使用Ti-Ni-Nb填料真空硬銲鈦合金之研究

Abstract

本研究採用鈦基填料Ti-35Ni-25Nb作為銲料，利用真空加熱爐作為熱源分別硬銲商用純鈦(CP-Ti)以及Ti-15-3兩種常見的基材合金，探討在不同的硬銲溫度下，利用電子微探分析儀(EPMA)以及掃描式電子顯微鏡(SEM)，進行顯微組織演化、接點剪力強度之研究。 在CP-Ti/Ti-35Ni-25Nb/CP-Ti的部分，可發現各溫度參數下銲道中皆出現介金屬化合物Ti2Ni，此種介金屬化合物的出現會嚴重影響材料機械性質，Ti2Ni本身呈現相當高的脆性，當施加應力時容易造成Ti2Ni本身的破裂、進而使破裂延伸，其主要出現在Ti2Ni和α-Ti的共析組織，此外，共析組織中兩相的交界也容易導致裂縫的延伸。在本實驗中發現將硬銲溫度提高至1200 ℃後，可降低Ti2Ni在銲道中的比例，同時也會提高剪力強度，其原因主要和填料內的Ni成分在硬銲過程後的分布有關，Ni在銲道中的濃度下降使得Ti2Ni不易形成，而將會變為形成α-Ti及β-Ti為主。Ti-15-3/Ti-35Ni-25Nb/Ti-15-3的部分，相同的，也會在銲道中發現介金屬化合物Ti2Ni，同樣嚴重影響到材料之機械性質，出現原因主要為共晶反應形成的β-Ti與Ti2Ni。隨著硬銲溫度提高至1200℃、或是在1100℃時將硬銲時間拉長至30分鐘後，Ti2Ni將不會出現在銲道內，銲道整體均為β-Ti，而剪力強度也會明顯提高，但在高溫時，由於硬銲溫度超過β-transus temperature許多，導致β-Ti容易晶粒粗化，故將硬銲時間拉長是較好的方法。

In this research, titanium-based filler Ti-35Ni-25Nb is used to braze CP-Ti and Ti-15-3 plates in vacuum. Microstructural evolution, shear strength, wetting behavior and phase identification are assessed in the experiment. Specimens prepared with standard metallographic procedure are examined using electron probe microanalyzer (EPMA) equipped with the wavelength dispersive spectroscope (WDS) and SEM for microstructural evolution observation and quantitative chemical analysis. In the part of CP-Ti/Ti-35Ni-25Nb/CP-Ti, intermetallic compound, Ti2Ni, appeared in the brazing zone under various temperature parameters. The appearance of this intermetallic compound can seriously affect the mechanical properties of this material. Ti2Ni exhibits high brittleness, and when shear strength is applied, it easily causes the fracture. It mainly occurs in the eutectoid structure of Ti2Ni and α-Ti. In addition, the phase boundary of the eutectoid structure also easily leads to the growth of cracks. In this experiment, it was found that increasing the brazing temperature to 1200°C can reduce the proportion of Ti2Ni in brazing zone and also increase the shear strength, which is due to the reduction of Ni in brazing zone after the brazing process. Ni in the brazing zone decreases, making it difficult for Ti2Ni to form, and will become dominated by the α-Ti and β-Ti. In the part of Ti-15-3/Ti-35Ni-25Nb/Ti-15-3, the intermetallic compound, Ti2Ni, is also found in the brazing zone, and the same, it will also seriously affect the mechanical properties of the material. However, as the brazing temperature is increased to 1200°C, or the brazing time is extended to 30 minutes at 1100°C, Ti2Ni will not appear in the brazing zone, the overall brazing zone is β-Ti, and the shear strength also be significantly improved.