Morphology Of Α-phase Research Articles

Effect of Initial Microstructure on the Temperature Dependence of the Flow Stress and Deformation Microstructure under Uniaxial Compression of Ti-407

In this study, the influence of initial microstructure and deformation temperature on the flow stress behavior and microstructural evolution of TIMETAL®407 (Ti-407) alloy are investigated. For this purpose, compression cylinders were β-annealed at 940 °C and then cooled to room temperature using furnace cooling, static air, and water quenching to promote three initial microstructures with different α lath thicknesses. The annealed cylinders were compressed isothermally in the range of 750 °C to 910 °C at a constant crosshead speed of 0.05 mm/s up to an engineering strain of −0.8. The resulting stress–strain curves are discussed in terms of the morphology and distribution of the α and β phases. It was found that flow stress is inversely proportional to deformation temperature for all initial microstructures. At the lowest temperatures, compressive yield strength was higher in water-quenched and air-cooled samples than in furnace-cooled specimens, suggesting that the acicular α-phase morphology obtained by rapid cooling could enhance mechanical strength by hindering dislocation motion. Two high-temperature flow regimes were determined based on the shape of the flow stress curves, indicating microstructural changes occurring during deformation. At higher temperatures, the effect of the initial microstructure is negligible as the primary α phase is transformed to the β phase at around 850 °C irrespective of the initial α-lath thickness.

Influence of α-Phase Morphology on Mechanical Characteristics, Cycle Oxidation, and Hot Corrosion Behavior of Ti-6Al-3Mo-2Nb-2Zr-2Sn-1.5Cr Alloy

Influence of α-Phase Morphology on Mechanical Characteristics, Cycle Oxidation, and Hot Corrosion Behavior of Ti-6Al-3Mo-2Nb-2Zr-2Sn-1.5Cr Alloy

Effect of Initial α-Phase Morphology on Microstructure, Mechanical Properties, and Work-Hardening Instability During Heat Treatment of TC21 Ti-Alloy

Effect of Initial α-Phase Morphology on Microstructure, Mechanical Properties, and Work-Hardening Instability During Heat Treatment of TC21 Ti-Alloy

Thermo-hydrogen refinement of microstructure to improve mechanical properties of Ti–6Al–4V fabricated via laser powder bed fusion

This paper describes the main results from an investigation into the consequences of thermo-hydrogen refinement of microstructure (THRM) after laser powder bed fusion (LPBF) of Ti–6Al–4V on the evolution of microstructure and mechanical properties using a set of experimental techniques. Porosity fraction, grain structure, phases, and crystallographic texture per phase are characterized using micro X-ray computed tomography, microscopy, and neutron diffraction. A hierarchical structure of acicular α-phase morphology formed inside the prior β grains by fast cooling during LPBF transforms into fine-grained globular microstructure by THRM, which facilitates homogeneous nucleation and growth of the low temperature phase with some retained β phase. Moreover, hydrogenated material during THRM has low activation energy for diffusion, which in conjunction with the surface energy of pores causes densification of the material, thereby closing porosity formed during LPBF. Such significant microstructural changes induced by the THRM treatment cause brittle material created by LPBF to become ductile. Significantly, the strength and ductility produced by THRM exceed the minimums set forth by the ASTM B348 standard for Ti-6Al-4V. Moreover, the treatment improves fatigue strength of the material. In particular, it improves the endurance limit and reduces the scatter in the measured fatigue strength data. Performance characteristics of the material can be further optimized for specific application requirements by tailoring microstructures using the LPBF and THRM processes.

The effect of thermomechanical treatments on the properties of powder metallurgy Ti–5Fe alloy

In this study, the low-cost Ti–5Fe alloy was fabricated by a combination of sintering plus thermomechanical treatment (TMT). The primary aim is to improve the tensile properties of the recently widely studied powder metallurgy Ti-xFe alloys made by the press and sinter process. The effect of hot forging or extrusion and subsequent annealing treatment on the microstructure and mechanical properties of the Ti–5Fe alloy was therefore studied. TMT from temperatures in the β-phase field severely changes the microstructure of the sintered alloy. The substantial deformation of the β-grains and the formation of fine α-phase have a significant effect on the mechanical properties. The yield and ultimate tensile strengths of the TMT alloys reach high values, from 1050 MPa to over 1200 MPa. The subsequent heat treatment results in the modification of the α-phase morphology and the partial loss of the crystallographic texture, leading to the enhancement of the elongation to values above 20%, despite of the high oxygen content of the alloy.

Modification of α-phase of wire + arc additive manufactured Ti-6Al-4 V alloy with boron addition

The deposition rate of the wire+arc additive manufacturing (WAAM) technique is high and its equipment and operating costs are low, making it suitable for fabricating large-size components with special-shape. For improving the high-strain-rate mechanical properties, 0.1 wt% boron was added to the Ti-6Al-4 V alloy wire to modify the microstructure of the boron-added titanium alloy fabricated via WAAM. In this study, the α-phase morphology and texture of as-built and β-annealed WAAM Ti-6Al-4 V-0.1B alloy were investigated by optical microscopy and electron backscatter diffraction technique. The addition of 0.1 wt% boron caused the length of the α-phase lamellae to reduce significantly in both the as-built and the annealed WAAM Ti-6Al-4 V-0.1B specimens. This was attributed to the combined action of the fine prior β-grains and the growth-inhibiting effect of the TiB particles on the α-phase. The continuous-grain-boundary α-phases were broken and even completely absent in both the as-built and the annealed WAAM Ti-6Al-4 V-0.1B specimens. Moreover, in both specimens, the α-phases exhibited two distinct fiber textures, 〈11−20〉 α and < 16 0–16 19 > α, parallel to the building direction. Further, the α-phases that had nucleated at the boundaries of the prior β-grains showed the appearance of the variant selection, which preferentially exhibited the former fiber texture.

Effect of boron on microstructure evolution and hot tensile deformation behavior of Ti-5Al-5V-5Mo-1Cr-1Fe alloy

Abstract Ti-5Al-5V-5Mo-1Cr-1Fe (Ti-55511), one of the near β-Ti alloys is considered to be the candidate material for high strength applications. However, the tendency to excessive grain growth under high temperatures limits its potential applications due to drastic reduction in strength with temperature and poses difficulties during forming. In present study, based on the understanding established for the workhorse Ti-6Al-4V and other Ti alloys, the near-β, Ti-55511 alloy was modified with 0.06 and 0.12 wt.% B to investigate the effect of boron on its microstructure and high temperature tensile behavior. The boron addition led to significant grain refinement and changes in morphology of α-phase from lamellar to globular. The high temperature tensile tests conducted over a range of temperatures and strain rates showed that the alloy with 0.06 wt% B displays superplastic characteristics with maximum elongation to failure of 385% at 1123 K and an initial strain rate of 1 × 10−3 s−1. The bare alloy and the alloy with higher boron content (0.12 wt.%) exhibited relatively higher flow stresses and consequently reduced superplastic elongations. Cyclic strain rate tests indicated that the alloy exhibits high strain rate sensitivity (m) values in the range of 0.3–0.8, which suggests that grain boundary sliding (GBS) is the dominant strain contributing mechanism for the observed superplasticity at elevated temperatures. Further, the detailed microstructural examination revealed that the coarser and elongated grain structure, which decreases GBS contribution and the presence of large fraction of titanium borides, which leads to an increased cavitation, respectively are the responsible factors for the observed reduced superplasticity characteristics in the bare alloy and the alloy with 0.12 wt.% B, respectively.

The Role of Martensitic Transformation in Thermomechanical Development of Microstructure and Plasticity of Two-Phase Ti-6Al-4V Titanium Alloy

Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.

Effect of α-phase morphology on low-cycle fatigue behavior of TC21 alloy

Low-cycle fatigue behavior of TC21 alloy with equiaxed α phase embedded in the β transformed matrix (EM) and full lamellar α phase (LM) was investigated. The results show that the EM microstructure possesses higher strength, ductility and longer fatigue life than those of the LM one. Dislocation structures are straight dislocation lines in both EM and LM; however, more dislocation tangles and debris were observed in the α than in the β phase. The planar slip predominates cyclic deformation in the α phase, and promotes strain concentration and crack initiation at α phase boundaries.

The Effect of Deformation and Irradiation with High-Energy Krypton Ions on the Structure and Phase Composition of Reactor Steels

The paper presents some results of a complex research of 12Cr18Ni10Ti stainless steel in the initial, deformed and irradiated ( 8436Kr+14, E=130MeV, Fmax=9x1015 ions/сm2) states using magnetometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD – analysis). Application of the EBSD method revealed differences between the non-irradiated and irradiated 12Cr18Ni10Ti steel specimens consisting in the fact that in the surface layer of an irradiated sample α-and ε - phases are formed. It was established that the fluence value affects the amount of magnetic α-phase. The study of the martensite α-phase morphology showed that in the deformed steel specimens there is αʹ- martensite of two scale levels.

Effect of Aging on Superelastic Behaviors of a Metastable β Ti-Mo-based alloy

Effect of aging on the tensile and superelasticity (SE) behaviors of Ti-9.8Mo-3.9Nb-2V-3.1Al (wt.%) alloy have been investigated. It is found that the ultimate tensile strength (UTS) and yield strength of aged alloy change with the aging temperature following a nonlinear relationship due to ω-phase and α-phase precipitates. The SE, especially elastic recovery behavior, is closely related with the morphology of α-phase precipitates, as well as ω-phase formed during aging. At a maximum tensile strain of 4%, the specimen aged at 673 K with ω + α-phase precipitates shows a superelastic recovery strain of 3.2%. Lots of α-phase precipitates, distributing homogeneously in specimen aged at 773 K, result in the lost of SE. A maximum recovery strain of 3.3% is obtained for specimens aged at 873 or 973 K for 30 min, with coarse short bar-like α-phase precipitates.

Three-dimensional visualization of the microstructure development of Sr-modified Al–15Si casting alloy using FIB-EsB tomography

Unmodified and Sr-modified (after 5 and 120 min of melt holding) Al–15Si alloys were investigated by transmission electron microscopy and focused ion beam tomography using energy-selective backscattered electrons for imaging. The three-dimensional visualization of the microstructure provided not only the true morphology of the Al–Si eutectic and Fe-rich intermetallics, but also allowed us to estimate their volume fractions. The evolution of Fe-rich α-phase morphology in the unmodified alloy proceeded during eutectic growth according to a model proposed. In the unmodified alloy, only Fe-rich α-phase was found, whereas in the Sr-modified alloy after 5 min of melt holding, two morphologies of Fe-rich phases were observed, namely a Fe-rich α-phase and a Fe-rich δ-phase. Both phases segregated mainly at modified eutectic grain boundaries. After 120 min of melt holding, the eutectic microstructure is similar to the unmodified structure again and only the Fe-rich α-phase could be observed.

THE EFFECTS OF MORPHOLOGY STRUCTURE FOR COPPER PHTHALOCYANINE SENSORS DETECT TO ORGANIC ACID

The copper phthalocyanine ( CuPc ) thin film gas sensors detect to organic acids that its detection behaviors will be affected morphology with quartz crystal microbalance (QCM) method. The amorphous structure has looser surface and finer particles; therefore, it has smaller surface area. Although it has more active sites to adsorb acid molecular, it gets smaller value of frequency change (Δf) than α-phase morphology. The β-phase morphology has the largest surface area, so it gets the smallest value of Δf. The response behavior is more rapid than recovery behavior with any morphology CuPc thin film gas sensors. The film surface of amorphous structure has more porous, it has faster response time and recovery time than other structures. The β-phase morphology can get slowest response and recovery time. The results show that the CuPc thin film gas sensors detect to organic acid behavior, for example methyl acid and ethyl acid, etc.; it was affected to its surface morphology change.

On the influence of austenitization on the morphology of α-phase in tempered Cu–Zn–Al shape memory alloys

The paper reports some austenitization effects on the α-phase morphology in a tempered martensitic Cu–21.57 Zn–7 Al (wt.%) shape memory alloy (SMA). By means of differential scanning calorimetry, X-ray diffraction and optical and electron microscopy, it has been shown that the effects of the stress-state induced in austenite persist even after martensitic transformation and tempering at 773 K. The two analyzed austenitization states, hot-pressed and homogenized, respectively, aimed to reproduce two steps of an industrial technologic flow for SMA manufacturing. Basically, austenitic hot-working diminished the size of disoriented α-phase precipitates while austenitic homogenization enabled the formation of a Widmanstätten structure with oriented long α-phase needles, among which those corresponding to α(1 1 1) intersect at about 70° and those corresponding to α(2 0 0) at 90°.

Structure and properties of isotactic polypropylene functionalized by ultraviolet irradiation

The structural, crystalline, thermal, morphological, and mechanical properties of isotactic polypropylene (iPP) functionalized by lower energy ultraviolet (UV) irradiation are studied by means of infrared spectroscopy (IR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetry (TG), thermomechanical analysis (TMA), polariscope, and mechanical measurements. After the UV irradiation in less than a few hours, the oxygen containing polar groups have been introduced onto iPP chains. DSC analysis shows that a new melting peak is observed around 150°C for the UV irradiated iPP, indicating that there is a α-phase to β-phase transition during UV irradiation process. Under polariscope, the morphology of the UV irradiated iPP is changed, and the deformed α-phase morphology can be observed. DSC and WAXD analysis reveal for the crystallinity of the UV-irradiated iPP increase with UV time, but the relative level and the order of β-phase increase and then decrease with increasing UV time. Under the controlled UV time, the thermomechanical deformation of iPP decrease, and the initial and final thermal degradation temperature of iPP rises up by 70 to 125°C higher, respectively, indicating that the UV-irradiated iPP has higher thermal stability than the non-UV irradiated iPP. The tensile and impact strength, the elongation at break, and the Young's modulus of the UV-irradiated iPP are enhanced, exhibiting the toughened and strengthened effects. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1456–1466, 2001

Characteristics of morphology and crystal structure of α-phase in two Al-Mn-Mg alloys

The characteristics of morphology and crystal structure of α-Al 12(Fe,Mn) 3Si phase in two Al-Mn-Mg alloys in as-cast and homogenized states have been studied. The results show that the morphology of primary α-particles is the same as that of primary β-particles in as-cast ingots and ‘Al-spots’ is only the characteristic of α-phase transformed from β-phase. α-precipitates are sterically irregular plates. The α-phase precipitated from solid solution and transformed from β-phase has an ordered body-centered cubic crystal structure. There is no obvious difference in the morphology of α-phase between two Al-Mn-Mg alloys. But in the alloy with high Si content there are more Mg 2Si needles, which then cause the α-precipitates in alignment along the direction [1 0 0] of Al matrix during heating at lower temperature.

Low cost synthesis and property evaluation of P/M Ti alloys and ti-based particulate composites

Ti-6A1-4V alloy and Ti-6Al-2Sn-4Zr-2Mo/10TiB particulate composites were synthesized using a hlended elemental powder metallurgy processing route. Microstructures and mechanical properties, such as tensile, creep, Young’s modulus and high-cycle fatigue-strength were evaluated. Special attention was paid to improve the high-cycle fatigue-strength of these two materials by modifying the matrix microstructure or process innovation. The fatiguecrackinitiation mechanism, relationship between α-phase morphology and high-cycle fatigue-strength, and other factors contributing to the increase in fatigue strength were analyzed.

Effect of microstructure, strength, and oxygen content on fatigue crack growth rate of Ti-4.5AI-5.0Mo-1.5Cr (CORONA 5)

Fatigue crack growth rate behavior in CORONA 5, an alloy developed for applications requiring high fracture toughness, has been examined for eight material conditions. These conditions were designed to give differences in microstructure, strength level (825 to 1100 MPa [120 to 160 ksi]), and oxygen content (0.100 to 0.174 wt pct), in such a manner that the separate effects of these variables could be defined. For all eight conditions, fatigue crack growth rates (da/dN) are virtually indistinguishable over the full spectrum of stress-intensity range (ΔK) examined,viz., 8 to 40 MPa√m (7 to 36 ksi√in). Concomitantly, it is noted that over the sizable solution annealing range studied (830° to 915 °C [1525° to 1675 °F]), the primary α-phase morphology was substantially invariant. Eachda/dN curve exhibits a bilinear form with a transition point (ΔKT) between 16 and 19 MPa√m (15 and 17 ksi√in). A change in microfractographic appearance occurs at ΔKT, as extensive secondary cracking along α/β interfaces is observed at all hypertransitional levels ofAK, but not for AK < ΔKT. For each material condition, the mean length of primary α platelets is approximately the same as the cyclic plastic zone size at ΔKT. Accordingly, locations ofAKT (and their similarity for the different material conditions) are rationalized in conformance with a cyclic plastic zone model of fatigue crack growth. Finally, the difference in behavior of CORONA 5, as compared to conventional α/β alloys such as Ti-6A1-4V, is rationalized in terms of crack path behavior.

Effect of α-phase morphology and distribution on the tensile ductility of a metastable beta titanium alloy

In a program to develop a metastable beta alloy with improved fracture toughness, it was found that the tensile ductility of the alloy Ti-8 Mo-4.5 Cr-2.5 Al was strongly dependent on both processing history and annealing temperature. Evaluation of the microfracture mode of tensile samples by scanning electron microscope and metallographic techniques showed that the presence of a continuous grain boundary alpha is the most significant parameter controlling the ductility and is highly detrimental. It is concluded that, for optimum processing, the material must be worked prior to aging to avoid this grain boundary phase. (SDF)