Martensitic Transformation In Cu Research Articles

Assessment of Entropy Differences from Critical Stress Versus Temperature Martensitic Transformation Data in Cu-Based Shape-Memory Alloys

The entropy differences per unit volume (ΔStrans) between the close-packed phases in a martensitic transformation (MT) in Cu-based shape-memory alloys are obtained from mechanical tests by measuring, as a function of temperature (T), the critical resolved stress (τ). Specifically, $$\Delta S^{\text{trans}}$$ values are obtained from the slope of τ versus T plots by invoking a relation which is straightforwardly derived from the classical Clausius–Clapeyron equation, viz., $$\frac{{{\text{d}}\tau }}{{{\text{d}}T}} = - \frac{{\Delta S^{\text{trans}} }}{\gamma },$$ where γ is the transformation shear strain. Motivated by the significant scatter of the so obtained $$\Delta S^{\text{trans}}$$ values, the thermodynamic bases of such evaluation procedure have been revised, by accounting for the nucleation step of a martensite plate. The interface, elastic strain, and chemical contributions to the Gibbs energy of nucleation have been considered. A new expression of the type $$\frac{{{\text{d}}\tau }}{{{\text{d}}T}} = {\varvec{\Omega}} - \frac{{\Delta S^{\text{trans}} }}{\gamma }$$ is obtained, where the Ω term involves the elastic properties and their temperature dependence. The new $$\tau {-} T {-} \Delta S^{\text{trans}}$$ relation is used to assess the $$\Delta S^{\text{trans}}$$ values corresponding to the 2H/18R and 18R/6R MTs in Cu–Al–Ni and Cu–Zn–Al alloys. The ΔStrans values obtained by the present approach fall on a scatter band centered around the zero value.

Spinodal decomposition and martensitic transformation in Cu–Al–Mn shape memory alloy

Isothermal treatments at 413 K were performed in Cu–Al–Mn shape memory alloy samples, to study their effects on the martensitic transformation. This procedure, within the miscibility gap, produces spinodal decomposition. After each aging thermal treatment, martensitic transformation was monitored using Differential Scanning Calorimetry (DSC). Spinodal decomposition significantly changes the characteristics of the martensitic transition, reducing the transformed volume and modifying the critical temperatures. Furthermore, transformation hysteresis loop narrows as the volume fraction of the spinodal precipitates increases. Effects of thermal cycling through the martensitic transformation were studied in aged alloy samples. It was found that cycling produces critical temperatures changes, an increase in the transformed volume fraction, and a wider hysteresis loop. The observed results were discussed considering the interaction between spinodal precipitates and martensitic plates.

Thermal stability of B2 CuZr phase, microstructural evolution and martensitic transformation in Cu–Zr–Ti alloys

The effects of minor Ti addition on the thermal stability of B2 CuZr phase, the microstructure and the martensitic transformation (MT) in Cu50Zr50−xTix (x = 0, 2.5, 7.5 and 10 at%) alloys were investigated. It was found that the crystallization products, i.e. Cu10Zr7 and Cu(Ti, Zr)2, of Cu–Zr–Ti amorphous alloys transform to B2 CuZr phase at high temperatures. The corresponding eutectoid transformation temperature gradually increases with increasing Ti content, implying the decrease of the thermodynamic stability of the B2 CuZr phase. The microstructures of Cu–Zr–Ti martensitic alloys were proven to contain B2 CuZr, CuZr martensite, Cu10Zr7, Cu(Ti, Zr)2, and ZrTiCu2 crystals. Dilatometric measurements reveal that the MT temperature reduces with increasing Ti content, which would be of electronic nature. With increasing thermal cycles, the MT temperature gradually decreases while the reverse MT temperature increases, which results from the enhancement of the dislocation density, the partial decomposition of the equiatomic CuZr crystals and the partially reversible MT.

Variation of Seebeck coefficient at martensitic transformation in Cu–Mn–Al alloy

Structure, electric and transport properties of Cu–Mn–Al shape memory alloy were studied in this work. Cu–Mn–Al ribbons were subjected to cooling and heating through temperature range of martensitic transition to examine change of these properties with temperature. Different contributions to thermopower were analyzed in terms of the Wiedemann–Franz law.

Bulk-like behavior in the temperature driven martensitic transformation of Cu–Zn–Al thin films with 2H structure

This paper reports on the possibility to obtain Cu–Zn–Al films with 2H martensitic structure by fixing the valence electron concentration per atom (e/a) ≈1.53. Films with thickness of ≈5μm with micrometric grains show martensitic transformation temperature and hysteresis values close to the ones found in bulk samples. This result is different to the one found in Cu–Zn–Al thin films with 18R martensitic structure and similar microstructure, in which the hysteresis presents an increment (≈10times) compared to bulk samples. This difference can be associated to the intrinsic nature of the 2H transformation which requires more undercooling to produce the nucleation of the martensitic phase. The driving force for the burst-type martensitic transformation decreases the influence of the microstructure in the transformation.

Effects of Heat Treatment and Deformation on 2H and 18R Martensites in Cu–9.97 % Al–4.62 % Mn Alloy

In this study, some physical and mechanical properties of martensitic transformation in Cu–9.97 % Al–4.62 % Mn (wt%) alloy were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and compression deformation test techniques. In SEM and XRD observations of Cu–9.97 % Al–4.62 % Mn alloy, two kinds of martensitic phases: thermally and deformation effect, \({\beta_{1}^{\prime}}\) and \({\gamma_{1}^{\prime}}\) from DO3 parent phase, and the type of the produced martensite structures were noted.

The influence of microstructure on the martensitic transformation in Cu–Zn–Al melt-spun ribbons

The martensitic transformation was investigated in a set of twin roller melt-spun Cu–Zn–Al shape memory alloys, solidified at tangential wheel speeds between 20 and 40 m/s. The resulting microstructures were analyzed using X-ray diffraction, optical and transmission electron microscopy techniques. The characteristic martensitic transformation temperature, M S, was determined for each condition by conventional resistometric methods. The ribbons are homogeneous in shape and for each quenching rate they exhibit a quite uniform M S temperature. By proper thermal treatments, the different factors affecting M S could be separately examined and from temperature measurements, the contribution of L21 antiphase boundaries evaluated. A calculation of this contribution using pair interchange energies is in good agreement with the experimental results.

Cryogenic treatment-induced martensitic transformation in Cu–Zr–Al bulk metallic glass composite

A martensitic phase transformation from the B2 to the B19’CuZr phase in the Cu–Zr–Al bulk metallic glass (BMG) composite was induced by cryogenic treatment (CT). The martensitic transformation causes the improvements of the microhardness and the ultimate compression fracture strength. When the cryogenic treatment time was 72 h, the microhardness and the ultimate compression fracture strength of the BMG composite increased about 18.55% and 37.5%, respectively.

Effects of ageing on bainitic and thermally induced martensitic transformations in ductile Cu–Al–Mn-based shape memory alloys

The effects of ageing at 473–573 K on the hardness, microstructure and thermoelastic martensitic transformation in Cu–Al–Mn-based shape memory alloys were investigated. It was found that hardness was dramatically increased by ageing due to the formation of fine bainitic plates and that the volume fraction of the bainite phase with ageing time can be described by the Austin–Rickett equation. The martensitic transformation temperatures decreased with the formation of bainite plates, mainly due to the composition change of the β-matrix. Moreover, the growth of thermally induced martensite plates was disturbed by the existence of bainite plates. Consequently, the transformation intervals ( M s– M f and A f– A s) and transformation hystereses ( A f– M s and A s– M f) increased with the progress of bainitic transformation.

Martensitic transformation of Cu on Ag(001) and Cu on Au(001) studied with classical molecular dynamics

Received 13 October 2008; revised manuscript received 29 December 2008; published 4 March 2009The growth of Cu thin films on Ag 001 and Au 001 substrates was modeled using molecular dynamicswith classical potentials. We observed that deposited atoms formed an unstable bcc or bcc/body-centered-tetragonal structure, in agreement with previous experiments. We show that the formation of such structures isrelated to film thickness and temperature that was analyzed in the interval from 200 to 600 K. bcc nucleationwas measured by observing the relation between thickness and temperature of the deposited thin film. Themartensitic transformation accompanied by a stripe pattern occurred as a consequence of the distortions causedby the underlying substrate lattice. The stripe patterns were measured as 57 and 61 A for Cu onAg and Cu onAu, respectively. Monolayer spacing and coordination number of atoms were calculated, clearly evidencing theformed structures. Local structures were studied using the Ackland-Jones method, to determine the phases ofthe deposited films.DOI: 10.1103/PhysRevB.79.115404 PACS number s : 68.55. a, 68.35.Ct, 68.35.Rh

Deformation-induced martensitic transformation in Cu–Zr–(Al,Ti) bulk metallic glass composites

Plastic deformation of Cu–Zr–(Al,Ti) bulk metallic glass (BMG) composites induces a martensitic phase transformation from the B2 to the B19′ CuZr phase. Addition of Ti to binary Cu–Zr increases the temperature above which the B2 CuZr phase becomes stable. This affects the phase formation upon quenching in Cu–Zr–Ti BMG composites. The deformation-induced martensitic transformation is believed to cause the strong work hardening and to contribute to the large compressive deformability with plastic strains up to 15%.

Crystallographic model for bcc-to-9R martensitic transformation of Cu precipitates in ferritic steel

A crystallographic model, which can calculate lattice invariant shear, habit plane and orientation relationship for bcc-to-9R martensitic transformation of Cu precipitates in low-alloyed transformation-induced plasticity (TRIP) steel, is suggested. At the early stage of ageing at 500°C, coherent bcc Cu clusters were formed and characterized by a periodic array of distinguished striations perpendicular to [001]α direction. On prolonged ageing for 10 h, spherical precipitates with banded contrast formed within ferrite matrix and high-resolution transmission electron microscopy (HRTEM) observations confirmed that these bands corresponded to the intervariant boundary of twinned 9R Cu precipitates lying parallel to the {110}α planes and showed an orientation relationship with α: , . Analytical equations for lattice invariant shear and habit plane were derived, and calculated to be 0.09669 and , respectively. The orientation relationship between 9R Cu precipitates and ferrite matrix, calculated using transformation matrix, was and. The deviation angles between the calculated and measured by HRTEM were approximately 0.1° in direction and 3.7° in plane, respectively. The present model successfully described the crystallographic features of bcc-to-9R martensitic transformation of Cu precipitates in ferritic steel.

Thermal stability of the martensitic transformation of Cu–Al–Ni–Mn–Ti

The development of new shape memory alloys with high martensitic transformation temperature increases the potential for applications. The development and use of these new alloys depends on the stability of the structure during cycling at high temperatures. If it is possible to guarantee that on alloys keeps the structure during cycling, then the alloy can be used because of the shape memory properties. The aim of this work is to obtain a kinetic model of the forward and backward martensitic transformation of two Cu–Al–Ni–Mn–Ti alloys. Differential scanning calorimetry has been performed in order to establish the kinetic stability of the martensite and the beta transformation.

AC calorimetric study of the thermoelastic martensitic transformation in Cu–Al–Ni alloys

We present an accurate study by AC calorimetry on the thermoelastic martensitic transformation in Cu–Al–Ni shape memory alloys , both under quasi-isothermal conditions and by using a dynamic method. The AC calorimetry results suggest that the martensitic transformation exhibits some kinetic effects strongly dependent on the temperature rate, in agreement with internal friction results. Calorimetric results obtained by DSC do not exhibit this behaviour, but dynamic measurements obtained under oscillating fields show a net dependence on the temperature rate.

Stress analysis of martensitic transformation in Cu–Al–Be polycrystalline and single-crystalline shape memory alloy

The aim of this study is to analyze the martensitic transformation in a shape memory alloy during a superelastic loading, focusing on internal strains, stresses and phases fractions. The behavior of the austenite phase is studied by X-ray diffraction stress analysis during in situ tensile test at room temperature. Both single-crystal and polycrystal samples have been investigated. The results are discussed with the aim to correlate the microstructural variations with the local stress state evolution in the austenitic phase while variants of martensite form and develop during a superelastic loading.

Neutron diffraction analysis of the β decomposition process in a texture free Cu–Al–Ni shape memory alloy

The atomic order of the metastable β phase influences on the characteristics of the martensitic transformation in Cu–Al–Ni shape memory alloys. On the other hand, the pro-eutectoid γ 1 precipitation and the eutectoid decomposition produce deleterious effects in the martensitic transformation. In this work, the Rietveld analysis performed on neutron diffraction spectra allows to determine the order, the volume fraction of the different precipitated phases and their evolution during heating in a Cu–14.37Al–4.2Ni (wt%) shape memory alloy.

Vibrational behavior of the β phase near martensitic transformation in Cu–Al–Ni shape memory alloys

Abstract The vibrational behavior of the metastable β phase near the martensitic transformation (MT) in a single-crystalline Cu–27.96 at.% Al–3.62 at.% Ni shape memory alloy (SMA) has been studied by resonant ultrasonic spectroscopy (RUS). This technique allows to determine simultaneously all the elastic constants C ij of anisotropic materials and also the internal friction Q −1 ( C ij ) associated to some particular elastic constant C ij . The evolution of the resonance frequencies with temperature has been studied and shows that the C ′ and C 44 elastic constants are the magnitudes which control the vibrational response of the β phase near the martensitic transformation. The internal friction value Q −1 associated to different resonance modes and their evolution has been measured and correlated to the elastic behavior of the alloy.

Stress-induced martensitic transformation in Cu–Al–Zn–Mn polycrystal investigated by two in-situ neutron diffraction techniques

In-situ neutron diffraction studies of internal strains, stresses and phase fractions in pseudoelastic Cu–Al–Zn–Mn shape memory alloy (SMA) evolving during two tensile load cycles at constant temperature are reported. The results are discussed with the aim of demonstrating the applicability of this experimental technique for the SMA research. Particularly, an experimental information on the mechanisms by which individual grains of the transforming polycrystal share the macroscopic stress – load partition – as well as quantitative information on the residual stress frozen in the austenite phase after the first cycle are discussed.

Influence of initial heating temperature on the reverse martensitic transformation of Cu–Zn–Al–Mn–Ni alloy

The influence of initial heating temperature on reverse martensitic transformation of Cu–Zn–Al–Mn–Ni alloy was investigated by differential scanning calorimetry. An exothermic X→M transition occurs just before the reverse martensitic transformation upon heating from 233 K to parent phase, and thus results in the decrease of start temperature of reverse martensitic transformation. X-Ray diffraction analysis indicates that X-phase has the similar structure to the martensite, which is the reason why the X→M transition only releases less energy upon heating.

The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy

The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy