Search

Room temperature tensile properties of polycrystal Ti–47Al–2Mn–2Nb alloy with near lamellar (NL) microstructures were investigated at the strain rates between 10−5 and 1000 s−1 using a self-designed Split-Hopkinson tensile bar setup with a rotating disk and conventional testing machine. It was found that tensile ductility varies within a narrow range with the strain rate, while dynamic strengths (σd) of the alloy are obviously higher than static strengths (σs). There exists linear relationship between σs and the logarithm of the strain rate (ln έ), and between σd and the strain rate itself (έ). Fractography analysis indicates that the alloy fractures in a mixed mode of predominant transgranular cleavage and minor intergranular cracking under static and dynamic strain rates. Environmental effect is excluded from the main cause for the room temperature brittleness of the investigated alloy. [ABSTRACT FROM AUTHOR]

Abstract: Si3N4 ceramic was self-jointed using a filler alloy of Cu–Pd–Ti, and the microstructure of the joint was analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15 (at.%), a high quality Si3N4/Si3N4 joint was obtained by brazing at 1100–1200°C for 30min under a pressure of 2×10−3 MPa. The microstructure of the Si3N4/Si3N4 joint which was observed by EPMA, XRD and TEM, and the results indicated that a reaction layer of TiN existed at the interface between Si3N4 ceramic and filler alloy. The center of the joint was Cu base solid solution containing Pd, and some reaction phases of TiN, PdTiSi and Pd2Si found in the Cu [Pd] solid solution. [Copyright &y& Elsevier]

Abstract: Si3N4 ceramic has been joined successfully to itself by brazing in a vacuum at 1373–1573K holding for 1.8ks using a Cu76.5Pd8.5Ti15 alloy filler. By observation and analysis of the microstructure of the joints, it is found that the joints comprise three parts: (1) a continuous reaction layer of TiN between Si3N4 and filler alloy, (2) a discontinuous reaction layer containing TiN, Pd2Si and Ti5Si3 connecting the continuous reaction layer, and (3) the Cu-based solid solution in the mid of the joint and some reaction products (TiN, Pd2Si, PdTiSi and Ti5Si3) in the solution. With increasing brazing temperature, both the thickness of the continuous reaction layer and amount of reaction phases increase, which improves the bending strength of the joints. When the brazing temperature surpasses 1473K, voids are formed in the joint because of the decomposition of the Si3N4 ceramic, leading to a decrease of the bond strength. The room-temperature bending strength of the joint brazed at 1423K reaches a maximum value of 155.8MPa. [Copyright &y& Elsevier]