing undercooling, the diffusivity of C was the most effective on the ferrite kinetics, though the ambiguity of treating interfacial energy was not yet clear.

Estimation of the System Free Energy of the Lath Martensite Phase in High Cr Ferritic Steels

2006 ◽  
Vol 15-17 ◽  
pp. 690-695 ◽  
Author(s):  
Tomonori Kunieda ◽  
Kensuke Akada ◽  
Yoshinori Murata ◽  
Toshiyuki Koyama ◽  
Masahiko Morinaga
Keyword(s):  
Free Energy ◽  
Ternary Alloy ◽  
Elastic Strain ◽  
Lath Martensite ◽  
Elastic Strain Energy ◽  
Martensite Phase ◽  
Interfacial Energies ◽  
Martensite Packet ◽  
Chemical Free Energy ◽  
Martensite Microstructure

The system free energy was estimated for the martensite phase of an Fe-Cr-C ternary alloy, 12Cr2W and 12Cr2W0.5Re steels. The system free energy of the martensite phase is defined as, Gsys = G0 + Estr + Esurf , where G0 is the chemical free energy, Esurf is the interfacial energy for the boundaries in the martensite microstructure, and Estr is the elastic strain energy due to the dislocations in the martensite phase. From the experimental results on SEM/EBSD, the total interfacial energies were estimated to be 0.83J/mol for the ternary alloy and 4.8J/mol for both 12Cr2W and 12Cr2W0.5Re steels in the as-quenched state. Also, the elastic strain energies were estimated to be 7.1J/mol for the ternary alloy, 9.6J/mol for 12Cr2W steel and 9.8J/mol for 12Cr2W0.5Re steel in the as-quenched state. So, the system free energy was about 7.9J/mol for ternary alloy. On the other hand, the system free energy was about 14.4J/mol for 12Cr2W steel and 14.6J/mol for 12Cr2W0.5Re steel. So, these microstructural energies operate as a driving force for the microstructure evolution, e.g., recovery of dislocations and the coarsening of the sub-structures such as martensite-packet, -block and -lath.

Two-Phase Microstructures Formed by Phase-Separation of Coherent Precipitates in Elastically Constrained Alloy Systems

2010 ◽  
Vol 638-642 ◽  
pp. 2215-2220 ◽  
Author(s):  
Minoru Doi
Keyword(s):  
Free Energy ◽  
Phase Separation ◽  
Surface Energy ◽  
Phase Region ◽  
Precipitate Phase ◽  
Two Phase ◽  
Phase Separations ◽  
Chemical Free Energy ◽  
Elastic Constraint ◽  
Alloy Systems

Coherent two-phase microstructures consisting of ordered precipitate and disordered matrix phases sometimes exhibit a phase-separation, which brings the split and/or the decelerated coarsening of precipitates. When the coherent two-phase microstructure of A1+L12 (+’) in Ni-base alloys are aged inside the two-phase region of A1+L12 , the L12 precipitate sometimes exhibit a phase-separation and A1 phase newly appears and grows in each L12 precipitate. Phase-separations of the same type to the above also take place due to ageing of coherent two-phase microstructures of A2+D03 and A2+B2 in Fe-base alloys: D03 and B2 precipitates sometimes exhibit phase-separations and A2 phase newly appears and grows in both precipitates. These types of phase-separation take place under the influence of chemical free energy. In the course of further ageing, the new disordered phases of A1 and A2 change their morphology in various ways depending on the elastic constraint: i.e. the morphology of new A1 or A2 phase is influenced by the elastic energies and the surface energy.

The role of chemical free energy and elastic strain in the nucleation of zirconium hydride

2013 ◽  
Vol 441 (1-3) ◽  
pp. 395-401 ◽  
Author(s):  
A.T.W. Barrow ◽  
C. Toffolon-Masclet ◽  
J. Almer ◽  
M.R. Daymond
Keyword(s):  
Free Energy ◽  
Elastic Strain ◽  
Zirconium Hydride ◽  
Chemical Free Energy

scholarly journals Measurements of to Temperatures of Supersaturated Si-As Alloys

1990 ◽  
Vol 205 ◽  
Author(s):  
Kwang-Ryeol Lee ◽  
Jeffrey A. West ◽  
Patrick M. Smith ◽  
M. J. Aziz ◽  
J. A. Knapp
Keyword(s):  
Free Energy ◽  
Pulsed Laser ◽  
Congruent Melting ◽  
Laser Melting ◽  
Concentration Region ◽  
Energy Functions ◽  
Congruent Melting Point ◽  
Liquid Phases ◽  
Chemical Free Energy ◽  
Beam Technique

AbstractThe congruent melting point, or To curve, of crystalline Si-As alloys has been measured in the range of 1.6 to 18.1 at. % arsenic by line source electron beam annealing. Alloys were created by ion implantation of As into 0.1mm Si-on-sapphire and crystallized by pulsed laser melting. To temperatures decrease from 1673±10K at 2.0 at.% As to 1516±30K at 18.1 at.% As. The results of these measurements are significantly higher than the previous results of studies using pulsed laser melting techniques. Advantages of the e-beam technique over previous techniques are discussed. Chemical free energy functions of the solid and liquid phases were calculated from existing thermodynamic data. The calculated To curve agrees with the measured values only in low concentration region (less than 8 at.%).

On the Chemical Free Energy of the Electrical Double Layer

Langmuir ◽  
2003 ◽  
Vol 19 (4) ◽  
pp. 1114-1120 ◽  
Author(s):  
Marian Manciu ◽  
Eli Ruckenstein
Keyword(s):  
Free Energy ◽  
Double Layer ◽  
Electrical Double Layer ◽  
Chemical Free Energy

SHS Processing of NiTi-Nb Smart Alloys

2011 ◽  
Vol 672 ◽  
pp. 175-178
Author(s):  
Radu Liviu Orban ◽  
Mariana Lucaci ◽  
Dana Salomie ◽  
Nicolaie Jumate ◽  
Liviu Brânduşan
Keyword(s):  
Free Energy ◽  
Cost Effective ◽  
Powder Mixtures ◽  
Transformation Temperatures ◽  
High Affinity ◽  
Free Energy Of Formation ◽  
Nb Content ◽  
The Common ◽  
Nb Additions ◽  
Energy Of Formation

Nb additions to NiTi smart alloys are known to lead to the PTT-hysteresis broadening and transformation temperatures raising – required in numerous applications. As Nb has a high affinity for oxygen, NiTi-Nb alloys processing by powder metallurgy, via SHS, from elemental Ni-Ti-Nb powder mixtures, seems to be more advantageous and cost-effective than by classical one. However, its application encounters difficulties determined by the NiTi higher Gibbs Free Energy of Formation than of Ni3Ti and NiTi2, possible Ni-Nb compounds formation, Nb acting as diluent in SHS. This research proved the possibility to overcome these difficulties and of NiTi-Nb alloys obtaining by SHS using energetically activated powder mixture by controlled Mechanical Alloying. Also, it was proved the possibility to reduce Nb content from the common one of 9 at.% to 5 at.% without a significant effect of transformation temperatures and hysteresis decreasing.

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