Keisuke Uenishi

Formation of a super-saturated solid solution in the AgCu system by mechanical alloying

Abstract Mechanical alloying in the AgCu system by the ball-milling and repeated rolling methods was performed. A super-saturated f.c.c. solid solution was formed in the entire composition range by ball milling. The lattice parameter change due to the super-saturated solid solution formation matched quite well with the reported result obtained by rapid quenching. Upon heating, the super-saturated solid solution decomposed into base silver and copper solutions, resulting in a large reduction of electrical resistivity.

Fabrication of a thick surface layer of Al3Ti on Ti substrate by reactive-pulsed electric current sintering

The thick intermetallic compound Al3Ti layer was formed by reactive-pulsed electric current sintering (PECS) of mechanically alloyed powders set on the Ti substrate to improve the wear and oxidation properties. During heating by PECS, Al and Ti in MA powders reacted to form an Al3Ti layer, and simultaneously reacted with the Ti substrate to achieve joining between the surface layer and substrate. The densification behavior of the synthesized surface layer, and the reaction kinetics between the surface layer and substrate were investigated. By holding at 1100 K for 180 s under 40 MPa, a fully dense and homogeneous Al3Ti surface layer with a thickness of about 1600 mm was obtained. However, a higher temperature (1210 K) or longer holding time (over 1800 s) was required to eliminate voids on the Al3Ti/Ti interface. The obtained Al3Ti layer exhibited almost the same properties as cast bulk Al3Ti for hardness, wear and oxidation. # 2000 Elsevier Science Ltd. All rights reserved.

Formation of surface layer based on Al3Ti on aluminum by laser cladding and its compatibility with ceramics

Intermetallic compound Al3Ti or intermetallic compound matrix composite (IMC) surface layers were formed on Al surface by laser cladding. To form sound IMC surface layers, laser conditions must be controlled to suppress the melting of base metal. With increasing the volume fraction of ceramics in the IMC layer, it needed higher laser power to obtain IMC layer although the control of laser conditions became easier. During laser cladding, TiB2 melted by laser irradiation and then homogeneously precipitated as fine particles at a cooling stage. On the contrary, TiC and SiC hardly melted and were dispersed in Al3Ti matrix. SiC reacted with Ti to form titanium-silicide or TiC, which made the composition of matrix richer in Al than Al3Ti and caused degradation of the wear property. IMC surface layer improved the wear property of Al substrate. The particle size as well as volume fraction of dispersoid ceramics aAected the wear property. # 1999 Elsevier Science Ltd. All rights reserved.

Nano-structured intermetallic compound TiAl obtained by crystallization of mechanically alloyed amorphous TiAl, and its subsequent grain growth

The amorphization process during mechanical alloying (MA) was investigated for the Al-50at%Ti and Al-50at%Ti-10vol%TiB2 powder mixtures. Pure metallic powders of Al and Ti were finely mixed and transformed to the amorphous phase after being milled for about 2880 ks. In the case of Al-50at%Ti-10vol%TiB2 powder, the amorphous alloys with a fine dispersion of TiB2 particles could be obtained for a shorter milling times than that required for the powders without TiB2 ceramics. As a result of heat treatment for the mechanically alloyed amorphous powders, a nanocrystalline intermetallic compound of TiAl (γ) could be produced. Subsequent grain growth of the γ phase during heat treatment was investigated by estimating the grain-growth exponent and the activation energy for grain growth. It was found from this estimation that the grain growth was further suppressed as the powders were mechanically alloyed for longer times. Furthermore, the addition of the TiB2 particles that could be dispersed during MA finely and homogeneously in the amorphous matrix was found to be effective for suppression of the γ grain growth especially at elevated temperatures as well as for a long annealing.

Nanostructured titanium-aluminides and their composites formed by combustion synthesis of mechanically alloyed powders

Ti-Al alloys have been recognized as one of the most prospective materials since they are equipped with the advantages of both high ductility and high weight to strength ratio. For the further enhancements of these properties, their microstructural improvement, especially grain refinements or composite with ceramics has been investigated by many researchers. In this research, nano structured Ti-Al or Ti-Al-TiB 2 alloys were prepared by the combustion synthesis (1) of mechanically alloyed (2) powders, benefits of which are the low temperature processing and the ease of nano composite formation by using the non-equilibrium state of mechanical alloying (MA) powders. Moreover, for the practical application of the nanostructured powders, both their sintering and grain growth behavior were investigated quantitatively as a function of the heat treatment temperature and time. Then the effect of MA time and TiB2 addition on the sintering and grain growth behavior was discussed. Finally, as an example for the practical application of this technique, the thick intermetallic compound Al 3Ti layer was formed by reactive-pulsed electric current sintering (PECS) (3) of mechanically alloyed powders set on the Ti substrate to improve the wear and oxidation properties of Ti.

Enhanced densification of combustion synthesized Ni–Al intermetallic compound by Si addition

Abstract Ni–Al intermetallic compound was combustion synthesized from a powder mixture of elemental Al, Ni, and Si and was simultaneously bonded with spheroidal graphite cast iron substrate (FCD). By heating a powder mixture of elemental Al and Ni, exothermal reaction occurred at about 873 K to form Ni–Al intermetallic compound. However, the synthesized compound included a large volume of voids or unreacted regions. It was confirmed that Si addition as well as applying pressure were effective to decrease the voids or unreacted regions. It is considered that higher flowability of Al–Si liquid enhanced the densification of Ni–Al compound. The identification and growth behavior of the reaction layers formed in the interface between compound layer and FCD substrate was investigated.

Processing of intermetallic compounds for structural applications at high temperature

The establishment of secondary processing methods is essential to enable the use of intermetallic compounds for structural applications at high temperature. Of the many processing methods, joining and surface modification techniques were examined in this work. Joining of TiAl was accomplished by laser welding without the formation of hard, metastable α 2 -phase. Joining was also achieved by the application of SHS (self-propagating high temperature synthesis) reaction. For the formation of a layer of intermetallic compound on a metal surface, the processing method must be selected according to the desired thickness of surface layer. Laser cladding and laser alloying were found to be reasonable techniques to obtain a layer thickness up to 1 mm, whereas spraying and SHS bonding methods were found to be effective for thicknesses of 1–2 mm and > 2 mm, respectively. The production of intermetallic matrix composite materials was found to be attainable by these methods.

Microstructure of mechanically alloyed Al-In alloys

Mechanical alloying (MA) starting from elemental powder mixtures was performed on immiscible Al-10, 30 and 50 at % In alloys. Al and In were finely mixed with increasing MA time and the crystal size of each element became up to 40 nm after MA for 1152 ks. With refinement of the structure, the hardness increased up to 120 Hv in Al-10 at % In alloy, a value larger than that obtained from the rule of mixtures. The melting temperature of In was recognized, by thermal analyses, to fall by about 3 K for mechanically alloyed Al-In alloy, showing the possibility of forming f.c.t In supersaturated solid solution. A new endothermal peak around 420 K, which corresponded with the melting temperature of metastable f.c.c. In, was recognized for mechanically alloyed Al-50 at % In alloy.

Wear and oxidation resistance of Al2O3 particle dispersed Al3Ti composite with a nanostructure prepared by pulsed electric current sintering of mechanically alloyed powders

Al3Ti-matrix composite layers containing Al2O3 particles were formed on Ti substrate by pulsed electric current sintering (PECS) of mechanically alloyed (MA) powders to improve the wear and oxidation properties of the Ti substrate. Reducing the grain size of each element by MA makes the combustion synthesis of Al3Ti possible at a lower temperature. The grain size formed by the combustion synthesis of Al–Ti–Al2O3 powder mechanically alloyed for 720 ks was about 10 nm and its growth during sintering was suppressed by the existence of Al2O3. The densification behavior of the powder was investigated quantitatively. The obtained Al3Ti/Al2O3 composite layer showed better wear and oxidation resistance than the monolithic Al3Ti layer. # 2001 Published by Elsevier Science Ltd.

Electromigration analysis of peripheral ultra fine pitch C2 flip chip interconnection with solder capped Cu pillar bump

In this report, the electromigration behavior of 80μm pitch C2 (Chip Connection) interconnection is studied and discussed. C2 is a peripheral ultra fine pitch flip chip interconnection technique with Cu pillars and Sn/Ag capped solder bumps formed on Al pads for wirebonding. The technique was reported in ECTC 2009. It allows an easy control of the space between dies and substrates just by varying the Cu pillar height. The control of the collapse of the solder bumps is not necessary, hence the technology is called the “C2 (Chip Connection)”. C2 bumps are connected to OSP surface treated Cu substrate pads on an organic substrate by reflow and no-clean process. C2 is a low cost ultra fine pitch Flip Chip interconnection. However, the electromigration behavior for such a small flip chip interconnection is still an open issue. The electromigration tests were performed on 80μm pitch C2 flip chip interconnection. The interconnections with two different solder materials were tested: Sn/2.5Ag and pure Sn. The effect of Ni barrier layer on the test is also studied. The tests showed that the presence of IMC layers reduce the atomic migration of Cu. The test also showed that the Ni barrier is also effective in reducing the migration of Cu atoms into Sn solder. The under bump metals (UBMs) are formed by sputtered Ti/Cu layers. The electro-plated Cu pillar height is 45μm and the solder height is 25μm for 80μm pitch. The die size is 7.3 mm square and the organic substrate is 20 mm square with 4 layers laminated prepreg with 310μm thickness. Electromigration test condition is 7–10 kA/cm2 at 125–170°C. Intermetallic compounds (IMCs) were formed prior to the test by aging process which is 2,000 hr at 150°C and then the electromigration tests were performed. We have studied the effect of IMCs thickness on electro-migration induced failure mechanism in C2 flip chip interconnection on an organic substrate.