Papers by Keyword: Intermetallic Compound (IMC)

Abstract: The use of Pb-free solder alloys are just newly developed materials and their properties are not well established and documented yet. So, the research to substitute the critical problem of the Pb solder alloy are increasing widely. To evaluate the shear property of solder joints according to temperature condition was predicted through the Shear-Punch test and FEM. By using the database according to this, the reliability evaluation technology of the solder joints tries to be formulated. In this paper, the solder used the Sn37Pb, Sn-4Ag and the Sn4Ag0.5Cu. When solder melted in the copper interface, the solder joints according to reflow times, each modeling required for the Shear- Punch was made in consideration of the IMC layer thickness. And the micro shear punch test was performed to obtain material properties of solder according to temperature condition. The shear properties of specimen which was modeled was predicted through FEM. It compared with the test value in which it obtains from Shear-Punch. Also, a method which can obtain shear properties of Pb-free solder joints easily and quickly using FEM was proposed.

Abstract: Microstructure of electromagnetic pulse tungstic electrode argon arc welding (EMP-TIG) welded Mg/Al dissimilar metal joint is studyed using optical microscope, scanning electron microscope, and X-ray diffraction. The results indicate that gas tungsten arc welding can provide Mg/Al joint with excellent microstructure and performance. The welding region is composed of Mg₃Al₂ phase, α(Mg), β(Li), and MgAl. The weld zone and the Al alloy base materials are well combined. There are massive MgAl phase dendrites in the weld area, which cause the significantly increase of hardness at weld zone. Near the Mg-8Li alloy base metal side of the weld zone, there exists a layer of 100~ 200μm equiaxed region. About 1μm Mg₃Al₂ reaction layer is distributed between Mg-8Li alloy base metal and the equiaxed grains. This reaction layer and the Mg-8Li alloy base metal, as well as the weld zone of equiaxed grains, have a good combination.

Abstract: In this paper, the fabrication of TiAl alloy powders by high-energy ball milling and heat preservation at low temperature and high vacuum using titanium powders of 30 micron and aluminum powders in the size of 9-12 micron. After being heated under the different time and temperature, the alloying of milled and heated powders of titanium and aluminum were investigated. The results show that the alloy powders with the main intermetallic compounds of TiAl and a small quantity of aluminum tri- titanium can be obtained through one hour high-energy ball milling and preserving heat 2 hours at 500°C, 3 hours at 600 °C in high vacuum. Furthermore, the transitional alloy phase Al2Ti was formed at 550 °C~600 °C, and it has an effect on the density of Ti-Al alloy powders in the diffusion synthesis. The fabrication of TiAl alloy powders with different density by sintering diffusion at low temperature and high vacuum is effective.

Abstract: When the use of lead was banned, the development of lead-free solders began to rise and was greatly explored. Presently, majority of the eutectic Pb-free solders are Sn-based and the most promising is ternary SnAgCu (SAC) solder. However, SnAgCu solder tends to become brittle in nature and excessive solder interfacial reactions. An attractive approach is by introducing alloying elements such as Ce, Fe and Zn into the SnAgCu solder, which allows for an increase of the mechanical properties and refine the solder microstructure as well as improve the wetting properties. The present work focuses on the effects of a series of elemental additions of 0.5% Ce, Fe and Zn into the basic Sn_3.0Ag_0.5Cu solder, in attempt to reduce the intermetallic compound (IMC) growth as well as joint reliability and reflow properties of the solder on Ni-P surface finish. The intermetallic compound Cu₆Sn₅, containing a small amount of dissolved Ni, was found to form preferentially on the Ni coating. This compound layer served as a barrier for direct reaction of Sn with the Ni-P coating. The P-rich Ni layer acts as a good diffusion barrier layer, which decreases the dissolution rate of the Ni-P layer hence decreases the growth of IMC thickness layer. It is also expected that with the addition of alloying elements, the wetting properties will be further enhanced.

Abstract: The X-ray diffraction and specific heat measurements have been performed for the ferromagnetic compounds (MnCo)_1-xGe within the concentration range 0.02 x 0.035. The compounds possess the hexagonal Ni₂In-type structure at elevated temperatures, while for the composition with x = 0.02 and 0.03 a spontaneous martensitic-type transition to the orthorhombic TiNiSi-type phase occurs at 283 and 221 K, respectively. We studied the entropy changes associated with the first-order structural transition and estimated the changes in magnetic, lattice, electronic entropies.

Abstract: Magnetic properties of the La_1xR_xMn₂Si₂ (R is Gd, Tb, Dy; 0 x 1) compounds were investigated using magnetic measurements on quasi-single crystals. The x-T concentration magnetic phase diagrams are constructed. All obtained x-T magnetic phase diagrams are found to be similar. Six magnetic structures are realized in the compounds at different concentrations x. It was shown that all the compounds have strong magnetic anisotropy with the c-axis as the easy direction. For the compounds with x = 0.2, the irreversible magnetization processes are observed which can be attributed to the existence of a compensation point at which the R and Mn magnetic sublattices compensate each other. The nature of various spontaneous and field-induced phase transitions is also discussed.

Abstract: The solidification of binary Al-Sc melts containing small amounts of scandium (< 2 wt.%) have been investigated. We studied concentration profiles in long Al-Sc as cast ingots formed by slow cooling of the liquid alloys. It was found that minor addition of transition metals like Ti can lead to the formation of large (about 10-20 μm) spherical intermetallic particles (Al₃Sc containing some amount of isomorphic Ti). These sphere-like particles are forming during the crystallization of liquid solution of Sc in Al (before the precipitation on nanosize spherical particles from the solid solutions). The results of SEM and EDX investigations of these alloys are also presented in this paper.

Abstract: Al-Si-Mg/AlN composites were prepared by stir casting technique. The amount of AlN added to Al-Si-Mg alloy was from 2 to 10 wt%. As-cast composites were solutionised at 540 °C for 4 h, quenched in warm water, 60 °C then artificially aged at 180 °C for 4 h. The microstructure of Al-Si-Mg matrix alloy contained dendritic α-Al, needle-like Si and very little inter-metallic compounds. As-cast Al-Si-Mg/AlN composites have rounded α-Al phase and needle-like Si where AlN particles dispersed surrounding α-Al. Needle-like Si transformed to spheroid after artificial aging. The size of α-Al phases of heat-treated composites containing 2 and 5 wt% AlN was bigger than that of as-cast composites whereas the heat-treated Al-Si-Mg/10% AlN composite has thin and elongated dendritic α-Al phases, and larger AlN particles.

Abstract: Jump frequencies of ¹¹¹In/Cd tracer atoms were measured for a series of layered phases La_nCoIn_3n+2 using the technique of perturbed angular correlation of gamma rays (PAC). The frequencies were determined by analysis of nuclear quadrupole relaxation produced by fluctuating electric field gradients. Samples were synthesized having nominal values n= 1, 2, 3, 5 and , with n= corresponding to the L1₂ phase LaIn₃. The phases form heuristically from LaIn₃ by replacing every (n+1)^th (100) mixed plane of La and In atoms with a plane of Co-atoms. For the n=1 phase, LaCoIn₅, jump frequencies were too small to detect. Two signals were observed, one for indium atoms next to the Co-planes and the other for more distant indium atoms. No relaxation was observed for atoms next to the Co-planes, indicating that there is no diffusion across the Co-planes. With increasing n, jump rates for the other In-atoms increased toward values observed for LaIn₃. Jump frequency activation enthalpies for n= 3 and 5 were observed to be the same as for n=, suggesting the same diffusion mechanism. However, the jump-frequency prefactors were found to be smaller for small n, which is attributed to reductions in the connectivity of the diffusion sublattice. We conclude that diffusion in the layered phases is remarkably similar to diffusion in LaIn₃ once the reduced connectivity is taken into account.

Abstract: Pure titanium and aluminum sheets were used to prepare titanium-aluminum diffusion couples. The diffusion couples were heated to temperatures 550, 575, 600, 625, 640, 650 and 700°C. SEM observations of the titanium-aluminum interface and EPMA results revealed that a TiAl₃ intermetallic layer has formed and thickened between the layers. Grain boundaries of the TiAl₃ compound, which were revealed by back-scattered electron imaging, indicated a size distribution across the layer. Finer grains which were located close to the titanium showed that TiAl₃ has nucleated at the Ti-TiAl₃ interface. Thus, the former grains which had formed close to the aluminum-rich side have grown and coarsened during annealing at high temperatures. Grain coarsening of TiAl₃ decreased the kinetics of the layer thickening.