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Our work entitled improvement of the mechanical properties of a Z80WCV 18-04-01 high-speed steel grooving cutter (three sizes) by heat treatment, the latter can play an essential role in improving the mechanical and structural properties of grooving mills. The results obtained showed that the heat treatments allow to obtain a favorable microstructure, with a martensitic phase formation and a homogeneous distribution of carbides. These structural changes have led to an increase in the hardness, strength and durability of the milling cutters to be grooved in addition, it has been observed that the application of cumulative revenues has a significant impact on the mechanical and structural properties. The successive revenues favored the transformation of quenching martensite into tempering martensite and the elimination of residual austenite, leading to a gradual increase in hardness and wear resistance. [ABSTRACT FROM AUTHOR]

Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to high strength and desirable plasticity. A lamellar structure is known for its high strength with limited plasticity, owing to its interface-strengthening effect. Thus, extensive efforts have been conducted to induce the lamellar structure and control the volume fraction of primary dendrites to enhance plasticity by tailoring the compositions. In this study, however, it was found that not only the volume fraction of primary dendrites but also the morphology of dendrites constitute key factors in inducing excellent ductility. We selected three compositions of Ti–Fe–Sn ultrafine eutectic composites, considering the distinct volume fractions and morphologies of β -Ti dendrites based on the Ti–Fe–Sn ternary phase diagram. As these compositions approach quasi-peritectic reaction points, the α ″ -Ti martensitic phase forms within the primary β -Ti dendrites due to under-cooling effects. This pre-formation of the α ″ -Ti martensitic phase effectively governs the growth direction of β -Ti dendrites, resulting in the development of round-shaped primary dendrites during the quenching process. These microstructural evolutions of β -Ti dendrites, in turn, lead to an improvement in ductility without a significant compromise in strength. Hence, we propose that fine-tuning the composition to control the primary dendrite morphology can be a highly effective alloy design strategy, enabling the attainment of greater macroscopic plasticity without the typical ductility and strength trade-off. [ABSTRACT FROM AUTHOR]

Elastic properties of materials and their changes with temperature are important for their applications in engineering. In the present study the influence of phase composition and temperature of AISI 4130 alloy on Young's modulus (Ed), shear modulus (Gd), and damping (Q−1) was carried out by the impulse excitation technique (IET). The material characterization was performed using confocal microscopy, XRD, SEM, HV, and dilatometry. A stable structure, composed of ferrite (BCC) and pearlite (α-Fe + Fe3C), was obtained by annealing. Metastable structure of martensite (BCT) was obtained by quenching. The Ed, Gd, and Q−1 were measured by varying the temperature from RT to 900 °C. The values of Ed and Gd, at RT, were determined as 201.5 and 79.2 GPa (annealed) and 190.13 and 76.5 GPa (quenched), respectively. In the annealed steel, the values Ed and Gd decrease linearly on heating up to 650 °C, with thermal expansion. In the quenched steel, weak changes occurred in the dilatometric curve, Ed, Gd, and Q−1, in the range of 350–450 °C, which indicated decompositions of the martensitic phase. A sharp decrease in the moduli and high peak of Q−1 were observed for both samples around 650–900 °C, revealing low lattice elastic stability of the phases during transformations α(BCC) + Fe3Cγ(FCC). [ABSTRACT FROM AUTHOR]

The chemical ordering and its effect on structure and elastic properties of Mg1-xScx alloys are studied by ab initio method. The MgSc alloys show strong chemical long range ordering tendency as the Sc concentration increase. The predicted martensitic phase of fully disordered alloy is hcp when the transformation occurs through the Burgers path. Chemical long range ordering could lead to a lattice distortion and results in a low symmetric orthorhombic martensitic phase, namely, there is a chemical-structural coupling in MgSc alloys. The chemical long range ordering also has strong hardening effect, the single crystalline elastic moduli C′, C44, Young’s modulus and Shear modulus are increased by 12.6%, 4.2%, 4.4% and 5% for Mg80Sc20 alloy, respectively. Electronic structure analysis showed that the additional s-d and p-d hybridization between near neighboring Mg and Sc ions in ordered phase is accounting for the elastic hardening and chemical-structural coupling in MgSc alloys.

Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to high strength and desirable plasticity. A lamellar structure is known for its high strength with limited plasticity, owing to its interface-strengthening effect. Thus, extensive efforts have been conducted to induce the lamellar structure and control the volume fraction of primary dendrites to enhance plasticity by tailoring the compositions. In this study, however, it was found that not only the volume fraction of primary dendrites but also the morphology of dendrites constitute key factors in inducing excellent ductility. We selected three compositions of Ti–Fe–Sn ultrafine eutectic composites, considering the distinct volume fractions and morphologies of β-Ti dendrites based on the Ti–Fe–Sn ternary phase diagram. As these compositions approach quasi-peritectic reaction points, the α″-Ti martensitic phase forms within the primary β-Ti dendrites due to under-cooling effects. This pre-formation of the α″-Ti martensitic phase effectively governs the growth direction of β-Ti dendrites, resulting in the development of round-shaped primary dendrites during the quenching process. These microstructural evolutions of β-Ti dendrites, in turn, lead to an improvement in ductility without a significant compromise in strength. Hence, we propose that fine-tuning the composition to control the primary dendrite morphology can be a highly effective alloy design strategy, enabling the attainment of greater macroscopic plasticity without the typical ductility and strength trade-off.

The consequences of cold deformation phase transformation in chromium–nickel steel 12Kh18N10T have been studied. A metallographic study of samples has been performed with an increase of up to ×10 000 and an increase in the proportion of martensite in austenitic steel as a result of cold plastic deformation has been shown. A durometric study has been carried out, and the character of metal hardening with increasing degree of deformation has been confirmed, which shows the presence of at least two hardening mechanisms: deformation and phase. A magnetic study has been carried out, and the intensity of the growth of the magnetic phase with increasing deformation has been revealed. A comparison is made with the known data on the intensity of the martensitic transition for the same grade of chromium–nickel steel under cold deformation conditions. [ABSTRACT FROM AUTHOR]

Elastic properties of materials and their changes with temperature are important for their applications in engineering. In the present study the influence of phase composition and temperature of AISI 4130 alloy on Young’s modulus (Ed), shear modulus (Gd), and damping (Q−1) was carried out by the impulse excitation technique (IET). The material characterization was performed using confocal microscopy, XRD, SEM, HV, and dilatometry. A stable structure, composed of ferrite (BCC) and pearlite (α-Fe + Fe3C), was obtained by annealing. Metastable structure of martensite (BCT) was obtained by quenching. The Ed, Gd, and Q−1 were measured by varying the temperature from RT to 900 °C. The values of Ed and Gd, at RT, were determined as 201.5 and 79.2 GPa (annealed) and 190.13 and 76.5 GPa (quenched), respectively. In the annealed steel, the values Ed and Gd decrease linearly on heating up to 650 °C, with thermal expansion. In the quenched steel, weak changes occurred in the dilatometric curve, Ed, Gd, and Q−1, in the range of 350–450 °C, which indicated decompositions of the martensitic phase. A sharp decrease in the moduli and high peak of Q−1 were observed for both samples around 650–900 °C, revealing low lattice elastic stability of the phases during transformations α(BCC) + Fe3Cγ(FCC).

The effect of hydrogen charging, ultrasonic treatment, and hydrogen charging after ultrasonic treatment on the fatigue life of VT6 alloy is investigated. Ultrasonic treatment causes the formation of a continuous nonetching α2(Ti3Al) layer within the surface layer, which reduces the fatigue life. Below this layer there are bands of the α2(Ti3Al) phase which, on the contrary, increase the fatigue life. These two effects together give a 1.3-fold increase in the fatigue life of the alloy. A catastrophic decrease in hydrogen charging after ultrasonic treatment is explained by the formation of regions of short-range displacements with a bcc lattice similar to the β phase. As a result of radial shear rolling, a martensitic phase with very high strength is formed in the alloy. Its formation is predicted by positron annihilation spectroscopy and is detected by transmission electron microscopy. The high stability of the martensitic phase contributes to the lower fracture toughness of the alloy processed by radial shear rolling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of multiaxial forging on magnetic properties have been carried out. • After the forging the hysteresis and temperatures of martensitic transtion decrease. • Forging does not affect the sensitivity of field-induced martensitic transformation. • Inverse MCE is due to the difference in the MCA energy of austenite and martensite. • Multiaxial isothermal forging improves mechanical and functional properties. The influence of as-cast and multiaxial isothermal forged structures on the sensitivity of martensite to the magnetic field and on the magnetocaloric effect in Ni-Mn-Ga-Si alloy has been studied. In the multiaxial isothermal forged state, a "necklace" structure is observed where large grains of 100–200 µm are encompassed by a layer of fine-grained structure. In this state, the martensitic transformation occurs with a shift towards the low-temperature region of about 10 K. Characteristic points of the martensitic transformation are evaluated in a magnetic field up to 12 T, revealing a sensitivity value of 0.6 K/T for both as-cast and multiaxial isothermal forged samples. Furthermore, an inverse magnetocaloric effect is identified within the martensitic transformation region for both as-cast and multiaxial isothermal forged samples under weak magnetic fields, up to 0.2 T. This inverse effect disappears at a magnetic field of 1.8 T, leaving only the direct magnetocaloric effect observable. These findings shed light on the intriguing interplay between microstructure, magnetic sensitivity, and magnetocaloric behavior in this Ni-Mn-Ga-Si alloy, offering valuable insights for potential applications in magnetic cooling technologies. [ABSTRACT FROM AUTHOR]

In this study, CuAl13−xTax (% mass x = 1; 1.5; 2; 2.5) shape-memory alloys were produced through arc-melting method. Phase transformation temperatures were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis. Microstructures were examined with the aid of optical microscopy, scanning electron microscopy–energy-dispersive X-ray (SEM–EDX) and X-ray diffraction (XRD). The ratios of electron per atom (e/a) for CuAl13−xTa1, CuAl13−xTa1.5, CuAl13−xTa2 and CuAl13−xTa2.5 were calculated as 1.52, 1.51, 1.50 and 1.49, respectively. DSC results showed that CuAlTa alloys belong to high-temperature shape-memory alloys. Also, it was identified that these alloys demonstrate 2 H (γ 1 ′) → DO 3 (β 1) → 18 R (β 1 ′) phase transformation. It was observed that both phase transformation temperature and oxidation sensitivity of the samples decreased with the increase in the amount of Ta. In the XRD analysis of CuAlTa HTSMA alloys, some phases were observed, including γ ′ , β ′ Cu9Al4, CuAl and Ta2Al3. These phases were supported by SEM–EDX results. The micro-hardness values of the alloys were increased by increasing Ta content. [ABSTRACT FROM AUTHOR]

Abstract A high elastic admissible strain (EAS), which is essential for bio-implant applications, is difficult to be achieved due to the synergy between the elastic modulus and the yield strength. Here, the EAS values of 1.94–2.50%, which are much higher than those (EAS <1.3%) of reported biomedical materials, have been achieved in a TiZr alloy by using cold rolling deformation. The highest EAS of 2.50% in the sample with a rolling strain of 0.37 can be attributed to its low elastic modulus due to the existence of nanoscale low-elastic modulus α″ phase with a volume fraction of ∼14% and its high strength resulted from the strengthening of high-density α″ phase boundaries. Highlights • A high elastic admissible strain (EAS) of 1.94–2.50% was achieved in TiZr alloy. • The high EAS can be attributed to the nanoscale low-elastic modulus α″ phase. • The high EAS can be tailored by cold rolling deformation. • This paper presents an alternative approach to fabricate high EAS materials. [ABSTRACT FROM AUTHOR]

The present study was undertaken to investigate the effect of continuous and discontinuous (cyclic) solution heat treatment on the athermal and isothermal ε martensite phase transformation in Co-28Cr-6Mo-0.3C implant alloy. The results showed that the cyclic solution heat treatment induced more of the athermal ε martensite phase in the alloy than that of the continues one. In addition, the cyclic heat treatment contributes to the development of more isothermal martensite phase during isothermal aging at 850 °C and, moreover, grain refinement in the area beneath the sample surface. The severity of grain refinement was highly significant adjacent to the surface and decreased by increasing the distance from the sample free surface. This novel grain refinement in high-carbon Co-Cr-Mo alloy was attributed to the generation of larger quenching thermal stresses introduced beneath the surface during cyclic solution treatment. The repetitive heating/cooling cycle modifies the surface properties, refines the grain size and leads to uniform dispersion of the secondary carbides. The corrosion resistance of the cyclically solution heat-treated samples was superior as compared to the as-cast one.

The process of martensitic α′(α″) phase decomposition in titanium alloys has not been sufficiently characterised in the literature - especially in terms of plastically deformed martensite. The research results of water-quenched Ti-6Al-4V alloy, subsequently cold deformed in compression test and tempered at the temperature range of 600-900°C for 1 and 2 h were presented in the paper. Light and scanning electron microscopy observations revealed the influence of plastic deformation on tempered martensite laths morphology - particularly at the temperature of 900°C - it favoured their fragmentation and spheroidisation. The effect of plastic deformation on characteristic temperatures of α′(α″)→α + β phase transformation, phase composition and alloying elements distribution in phase constituents of Ti-6Al-4V alloy was identified and evaluated too. This paper is part of a thematic issue on Titanium. [ABSTRACT FROM AUTHOR]

A mean-field model based on the elasticity theory of point defects has been developed to investigate the role of uniform stress fields on the long-range ordering of carbon atoms in bct-iron. From an analysis of the thermodynamic equilibria, composition – temperature – stress state diagrams are derived. We demonstrate that ferrite, martensite and supercritical iron are various instances of the same bct-iron phase region. A coherent mapping of the phase transitions is drawn, identifying (i) continuous transitions such as ferrite ordering, martensite enhanced ordering and ferrite – martensite transformation, and (ii) discontinuous transitions such as temperature-induced martensite and stress-induced martensite. Our analysis is supported by rigid-lattice Monte Carlo simulations. Recently published experimental results on highly-drawn perlitic wires are re-interpreted in terms of supercritical iron, rather than strain-induced martensite. Novel low-temperature thermomechanical treatments of supersaturated ferrite are suggested, for improved nanostructure design of martensitic steels. [ABSTRACT FROM AUTHOR]

Metallic glass composites containing shape memory crystals demonstrate strain hardening owing to the deformation-induced martensitic transformation, which encompasses the B2 ⇌ B19′/B33 (martensite) transformation in Zr-based metallic glasses. However, the impact of the B19' martensitic phase on strain hardening remains ambiguous. In this study, we conduct a rapid annealing treatment of Zr 45 Cu 45 Al 10 bulk metallic glass at 748 K to form the B19' phase and employ small-angle neutron scattering to explore its evolution. The B19' phase forms in the first 10 min of annealing treatment and begins to grow after 30 min. The presence of the B19' phase significantly increases the strain rate sensitivity and irreversible plastic deformation. These findings not only deepen our understanding of the role of the B19' phase in metallic glass composites but also offer a methodology to enhance their mechanical properties through modulation of the B19' phase. • SANS reveals that B19 'phase forms in the first 10 min and begins to grow after 30 min with 748 K annealing in Zr 45 Cu 45 Al 10. • The size of B19' is associated with the strain rate sensitivity and irreversible plastic deformation in MGCs. • With the crystalline phase formation, the deformation mechanism is transformed to phase transformation-mediated plasticity. [ABSTRACT FROM AUTHOR]

• Strong chemical long range ordering tendency was observed in MgSc alloys. • Chemical-structural coupling is the main reason for forming orthorhombic phase in MgSc alloys with large Sc concentration. • Chemical long range ordering has significant elastic hardening effect both on Austenite phase and martensitic phase. The chemical ordering and its effect on structure and elastic properties of Mg 1- x Sc x alloys are studied by ab initio method. The MgSc alloys show strong chemical long range ordering tendency as the Sc concentration increase. The predicted martensitic phase of fully disordered alloy is hcp when the transformation occurs through the Burgers path. Chemical long range ordering could lead to a lattice distortion and results in a low symmetric orthorhombic martensitic phase, namely, there is a chemical-structural coupling in MgSc alloys. The chemical long range ordering also has strong hardening effect, the single crystalline elastic moduli C′ , C 44 , Young's modulus and Shear modulus are increased by 12.6%, 4.2%, 4.4% and 5% for Mg 80 Sc 20 alloy, respectively. Electronic structure analysis showed that the additional s-d and p-d hybridization between near neighboring Mg and Sc ions in ordered phase is accounting for the elastic hardening and chemical-structural coupling in MgSc alloys. [ABSTRACT FROM AUTHOR]

A deep surface modified TiZr layer was fabricated by high-intensity low-energy titanium ion implantation into zirconium alloy Zr-1Nb. Gas-phase hydrogenation was performed to evaluate protective properties of the modified layer against hydrogen permeation into Zr-1Nb alloy. The effects of ion implantation and hydrogen on microstructure, phase composition and elemental distribution of TiZr layer were analyzed by scanning electron microscopy, X-ray diffraction, and glow-discharge optical emission spectroscopy, respectively. It was revealed that TiZr layer (~10 μm thickness) is represented by α′ + α(TiZr) lamellar microstructure with gradient distribution of Ti through the layer depth. It was shown that the formation of TiZr layer provides significant reduction of hydrogen uptake by zirconium alloy at 400 and 500 °C. Hydrogenation of the modified layer leads to refinement of lamellar plates and formation of more homogenous microstructure. Hydrogen desorption from Ti-implanted Zr-1Nb alloy was analyzed by thermal desorption spectroscopy. Hydrogen interaction with the surface modified TiZr layer, as well as its resistance properties, are discussed.

The martensitic phase transformation of the metastable austenitic steel increases yield strength and ultimate stress, but decreases ductility. Evolution of the martensite depends on both plastic strain and stress triaxiality. Experiments at room temperature reveal that the martensitic phase transformation in the austenitic stainless steel 06Cr19Ni10 becomes obvious only for large strains, e.g. > 30 % . Increasing the material temperature may diminish the phase transformation significantly. By testing specially fabricated specimens, the cold hardening of the material was decomposed into a plastic strain related part and a martensitic phase part. Comparison with experiments confirms that the mechanical behavior of the austenitic-martensitic material can be described by J 2 plasticity, combining with the Santacreu model for the phase transformation. Furthermore, the stress-controlled fatigue experiments on the distorted stainless steel display that in the high cycle fatigue regime the plastic strain improves the material's fatigue resistance, while the martensitic phase transformation increases the fatigue property in the finite life regime. However, in the ε - N diagram the benefits from the martensitic phase transformation decrease with loading amplitude and the plastic deformation may reduce fatigue performance. In the LCF region the distorted material shows generally worse fatigue property than the base material. [ABSTRACT FROM AUTHOR]

In applying eddy current testing to evaluation of fatigue cracks in austenite stainless steels, various influential factors are needed to be considered, such as martensite transformation of austenitic phase, crack closure, and oxide formation between crack faces, and so on. In this study, influential factors of heating of fatigue cracks in type 316 austenitic stainless steels are evaluated through experimental and numerical analysis. Signal phase shift and amplitude decrease by heating is systematically discussed. [ABSTRACT FROM AUTHOR]

The realistic loading condition for many components is multiaxial arising from multidirectional loading or geometry complexities. In this study, some multiaxial stress-based classical and critical plane fatigue models are briefly reviewed and their application for martensitic Nitinol under torsion and in-phase axial-torsion loading is evaluated. These models include von Mises equivalent stress, Tresca, Findley, McDiarmid, and a proposed stress-based Fatemi–Socie-type model. As the fatigue cracks appear to be on the maximum shear plane for the martensitic Nitinol, all the models examined here consider the shear stress as the primary damage parameter. Among all the models considered in this study, the proposed Fatemi–Socie-type model provides a better prediction for fatigue lives when compared to torsion and in-phase multiaxial fatigue experimental data from literature. Analyses indicate that critical plane approaches are more appropriate for multiaxial fatigue prediction of Nitinol alloys, at least in martensitic phase. Finally, recommendations are made to calibrate more reliable multiaxial fatigue models for Nitinol. [ABSTRACT FROM AUTHOR]

Cu 100− x Zr x (x = 50, 54, 60 and 66.6) polycrystalline alloys were prepared by arc-melting. The crystal structure of the ingots has been examined by X-ray diffraction. Non-equilibrium martensitic phases with monoclinic structure were detected in all the alloys except Cu 33.4 Zr 66.6 . Temperature dependencies of electrical resistivity in the temperature range of T = 4–300 K have been experimentally obtained as well as room temperature values of Hall coefficients and thermal conductivity. Electrical resistivity demonstrates anomalous behavior. At the temperatures lower than 20 K, their temperature dependencies are non-monotonous with pronounced minima. At elevated temperatures they have sufficiently non-linear character which cannot be described within framework of the standard Bloch–Grüneisen model. We show that experimental resistivity dependencies may be perfectly fitted by generalized Bloch–Grüneisen model with variable Debye temperature. We found that both the electrical resistivity and the Hall coefficients reveal metallic-type conductivity in the Cu–Zr alloys. The estimated values of both the charge carrier mobility and the phonon contribution to thermal and electric conductivity indicate the strong lattice defects and structure disorder. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation energy/atom and electronic properties of the α″ phase calculated. [•] The instability of the α″ phase increases with increase in Nb concentration. [•] A limit of Wyckoff positions obtained by symmetry of Cmcm space group verified. [•] β→α″ transformation is related with smaller strains along three principal axes. [ABSTRACT FROM AUTHOR]

This study discusses the electromagnetic modeling of fatigue cracks in plant environment to improve accuracy of depth sizing with eddy current testing. For the purpose, the factors that influence eddy current signals of fatigue cracks are evaluated. Here, martensitic layer and oxide fillings in fatigue cracks are focused on as influencing factors, and oxides are systematically filled in fatigue cracks by thermal treatment. The measured EC signals change depending on the presence and type of filling oxides. Numerical simulations are conducted to discuss the electromagnetic modeling of cracks with oxide fillings. The types of oxides in the cracks are identified by Raman spectroscopy, and the martensitic layers in vicinity of crack faces are observed by magnetic force microscopy. These results support for the electromagnetic model of environmental fatigue cracks developed in this study. [ABSTRACT FROM AUTHOR]

The magnetocaloric and electrical properties in annealed Si-doped Ni48Mn39In13-xSix Heusler alloy ribbons with x=0–3 have been investigated. These ribbons crystallize in a partially ordered B2 phase structure. It was observed that both the martensitic structural transition TM and the Curie temperature TC of austenitic phase decrease with increasing Si contents. The small amount of Si in the In position modifies the peak value of positive magnetic entropy change \Delta SM for a magnetic field change H=50\ kOe, which vary from 20.2 J\cdot kg^-1\cdotK^-1 for x=0 to 23.1 J\cdot kg^-1\cdotK^-1 for x=1, and then decrease to 10.1 J\cdot kg^-1\cdotK^-1 for x=3. Meanwhile, the magnetoresistance associated with the martensitic transformation was found to be -45% for x=2 at T=192\ K for a magnetic field change of 50 kOe. [ABSTRACT FROM AUTHOR]

The crystal structure of the modulated, low-temperature martensitic phase in Ni2.41Fe0.59Ga ferromagnetic shape memory alloy (FSMA) has been determined by Rietveld refinement of neutron powder diffraction data. The structure shows an incommensurate modulated crystal lattice with some analogies with the 7M modulated martensitic structure found in Ni2Mn1.2Ga0.8 Heusler alloy. The observed type of lattice modulation with q =0.3521c ∗ gives rise to a new type of martensitic crystal structure in the FSMAs. [Copyright &y& Elsevier]

Abstract: In this study, (CuZr)95Al5 and (CuZr)90Al10 alloy plates with thickness of 1mm were prepared by suction cast. Microstructural characterization shows that (CuZr)95Al5 plate contains strip-like martensite phase and the (CuZr)90Al10 plate contains sparse CuZr nanocrystals distributed at the amorphous matrix. Thermal stabilities of the two alloys were measured by DSC. For the evaluations of mechanical properties, rectangular blocks and dogbone specimen were cut off from the alloy plates and used for room temperature compression and tensile tests respectively. It reveals that significant work hardening with 5.5% plastic strain before failure were obtained for (CuZr)95Al5 under compression tests, while (CuZr)90Al10 exhibits very little plasticity. In tension, both alloy plates exhibit high fracture strength before catastrophic failure. The interaction between the shear bands and martensite phase were studied and the deformation behavior of the both alloys was discussed. [Copyright &y& Elsevier]

Abstract: For the first time, the 7M modulated structure, frequently observed in ferromagnetic shape memory Ni–Mn–Ga martensitic phases, is solved by powder diffraction analysis. Two polycrystalline samples with composition Ni2Mn1.2Ga0.8 and Ni2.15Mn0.85Ga, respectively, showing a 7M martensitic state stable at room temperature, were studied. The determination of the modulated crystal structure of Ni2Mn1.2Ga0.8 martensite was achieved by refining the X-ray powder diffraction pattern by the Rietveld method. The basic structure belongs to monoclinic symmetry. The crystal structure, solved within the superspace approach, is found to show an incommensurate 7M modulation with q =0.308c ∗. The Rietveld refinement for Ni2.15Mn0.85Ga martensite on the basis of neutron powder data surprisingly provides a very similar incommensurate 7M structure with the same periodicity and analogous modulation function. The incommensurate structure presents typical displacive modulation with several analogies with the Zhdanov (5, )2 stacking sequence. [Copyright &y& Elsevier]

The microstructure of multiphase steels assisted by transformation-induced plasticity consists of grains of retained austenite embedded in a ferrite-based matrix. Upon mechanical loading, retained austenite may transform into martensite, as a result of which plastic deformations are induced in the surrounding phases, i.e., the ferrite-based matrix and the untransformed austenite. In the present work, a crystallographically based model is developed to describe the elastoplastic transformation process in the austenitic region. The model is formulated within a large-deformation framework where the transformation kinematics is connected to the crystallographic theory of martensitic transformations. The effective elastic stiffness accounts for anisotropy arising from crystallographic orientations as well as for dilation effects due to the transformation. The transformation model is coupled to a single-crystal plasticity model for a face-centered cubic lattice to quantify the plastic deformations in the untransformed austenite. The driving forces for transformation and plasticity are derived from thermodynamical principles and include lower-length-scale contributions from surface and defect energies associated to, respectively, habit planes and dislocations. In order to demonstrate the essential features of the model, simulations are carried out for austenitic single crystals subjected to basic loading modes. To describe the elastoplastic response of the ferritic matrix in a multiphase steel, a crystal plasticity model for a body-centered cubic lattice is adopted. This model includes the effect of nonglide stresses in order to reproduce the asymmetry of slips in the twinning and antitwinning directions that characterizes the behavior of this type of lattices. The models for austenite and ferrite are combined to simulate the microstructural behavior of a multiphase steel. The results of the simulations show the relevance of including plastic deformations in the austenite in order to predict a more realistic evolution of the transformation process. [ABSTRACT FROM AUTHOR]

We report results of ab initio calculations of the ferromagnetic Heusler alloy Ni2MnGa. Particular emphasis is placed on the stability of the low temperature tetragonal structure with c/a=0.94. This structure cannot be derived from the parent L21 structure by a simple homogeneous strain associated with the soft elastic constant C′. In order to stabilize the tetragonal phase, one has to take into account shuffles of atoms, which form a wave-like pattern of atomic displacements with a well defined period (modulation). While the modulation is related to the soft acoustic [1 1 0]-TA2 phonon mode observed in Ni2MnGa, we obtain additional atomic shuffles, which are related to acoustic-optical coupling of the phonons in Ni2MnGa. In addition, we have simulated an off-stoichiometric system, in which 25% of Mn atoms are replaced by Ni. The energy of this structure also exhibits a local minimum at c/a=0.94. This allows us to conclude that both shuffles and atomic disorder stabilize the c/a=0.94 structure. In both cases the stability seems to be associated with a dip in the minority-spin density of states (DOS) at the Fermi level, being related to the formation of hybrid states of Ni d and Ga p minority-spin orbitals. [Copyright &y& Elsevier]

We have studied the effects of partial substitution of In by Si on the magnetic and exchange bias properties of bulk Ni50Mn35In15 Heusler alloys through magnetization measurements. Zero-field and field-cooled magnetization measurements were performed in fields up to 5 T. It was observed that an increase in the Si concentration strongly affects the ground state of the martensitic phase and the magnetic properties of compounds. It was found that exchange bias increases with increasing conduction electron concentration, and the maximum bias field was found to be ≈0.017 T at S K for a cooling field of H = 5 T. [ABSTRACT FROM AUTHOR]

The present study was undertaken to investigate the effect of continuous and discontinuous (cyclic) solution heat treatment on the athermal and isothermal ε martensite phase transformation in Co-28Cr-6Mo-0.3C implant alloy. The results showed that the cyclic solution heat treatment induced more of the athermal ε martensite phase in the alloy than that of the continues one. In addition, the cyclic heat treatment contributes to the development of more isothermal martensite phase during isothermal aging at 850 °C and, moreover, grain refinement in the area beneath the sample surface. The severity of grain refinement was highly significant adjacent to the surface and decreased by increasing the distance from the sample free surface. This novel grain refinement in high-carbon Co-Cr-Mo alloy was attributed to the generation of larger quenching thermal stresses introduced beneath the surface during cyclic solution treatment. The repetitive heating/cooling cycle modifies the surface properties, refines the grain size and leads to uniform dispersion of the secondary carbides. The corrosion resistance of the cyclically solution heat-treated samples was superior as compared to the as-cast one. [ABSTRACT FROM AUTHOR]