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The globularization behavior of the basketweave microstructure in TC17 alloy is quantitatively analyzed during deformation and subsequent heat treatment. Collaborative behavior in the α lamellae and β phase evolution are proposed to affect globularization based on the transmission electron microscopy (TEM) and high-resolution electron backscatter diffraction (EBSD) observations as follows: (i) the interleaved α lamellae restrain the rotation of neighboring α lamellae and promote the formation of low-angle boundaries (LABs) and grooves, and then (ii) the β phase has a positive effect on facilitating the complete separation of α lamellae during deformation. During heat treatment, (iii) the formation of the LABs in the β grain interiors accelerates the appearance of necklace-like α grains, and (iv) the α lamellae promotes the break-up of β phase while the β phase has a positive effect on facilitating the complete separation of α lamellae. In other words, Collaborative behavior in α lamellae and β phase evolution promotes the globularization of TC17 alloy containing a basketweave microstructure. Except for the boundary splitting and termination migration, the mechanism of substructure rotation also participates in the globularization of TC17 alloy containing a basketweave microstructure, which is different to that of the alloys containing a colony microstructure. [ABSTRACT FROM AUTHOR]

Second phase particles (SPPs) that are formed during melting process have a significant effect on the hot extrusion and re-extrusion processes of NiTi. In the present work, the evolution of Ti 4 Ni 2 O x (with x ≤ 1) particles during hot extrusion and re-extrusion of near equiatomic Ti-50.6 at.% Ni billets, and their effects on the surrounding matrix microstructure were studied using OM, SEM, TEM and EBSD. The analyses indicate that Ti 4 Ni 2 O x (with x ≤ 1) are the particles that precipitate in the austenite matrix. After hot extrusion and re-extrusion, some particles are elongated and preferentially oriented along the ED. Eventually, these elongated particles are located at the grain boundaries. The size distribution of the SPPs is non-uniform after the first hot extrusion, and this non-uniformity increases after re-extrusion. The presence of non-deforming SPPs produces inhomogeneous deformation with a sharp increase in dislocation density in the surrounding matrix. This is shown to exert a profound effect on the processes of recovery and recrystallization for the surrounding matrix. [ABSTRACT FROM AUTHOR]

As-received and vacuum arc-cast near equiatomic Ti-50.6 at.% Ni billets were extruded and re-extruded at 815 °C at Case Western Reserve University (CWRU) with an extrusion ratio of 4 to 1. The effects of arc-casting, extrusion and re-extrusion on the grain size, volume fraction of recrystallized grains, grain boundary misorientation and texture were analyzed via the high-resolution electron backscatter diffraction (EBSD). The results show that extruding and re-extruding the as-received NiTi shape memory alloy produces a 〈111〉texture//ED and {110}〈uvw〉texture//TD. The size of austenite grains and the volume fraction of recrystallized grains significantly decrease but the fraction of LABs slightly increases and the grain size distribution becomes more homogeneous for the re-extruded NiTi in comparison to the first extrusion. For the vacuum arc-cast extruded NiTi shape memory alloy, the microstructure predominantly consists of elongated austenite grains. There is a strong {001}〈001〉texture//TD at the Butt (i.e. as-cast NiTi). Re-extrusion of the vacuum arc-cast NiTi shape memory alloy produces a material that exhibits two strong textures: ( 110 ) [ 1 1 ¯ 0 ] //CD(ED) and {001}〈100〉//TD in the Extrudate ①. The re-extruded material exhibits few elongated grains at this location. Instead, the second extrusion of the as-cast material produces fine and equiaxed recrystallized grains. [ABSTRACT FROM AUTHOR]

[Display omitted] • The distribution probability of lamellar intersection is modelled to describe the relationship of various α lamellae. • The distributed relationship between lamellar and globular grains is described by the equivalent circle method. • The effect of grain orientation and size is considered compared to the classical grain distribution probability model. • The novelty nearest-surface function is established and used to reveal the uniformity of different morphology grains. A novel probability model of grain morphology distribution considering the orientation and size of non-spherical grains, including P 01 (r) , P 11 (r) , P 02 (r) , P 33 (r) , P 12 (r) , is established based on the nearest-surface function, and it is used to reveal the dispersion and uniformity degree of different morphology grains in titanium alloys. Especially, the distribution probability of lamellar α intersection is introduced instead of the distributed relationship of different α lamellae, and the distributed relationship between lamellar and globular grains is transformed into the distribution of globular grains by the equivalent circle method. Then, several corresponding distribution probabilities are selected in terms of describing different microstructure states (equiaxed, basketweave, duplex microstructures). The model is applied to the quantitative analysis of TC4 alloy with different morphology grains. The results show that the distribution of α grains with different morphology in the β matrix becomes more inhomogeneous with increasing height reduction and cooling rate. Moreover, the larger the globular α size is, the greater the aggregation degree and the smaller the uniformity of other α grains around it is. The reliability of probability model is verified by the comparison between the predicted and the measured frequency distributions for the nearest neighbor surface distance r. [ABSTRACT FROM AUTHOR]

Abstract: The internal state variable approach nowadays is more and more used to describe the deformation behavior in all of the metallic materials. In this paper, firstly the dislocation density rate and the grain growth rate varying with the processing parameters (deformation temperature, strain rate and strain) are established using the dislocation density rate as an internal state variable. Secondly the flow stress model in high temperature deformation process is analyzed for each phase of titanium alloys, in which the flow stress contains a thermal stress and an athermal stress. A Kock–Mecking model is adopted to describe the thermally activated stress, and an athermal stress model is established using two-parameter internal state variables. Finally, a constitutive model coupling the grain size, volume fraction and dislocation density is developed based on the microstructure and crystal plasticity models. And, the material constants in present model may be identified by a genetic algorithm (GA)-based objective optimization technique. Applying the constitutive model to the isothermal compression of Ti–6Al–4V titanium alloy in the deformation temperature ranging from 1093 to1303K and the strain rate ranging from 0.001 to 10.0s−1, the 20 material constants in those models are identified with the help of experimental flow stress and grain size of prior α phase in the isothermal compression of Ti–6Al–4V titanium alloy. The relative difference between the predicted and experimental flow stress is 6.13%, and those of the sampled and the non-sampled grain size are 6.19% and 7.94%, respectively. It can be concluded that the constitutive model with high prediction precision can be used to describe the high temperature deformation behavior of titanium alloys. [Copyright &y& Elsevier]

Abstract: The effect of the deformation temperature, deformation degree, strain rate and their interaction on the microstructure and mechanical properties in the high temperature deformation of Ti-6Al-4V alloy was investigated. The experimental results show that the deformation degree and strain rate have significant influence on the microstructure and mechanical properties, in which finer microstructure and higher tensile strength can be obtained at a middle deformation degree and a higher strain rate. The interactions between the deformation temperature and the deformation degree or the strain rate in the high temperature deformation of Ti-6Al-4V alloy are significant, especially being deformed at the temperature just under the β transus, the ductility and tensile strength are sensitive to all of processing parameters including their interactions. So the interactions should be considered to optimize the processing parameters in order to meet the requirements of the mechanical properties. [Copyright &y& Elsevier]

Abstract: The modeling of constitutive relationships and microstructural variables of the Ti–6.62Al–5.14Sn–1.82Zr alloy during high temperature deformation by using a fuzzy set and artificial neural network (FNN) technique with a back-propagation learning algorithm is the basis of this research. To obtain experimental results for the modeling, the isothermal compression of the titanium alloy in different deformation scenarios was conducted and quantitative metallography was thus obtained. The predicted results of flow stress and microstructural variables, including grain size and volume fraction of the α phase, are compared with the experimental data and the difference is less than 15%. The predicted results are consistent with the experimental data. Furthermore, the comparison between the predicted results of flow stress based on the FNN approach and those by using the regression method has illustrated that the FNN approach is efficient in predicting the flow stress of the alloy. [Copyright &y& Elsevier]

To establish the relationship between mechanical properties and microstructural features, it is necessary to comprehensively describe microstructural characterizations. In present study, an efficient and innovative quantitative method of interleaved degree in lamellar microstructure was developed. Firstly, four types of microstructural variables were defined as key factors that confirmed the microstructural features. Lath length (L) and variation coefficient for distribution of lath angle (CV) were measured to obtain dimension information of laths, and number of lath intersecting points per area (N) and uniformity of lath intersecting points (U) were defined to describe the lath distribution and the lath intersection complexity. Then, the microstructural variables were normalized based on multiple attribute decision-making. Finally, the equation of interleaved degree in lamellar microstructure was established based on entropy weight method. Present quantitative method was applied to analyze the interleaved degree of TC17 alloy containing a basketweave microstructure. It was shown that interleaved degree was higher at a deformation temperature of 930 °C, a height reduction of 40% and a strain rate of 0.1 s−1 and decreased with increasing cooling time. Besides, a model that can theoretically calculate fracture toughness based on tensile properties was utilized to prove the prediction ability of interleaved degree. Unlabelled Image • Equations of microstructural variables are deduced and model of interleaved degree in lamellar microstructure is established. • Interleaved degree is affected by several processing parameters, but mainly depends on cooling time. • Variant selection of α phase causes interleaved degree change and random α variant formation causes high interleaved degree. • Interleaved degree and fracture toughness is proved to be positively related. [ABSTRACT FROM AUTHOR]