Role of Intermetallics on Fatigue Behaviuor of Stainless Steel Adhered by Sn

Jianjun Guan,Yan Zhao,Feng Liu,Jie Zhao 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.6

The fatigue property of 304 stainless steel (SS) adhered by Fe-Sn intermetallics was investigated. The microstructure of crack nucleation and crack propagation was observed, and the influence of Fe-Sn intermetallics on fatigue failure was analyzed. Fatigue tests at stress ratio of R = -1 were performed using a sine waveform at 20 Hz frequency under load control. In addition, the morphology and microfractography of the Fe-Sn intermetallics were examined under a scanning electron microscope. Results demonstrated that the adherence of the interfacial (Fe, Cr)Sn2 layer reduced the fatigue life of the 304 SS substrates. The fatigue cracks also exhibited the intergranular fracture characteristics of the intermetallics. The brittle (Fe, Cr)Sn2 intermetallics were apt to fatigue crack nucleation. The interfacial metallurgical bonding, which was caused by diffusion reaction between Fe and Sn atoms, led to crack propagation into the SS substrate.

Fabrication and Compressive Properties of Porous TiAl-Mn Intermetallics by Powder Metallurgical Route

Jong-Myeong Kim,Jewoosoo Kim,Seok-Heon Yoon,현승균,Mok-Soon Kim 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.2

We investigated the effects of process parameters on the microstructure and compressive properties of reactive-sintered porous TiAl-based intermetallics. Different extrusion ratios were selected in order to change the as-extruded microstructure and thus obtain various types of porous structures (unidirectional and spherical pores) after reactive sintering. In addition, different environmental conditions, such as vacuum and air,were used during the reactive sintering stage. It was revealed that the compressive strength is influenced by the unidirectionalty of the pores. High unidirectionalty led to higher yield strength at room temparature and at 1073 K. The compressive properties of the porous TiAl intermetallics were also influenced by the environment where reactive sintering is carried out.

Effect of Mechanical Alloying on the Microstructural Evolution of Al60Cr30Si10 Alloys Processed by Spark Plasma Sintering

Jeong‑Han Lee,Ik‑Hyun Oh,Jun‑Ho Jang,Ju‑Hun Kim,Sung‑Kil Hong,Hyun‑Kuk Park 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

In this study, Al, Cr and Si fine powders were alloyed by planetary ball milling to investigate their microstructural evolution,following their mechanical alloying behavior. The formation of Al(Cr) supersaturated solid solution by the Cr grainsembedded in Al-matrix, which contributed substitutional structure is discussed in relation to their structural evolution inaccordance with the distortion of a crystal lattice. The compacts of Al–Cr–Si alloys were prepared by rapid sintering withina short time by dense consolidation above the density of 99.9% as the formation of intermetallics, except in the case of thedistribution of single-phases induced by the Al-melting. The formation behavior of intermetallics was dominated by dependenceon the structures of the milled-powder and subsequent sintering temperature. To estimate the consolidated behaviorsof compacts, various approaches derived from TEM and XRD analysis were taken to obtain microstructural evidences ofthe inter-diffusion, following the presence of thermally stable intermetallics.

Nb-Si-B계에서 Nb+T2 공존 영역의 미세조직 특성

주수현 ( Soo Hyun Choo ),김영도 ( Young Do Kim ),오승탁 ( Sung Tag Oh ),이성 ( Seong Lee ),류성수 ( Sung Soo Ryu ),석명진 ( Myung Jin Suk ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.1

Intermetallic-based materials are interesting for high temperature structural applications because of their good mechanical properties and enhanced oxidation resistance. In this study microstructural examination of the Nb-Si-B alloys at Nb-rich compositions was performed. The Nb-rich corner of the Nb-Si-B system is very attractive because the constituent phases are Nb (a ductile and tough phase with a high melting temperature) and T2 (a very hard intermetallic compound with favorable oxidation resistance), which make a good combination for high temperature structural materials. At compositions lower than 82 at%Nb the microstructure shows the T2 primary phase and eutectic (T2+Nb), while the Nb primary phase and eutectic were formed at higher compositions. Hardness tests (Rockwell A-scale and micro Vickers) were carried out to estimate the optimal composition for good mechanical properties. (Received January 13, 2014)

Influence of p-Type Double-Doping on the Crystals and Electronic Structures of Two Polar Intermetallics: La4.57(1)Li0.43Ge3.80(3)In0.20 and Nd4.32(1)Li0.68Ge3.87(3)In0.13

전지은,이준수,유태수 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.9

Two quaternary polar intermetallic compounds La4.57(1)Li0.43Ge3.80(3)In0.20 and Nd4.32(1)Li0.68Ge3.87(3)In0.13 were synthesized using a conventional high temperature synthetic method as we attempted to introduce the p-type double-doping of Li and In for RE and Ge in the RE5-xLixGe4-y (RE = rare-earth metals) system, and their crystal structures were characterized by single crystal X-ray diffraction experiments. The two title compounds crystallize in the orthorhombic space group Pnma (Pearson code oP16, Z = 4) with six crystallographically independent asymmetric atomic sites and adopt the Gd5Si4-type structure. Overall crystal structures of two isotypic title compounds can be described as a 1:1 assembly of the hypothetical 2-dimensional (2D) RE2(RE/Li)(In/Ge)2 layered structure adopting the Mo2FeB2-type structure and the dumbbell-shaped inter-slab (In/Ge)2 dimers bridging two such neighboring 2D layers along the crystallographic b-axis direction. The observed ?direction selective? structural transformation from the Sm5Ge4-type to the Gd5Si4-type structure can be understood as a result of the simultaneous double-doping by the relatively smaller amount of Li substitution for La at the RE3 site than that in the La4LiGe4 and the partial In substitution for Ge at both of the M1 and M3 sites. The site-preference of In for two particular anionic sites were thoroughly studied using four hypothetical La4LiGe3In models having different atomic arrangements by the tight-binding linear muffin-tin orbital (TB-LMTO) method. The overall electronic structure and individual chemical bonding influenced by the given double-doping were also discussed on the basis of the density of states (DOS) and crystal orbital Hamilton population (COHP) curves analyses.

Crystal Structure, 7Li NMR, and Structural Relationship of Two Rare-Earth Metal Richer Polar Intermetallics: La15Ge9Li1.50(16) and La7Ge3

Gnu Nam,조홍일,옥강민,김종식,유태수 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.8

Two novel polar intermetallic compounds have been synthesized by a high-temperature reaction method, and their crystal structures have been characterized by both single-crystal and powder X-ray diffractions. La15Ge9Li1 .50(16) crystallizes in the hexagonal space group P63 mc (Z = 2, Pearson code hP52) with nine crystallographically independent sites in the unit cell, and the lattice parameters are a = 15.516(2) and c = 6.895(2) Å. The overall crystal structure can be described as a √3 × √3 × 1 superstructure of the parent compound La5Ge3 adopting the Mn5Si3-type, and such a superstructure transformation should be attributed to the particular ordering patterns of interstitial Li atoms at the Wyckoff 2a and 2b sites with different occupation factors. La7Ge3 also crystallizes in the hexagonal P63 mc space group (Z = 2, Pearson code hP20) with three La and one Ge non-equivalent sites in the unit cell. The lattice parameters are a = 10.666(1) and c = 6.357(1) Å. The crystal structure of La7Ge3 shares some similarities with La15Ge9Li1.50(16) and its parent compound La5Ge3, such as the one-dimensional (1D) zigzag confacial La6 octahedra chains and the 1D zigzag La atomic chains. Theoretical investigations using tight-binding linear muffin-tin orbital (LMTO) method provide a comprehensive understanding about electronic structures and chemical bonding of two title compounds based upon density of states (DOS) and crystal orbital Hamilton population (COHP) analyses. The solid-state 7Li NMR spectrum measurement proves the existence of two independent interstitial Li positions at two distinctive octahedral sites in La15Ge9Li1.50(16).

2 상 Ti₃Al-xNb 계 금속간 화합물들의 초소성 특성에 미치는 상분율의 영향

김지식 한국소성가공학회 2002 소성가공 : 한국소성가공학회지 Vol.11 No.5

A study has been made to investigate the boundary sliding and its accommodation mode with respect to the variation of $\alpha$$_2$/$eta$ volume fraction during superplastic deformation of two-phase Ti$_3$Al-xNb intermetallics. Step strain rate and load relaxation tests have been performed at 950, 970 and 99$0^{\circ}C$ to obtain the flow stress curves and to analyze the deformation characteristics by the theory of inelastic deformation. The results show that the grain matrix deformation and boundary sliding of the three intermetallics containing 21, 50 and 77% in $eta$ volume fractions are well described by the plastic deformation and viscous flow equations. Due to the equal accommodation of both $a^2$ and $\beta$ phases, the accommodation modes for fine-grained materials are in good agreement with the iso-strain rate models. The sliding resistance analyzed for the different boundaries is the lowest in the $\alpha$$_2$/$\alpha$$_2$ boundary, and increases in the order of $\alpha$$_2$/$\alpha$$_2$<< $\alpha$$_2$/$\beta$ = $\beta$/$\beta$, which plays an important role in controlling the superplasticity of the alloys with the various $\alpha$$_2$/$\beta$ phase ratio.

Effect of Mg12Nd and Mg3Nd On the Corrosion Behavior of Mg‒3 wt%Nd Alloy in Saline Solution

Kaihua Yuan,Jianfeng Wang,Yufeng Sun,Shijie Zhu,Hairong Liu,Shaokang Guan 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.5

In this paper, the precipitates of the Mg‒3 wt%Nd alloy in the as-cast state and after heat treatment at 540 ℃ for 12 h wereinvestigated and related to the corrosion behavior in saline solution. For the as-cast specimen, the network and sphericalβ-phases (Mg12Nd) act as the anodes relative to Mg matrix at the initial stage of immersion in saline solution. Withincreasing the immersion time, the intergranular corrosion caused by the preferential dissolution of the reticular β-phaseleads to the detachment of Mg fragments. For the heat-treated specimen, the plate-shaped β1-phases (Mg3Nd) distributedevenly in the grain interior act as the micro-cathodes. The corrosion pits are prone to extend horizontally and connectedeach other, resulting in an uniform corrosion status and a relatively lower corrosion rate. This result is helpful for developingthe biomedical Mg‒Nd base alloys with a good degradation property by adjusting the precipitation of intermetallics.

Fe-(20, 45) wt% Gd 금속간 화합물의 기계적 특성 및 부식 거동 연구

강보경,백열,최용,문병문 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.2

Fe-(20, 45 wt%) Gd intermetallics were vacuum arc melted as the mother alloy of a neutron shielding and absorbing material. The structure of the cast Fe-20 wt% Gd intermetallics had primary dendrites with a short width of about 2 μm, which became coarse with increasing Gd content. The final compositions of the Fe-20 wt% Gd and Fe-45 wt% Gd intermetallics determined by Rietveld refinement were mainly Fe3Gd with 26.6 at% Fe2Gd, and Fe3Gd with various intermetallics like 13.9 at% Fe2Gd, 7.3 at% Fe9Gd and 3.9 at% Fe17Gd2, respectively. The micro-hardnesses, yield strength, ultimate compressive strength and elongation of the Fe-20 wt% Gd intermetallics were 629±12 Hv, 753 MPa, 785 MPa and 4%, respectively, and those of the Fe-45 wt% Gd intermetallics were 741±13 Hv, 772 MPa, 823 MPa and 3%. Passivity was not present in artificial sea water at room temperature. The corrosion potentials and the corrosion rates of the Fe-20 wt% Gd and Fe-45 wt% Gd intermetallics were –624 mVSHE, 2.771 mA/cm2, and –804 mVSHE, 3.397 mA/cm2, respectively. The corroded surface of the Fe-Gd intermetallics contained corrosion products like gadolinium with iron, which detached to leave a trail of pits.

Cu 첨가에 따른 nanocrystalline ${Ll_2}{Al_3}Hf$ 금속간 화합물의 기계적 합금화 거동 및 진공열간 압축성형거동

김재일,오영민,김선진,Kim, Jae-Il,O, Yeong-Min,Kim, Seon-Jin 한국재료학회 2001 한국재료학회지 Vol.11 No.8

고온구조용 재료로 사용이 기대되는 $Al_3$Hf금속간 화합물의 단점인 낮은 연성을 개선하기 위하여 SPEX mill을 이용한 기계적 합금화 과정에서의$ Ll_2$상 생성거동과 이에 미치는 제3원소의 영향, 그리고 이들 금속간 화합물의 진공열간 압축성형 거동을 조사하였다. Al과 Hf 혼합분말을 기계적 합금화한 결과에 따르면 6시간 milling후에 $L_2$Hf 금속간 화합물이 생성되었으며, 이때 결정립 크기가 7~8nm 정도인 nanocrystalline이 형성되었다. Cu를 첨가한 경우에는 10시간 milling 후에 2원계와 동일한 $Ll_2$구조의 금속간 화합물이 생성되었으며, 격자상수는 Cu의 함량이 증가함에 따라 감소하였다. 2원계 $Al_3$Hf 금속간 화합물의 경우에 $Ll_2$상에서 $D0_{23}$ 상으로의 변태 시작온도는 $380^{\circ}C$ 정도였으며, 변태 종료온도는 열처리시간에 따라 $480^{\circ}C$에서 $550^{\circ}C$ 정도를 나타내었다. Cu 함량이 증가함에 따라 변태 시작온도는 상승하였으며 10at.%의 Cu 첨가는 변태 시작온도를 $700^{\circ}C$까지 상승시켰다. 2원계 Al-25at.%Hf 혼합분말의 VHP 성형시 750MPa, $400^{\circ}C$, 3시간에서 약 89%의 비이론 밀도를 얻을 수 있었다. 같은 온도에서 Cu를 10at.% 첨가한 경우의 VHP 성형시 90%정도의 비이론 밀도를 보여 2원계 $A1_3$Hf보다 성형성이 약간 증가하는 것을 볼 수 있었으며, 성형온도를 $500^{\circ}C$로 증가시킨 경우에는$ Ll_2$상에서 $D0_{23}$상으로의 상변화나 결정립의 증가없이 약 92.5%의 비이론 밀도를 얻을 수 있었다. To improve the ductility of $A1_3Hf$ intermetallics, which are the potential high temperature structural materials, the mechanical alloying behavior. the effect of Cu addition on the $Ll_2$ phase formation and the behavior of vacuum hot-pressed consolidation were investigated. During the mechanical alloying by SPEX mill, the $Ll_2 A1_3Hf$ intermetallics with the grain size of 7~8nm was formed after 6 hours of milling in Al-25at.%Hf system. The $Ll_2$ Phase of Al_3Hf$ intermetallics with the addition of 12.5at.%Cu, similar to that of the binary Al-25at.% Hf, was formed, but the milling time necessary for the formationof the $Ll_2$ phase was delayed form 6 hours to 10 hours. The lattice parameter of ternary $Ll_2(Al+Cu)_3Hf$ intermetallics decreased with the increase of Cu content. The onset temperature of $Ll_2$ to $D0_{23}$ phase in $Al_3Hf$ intermetallics was around 38$0^{\circ}C$, the temperature upon completion varied from 48$0^{\circ}C$ to 5$50^{\circ}C$ as the annealing time. The onset temperature of $Ll_2$ to $D0_{23}$ phase transformation in $(Al+ Cu)_3Hf$ intermetallics increased with the amount of Cu and the highest onset temperature of $700^{\circ}C$ was achieved by the Cu addition of 10at.%. The relative density increased from 89% to 90% with the Cu addition of 10at.% in $Al_3Hf$ intermetallics hot-pressed in vacuum under 750MPa at 40$0^{\circ}C$ for 3 hours. The relative density of 92.5% was achieved without the phase transformation and the grain growth as the consolidation temperature increased from 40$0^{\circ}C$ to 50$0^{\circ}C$ in $(Al+Cu)_3Hf$ intermetallics hot-pressed in vacuum under 750MPa for 3 hours.