Susceptibility of crystalline alloys to deformational amorphization during torsion under quasi-hydrostatic pressure

Features of the transition of Ni₅₀Ti₃₀Hf₂₀, Ti₅₀Ni₂₅, Zr₅₀Ni₁₈Ti₁₇Cu₁₅, and Fe₇₈B_8.5Si₉P_4.5 crystalline alloys with different susceptibilities to amorphization upon annealing and in the amorphous state during intense deformation in a Bridgman chamber are considered. The single- and two-phase crystalline states of the chosen alloys are obtained in different annealing modes. It is shown that the amorphizing rate of crystalline alloys differ substantially at the same degree of deformation; i.e., single-phase crystalline alloys based on titanium nickelide and iron amorphize well, while zirconium-based alloy amorphizes weakly in a manner similar to two-phase iron alloy. We believe that the LDA of crystalline alloys and their corresponding crystalline phases is determined by mechanical, thermodynamic, and concentration factors.     

Formation of nanostructured states in ternary TiNiFe-based shape memory alloys during megaplastic deformation and subsequent heat treatment

The ternary metastable TiNiFe alloys that exhibit a low-temperature shape memory effect and are subjected to plastic deformation by rolling or high-pressure torsion followed by heat treatment are studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electrical resistivity measurements. It is found that moderate plastic deformation of a Ti₅₀Ni₄₉Fe₁ alloy at room temperature initiates the thermoelastic B2 ? B19’ martensitic transformation and the formation of a developed banded dislocation and twin substructure in the B19’ martensite. This deformation of a Ti₅₀Ni₄₇Fe₃ alloy forms a similar dislocation substructure but in B2 austenite. Megaplastic deformation by high-pressure torsion causes amorphization in the Ti₅₀Ni₄₉Fe₁ alloy and nanofragmentation in the Ti₅₀Ni₄₇Fe₃ alloy. The evolution of the nanostructure and the martensitic transformations in TiNiFe-based ternary alloys is studied during plastic deformation and subsequent annealing at various temperatures.     

Martensitic transformation in amorphous-crystalline Ti-Ni-Cu and Ti-Hf-Ni-Cu thin ribbons

Martensitic transformations and strain variation in amorphous-crystalline thin ribbons of Ti₅₀Ni₂₅Cu₂₅, Ti_40.7Hf_9.5Ni_44.8Cu₅ and Ti_40.7Hf_9.5Ni_39.8Cu₁₀ alloys were investigated. The amorphous-crystalline state in the samples was produced by an interruption of the isothermal crystallization in DSC apparatus. The volume fraction of the crystalline phase V_cryst in the samples was varied from 10 to 100%. Transformation temperatures in amorphous-crystalline thin ribbons of Ti₅₀Ni₂₅Cu₂₅ alloy depended only slightly on the crystalline volume fraction. On the contrary, the strong dependence of the martensitic transformation temperatures on the volume of crystalline phase was obtained in Ti_40.7Hf_9.5Ni_44.8Cu₅ and Ti_40.7Hf_9.5Ni_39.8Cu₁₀ alloys. Moreover, it was found that the intervals of the direct transformation are extremely narrow, whereas the intervals of the reverse transformation are unusually wide. As the crystalline volume fraction rises, both the direct transformation interval and the reverse one decrease, and the transformation temperatures increase. It was shown that increase of the Cu-content in Ti_40.7Hf_9.5Ni_{49.8 -x}Cu_x (x = 5, 10%) alloys results in decrease of the transformation temperatures, of the temperature interval of the reverse transformation on heating and of the hysteresis, while the temperature interval of the direct transformation on cooling widens     

Features of the surface layers of TiNi-based alloy thin ribbons

The chemical composition of the surface of TiNi-based alloys in the form of ribbons produced by rapid melt quenching in oxygen-containing environment has been investigated. It is shown that titanium oxide is formed on the Ti₅₀Ni₂₅Cu₂₅ alloy surface, while on the Ti_39.2Ni_24.8Cu₂₅Hf₁₁ alloy surface titanium and hafnium oxides are formed. Atomic-force microscope images reveal crystalline structures of titanium oxide with sizes of up to 500 × 500 nm² on the surface of the Ti₅₀Ni₂₅Cu₂₅ sample. After removing the surface oxide layer by ion etching, the ratio of elements becomes close to the stoichiometric composition.     

Experimental valence-band study of Ti(NiCu) alloys with different compositions and crystal structures

The density of valence-band electronic states of Ti(NiCu) alloys with different crystal structures and elemental compositions has been studied by X-ray photoelectron spectroscopy. It has been established that the change in the crystal state initiated by a martensitic transformation or a transition from the amorphous state to the crystal state does not affect the valence-band electronic state density distribution of the Ti₅₀Ni₅₀ and Ti₅₀Ni₂₅Cu₂₅ alloys. It has been shown that a change in the elemental composition leads to a noticeable redistribution of the electronic density in alloys of the Ti₅₀Ni_{50 ? x} Cu _x system (x = 0, 10, 15, 25, 30, 38, 50 at. %). As the copper concentration in the Ti(NiCu) alloys increases, the contribution of the Ni d states in the vicinity of the Fermi level decreases, with the d band of nickel shifting toward higher binding energies, and that of copper, toward lower binding energies.     

Phase transformations and structure of Ni–Mn–In alloys with varying ratio Ni/Mn

The fine structure of Ni–Mn–In alloys has been studied when manganese atoms are substituted for nickel atoms in an annealing state. The concentration dependence of the critical temperatures and the structures of the alloys have been discussed. It has been found that, as manganese atoms replace nickel atoms, the structure after annealing is changed from a two-phase (L2₁ + martensite) to single-phase L2₁ structure. The martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy is accompanied by the formation of modulated 14M martensite.     

Shape memory behaviour of annealed Ti48.5Ni(51.5− x )Cu x (x = 6.2–33.5) thin films

The shape memory behaviour of (Ni,Cu)-rich Ti–Ni–Cu thin films (Ti_48.9Ni_44.9Cu_6.2, Ti_48.5Ni₄₀Cu_11.5, Ti_48.6Ni_35.9Cu_15.5, Ti_48.3Ni_28.4Cu_23.3, Ti_48.3Ni_23.9Cu_27.8 and Ti_48.5Ni₁₈Cu_33.5) annealed at 773, 873 and 973 K for 1 h was investigated. The films with 6.2, 11.5–15.5 and 23.3–33.5 at% Cu showed a single-stage deformation due to a B2 ? B19′ transformation, a two-stage deformation due to the B2 ? B19 ? B19′ transformation and a single-stage deformation due to the B2 ? B19′ transformation, respectively. The martensitic transformation start temperature (M _s) increased with increasing Cu content and then levelled off for more than 15 at% Cu, indicating a high Ms temperature of 345 K. Temperature hystereses were almost 15 K for all films with more than 10 at% Cu. The critical stress for slip increased with increasing Cu content and increased significantly for the Ti_48.5Ni₁₈Cu_33.5 film, whereas the maximum recoverable strain significantly decreased for the Ti_48.5Ni₁₈Cu_33.5 film. With decreasing annealing temperature, the critical stress for slip increased, but the M _s temperature decreased. It was found that films with 11.5 at% Cu or more, annealed at 873 K, showed a high martensitic transformation temperature and a high critical stress for slip.     

Two-way shape memory in a nanoscale sample of Ti49.5Ni25.5Cu25.0 alloy with a partially ordered structure

The dependence of the thermomechanical properties and structure of rapidly quenched Ti_49.5Ni_25.5Cu_25.0 alloy on the annealing conditions has been studied. A sample with a partially ordered structure is found to have two-way shape memory effect during single deformation. An alloy sample 17 × 10 × 0.07 μm in size has been prepared and trained. It is shown to demonstrate two-way shape memory behavior.     

Microstructure and shape memory behaviour of annealed Ti51.5Ni(48.5- x )Cu x ( x = 6.5–20.9) thin films

Ti-rich Ti–Ni–Cu amorphous films (Ti_51.9Ni_41.6Cu_6.5, Ti_51.6Ni_36.8Cu_11.6, Ti_51.5Ni_33.1Cu_15.4 and Ti_51.7Ni_27.4Cu_20.9), formed by sputtering, were annealed at 773, 873 and 973?K for 1?h and their structures and shape memory behaviours investigated. All the films annealed at 773?K for 1?h exhibited Guinier–Preston (GP) zones, but these precipitates were absent after annealing at 873?K or higher. Instead of GP zones, coherent plate precipitates of a Ti₂Cu phase were formed in films annealed at 873?K for 1?h, when the Cu content was between 11.6 to 20.9 at.%. The strain–temperature curves under constant stresses of Ti_51.6Ni_36.8Cu_11.6 and Ti_51.5Ni_33.1Cu_15.4 films showed a two-step deformation associated with the B2???B19???B19′ transformation, whereas Ti_51.9Ni_41.6Cu_6.5 and Ti_51.7Ni_27.4Cu_20.9 films showed a single-step deformation associated with the B2?B19′ and B2?B19 transformations, respectively. The two kinds of plate precipitates, GP zones and a Ti₂Cu phase were found to be effective to increase the critical stress for plastic strain.     

Study of the heat treatment influence on the formation of nanostructured state in bulk titanium nickelide alloys subjected to severe plastic deformation

The influence of annealing on bulk samples of Ti_49.4Ni_50.6 alloy subjected to severe plastic deformation by torsion under high pressure has been studied by transmission electron microscopy and X-ray diffractometry. It is found that a homogeneous nanocrystalline state is formed in the bulk samples after annealing.     

Amorphization of bulk TiNi-based alloys by severe plastic deformation under high pressure torsion

The structure of bulk samples of Ti_49.4Ni_50.6 alloy after severe plastic deformation by torsion (SPDT) under high pressure have been studied by transmission and scanning electron microscopies. It is found that SPDT by five to seven turns led to almost complete alloy amorphization.     

Crystallization behaviour in a new multicomponent Ti16.6Zr16.6Hf16.6Ni20Cu20Al10 metallic glass developed by the equiatomic substitution technique

A new amorphous Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ alloy has been developed using the novel equiatomic substitution technique. Melt spinning Ti_16.6Zr_16.6Hf_16.6Ni₂₀Cu₂₀A1₁₀ forms an amorphous phase with a large supercooled liquid region, ΔT=70°C. After isothermal annealing within the supercooled liquid region for 3 h at 470°C, the amorphous alloy crystallizes to form a fine-scale distribution of 2–5 nm nanocrystals, and the supercooled liquid region increases to ΔT=108°C. Atomic-scale compositional analysis of this partially crystalline material using a three-dimensional atom probe (3DAP) is unable to detect any compositional difference between the nanocrystals and the remaining amorphous phase. After annealing for 1 hr at 620°C, the amorphous alloy crystallizes to form 20–50nm equiaxed grains of a hexagonal-type C14 Laves phase with lattice parameters a = 5.2Å and c = 9.0 Å. 3DAP analysis shows that this Laves phase has a composition very close to that of the initial amorphous phase, suggesting that the alloy crystallizes via a polymorphic rather than a primary crystallization mechanism, despite the complexity of the alloy composition.     

In situ synchrotron X‐ray diffraction analysis of deformation behaviour in Ti–Ni‐based thin films

Deformation mechanisms of as‐deposited and post‐annealed Ti_50.2Ni_49.6, Ti_50.3Ni_46.2Cu_3.5 and Ti_48.5Ni_40.8Cu_7.5 thin films were investigated using the in situ synchrotron X‐ray diffraction technique. Results showed that initial crystalline phases determined the deformation mechanisms of all the films during tensile loading. For the films dominated by monoclinic martensites (B19′), tensile stress induced the detwinning of 〈011〉 type‐II twins and resulted in the preferred orientations of (002)_B19′ parallel to the loading direction (∥ LD) and (020)_B19′ perpendicular to the LD (⊥ LD). For the films dominated by austenite (B2), the austenite directly transformed into martensitic variants (B19′) with preferred orientations of (002)_B19′ ∥ LD and (020)_B19′ ⊥ LD. For the Ti_50.3Ni_46.2Cu_3.5 and Ti_48.1Ni_40.8Cu_7.5 films, martensitic transformation temperatures decreased apparently after post‐annealing because of the large thermal stress generated in the films due to the large differences in thermal expansion coefficients between the film and substrate.     

Phase transformations in crystalline Ti-Ni-Cu alloy upon severe plastic deformation

X-ray diffraction and transmission electron microscopy were used to study features of the structural and phase transformations of initially crystalline T1₅₀Ni₂₅Cu₂₅ alloy upon severe plastic deformation in a Bridgman cell. Three cycles of successive phase transitions of the crystal ⟹ amorphous state and amorphous state ⟹ crystal type were revealed under continually increasing deformation. The results are explained within the superposition of different channels of elastic energy dissipation at severe plastic deformation.     

On the nature of the “double” yield point in Ti<Subscript>50</Subscript>Ni<Subscript>25</Subscript>Cu<Subscript>25</Subscript> alloy upon high-pressure torsion

The anomalous phenomenon of the “double” yield point attributed with the “crystal ? amorphous state” phase transition during high-pressure torsion of Ti₅₀Ni₂₅Cu₂₅ alloy has been analyzed experimentally and theoretically. Satisfactory correlation between experimental data and theoretical hypothesis has been found.     

The behavior of 3d electrons and defects in TiAl-based alloys containing V and Cu studied by positron annihilation

Information of defects and 3d electrons in transition metals (Ti, V, Cu) and TiAl-based alloys (Ti₅₀Al₅₀, Ti₅₀Al₄₈V₂, Ti₅₀Al₄₈Cu₂) can be extracted from the positron lifetime and coincidence Doppler broadening spectra. The results show that the 3d electron signals for the transition metals Ti, V and Cu increase with the number of 3d electrons. The 3d electron signal and the electron density for binary TiAl alloy are relatively low due to the (Ti)3d-(Al)3p interactions. The addition of V and Cu atoms to TiAl alloy leads to the increase in the electron densities in bulk and the defects on grain boundaries simultaneously, as well as the enhancement of the 3d electron signal. The 3d electron signal in the spectrum of Ti₅₀Al₄₈Cu₂ alloy is higher than that of Ti₅₀Al₄₈V₂ alloy.     

Microstructure of annealed Ti48.5Ni(51.5– x )Cu x (x = 6.2–33.5) thin films

(Ni, Cu)-rich Ti–Ni–Cu amorphous films with a Cu content of 6.2–33.5 at. % formed by sputtering were annealed at 773, 873 and 973 K for 1 h and their microstructures investigated. Two types of precipitate were observed in the annealed films: a Ti(NiCu)₂ phase for the Ti_48.5Ni₄₀Cu_11.5, Ti_48.6Ni_35.9Cu_15.5, Ti_48.3Ni_28.4Cu_23.3 and Ti_48.3Ni_23.9Cu_27.8 films, plus a TiCu phase for the Ti_48.5Ni₁₈Cu_33.5 films. These precipitates were found to have coherency with the B2 matrix in the films annealed at 773 K and were densely distributed within the grains. However, in the films annealed at 873 K, their size increased 10-fold and their density decreased. Annealing at 973 K promoted grain-boundary precipitation and, accordingly, the density of the precipitates in the grain interiors decreased. On the other hand, the annealed Ti_48.9Ni_44.9Cu_6.2 films showed no precipitates in their grain interiors, but the number of grain-boundary precipitates increased with increasing annealing temperature. It was also found that grain size decreased with increasing Cu content and was significantly decreased for the Ti_48.5Ni₁₈Cu_33.5 films.     

Effect of the chemical composition on amorphization of titanium-nickelide-based alloys with fast neutrons

The structural state of a Ti₅₀Ni₄₇Fe₃ single crystal irradiated with fast neutrons (F = 2.5 × 10²⁰ cm^?2) at a temperature of 340 K was studied using thermal neutron diffraction. The alloy of this chemical composition was chosen in searching for a radiation-resistant shape memory material. It is established that this alloy retains its crystalline state after irradiation, whereas the Ti₄₉Ni₅₁ crystal studied previously is completely amorphized after similar irradiation. A detailed analysis of the structural state of the irradiated ternary alloy allowed us to discover the main physical causes of its radiation resistance.     

Ordering kinetics in nickel alloys with tungsten and molybdenum at t=800°C

The kinetics of the transition of alloys Ni-W and Ni-W-Mo along the slit Ni+20 at. % (W+Mo) from the disordered into the ordered state after deformation and isothermal annealing at t=800°C for 1, 2, 5, 10, 20, 50 and 100 hours is studied in this paper. It is established that ordering occurs in the alloys according to the type Ni₄Mo. The degree of long-range order was estimated according to the degree of tetragonality (c/a) of the elementary cells of Ni₄W and Ni₄(W, Mo) that depended on the annealing time and alloy composition. The presence of a ternary superstructure of Ni₄(W, Mo) of the type Dl_a in ternary Ni-W-Mo alloys with 20 at.% (W+Mo) is confirmed by x-ray diffraction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 78–82, June, 1990.     

Near surface composition of some alloys by X-ray photoelectron spectroscopy

Chemical compositions of the alloys of CuNi (Cu_0.10Ni_0.90, Cu_0.30Ni_0.70, Cu_0.70Ni_0.30) and BiSb (Bi_0.80Sb_0.20, Bi_0.64Sb_0.34, Bi_0.55Sb_0.45) are determined by X-ray photoelectron spectroscopy. The stoichiometries are determined and are compared with the bulk compositions. Possible sources of systematic errors contributing to the results are discussed. Errors arising out of preferential etching in these alloys have been investigated. It has been inferred from such studies that the preferential etching does not enrich the surface composition with a particular component for the two systems reported here. Quantitative results of CuNi system indicate that the surface regions of the Cu_0.70Ni_0.30 alloy is Cu-rich, although no such evidence is observed in case of BiSb system.