Crack growth and cracking behavior of Alloy 600/182 and Alloy 690/152 welds in simulated PWR primary water

임연수,김동진,김성우,김홍표 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.1

The crack growth responses of as-received and as-welded Alloy 600/182 and Alloy 690/152 welds toconstant loading were measured by a direct current potential drop method using compact tensionspecimens in primary water at 325 C simulating the normal operating conditions of a nuclear powerplant. The as-received Alloy 600 showed crack growth rates (CGRs) between 9.6 10 9 mm/s and3.8 10 8 mm/s, and the as-welded Alloy 182 had CGRs between 7.9 10 8 mm/s and 7.5 10 7 mm/swithin the range of the applied loadings. These results indicate that Alloys 600 and 182 are susceptible tocracking. The average CGR of the as-welded Alloy 152 was found to be 2.8 10 9 mm/s. Therefore, Alloy152 was proven to be highly resistant to cracking. The as-received Alloy 690 showed no crack growtheven with an inhomogeneous banded microstructure. The cracking mode of Alloys 600 and 182 was anintergranular cracking; however, Alloy 152 was revealed to have a mixed (intergranular þ transgranular)cracking mode. It appears that the Cr concentration and the microstructural features significantly affectthe cracking resistance and the cracking behavior of Ni-base alloys in PWR primary water

Influence of Various Additional Elements in Al Based Filler Alloys for Automotive and Brazing Industry

Ashutosh Sharma,Y.S. Shin,Jae-Pil Jung 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.5

Aluminium and its alloys are widely used in brazing various components in automotive industries due to their properties like lightweight, excellent ductility, malleability and formability, high oxidation and corrosion resistance, and high electrical and thermal conductivity. However, high machinability and strength of aluminium alloys are a serious concern during casting operations. The generation of porosity caused by dissolved gases and modifiers affects seriously the strength and quality of cast product. Brazing of Al and its alloys requires careful monitoring of temperature since theses alloys are brazed at around the melting temperature in most of the aluminium alloys. Therefore, the development of low temperature brazing filler alloys as well as superior strength Al alloys for various engineering applications is always in demand. In various heat exchangers and automotive applications, poor strength of Al alloys is due to the inherent porosities and casting defects. The unstable mechanical properties is therefore needed to be controlled by adding various additive elements in the aluminium and its alloys, by a change in the heat treatment procedure or by modifying the microstructure. In this regard, this article reports the effect of various elements added in aluminium alloys to improve microstructure, brazeability, machinability, castability as well as to stabilize the mechanical properties.

기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H₂O의 역할과 시효석출거동

김일호,권숙인,이원식,채수원,황선근,김명호,Kim Il-Ho,Kwun S.I.,Lee Won-Sik,Chae S.W.,Hwang S.K.,Kim M.H. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.3

The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.

치과 임플란트용 순 Ti의 접촉부식 거동

김교한,허만수,김형일,황운석,高田 雄京,奧野 攻 대한치과기재학회 1999 대한치과재료학회지 Vol.26 No.4

One of the fields in which titanium(Ti) is becoming increasingly valuable is the field of biomaterials. Ti had shown its good corrosion resistance, high strength to weight ratio, and compatibility with human tissues. Such applications of Ti in this area involve replacing stainless steel and cobalt-chromium alloy implant which are used in skull, shoulder joint, spine, and dental implant. In dental field, titanium has been used as dental implant, so it becomes necessary to examine and estimate the anti-corrosion ability of Ti and its alloys at the severe conditions such as crevice corrosion and galvanic corrosion. The purposes of this study was to examine the corrosion mechanisms of the pure Ti showing good corrosion resistance under an oral corrosion environment when it is coupled with dental casting Type Ⅱ and Type Ⅳ gold alloys. These coupling corrosion mechanisms were studied in three conditions. First was by measuring the resting potential of pure Ti, when it was uncoupled and coupled with Type Ⅱ and Type Ⅳ alloys. Second was by measuring anode polarization behavior of pure Ti, Type Ⅱ and Type Ⅳ alloys, and third was by detecting dissolved ions from the pure Ti, uncoupled and coupled with Type Ⅱ and Type Ⅳ gold alloys which were immersed in 0.9% NaCl solution for 7 days. The resting potential showed a low potential value at the initial stage but increasing into a high value (to 0.18 V) with time elapse and reached a stable value. On the contrary, the potentials of Type Ⅱ and Type Ⅳ gold alloys were in their values at the initial stage of immersion, then decreased with the time and reached stable values, being higher than the value of pure Ti. When pure Ti coupled with Type Ⅱ and Type Ⅳ gold alloys, the resting potential of coupled one was between the values of each one. When Type Ⅱ and Type Ⅳ gold alloys were coupled with pure Ti, there was an increase in Ag, Cu, and Zn. Also, Zn ions released the high potential precious metal alloys, compared to the uncoupled case. Ti ion was not detected at any cases of pure Ti or coupled with gold alloys. It was thought that one of the causes of the increase in Ag, Zn, and Cu ions when Ti was coupled with dental gold alloys was that Ag, Zn, and Cu ions were selectively dissoluted from the Ag rich regions around grain boundary and the casting defects. In conclusions, the results of this study suggest that the pure Ti was very stable when coupled with the gold alloys in oral cavity.

Tribological Performance of Cu-Ni Alloy Nanoparticles Synthesized using a Pulsed-Wire Evaporation Method

오정석,이창규 대한금속·재료학회 2008 METALS AND MATERIALS International Vol.14 No.4

Cu-Ni alloy nanoparticles were produced using a pulsed-wire evaporation method in Ar gas. The synthesized Cu-Ni alloy nanoparticles had an average size of 150 nm, were spherical in shape and agglomerated. We investigated the tribological properties of dispersion-stabilized Cu-Ni alloy nanoparticles when used as a solid lubricant in oil at ambient temperature. The sedimentation behavior of Cu-Ni alloy nanoparticles in oil was examined using Turbiscan LAb. The particles were clearly quantified using delta backscattering profiles and peak thickness kinetics as functions of time. The rubbing surfaces were characterized after a friction test using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). We found that dispersed Cu-Ni nanoparticles as a solid lubricant in oil had superior dispersion stability properties for over 48 h. Dispersed Cu nanoparticles in oil showed a low friction coefficient and good wear rate compared to oil only. Dispersed Cu-Ni alloy nanoparticles had superior friction reduction and antiwear properties compared to Cu nanoparticles, and these effects increased with the Ni content in the alloy. However, non-dispersed Cu-Ni alloy nanoparticles had poor antiwear properties. Dispersion-stabilized Cu-Ni alloy nanoparticles in oil enhanced the rolling effect of spherical nanoparticles between rubbing surfaces during friction processes. Cu-Ni alloy nanoparticles were produced using a pulsed-wire evaporation method in Ar gas. The synthesized Cu-Ni alloy nanoparticles had an average size of 150 nm, were spherical in shape and agglomerated. We investigated the tribological properties of dispersion-stabilized Cu-Ni alloy nanoparticles when used as a solid lubricant in oil at ambient temperature. The sedimentation behavior of Cu-Ni alloy nanoparticles in oil was examined using Turbiscan LAb. The particles were clearly quantified using delta backscattering profiles and peak thickness kinetics as functions of time. The rubbing surfaces were characterized after a friction test using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). We found that dispersed Cu-Ni nanoparticles as a solid lubricant in oil had superior dispersion stability properties for over 48 h. Dispersed Cu nanoparticles in oil showed a low friction coefficient and good wear rate compared to oil only. Dispersed Cu-Ni alloy nanoparticles had superior friction reduction and antiwear properties compared to Cu nanoparticles, and these effects increased with the Ni content in the alloy. However, non-dispersed Cu-Ni alloy nanoparticles had poor antiwear properties. Dispersion-stabilized Cu-Ni alloy nanoparticles in oil enhanced the rolling effect of spherical nanoparticles between rubbing surfaces during friction processes.

고용 강화 및 결정립 미세화를 통한 마그네슘 합금 주조재의 기계적 물성 향상

김상훈,문병기,유봉선,박성혁 한국주조공학회 2017 한국주조공학회지 Vol.37 No.6

This study investigated the effects of the addition of Zn, Ca, and SiC on the microstructure and mechanical properties of Mg-Al alloys. The tensile properties of homogenized Mg-xAl (x = 6, 7, 8, and 9 wt.%) alloys increased with increasing Zn content by the solid-solution strengthening effect. However, when the added Zn content exceeded the solubility limit, the strength and ductility of the alloys decreased greatly owing to premature fracture caused by undissolved coarse particles or local melting. Among the MgxAl- yZn alloys tested in this study, the AZ74 alloy showed the best tensile properties. However, from the viewpoints of the thermal stability, castability, and tensile properties, the AZ92 alloy was deemed to be the most suitable cast alloy. Moreover, the addition of a small amount (0.17 wt.%) of SiC reduced the average grain size of the AZ91 alloy significantly, from 430 μm to 73 μm. As a result, both the strength and the elongation of the AZ91 alloy increased considerably by the grain-boundary hardening effect and the suppression of twinning behavior, respectively. On the other hand, the addition of Ca (0.5-1.5 wt.%) and a combined addition of Ca (0.5-1.5 wt.%) and SiC (0.17 wt.%) increased the average grain size of the AZ91 alloy, which resulted in a decrease in its tensile properties. The SiC-added AZ92 alloy exhibited excellent tensile properties (YS 125 MPa, UTS 282 MPa, and EL 12.3%), which were much higher than those of commercial AZ91 alloy (YS 93 MPa, UTS 192 MPa, and EL 7.0%). The fluidity of the SiC-added AZ92 alloy was slightly lower than that of the AZ91 alloy because of the expansion of the solid-liquid coexistence region in the former. However, the SiC-added AZ92 alloy showed better hot-tearing resistance than the AZ91 alloy owing to its refined grain structure.

다이캐스팅용 Al-Zn-Mg-Fe 합금의 특성에 미치는 Zn 및 Mg 첨가의 영향

김기태 ( Ki Tae Kim ),임영석 ( Young Suk Kim ),신제식 ( Je Sik Shin ),고세현 ( Se Hyun Ko ),김정민 ( Jeong Min Kim ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.4

The effects of alloying elements on the solidification characteristics, microstructure, thermal conductivity, and tensile strength of Al-Zn-Mg-Fe alloys were investigated for the development of high strength and high thermal conductivity aluminum alloy for die casting. The amounts of Zn and Mg in Al-Zn-Mg-Fe alloys had little effect on the liquidus / solidus temperature, the latent heat for solidification, the energy release for solidification and the fluidity of Al-Zn-Mg-Fe alloys. Thermo-physical modeling of Al-Zn-Mg-Fe alloys by the JMatPro orogram showed MgZn2, AICuMgZn and Al3Fe phases in the microstructure of the alloys. Increased amounts of Mg in Al-Zn-Mg-Fe alloys resulted in phase transformation, such as MgZn2⇒MgZn2+ AICuMgZn⇒AICuMgZn in the microstructure of the alloys. Increased amounts of Zn and Mg in Al-Zn-Mg-Fe alloys resulted in a gradual reduction of the ther-mal conductivity of the alloys. Increased amounts of Zn and Mg in Al-Zn-Mg-Fe alloys had little effect on the tensile strength of the alloys.

백색 5K Au-Ag-In 합금재의 인듐 첨가량에 따른 물성 변화

송정호,송오성,Song, Jeongho,Song, Ohsung 한국재료학회 2017 한국재료학회지 Vol.27 No.7

In order to replace 14K white gold alloys, the properties of 5K white gold alloys (Au20-Ag80) were investigated by changing the contents of In (0.0-10.0 wt%). Energy dispersive X-ray spectroscopy (EDS) was used to determine the precise content of alloys. Properties of the alloys such as hardness, melting point, color difference, and corrosion resistance were determined using Vickers Hardness test, TGA-DTA, UV-VIS-NIR-colorimetry, and salt-spray tests, respectively. Wetting angle analysis was performed to determine the wettability of the alloys on plaster. The results of the EDS analysis confirmed that the Au-Ag-In alloys had been fabricated with the intended composition. The results of the Vickers hardness test revealed that each Au-Ag-In alloy had higher mechanical hardness than that of 14K white gold. TGA-DTA analysis showed that the melting point decreased with an increase in the In content. In particular, the alloy containing 10.0 wt% In showed a lower melting temperature (> $70^{\circ}C$) than the other alloys, which implied that alloys containing 10.0 wt% In can be used as soldering materials for Au-Ag-In alloys. Color difference analysis also revealed that all the Au-Ag-In alloys showed a color difference of less than 6.51 with respect to 14K white gold, which implied a white metallic color. A 72-h salt-spray test confirmed that the Au-AgIn alloys showed better corrosion resistance than 14K white gold alloys. All Au-Ag-In alloys showed wetting angle similar to that of 14K white gold alloys. It was observed that the 10.0 wt% In alloy had a very small wetting angle, further confirming it as a good soldering material for white metals. Our results show that white 5K Au-Ag-In alloys with appropriate properties might be successful substitutes for 14K white gold alloys.

Ti 및 Mo 첨가에 따른 치과 CAD/CAM용 Ni-Cr 및 Co-Cr합금의 표면분석

문대선(Dae-Sun Moon),최한철(Han-Cheol Choe) 한국표면공학회 2018 한국표면공학회지 Vol.51 No.3

In this study, surface analysis of Ni-Cr and Co-Cr alloys with addition of Ti and Mo for dental CAD/CAM use has been researched experimentally. The surface characteristics of the alloys were examined by Vickers hardness test, bonding strength test, surface roughness test, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction spectroscopy. The shrinkage of the sintered Ni-Cr alloy alloy was slightly larger than that of Ni-Cr-Ti alloy, and larger than Co-Cr alloy. Also, the addition of Mo showed a tendency to decrease shrinkage somewhat. From the result of XRD analysis, NiCr, Ni₃Cr and Ni₃Ti were observed in the sintered Ni-13Cr-xTi and Ni-13Cr-xMo alloys. In addition, σ-CrCo, Co₂Mo₃ and TiCo₂ were formed in the sintered Co-Cr-xTi and Co-Cr-xMo alloys. Surface hardness of Ti and Mo added alloy was higher than those of Ni-Cr and Co-Cr alloy. The bond strength between sintered alloy and porcelain was 16.1 kgf/㎟ for Ni-13Cr alloy, 17.8 kgf/㎟ for Ni-13Cr-5Ti alloy, and 8.2 kgf/㎟ for Ni-13Cr-10Ti alloy, respectively.

ADC12 다이캐스팅 합금의 미세조직 및 기계적 특성에 미치는개량 원소 첨가의 영향

강연지,윤상일,김동현,이기안 한국소성∙가공학회 2019 소성가공 : 한국소성가공학회지 Vol.28 No.1

In this study, various alloying elements (Cr, Sr, Ca, Cd) were added to improve the mechanical properties of ADC12 fabricated by a die casting process. The effect of alloying elements on the microstructure and mechanical properties were investigated. The phase analysis results of the modified ADC12 alloy with conventional ADC12 alloy, showed the similar characteristics of Al matrix, Si phase, CuAl2 phase and the Fe intermetallic phase. As a result of the microstructure observation, the secondary dendrite arm spacing (SDAS) was shown to have decreased after the addition of the alloying elements. The eutectic Si phase, which existed as flake form in the conventional ADC12 alloy, was modified finely as a fiber form in the modified ADC12 alloy. It was observed that the CuAl2 phase as the strengthening phase was relatively finely distributed in the modified ADC12 alloy. The Fe intermetallic appeared as a Chinese script shaped Al6 (Mn,Fe) which is detrimental to mechanical properties in conventional ADC12 alloy. On the other hand, in the modified ADC12 alloy, polyhedral α-Al15Si2 (Fe,Mn,Cr)3 was observed. The tensile properties were improved in the modified ADC12 alloy. The yield strength and tensile strength increased by 12.4% and 10.0%, respectively, in the modified ADC12 alloy, and the elongation was also seen to have been increased. As a result of the pin on disk wear test, the wear resistance properties were also improved by up to about 7% in the modified ADC12 alloy. It is noted that the wear deformation microstructures were also observed, and it was found that the fine eutectic Si and strengthening phases greatly improved abrasion resistance.