| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 96 === Infrared vacuum brazing γ-TiAl/Ti-6Al-4V and α2-Ti3Al/ Ti-6Al-4V two kinds of samples using three Ti-based fillers: 60Ti-15Cu-25Ni, 70Ti-15Cu-15Ni and 40Ti-20Zr-20Cu-20Ni. For 60Ti-15Cu-25Ni and 70Ti-15Cu-15Ni fillers to braze γ-TiAl and Ti-6Al-4V, their brazed zone microstructures are quite similar. Next to γ-TiAl base metal, two layers are formed: one is composed of α2-Ti3Al+γ-TiAl lamellar mixtures and the other is a continuous α2-Ti3Al layer. The residual filler in the brazed zone is composed of Ti2Ni and Ti2Cu in which the decrement of residual filler can be achieved by increasing the brazing time and/or temperature. However, the thicknesses of the continuous α2-Ti3Al layer and α2-Ti3Al+γ-TiAl lamellar do not change by using different brazing conditions. When the residual filler is still existence, the crack will form in it and propagate until the sample failure. If the residual filler is already eliminated, the crack will form in the continuous γ-TiAl layer. For α2-Ti3Al/ Ti-6Al-4V sample, as compared to γ-TiAl/Ti-6Al-4V sample, there is no α2-Ti3Al+γ-TiAl lamellar and no a continuous α2-Ti3Al layer. When using 40Ti-20Zr-20Cu-20Ni filler, the brazed zone becomes more complicated. The most distinctive point is the residual filler can be composed of three intermetallics. The crack is also formed in the residual filler and then propagate until the sample failure. Because the Zr atoms are difficult to diffuse directly into two base metals, no matter how high of brazing temperature and how long of brazing time, the residual filler will not disappear. However, shear stress in this case can reach about 390MPa.
|
|---|
