Dilatometric Analysis and Microstructural Investigation of the Sintering Mechanisms of Blended Elemental Ti-6Al-4V Powde
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TI-6AL-4V alloy is known as the ‘‘work horse’’ of the titanium industry because it offers a combination of high strength, light weight, formability, and corrosion resistance.[1] Among the fabrication techniques for Ti alloy components, powder metallurgy (PM) has been used widely to reduce the substantial production cost, which is one of the main obstacles to more widespread applications.[2] In the early stages of development, however, most Ti-PM prototypes could not be used for real applications due to the high level of chloride in raw powders and the low quality of the facilities.[2] Since the 2000s, such drawbacks have been addressed and several Ti-PM techniques have been commercialized, including powder injection molding, hot isostatic pressing, press-and-sinter, and additive
YOUNGMOO KIM, Ph.D. Candidate, is with the Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea, and with the Agency for Defense Development, P.O. Box 35, Yuseong-gu, Daejeon 34186, Republic of Korea. JUNHO LEE and BIN LEE, Ph.D. Candidates, and SOON HYUNG HONG, Professor, are with the Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology. Contact email: [email protected] HO JIN RYU, Associate Professor, is with the Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology. Contact email: hojinryu@kaist. ac.kr. Manuscript submitted January 15, 2016. Article published online June 15, 2016 4616—VOLUME 47A, SEPTEMBER 2016
manufacturing.[2] Presently, the press-and-sinter process using blended elemental (BE) powders produced by mixing of Ti and alloying elemental particles is known to be technically the simplest and most economically efficient process.[3] Additionally, hydrogen sintering of TiH2 as opposed to Ti powder, and its influence on the mechanical properties have been studied.[4,5] Previous investigations on this technique have focused on process design to decrease the ‘‘buy-to-fly’’ ratio, defined as the weight ratio between the input of the raw material and the component itself.[6–8] However, the performance of the components made from BE powders can be influenced by uniform microstructures and good chemical homogeneity, as well as high sintered density and low interstitial impurities.[9] Accordingly, because such factors are determined largely by sintering conditions, it is important to understand the densification mechanism to affect the performance of Ti-PM parts. Many studies on the densification of CP-Ti and Ti alloy powders under various sintering conditions have been reported.[10–20] Through series of dilatometry tests, Panigrahi investigated the sintering behaviors of micrometric and nanosized Ti powders, as well as Ti-50Ni elemental powders, to estimate the activation energies for sintering and grain growth.[10–12] Yang and Qian studied the main sintering mechanisms and microstructural evolution during the heating of Ti-Fe-Si and Ti-10V-2Fe-3Al
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