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1

Large Deformation Constitutive Theory for a Two-Phase Shape Memory Alloy

Panoskaltsis V., Polymenakos L. C., Soldatos D.

Engineering Transactions

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2014

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Vol. 62, iss. 4

355–-380

EN

In this work we examine significant theoretical issues related to the constitutive modelling of a two-phase shape memory alloy which undergoes large deformations. For this purpose, we propose a new generalized plasticity based model. The model is based on a standard fractions approach and considers a local multiplicative decomposition of the deformation gradient into elastic and inelastic (transformation induced) parts, as its basic kinematic assumption. We also assess the ability of the model in simulating several patterns of the complex behavior of the material in question, by three representative numerical examples. These examples comprise a standard uniaxial tension problem, a torsion problem and an additional problem dealing with non-conventional pseudoelastic response.

2

Wpływ parametrów obróbki cieplnej na trwałość zmęczeniową natlenionego powierzchniowo stopu Ti-6Al-4V

Hepner M., Rozumek D.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2009

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z. 95

45-46

3

Wielowarstwowe biomateriały tytanowe: mikrostruktura i właściwości mikro-mechaniczne

Moskalewicz T., Kot M., Zimowski S., Rakowski W., Czyrska-Filemonowicz A.

Archiwum Nauki o Materiałach

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2003

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T. 24, nr 3

185-200

PL

W pracy przeprowadzono szczegółową charakterystykę mikrostruktury dwufazowych (alfa+beta) stopów tytanu (Ti-6Al-4V i Ti-6Al-7Nb) w stanie dostawy oraz po azotowaniu w warunkach wyładowania jarzeniowego. Posługując się metodami transmisyjnej mikroskopii elektronowej (TEM) określono skład chemiczny faz alfa i beta w stanie dostawy i po azotowaniu. Badania cienkich folii wykonanych z przekrojów poprzecznych próbek pozwoliły na precyzyjną charakterystykę mikrostruktury warstw azotowanych. Wykorzystując metodę dyfrakcji elektronów wykonano analizę faz występujących w warstwach azotowanych. Stwierdzono, że warstwy azotowane mają budowę wielowarstwową i składają się z kilku morfologicznie różnych "podwarstw", a zewnętrzna podwarstwa delta-TiN na obu badanych stopach ma nanokrystaliczną strukturę. Pomiary właściwości mikro-mechanicznych (mikrotwardość, moduł Younga) warstw azotowanych wykazały występowanie wyraźnej korelacji pomiędzy mikrostrukturą warstw, a ich właściwościami mikro-mechanicznymi. Próby scratch-test" wykazały, że warstwy azotowane mają dobrą przyczepność do badanych stopów tytanu.

EN

In the present study, the microstructure of the two phase (alpha+beta) titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) as received materials as well as after nitriding process in glow discharge conditions, has been examined. Using transmission electron microscopy (TEM) methods, the chemical composition of alpha and beta phases in the as received materials and in materials after nitriding process were estimated. The investigation of cross-sectional thin foils allows for precise microstructure characterisation of the nitrided layers. Phase identification within the layers was carried out by electron diffraction. TEM investigations revealed a very complex multilayered microstructure of the nitrided layers. The delta-TiN outer nitride sublayer formed on two investigated alloys was consisted of nanocrystallites. The measurements of micro-mechanical properties (microhardness, Young modulus) of nitrided layers showed the distinct correlation between the microstructure of surface layers and their micromechanical properties. The results of "scratch-test" experiment showed that the nitrided layers exhibit a good adhesion to the surface of titanium alloys investigated.

4

Rola mikrostruktury w procesie wysokotemperaturowego utleniania stopów TiAl.

Gil A., Niewolak L., Penkalla H.J., Quadakkers W.J., Czyrska-Filemonowicz A.

Inżynieria Materiałowa

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2001

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R. XXII, nr 1

41-46

PL

W pracy przedstawiono wyniki badań mikrostruktury stopów Ti-50Al, Ti-48Al-2Cr i Ti-48Al-2Ag. Potwierdzono, że tworzenie ochronnej zgorzeliny Al2O3 na dwufazowych stopach TiAl zachodzi tym łatwiej, im większy jest stopień dyspersji faz alfa2-TiAl i gamma-TiAl. Metodami analitycznej transmisyjnej mikroskopii elektronowej wykazano, że dodatek srebra do stopów TiAl stabilizuje w nich fazę gamma-TiAl eliminując zarazem fazę alfa2-Ti3Al odpowiedzialną za tworzenie nieochronnego tlenku TiO2.

EN

The results of the microstructural studies of the alloys Ti-50Al, Ti-48Al-2Cr, Ti-48Al2Ag are presented. It was confirmed that the formation of the protective alumina scale on the two-phased TiAl alloys occurs more easier if the alpha2-Ti3Al phase is finely dispersed in the gamma-TiAl matrix. It has been shown using the analytical transmission electron microscopy that silver additions cause stabilisation of the gamma-TiAl phase and elimination from the alloy of the alpha2-Ti3Al phase, which is responsible for the formation of the non-protective TiO2-type scale.

5

Effect of heat treatment on the microstructure and mechanical properties of Ti-6Al-2Mo-2Cr-Fe alloy.

Szkliniarz W., Chrapoński J.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

896-899

EN

The paper presents the results of investigations concerning the effect of heat treatment consisting in isothermal annealing performed according to three different schemes, on changes of the microstructure and strength properties of a two-phase coarse-grained titanium alloy. It has been found that a change of the primary phase a form into one similar to spheroidal leads to a considerable improvement of the alloy's plasticity, with simultaneous maintaining of the strength properties which are comparable to the initial state.

PL

W pracy przedstawiono wyniki badań dotyczące oddziaływania obróbki cieplnej, polegającej na izotermicznym wyżarzaniu, prowadzonym wg trzech różnych schematów, na zmiany mikrostruktury i właściwości mechanicznych gruboziarnistego, dwufazowego stopu tytanu. Stwierdzono, że uzyskana w wyniku długotrwałego wyżarzania zmiana postaci pierwotnej fazy a z płytkowej na zbliżoną do sferoidalnej prowadzi do znacznej poprawy plastyczności stopu, przy zachowaniu właściwości wytrzymałościowych porównywalnych do stanu wyjściowego.

6

Some property of two-phase Co-Cr-Ni-Ti alloy.

Surowska B.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

576-579

EN

The effect of heat treatment and cold work onto mechanical properties and corrosion resistance have been investigated for wrought Co-20Cr-10Ni-0.7Ti alloy. The structure of this alloy consists of two phases: fcc (beta-Co solid solution) and hcp (alpha-Co solid solution). The effect of temperature and time of solution treatment on amount of alpha-Co phase and the effect of cold work on this structural parameter have been studied. The tensile strength, fatigue strength and the compressive stress-strain curves for two degrees of forging were determined. Moreover, the dependence between the strain and corrosion resistance was determined. The alpha-Co percentage increased from about 25% before heat treatment to about 55% after solution treatment. During cold work the amount of alpha-Co phase reached maximum value for the strain epsilon=0.2. The best pitting corrosion resistance was achieved after solution treatment in 1473K/2h/water. Positive effect of cold work upon the resistance to pitting corrosion was found. Rapid increase of breakdown potential was recorded for samples with strain epsilon=0.12. Further increase of strain resulted in slight changes of this potential.

7

Internal oxidation of silver-sulphur alloys.

Kosec L., Smajic N., Horvat-Kovacic S.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

620-624

EN

Silver - sulphur alloys fulfill conditions for internal oxidation. For the difference from sulphur oxides silver oxide (Ag2O) is not stable at temperatures over 180 degrees centigrade and 1 atm. pressure of oxygen. Both the elements in small concentrations are soluble in silver. The solubility of sulphur is higher than that of oxygen. The diffusion rate of oxygen in silver is higher as compared to that of sulphur. Peculiarities of internal oxidation of silver - sulphur alloys come from their two - phase microstructures and gaseous products of the oxidation.

8

Influence of ageing time and temperature on mechanical properties of two-phase titanium alloy Ti-6Al-2Mo-2Cr at high temperature.

Sieniawski J., Filip R., Kubiak K.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

536-539

EN

In the paper results of high temperature tensile properties investigations of two phase titanium alloy Ti-6Al-2Mo-2Cr have been presented. Ultimate tensile strength - Rm 0.2% proof stress - R0.2, elongation-A5 and reduction in area - Z have been determined in static tensile test at room and high temperature. It was found that combination of the highest mechanical properties of the alloy with good plasticity can be obtained by aging in temperature range 723-823 K for 5-10 hours. On the basis of testing results it has been concluded that the alloy studied can be used for structural elements of the machines working at temperature up to 723 K.

9

Effect of heat treatment on tensile properties and fracture toughness of two-phase alpha+beta titanium alloy Ti-6Al-2Mo-2Cr.

Kubiak K., Sieniawski J., Ziaja W.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

572-575

EN

In the paper results of the investigation on the effect of microstructure on room temperature tensile properties and fracture toughness of two-phase alpha+beta titanium alloy Ti-6Al-2Mo-2Cr have been presented. Microstructure has been varied by changes in the cooling rate from the solution treatment temperature and ageing time and temperature. Mechanical properties examined show strong dependence on the heat treatment conditions, especially aging conditions. It has been attributed mainly to amount and morphology of alpha phase obtained after heat treatment. The higher volume fraction of lamellar alpha phase, and the coarser the lamellar alpha structure, the higher the fracture toughness.