In Situ Heating Transmission Electron Microscopy Observation of Nanoeutectic Lamellar Structure in Sn–Ag–Cu Alloy on Au Under-Bump Metallization

We investigated the microstructural evolution of Sn96.4Ag2.8Cu0.8 solder through in situ heating transmission electron microscopy observations. As-soldered bump consisted of seven layers, containing the nanoeutectic lamella structure of AuSn and Au5Sn phases, and the polygonal grains of AuSn2 and AuSn4, on Au-plated Cu bond pads. Here, we found that there are two nanoeutectic lamellar layers with lamella spacing of 40 and 250 nm. By in situ heating above 140°C, the nanoeutectic lamella of AuSn and Au5Sn was decomposed with structural degradation by sphering and coarsening processes of the lamellar interface. At the third layer neighboring to the lamella layer, on the other hand, Au5Sn particles with a zig-zag shape in AuSn matrix became spherical and were finally dissipated in order to minimize the interface energy between two phases. In the other layers except both lamella layers, polycrystal grains of AuSn2 and AuSn4 grew by normal grain growth during in situ heating. The high interface energy of nanoeutectic lamella and polygonal nanograins, which are formed by rapid solidification, acted as a principal driving force on the microstructural change during the in situ heating.

Effects of Nb and V on the Microstructure and Properties of Rolled Non-Quenched and Tempered Steels

The property and microstructure of rolled non-quenched and tempered steels of Nb-V comprehensive micro alloying have been investigated .The mechanical properties and the load –displacement curves were measured respectively by using electron tension test machine and digital-impact test machine . The microstructure and fracture surface of impact samples were observed with SEM .The results show that micro-alloying Nb and V non-quenched and tempered steel behaves higher tension strength and toughness than that of only V micro-alloying one under the condition of about same plasticity. Improvement of the properties is related with that Nb can effectively make fine pearlite group and inter-lamella spacing at the impact fracture pearlite flakes. Corresponding relationship between various domain of fracture morphology and characteristics points at the curve of digital impact has been discussed.

Effect of Heat Treatment and Composition on Grain Size and Lamellar Spacing of a Lamellar TiAl Alloy

The article presents the results of optical microscopy, scanning electron microscopy (SEM), Transmission Electron Microscope (TEM) conducted on a Ti–46.5Al–2.5V-1.0Cr–0.3Ni alloy before and after different heat treatments. Heat treatment of the alloy at 1340°C followed by cooling leads to the formation of the fully lamellar microstructure which consists of γ lamellae mostly and of small amount of α2 lamellae. The cooling rate of 50°C/min in alloy tcx1-G produced an optimal microstructure. This cooling rate generated finest lamellae with the smallest individual lamella spacing among the alloys.

Nanostructured Bulk Copper Fabricated by Accumulative Roll Bonding

In this study, we tried to fabricate the nanostructured bulk copper alloys by a severe plastic deformation process. The sheets of copper alloys (OFC, PMC90, and DLP) were heavily deformed to an equivalent strain of 6.4 by the accumulative roll-bonding (ARB) process. The microstructure and the mechanical property of the fabricated specimens were systematically investigated. The microstructure was finely subdivided with increasing the equivalent strain by the ARB process. The severely deformed copper alloys exhibited the ultrafine lamellar boundary structure where the mean lamella spacing was about 200 nm. The strength significantly increased with decreasing the lamella spacing in the ARB processed copper alloys. Especially, the tensile strength of the DLP alloys ARB processed by 8 cycles (the equivalent strain of 6.4) reached to 520 MPa, which was about three times higher than that of same materials with conventional grain size of 10–100 μm. On the other hand, the total elongation greatly dropped only by 1 ARB cycle corresponding to an equivalent strain of 0.8, which was around 3%. However, the total elongation increased again with increasing the number of the ARB cycle, and it reached to 10% after 8 cycles. The recovery of the total elongation could be recognized in all studied copper alloys. The obtained stress–strain curves showed that the improvement of the total elongation was caused by the increase in the post-uniform elongation. It can be concluded that the nanostructured copper alloys sheets having high strength without a large loss of ductility could be fabricated by the ARB process.