• Journal of Korea Foundry Society
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• v.7 no.2
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• pp.108-113
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• 1987

Al-Cr alloy with composition in the range from 1.5 wt% to 10 wt% Cr were rapidly solidified from the melt by the single roller method. The supersaturated solid solution was obtained up to 6 wt% Cr in Al-Cr alloy for $20{\mu}m$ thickness. Lattice parameter decreased with increasing Cr content at the rate of 0.00456A per wt% Cr up to 6 wt% Cr. Microhardness increased with increasing Cr content at the rate of $10\;Kg/mm^2$ per wt% Cr up to 6 wt% Cr. Microhardness measurements on the Al-6 wt% Cr supersaturated solid solution annealed isothermally showed no sign of age hardening. Decomposition temperature, determined by lattice parameter changes and microhardness changes, was $470^{\circ}C$ for Al-6 wt% Cr supersaturated solid solution. Transmission electron microscopy showed that decomposition within one hour below $400^{\circ}C$ occurred at grain boundaries only, and also the additional decomposition within grains being evident at $450^{\circ}C$ The coarse precipitate structure showed at $500^{\circ}C$ and $550^{\circ}C$, respectively. The coarse precipitate structure is considered $Al_7Cr$.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.58-62
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high n austenitic steels. After measuring the internal stress in minimum creep rate state under applied stress of 236MPa at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band widths and values of internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.332-337
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• Transactions of Materials Processing
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• v.28 no.3
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• pp.123-129
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• 2019

Hypereutectic Al-Si alloys have been widely utilized for wear-resistant components in the automotive industry. In order to expand the application of Hypereutectic Al-Si alloys, the addition of alloying elements forming a stable precipitate at high temperature is required. Thermally stable inter metallic compounds can be formed through the addition of transition elements such as Fe, Ni to Al alloys. However, the amount of transition element to be added to Al alloys is limited due to their low solid solubility. Also, hypereutectic Al-Si-Fe alloys form coarse primary Si phases and needle-shaped intermetallic compounds during solidification in the general casting processes. In this study, the effects of the destruction of Intermetallic compound and Si phase are investigated via hot extrusion. Both the microstructure and mechanical properties are discussed under different extrusion conditions.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.2
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• pp.53-60
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• 2017

The aim of this study is to examine a feasibility to substitute Ti for Ta in reduced activation ferritic/martensitic (RAFM) steel by comparing a Ti-added RAFM steel with a conventional Ta-added RAFM steel. The microstructures and mechanical properties of Ta-, and Ti-added RAFM steels were investigated and a relationship between microstructures and mechanical properties was considered based on quantitative analysis of precipitates in two RAFM steels. Ta-, and Ti-added RAFM steels were normalized at $1000{\sim}1040^{\circ}C$ for 30 min and tempered at $750^{\circ}C$ for 2 hr. Both RAFM steels had very similar microstructures, that is, typical tempered martensite with relatively coarse $M_{23}C_6$ carbides at boundaries of grain and lath, and fine MX precipitates inside laths. The MX precipitates were identified as TaC in Ta-added RAFM steel and TiC or (Ti, W)C in Ti-added RAFM steel, respectively. It is believed that these RAFM steels show similar tensile and Charpy impact properties due to similar microstructures. Precipitate hardening and brittle fracture strength calculated with quantitative analysis of precipitates elucidated well the similar behaviors on the tensile and Charpy impact properties of Ta-, and Ti-added RAFM steels.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.11a
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• pp.8-8
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• 2002

TiC core/(Ti,Mo)C rim structure in TiC-$Mo_2C$-Ni base cermet which is generally prepared by sintering below 145$0^{\circ}C$ had been believed to be generated by the solid diffusion of Mo atoms 1 into TiC grains (D. Moskowitz and M.Humenik, 1r.:1966). Afterward, it was clarified that the c core/rim structure is generated by solution/re-precipitation mechanism : (1) $Mo_2C$ grains and s small TiC grains dissolve into the Ni liquid, (2) the dissolved Mo, Ti and C atoms migrate to the s surface of TiC coarse grains, (3) the Mo, Ti and C precipitate on the surface of TiC coarse g grains and form (Ti,Mo)C solid solution rim, and (4) the Ostwald ripening (grain growth by s solution/re-precipitation mechanism) of TiC-core/(Ti,Mo)-rim grains continues, and thus the w width of (Ti,Mo)C rim (at the same time, the grain size) increases with sintering time, etc. ( (H.Suzuki, K.Hayashi and O.Terada: 1973). The TiC-core was found not to disappear even by s sintering at 190$0^{\circ}C$ (ibid.: 1974) Recently, FeSi core/$Fe_2Si_5$-rim structure in Fe-66.7at%Si thermoelectric aIloy was found to also h hardly shrink and disappear by long heating at an appropriate temperature (1999: M.Tajima and K K.hayashD. Then, the authors considered its cause, and clarified experimentaIly that the disappearance of FeSi-core/$Fe_2Ski_5$-rim structure could be attributed to the exhaustion of diffusion-contributable vacancies in core/rim structure (N.Taniguchi and K.Hayashi:2001). At p present, the authors and my coworker are investigating whether the non-disappearance of TiC c core can be explained also from the new hypothesis "Exhaustion of diffusion-contributable v vacancies in corelrim structure".ure".uot;.

• Journal of Korea Foundry Society
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• v.39 no.1
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• pp.7-13
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• 2019

Few studies of large blooms over 700 mm thick among those used for the forging of raw materials have been reported. The cooling rate difference between the surface and the center of a large bloom is large, and the degradation of the mechanical properties is likely in cases involving excessively coarse precipitates resulted from the slow cooling rate of a large bloom after casting. Therefore, a schematic investigation of the growth behaviors of precipitates while varying their locations in blooms is necessary. The dissolution behaviors of precipitates were investigated by simulating a reheating process during which the bloom is heated to a high temperature. The segregation behavior of the as-cast large bloom was also investigated. Reheating specimens were obtained after an isothermal heat treatment at $1150^{\circ}C$ with various holding times to simulate the reheating process, with the samples undergoing a subsequent water quenching step. The precipitates were extracted using an electrolytic extractor and a particle size analysis was conducted with the aid of SEM, EDS, and TEM. In the present work, Al oxide, MnS and Nb carbide were mainly observed.

• Corrosion Science and Technology
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• v.4 no.5
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• pp.211-216
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• 2005

Failure analysis of the latch ram ball and the C-ram ball with the trade name AFBMA Gr. 50 Colmonoy No. 6, has been performed to identify the root cause of the failure. The study required the extraction of the both failed and normal balls from the nuclear fuel exchanger. Microstructures of both balls were examined after polishing and etching. Breaking tests of both the ball revealed similarity in cleavage surfaces. Fracture surfaces of both failed ball and normal ball after breaking test were examined with SEM and EDX. Microstructure of the ball revealed an austenite phase with coarse Cr rich precipitate. Indented marks observed on the surface of the failed ball are believed to be produced by overloading. In the light of the afore mentioned observations and studies, the failure mechanism of the ball in nuclear fuel exchanger seem to be caused by impact or mechanical overloading on ball.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.2
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• pp.85-94
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• 1992

Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick (MMeHT) methods. The size of ${\gamma}^{\prime}$ and ${\gamma}^{\prime\prime}$ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine ${\gamma}^{\prime\prime}$ precipitate and very coarse particles due to exess growth of ${\gamma}^{\prime\prime}$, which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like ${\delta}$ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.131-139
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• 1993

Abstract Alloying elements such as AI, Ti, Nb and B in the extra low carbon AI-killed steel precipitate as nitrides or carbides and change the recrystallization texture structure of the steel during heattreatment with the result of strong effects on the deep drawability of the steel sheet. In this study the effects of fine precipitates such as nitrides and carbides on the texture of extra low carbon steels into which Ti, Nb, B, P, Si and Mn were added as alloying elements were investigated by means of TEM, SEM and optical microscopic analyses. Fine N$b_2$C and T$i_2$AIN precipitates are mainly observed in the steel containing both Nb and Ti, while fine AIN and coarse BN precipitates are observed in the Nb~containing steel and coarse T${i_4}{N_3}$ and ${N_10}{N_22}$/T$i_68$ precipitates are observed in the Ti-containing steel. The grain size of the Ti containing steel is larger than that of the Nb containing steel and that of the one containing both Nb and Ti.