Martensite In Ti Research Articles

Composition dependence of phase transformation and shape memory effect of Ti-Zr-Pd-Pt high temperature shape memory alloys

Ti-Zr-Pd-Pt alloys have been considered as potential candidates for high-temperature shape memory alloys (HT-SMAs). In this study, nine alloys were prepared to investigate the effect of multi-component alloying on the phase transformation and shape memory effect. The structural phase diagram of martensite in Ti–Zr–Pd–Pt quaternary alloys was firstly systematically investigated to provide insights and predictions for further research. The phase transformation is divided into three groups: typical martensitic transformation (MT) area, supercooling-controlled phase transformation area and diffusion-assisted phase transformation area. The martensite structure changes from B19 to B33 with the addition of Zr over 25 %. The contribution of Pt contents to raising the martensitic transformation temperature (MTT) became less pronounced with increasing Zr contents. As for shape recovery, over 87 % shape recovery was obtained even under 300 MPa in Ti-10Zr-Pd-Pt alloys, among which Ti-10Zr-15Pt-35Pd presents the highest recovery ratio of over 97 %.

Reorientation induced plasticity in full αʺ martensite Ti-9V-1Fe-4Al alloy

The microstructure and deformation mechanism of a full orthorhombic αʺ martensite Ti-9V-1Fe-4Al (wt.%) alloy were investigated by XRD, TEM, EBSD analyses and tensile tests. The results show that the quenched alloy has a twinned-martensite microstructure and {111}αʺ type I internal twins are formed as the lattice invariant shear for martensite transformation. The alloy plastically deforms by a complex reorientation of αʺ martensite variants via the movement of the inter-variant boundaries of <211>α′′ type Ⅱ twin, and deformation twinning of {111}α′′ type I internal twin and of newly generated {011}αʺ compound twin in primary twinned martensites. {130}α′′<3¯ 10>α′′ and {110}α′′<1 1‾ 0>α′′ plastic twins were not observed in the alloy. Such a kind of deformation induced martensite reorientation results in a good combination of strength and plasticity with yielding strength of 480 MPa, tensile strength of 1030 MPa and elongation of 23% in the alloy. The calculated results further show that the shears of {111}α′′ type I, <211>α′′ type II and {011}α′′ compound twins and the shuffle of {111}α′′ type I twin increase, while the shears of {130}α′′<3‾ 10>α′′ and {110}α′′<1 1‾ 0>α′′ twins and the shuffle of {130}α′′<3‾ 10>α′′ twin decrease with an increase of the lattice parameter ratio bα′′/aα′′. The shears of these activated twinning systems are larger than those of {130}α′′<3‾ 10>α′′ and {110}α′′<1 1‾ 0>α′′ twins, and the shuffle of {111}α′′ type I twin is also bigger than that of {130}α′′<3‾ 10>α′′ twin in the present alloy, which implies that the operative twining modes cannot be derived simply in terms of the shear and shuffle magnitude in full αʺ martensite Ti based alloys.

Optimizing Structural and Mechanical Properties of an Industrial Ti-6246 Alloy below β-Transus Transition Temperature through Thermomechanical Processing.

This study aims to investigate the effect of hot deformation on commercially available Ti-6246 alloy below its β-transus transition temperature at 900 °C, knowing that the α → β transition temperature of Ti-6246 alloy is about 935 °C. The study systematically applies a thermomechanical processing cycle, including hot rolling at 900 °C and solution and ageing treatments at various temperatures, to investigate microstructural and mechanical alterations. The solution treatments are performed at temperatures of 800 °C, 900 °C and 1000 °C, i.e., below and above the β-transus transition temperature, for 9 min, followed by oil quenching. The ageing treatment is performed at 600 °C for 6 h, followed by air quenching. Employing various techniques, such as X-ray diffraction, scanning electron microscopy, optical microscopy, tensile strength and microhardness testing, the research identifies crucial changes in the alloy's constituent phases and morphology during thermomechanical processing. In solution treatment conditions, it was found that at temperatures of 800 °C and 900 °C, the α'-Ti martensite phase was generated in the primary α-Ti phase according to Burger's relation, but the recrystallization process was preferred at a temperature of 900 °C, while at a temperature of 1000 °C, the α″-Ti martensite phase was generated in the primary β-Ti phase according to Burger's relation. The ageing treatment conditions cause the α'-Ti/α″-Ti martensite phases to revert to their α-Ti/β-Ti primary phases. The mechanical properties, in terms of strength and ductility, underwent an important beneficial evolution when applying solution treatment, followed by ageing treatment, which provided an optimal mixture of strength and ductility. This paper provides engineers with the opportunity to understand the mechanical performance of Ti-6246 alloy under applied stresses and to improve its applications by designing highly efficient components, particularly military engine components, ultimately contributing to advances in technology and materials science.

Effect of Hf on the lattice invariant shear and self-accommodation of martensite in Ti–Ni–Hf alloys

Effect of Hf on the lattice invariant shear and self-accommodation of martensite in Ti–Ni–Hf alloys

Twinning-induced Plasticity Mechanism of α″-martensitic Titanium Alloy

The deformation mechanisms of an α″-martensitic Ti–8Mo alloy were investigated by ex-situ electron microscopy tensile tests. Two deformation twins, {110}〈11¯0〉α″ and {130}〈3¯10〉α″ were simultaneously generated by two pathways: (1) direct from primary laths and (2) via reorientation twins. The generation of deformation twinning is strongly dependent on orientation and follows Schmid's law. The dominant twinning in α″ martensite was determined by comparing the shuffle magnitudes calculated from the lattice parameter and the magnitude of lattice modulation. {110}〈11¯0〉α″ and {130}〈3¯10〉α″ twins are activated simultaneously in Ti alloys with a low β-stabilizer content, such as Ti–8Mo alloy.

Microstructural and Interfacial Characterization of Ti–V Diffusion Bonding Zones

Ti and V were bonded together and subjected to high-temperature treatment at 1000 or 1100 °C for 16 h to study the microstructural evolution and interfacial behavior of Ti–V diffusion interfaces. The samples were prepared by electro-polishing and analyzed using scanning electron microscopy, electron probe microanalysis, electron back-scattered diffraction, and nano-indentation. The results indicated that Ti–V diffusion bonding interfaces comprises a martensite Ti zone, a body-center-cubic Ti (β-Ti) zone, and a V-based alloy zone. They are divided by two composition interfaces with V contents of ~13.5% and ~46%. The original interface between the pure Ti and the V alloy substrate falls within the β-Ti zone. The observation of acicular-martensite rather than lath-martensite is due to the distortion caused by the β-to-α phase transformation in the adjacent pure Ti. The recrystallization of β-Ti is distributed along the interface direction. The hardness varies across the Ti–V interface bonding zones with the maximum value of 7.9 GPa.

The formation of a high-strength state in martensitic Ti Grade 4 by ECAP

This work is aimed at studying the features of initial Ti Grade 4 structure that affects the changes in its structure and properties during equal channel angular pressing (ECAP). A hot-rolled and martensite structure state, obtained in the process of water quenching from 950 °C were used as initial states. It has been established that ECAP of titanium in an initial martensitic state leads to the formation of a finer and more homogeneous structure than ECAP of a hot-rolled state. The share of high-angle boundaries reaches 80%, and the average size of structural fragments is 220 ± 80 nm. After ECAP at 400 °C, recrystallized grains are observed. As a result, the ECAP of titanium in the initial martensitic state leads to more significant hardening of up to 1100 ± 20 MPa compared to the hot-rolled state of –950 ± 15 MPa. This will make it possible to reduce the number of technological operations, as well as improve the strength resource for heat treatment aimed at ductility enhancement in ultrafine-grained titanium.

Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

Formation Mechanism of Tempering-Induced Martensite in Ti–10Mo–7Al Alloy

Binary Ti–Fe system. Part II: Modelling of pressure-dependent phase stabilities

Based on the experimental and calculated data from literature, the thermodynamic assessment of the binary Ti–Fe system under hydrostatic pressure was performed. The pressure-independent part of the Gibbs energy was modelled using the heat capacity data. The description of the pressure-dependent part of the Gibbs energy was based on the molar volume, thermal expansion and bulk modulus data, and on their pressure derivatives. Using the Murnaghan equation of state, the binary phase stabilities in the Ti–Fe system were assessed to reproduce the experimental results in the pressure range between 2.3 and 2.7 GPa. The thermodynamic functions were converted into the parameters of a phenomenological pressure model, which is implemented in the Thermo-Calc software. The reliability of the assessment is illustrated on the unary systems Ti and Fe containing high-temperature and high-pressure phases, and on the binary Ti–Fe system containing intermetallic phases TiFe and TiFe2 in addition to the terminal solid solutions. It is shown that the calculation of the T0 lines can help in understanding the formation of α′-Ti(Fe) martensite and the high-pressure phase ω-Ti and its metastability at atmospheric pressure.

Surface Alloying and Improved Property of Nb on TC4 Induced by High Current Pulsed Electron Beam

In this paper, an Nb alloying layer on a TC4 alloy was fabricated by using high-current pulsed electron beam (HCPEB) irradiation to improve surface performance. X-ray diffraction (XRD), optical microscopy (OM), laser surface microscope (LSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the phase composition and microstructure of the surface layer. The microhardness, wear tests and corrosion resistance were also examined. The results show that after HCPEB alloying, a Nb-alloyed layer was formed with about 3.6 μm in thickness on the surface of the sample, which was mainly composed of α’-Ti martensite, β-Ti equiaxial crystals, and NbTi4 particles. After HCPEB irradiation, the surface hardness, wear resistance and corrosion resistance of Nb alloying layer on TC4 alloy were improved compared to the initial samples.

The microstructures and mechanical properties of martensite Ti and TiN phases in a Ti6Al4V laser-assisted nitriding layer

A fiber laser assisted the preparation of a nitride layer on the Ti6Al4V surface in a pure nitrogen atmosphere. Through SEM, XRD, and XPS analyses, the nitride layer is found to be mainly composed of dendritic TiN phase and an interdendritic α′-Ti phase. Not only the true crystal structure of the two main phases (TiN and α′-Ti) were directly characterized using TEM, but also the mechanical properties were tested by micro-indentation and nano-indentation methods for the first time.It is found that the nano-hardness of the TiN phase is 2609 HV, and the elastic modulus is 208 GPa. During the TiN dendritic fracture process, the primary dendrites undergo near ductile fracture along the growth direction of the secondary dendrites, and microcracks, bifurcations, deflection, etc. occur to form a crack-toughening mechanism. The nano-hardness of α′-Ti is 632 HV, and the elastic modulus is 142.8 GPa. The entanglement of two sets of parallel dislocations in α′-Ti crystals forms subgrain boundaries, which exert a positive influence on work hardening and fine-grain strengthening. • A large number of parallel dislocation groups in the generated TiN. • TiN dendrites not only have near ductile fracture, but also have crack toughening; • A large number of parallel dislocation groups and subgrain boundaries in the α′-Ti.

The role of thermomechanical processing routes on the grain boundary network of martensite in Ti–6Al–4V

The influence of thermomechanical processing (TMP) of a Ti–6Al–4V alloy on the transformation texture and intervariant boundary network were investigated by conventional EBSD mapping along with the five-parameter boundary analysis approach. The texture characteristics of Ti–6Al–4V subjected to deformation in the β regime followed by the β→α martensitic transformation were examined using visco-plastic self-consistent simulation and forward calculation of the transformation texture. Comparison of the simulated and experimental texture characterisitcs revealed that the transformed α′ texture was dominated by the variant selection associated with substructure development in the β parent phase and the occurrence of specific self-accommodating α′ variants in the microstructure, promoting the quadrilateral and/or V shape variant arrangement. This resulted in a progressive increase in the 63.26°/[10‾553‾] intervariant boundaries with the strain increment, at the expense of 60°/[112‾0]. Moreover, the grain boundary network for all conditions was dominated by the triple junctions (grain boundary network) terminating on 63.26°/[10‾553‾] and 60°/[112‾0] intervariants. It is shown that the elastic interactions among the variants during the martensitic transformation is the dominant parameter affecting the grain boundary network, despite the presence of dislocation based variant selection.

Effect of texture on shape memory property of Ti–16Nb high temperature shape memory alloy

Microstructure evolution, texture and shape memory properties of the martensitic Ti−16Nb (at.%) alloy subjected to cold rolling and post deformation annealing were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and Schmid factor analyses. The present alloy deforms mainly by twinning of the {111}o type I or its conjugate, the 211o type II twins along with slip of martensite, when cold-rolled in martensite state. The {112}b111‾b texture of the ex-β grains, in which parallel martensite plates with the {111}o type I or the 211o type II twin relation grow, are formed after post-deformation annealing at 700 °C for 30 min. The orientation effect of {112}b111‾b texture on the Ti−16Nb alloy is analyzed. Both experimental results based on tensile tests and theoretical Schmid factor analysis converge satisfactorily. In result the critical stress for reorientation of martensite variants decreases first, and increases then, as the deviation angle increases. Schmid factor for martensite slip decreases remarkably in the textured Ti−16Nb alloy while the loading direction is parallel to the rolling direction. As a result, slip is introduced difficultly in such case and a total recovery strain of 5% is obtained.

In-situ observation of nucleation, growth and interaction of deformation-induced [formula omitted] martensite in metastable Ti–10V–2Fe–3Al

Microstructure evolution, dominated by the formation of deformation-induced α″ martensite during the 3-point bending of a metastable β Ti–10V–2Fe–3Al alloy containing 5% α, was observed in-situ using forward-scatter electron imaging and electron backscattering diffraction. α″ plates nucleated heterogeneously from {580}α″ habit planes at α-β interfaces and triggered the nucleation of additional α″ plates at the advancing interface during growth and upon impingement with high-angle boundaries. Further thickening of the impinged α″ plates led to a build-up of strain energy which induced 13031‾0α'' twinning within obstacle-forming α″ plates. Until now, this twinning system was observed in Nb and Ta alloyed Ti shape memory alloys only. This in-situ study is also the first to document the activation of 13031‾0α'' twinning by α″ impingement in a metastable β matrix. The first forming variants were {011}α″ compound twin-related variant pairs, each forming from up to two individual habit planes. These variant pairs were consistently predicted by determining the grain-average stress with finite element analysis and computing the available work from the transformation strain of the α″ variants. At higher indenter loads, grains that were unfavourably oriented to martensite formation accommodated the local stress by forming aggregates of different α″ variants, obeying either {111}α″ type I or 211α'' type II twin relationships. Scanning transmission electron microscopy revealed α″ substructures comprising columnar domains oriented perpendicular to the habit plane along with the absence of lattice invariant deformation. The growth of α″ plates involved ledge formation at α″-β interfaces.

Microstructure and Mechanical Properties Evolution during Solution and Ageing Treatment for a Hot Deformed, above β-transus, Ti-6246 Alloy

The present study investigates the influence of hot-deformation, above β-transus and different thermal treatments on the microstructural and mechanical behaviour of a commercially available Ti-6246 titanium-based alloy, by SEM (scanning electron microscopy), tensile and microhardness testing techniques. The as-received Ti-6246 alloy was hot-deformed—HR by rolling, at 1000 °C, with a total thickness reduction (total deformation degree) of 65%, in 4 rolling passes. After HR, different thermal (solution—ST and ageing—A) treatments were applied in order to induce changes in the alloy’s microstructure and mechanical behaviour. The applied solution treatments (ST) were performed at temperatures below and above β-transus (α → β transition temperature; approx. 935 °C), to 800 °C, 900 °C and 1000 °C respectively, while ageing treatment at a fixed temperature of 600 °C. The STs duration was fixed at 27 min while A duration at 6 h. Microstructural characteristics of all thermomechanical (TM) processed samples and obtained mechanical properties were analysed and correlated with the TM processing conditions. The microstructure analysis shows that the applied TM processing route influences the morphology of the alloy’s constituent phases. The initial AR microstructure shows typical Widmanstätten/basket-weave-type grains which, after HR, are heavily deformed along the rolling direction. The STs induced the regeneration of α-Ti and β-Ti phases, as thin alternate lamellae/plate-like structures, showing preferred spatial orientation. Also, the STs induced the formation of α′-Ti/α″-Ti martensite phases within parent α-Ti/β-Ti phases. The ageing treatment (A) induces reversion of α′-Ti/α″-Ti martensite phases in parent α-Ti/β-Ti phases. Mechanical behaviour showed that both strength and ductility properties are influenced, also, by applied TM processing route, optimum properties being obtained for a ST temperature of 900 °C followed by ageing (ST2 + A state), when both strength and ductility properties are at their maximum (σUTS = 1279 ± 15 MPa, σ0.2 = 1161 ± 14 MPa, εf = 10.1 ± 1.3%).

On the grain boundary network characteristics in a martensitic Ti–6Al–4V alloy

The characteristics of the intervariant boundary network that resulted from the $$\beta \to \alpha^{\prime}$$ martensitic phase transformation in a Ti–6Al–4V alloy were studied using the crystallographic theories of displacive transformations, five-parameter grain boundary analysis and triple junction analysis. The microstructure of Ti–6Al–4V martensite consisted of fine laths containing dislocations and fine twins. The misorientation angle distribution revealed four distinct peaks consistent with the intervariant boundaries expected from the Burgers orientation relationship. The phenomenological theory of martensite predicted four-variant clustering to have the lowest transformation strain among different variant clustering combinations. This configuration was consistent with the observed Ti–6Al–4V martensitic microstructure, where four-variant clusters consisted of two pairs of distinct V-shape variants. The $$63.26^\circ /[\overline{10}\, 5\, 5\, \overline{3}]_{{\alpha^{\prime}}}$$ and $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ intervariant boundaries accounted for ~ 38% and 33% of the total population, respectively. The five-parameter boundary analysis showed that the former had a twist character, being terminated on the $$(\overline{3}\, 2\, 1\, 0)_{{\alpha^{\prime}}}$$ plane, and the latter revealed a symmetric tilt $$(1\, 0\, \overline{1}\, 1)_{{\alpha^{\prime}}}$$ boundary plane. The $$63.26^\circ /[\overline{10}\, 5\, 5\, \overline{3}]_{{\alpha^{\prime}}}$$ and $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ had the highest connectivity at triple junctions among other intervariant boundaries. Interestingly, the boundary network in Ti–6Al–4V martensite was significantly different from the commercially pure Ti martensite, where only $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ intervariant boundaries largely were found at triple junctions due to the formation of three-variant clustering to minimize the transformation strain. This difference is thought to result from a change in the martensitic transformation mechanism (slip vs twinning) caused by the alloy composition.

Microstructural characterization of different metal matrix composite claddings reinforced by TiC through YAG laser cladding

In this work, a YAG laser was used to clad TiC-reinforced metal matrix composite layers on the surface of different types of metals; low carbon steel, high C–Cr bearing tool steel, spheroidal graphite cast iron and commercially pure titanium. The cladding processes were carried out at heat inputs ranging from 175 J mm−1 to 700 J mm−1 and at a fixed traveling speed of 4 mm s−1. The microstructures of the cladding layers were investigated in detail. In all cases, TiC-surface metal matrix composite layers were successfully formed at different laser heat inputs on all the metal surfaces. A few TiC particles seemed as fine dendrites after the laser treatment. The amount of dendritic TiC has a direct relationship with the laser heat input. For low carbon steel, the clad layer showed a martensitic structure, with sound metallurgical bonding to the base metal and without any defects at the highest laser heat input used in this study (700 J mm−1). In the case of high C–Cr bearing tool steel, lower laser heat inputs were enough to form a sound clad layer consisting of fine TiC dendrites distributed in a matrix of martensite laths, some retained austenite and acicular carbides. Laser heat input of 175 J mm−1 was enough to build a defect-free clad layer on spheroidal graphite cast iron. The matrix comprised of cementite, martensite, and some blocks of retained austenite. Cracking appears at a higher heat input of 500 J mm−1 in the spheroidal graphite cast iron. The matrix of the clad layer on pure Ti substrate was α′-Ti martensite, which decreased by increasing the laser heat input.

TEM investigations of active screen plasma nitrided Ti6Al4V and Ti6Al7Nb alloys

Direct current plasma nitriding (DC PN) helped to lower processing temperature as compared gas nitriding (GN) allowing to protect the surface with a layer of TiN compound and preserve the mechanical properties of the core material, which otherwise might lose its fine grain microstructure. However, samples of more complicated shapes are subjected to edge effects resulting in their overheating and uneven coverage. Introduction of active screen plasma nitriding (AS PN) should take care of both of these disadvantages, but the understanding on its effect on the compound and diffusive layers of processed parts is far from being clear. The present experiment was aimed at comparing the microstructure and the phase composition of DC PN and AS PN treated Ti6Al4V and Ti6Al7Nb alloys at temperatures of 680 °C and 740 °C. The microstructure investigations were performed with TEM/EDS methods, while phase analysis relied on electron diffraction indexing. It showed that switching from DC PN to AS PN resulted in covering it with a compact TiN layer backed with α″-Ti(N) martensite and Ti3Al-type layers, i.e. same as in the former case (DC PN) except the missing δ′-Ti2N layer. Additionally, it changes nitriding mechanism from absorption-diffusion of nitrogen ions to adsorption-diffusion of these species, what is a reason of slowing down of the rate of nucleation and growth of both the compound and diffusive layers. The growth of β-Ti(N) layer, which changes on cooling to α″-Ti(N) is controlled by in-diffusion of nitrogen to its front.

Oxygen induced crystal structure transition of martensite in Ti–Nb–Fe alloys

The role of oxygen in the martensitic transformation and corresponding mechanical properties was studied in Ti–8Nb–2Fe base alloy. Abundant hexagonal α′ martensite formed in the base alloy and exhibited low strength. Oxygen induced strain field enhanced the shuffling process but hindered {112¯}β〈111〉β shearing during martensitic transformation therefore distorted the hexagonal α′ martensite to orthorhombic α″ martensite, causing remarkable strength enhancement.

The Microalloying Effect of Ce on the Mechanical Properties of Medium Entropy Bulk Metallic Glass Composites

Novel ultra-strong medium entropy bulk metallic glasses composites (BMGCs) Fe65.4−xCexMn14.3Si9.4Cr10C0.9 and Ti40−xCexNi40Cu20 (x = 0, 1.0), through the martensite transformation induced plasticity (TRIP effect) to enhance both the ductility and work-hardening capability, were fabricated using magnetic levitation melting and copper mold suction via high frequency induction heating. Furthermore, the Ce microalloying effects on microstructure and mechanical behaviors were studied. The Fe-based BMGCs consisted of face-centered cubic (fcc) γ-Fe and body-centered cubic (bcc) α-Fe phase, as well as Ti-based BMGCs containing supercooled B2-Ti (Ni, Cu) and a thermally induced martensite phase B19’-Ti (Ni, Cu). As loading, the TRIP BMGCs exhibited work-hardening behavior, a high fracture strength, and large plasticity, which was attributed to the stress-induced transformation of ε-Fe martensite and B19’-Ti (Ni, Cu) martensite. Ce addition further improved the strengthening and toughening effects of TRIP BMGCs. Adding elemental Ce enhanced the mixing entropy ΔSmix and atomic size difference δ, while reducing the mixing enthalpy ΔHmix, thus improving the glass forming ability and delaying the phase transition process, and hence prolonging the work-hardening period before fracturing. The fracture strength σf and plastic stress εp of Ti39CeNi40Cu20 and Fe64.4CeMn14.3Si9.4Cr10C0.9 alloys were up to 2635 MPa and 13.8%, and 2905 MPa and 30.1%, respectively.