다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Metastable β titanium alloys are widely used in the biomedical, automotive, and aerospace industry, due to their excellent corrosion resistance, fatigue strength, biocompatibility, and easy formability. Besides all these use areas, the suitable microstructure of the alloys for heat treatment increases the efficient usability day by day. In literature research, it has been found that heat treatment types such as cryogenic treatment and precipitation hardening can be applied efficiently to the alloys. Optimum strength/ductility, wear resistance, creep strength, and fatigue strength can be obtained with these heat treatments. For this reason, it has become important to understand the effect of heat treatments on the microstructural and mechanical properties of the alloys and parameters affecting this heat treatment efficiency. Precipitation hardening includes solution and aging treatment steps. The solution treatment can be applied at temperatures below and above the β transition temperature. While the aging treatment can be applied in four different ways, in the review article, the effects of single step and duplex aging treatment, which are applied with high efficiency, are emphasized. Precipitation hardening efficiency affects the chemical composition of the alloys, heat treatment steps, treatment temperature and times, and heating/cooling rate. The cryogenic treatment provides the formation of martensite α phases in metastable β titanium alloys cooled below the martensitic transformation temperature. Higher-strength and hardness have been obtained in the studies where aging treatment was applied after cryogenic treatment. Cryogenic treatment efficiency determines chemical composition of the alloys, treatment temperature and time, the heating/cooling rates, and heat treatments applied after cryogenic treatment.

A review on heat treatment efficiency in metastable β titanium alloys: the role of treatment process and parameters

Characteristic effects of alloying elements on β solidifying titanium aluminides: A review.

Dynamic recrystallization and hot processing map of Ti-48Al-2Cr-2Nb alloy during the hot deformation

Ti-rich body-centered cubic (BCC, β) high-entropy alloys having compositions Ti35Zr27.5Hf27.5Nb5Ta5, Ti38Zr25Hf25Ta10Sn2, and Ti38Zr25Hf25Ta7Sn5 (in at%) were designed using bond order (Bo)-mean d-orbital energy level (Md) approach. Deformation mechanisms of these alloys were studied using tensile deformation. The alloys showed exceptionally high strain-hardening and ductility. For instance, the alloys showed at least twofold increment of tensile strength compared to the yield strength, due to strain-hardening. Post-deformation microstructural observations confirmed the transformation of β to hexagonal close packed (HCP, α′) martensite. Based on microstructural investigation, stress–strain behaviors were explained using transformation induced plasticity effect. Crystallographic analysis indicated transformation of β to α′ showed strong variant selection (1 1 0)β//(0 0 0 1)α′, and [1 − 1 1]β//[1 1 − 2 0]α′.

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Exceptionally high strain-hardening and ductility due to transformation induced plasticity effect in Ti-rich high-entropy alloys

In this study, we investigate the twinning behavior and dynamic recrystallization (DRX) of Mg–7Sn–3Zn alloy under a high strain rate (10 s−1) during hot compression deformation. At a relatively low temperature (300 °C) and high strain rate (10 s−1), the preferential occurrence of multiple { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin variant at the initial compressed stage is attributed to the Schmid factor (SF) criterion, and the following { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin variants nucleate because of the geometric compatibility factor mʹ of the ortho-position twin pair. Because of the growth and interaction between the ortho-position { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin pairs, the volume fraction of 60° 10 1 ‾ 0 > boundaries evidently increases. Moreover, as the logarithmic strain increases, the volume fraction of { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins and 60° 10 1 ‾ 0 > boundaries significantly decreases, and a few { 10 1 ‾ 1 } 10 1 ‾ 2 > compression twins and { 10 1 ‾ 2 }–{ 10 1 ‾ 1 } double twins form. Then, twinning-induced dynamic recrystallization (TDRX) as a primary DRX mechanism occurs in { 10 1 ‾ 1 } 10 1 ‾ 2 > compression twins and { 10 1 ‾ 2 }–{ 10 1 ‾ 1 } double twins. These results indicate that at a high temperature (400 °C) and 10 s−1, certain { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins form during the early stage compression in accordance with the SF criterion, and discontinuous DRX (DDRX) occurs along the original grain boundaries because of the higher deformation temperature, which increases the nucleation rate and promotes the migration of grain boundaries. With the accumulation of logarithmic strain, continuous DRX (CDRX) occurs. The recrystallization grains consume the twin boundaries, which causes the { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins to merge. Under the same logarithmic strain, when the deformation temperature increases from 300 °C to 400 °C, the DRX process is significantly improved.

Twinning and dynamic recrystallization of Mg–7Sn–3Zn alloy under high strain rate hot compression

The activation energy of the β → α/ω phase transformation increased monotonously with the application of a continuous heating process to a Ti-15Mo-2.7Nb-3Al-0.2Si alloy. Precipitation behaviour of the alloy aged at different temperatures were analysed with scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. Selected-area diffraction patterns of the ω, ω/α and α phases in the alloy aged at different temperatures indicated that the type of phase transformation was influenced by the precipitation process. Precipitate-free zones in the alloy aged at 450 °C for 8 h were harmful to the mechanical performance. Fine α precipitates with an obvious texture were obtained in the alloy aged at 500 °C. A good combination of tensile properties with an ultimate tensile strength of 1310 MPa and an elongation of 13.5% were obtained due to the expected microstructure and texture of the precipitates that transformed in the specimen when it was aged at 500 °C for 8 h. The size of the precipitates increased with increasing aging temperature. Furthermore, the amount of precipitates and their degree of texture decreased substantially in the alloy aged at 600 °C. The investigation of the tensile properties and fractures also revealed a correlation between the mechanical properties and precipitation behaviour in the Ti-15Mo-2.7Nb-3Al-0.2Si alloy aged at different temperatures.

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Precipitation behaviour during the β → α/ω phase transformation and its effect on the mechanical performance of a Ti-15Mo-2.7Nb-3Al-0.2Si alloy.

A β-solidifying Ti-43Al-2Cr-2Mn-0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α2 lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α2 lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α2 lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

https://www.mdpi.com/1996-1944/12/8/1203/pdf

The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a β-solidifying TiAl alloy. The initial lamellar microstructure of an as-cast alloy was remarkably refined and homogenized by three-step MDF. High temperatures and multi-pass deformations were conducive to the decomposition of lamellae. A crack-free billet was obtained through three-step MDF, with a deformation temperature of 1250 °C and a forging speed of 0.1 mm/s, indicating that MDF can be applied to β-solidifying TiAl alloys by the proper control of the alloy composition and process parameters. Microstructural observation showed that the billet mainly consists of fine and equiaxed γ grains and a small amount of β phase. The tensile properties of the multi-directional forged alloy were also significantly improved, due to microstructure refinement. The ultimate tensile strength (UTS) and elongation (δ) at room temperature were 689.4 MPa, and 0.83%, respectively. The alloy exhibits excellent ductility at 700 °C. When the temperature was increased to 700 °C, the UTS decreased to 556 MPa and δ increased to 5.98%, indicating that the alloy exhibits excellent ductility at 700 °C. As the temperature further increased to 750 °C, δ dramatically increased to 46.65%, indicating that the ductile-brittle transition temperature of the alloy is between 700 °C and 750 °C.

https://www.mdpi.com/1996-1944/12/9/1381/pdf

Effect of Multi-Directional Forging on the Microstructure and Mechanical Properties of β-Solidifying TiAl Alloy.

The evolution of microstructure and texture was investigated during deformation and recrystallization processes in pure polycrystalline niobium. Optical microstructure, X-ray diffraction, transmission electron microscopy, and electron back-scattered diffraction analyses revealed variant behaviors during deformation and recrystallization; herein, the niobium was compressed under 0.01, 0.1, and 1 s−1 strain rates. As the compressive reduction and strain rate increased, more slips interacted in the deformation process, and the {001} 〈110〉 components became the most important textures in the compressed niobium. For the niobium specimens annealed at 1173 K (900 °C), the (111) [1-10], (111) [0-11], and (010) [1-11] orientations were the main textures. Moreover, the (111) [0-11] and (111) [1-10] orientations became weaker in the annealed niobium as the strain rate increased. The {111} components were the primary textures in the compressed niobium specimen recrystallized at 1323 K (1050 °C). The results showed that the texture intensity decreased and Schmid factors increased in the recrystallized niobium as the strain rate increased. The high Schmid factor also implied that compression under a high strain rate before recrystallization would be optimal for continuous deformation in polycrystalline niobium.

Ning Cui

Papers

Twinning and dynamic recrystallization of Mg–7Sn–3Zn alloy under high strain rate hot compression

Precipitation behaviour during the β → α/ω phase transformation and its effect on the mechanical performance of a Ti-15Mo-2.7Nb-3Al-0.2Si alloy.

The Directional Solidification, Microstructural Characterization and Deformation Behavior of β-Solidifying TiAl Alloy

Effect of Multi-Directional Forging on the Microstructure and Mechanical Properties of β-Solidifying TiAl Alloy.

Effects of Strain Rate and Annealing Temperature on the Evolution of Microstructure and Texture in Pure Niobium