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진공 원심 주조된 Ti-6Al-4V 합금의 주조 및 열처리에 따른 미세조직과 기계적 특성
이현우,공병욱,김승언,주윤곤,윤석현,이재현 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.4
The Ti-6Al-4V alloy has been widely used for structural materials due to high specific strength property, however it is difficult to cast because of high reactivity at high temperature. In this study casting characteristics and post-casting heat treatment were studied in the cast Ti alloy. The cast alloy was prepared using high-frequency induction heating and horizontal vacuum centrifugal casting to reduce reaction with crucible and mold by minimizing overheating of the molten metal and casting fast. In the thin casting with a thickness of 2 mm, α’ martensite was observed, and in the casting with a thickness of 4~8 mm, α+β Widmanstätten was observed. As the thickness of the casting increased, the grain size, α-lath width, and α-case thickness increased. Accordingly, as the thickness of the casting increased, the hardness of the matrix decreased and the hardness of the surface increased. In addition, when the casting was heat treated below the β-phase transformation temperature, the α-lath width increased, and when quenched after heat treatment in the β-phase transformation temperature region, an α’ martensite was formed. On the other hand, when the casting was heat treated in the atmosphere, it was confirmed that the elongation was very low because hydrogen and oxygen in the atmosphere were induced. In addition it was confirmed that casting defects can be removed through HIP.
정밀주조된 Ti-6Al-4V 합금 판재의 피로성질에 미치는 판재 두께의 영향
吳振根,李玎求,金洛俊,李星鶴,李義徽 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7
Effects of plate thickness on high-cycle fatigue properties and fatigue crack propagation behavior of investment-cast Ti-6Al-4V alloy plates having Widmansta¨tten structure were investigated in this study. High-cycle fatigue test and fatigue crack propagation test were conducted on three cast plates having different thickness, and then the test data were analyzed in relation with microstructures, tensile properties, and fatigue fracture mode. The high-cycle fatigue results indicated that fatigue strength of the three cast plates was quite similar because of their similar tensile strength. In the case of the fatigue crack propagation, the thicker cast plate composed of thinner α platelets had the slightly faster crack propagation rate than the other plates. The effective microstructural factor determining the fatigue crack propagation rate was found to be the thickness of a platelets because it was well matched with the reversed cyclic plastic zone size calculated in the threshold ΔK regime.
Xiaohan Tang,Mingfa Ren,Fanzi Bu,Guoqing Chen,Gang Li,Tong Li 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.2
Split-Hopkinson pressure bar (SHPB) was adopted to study the dynamic response of a specifically designed Hot isotropically processed (HIP) Casting Titanium alloy (Ti-6Al-4V). The strain-stress curves were obtained in a range of strain rate (10 -3 ~2.6×10 3 /s) to study the constitutive relationships and the Johnson-Cook model is developed to describe this dynamic constitutive law. It can be found that the static microstructure of this specific HIP casting Ti-6Al-4V is lamellar structure. When the loading increases (strain rate higher than 10 3 /s), this lamellar structure changes to basket weave structure, which further changes the mechanical strength and plasticity.
Development and Evaluation of a Novel Inclusion Seeding Methodology for Ti-6Al-4V Castings
( Paul L. Ret ),( Jerald R. Brevick ),( Yong K. Park ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 METALS AND MATERIALS International Vol.13 No.4
Hard alpha inclusions in titanium (Ti) investment castings are generally known to have detrimental effects on the mechanical properties of these castings. However, actual inclusions are infrequent and occur in random locations in castings. As a result, it is difficult to obtain tensile or fatigue test specimens of titanium castings with inclusions in the gage section. Quantifying the adverse influence of inclusions on the mechanical properties of castings is, therefore, extremely challenging. To address this problem, a novel artificial inclusion seeding methodology was developed to emulate actual Ti investment casting inclusions. Prefabricated inclusions were seeded into machined holes in cast Ti-6Al-4V plates, the holes were back-filled with plugs of the same Ti alloy and were then electron-beam (EB) welded closed. Hot isostatic pressing (HIP) was utilized to incorporate the inclusions fully into the cast titanium material. Finally, the plates were machined to create mechanical test specimens with inclusions centered in the gage region. Test specimens created by means of this novel artificial seeding methodology were evaluated and found to be equivalent to Ti casting specimens containing actual cast-in inclusions.
Effect of Solution Treatment and Short Time Aging on Mechanical Properties of Cast Ti-6Al-4V Alloy
Oh, Seong-Tak,Woo, Kee-Do,Kwak, Seung-Mi,Kim, Jae-Hwang Materials Research Society of Korea 2016 한국재료학회지 Vol.26 No.5
The effect of heat treatment on the microstructure and mechanical properties of cast Ti-6%Al-4%V alloy was investigated. Heat treatment of cast Ti-6Al-4V alloy was conducted by solution treatment at $950^{\circ}C$ for 30 min; this was followed by water quenching and then aging at $550^{\circ}C$ for 1 to 1440 min. The highest hardness of the heat-treated specimens was obtained by solution treatment and subsequent aging for 5 min due to precipitates of fine ${\alpha}$ that formed from retained ${\beta}$ phase. The tensile strength of this alloy increased without dramatic decrease of the ductility due to microstructural refinement resulting from the decomposition of ${\alpha}^{\prime}$ martensite into fine ${\alpha}$ and ${\beta}$ phases, and also due to the fine ${\alpha}$ phase formed from the retained ${\beta}$ phase by aging treatment for 5 min. In addition, this strengthening might be caused by the transformation induced plasticity (TRIP) effect, which is a strain-induced martensite transformation from the retained ${\beta}$ phase during deformation, and which occurs even after aging treatment at $550^{\circ}C$ for 5 min.