鈦鋁介金屬複合材料的生成反應特性與其高溫性質之研究

Abstract

本研究係以擠壓鑄造的方式製作TiO2強化鋁合金(A356)複合材料,然後再行熱處理以內造生成含有Al2O3強化相的TiAl3介金屬基複合材料。根據熱差掃描分析結果顯示，當TiO2與Al的反應溫度發生在A356的共晶溫度以上時,此反應機制可分解為二個步驟；先是Al2O3的形成，再接著是TiAl3的形成。前者為一維擴散機制所控制,後者為一級反應機制所控制。 根據Al2O3/TiAl3在氧氣氛中,7000C、8000C、9000C溫度下的氧化測試結果顯示，該材料在氧化初期與後期有著明顯不同的速率。進一步觀察指出，此氧化速率的差異乃是由於先生成過渡態的θ-Al2O3，然後再轉換成穩定態的α-Al2O3所致。 此外,在溫度對抗壓強度的影響方面,根據測試結果顯示,TiO2/Al的複合材在4000C時已因發生軟化而失去其原有在室溫下的高強度，從525MPa下降到275MPa；但Al2O3/TiAl3則不然，4000C時的強度只從室溫下的550MPa下降到500MPa而已，顯示其在高溫下確實保有良好的強度。

In the present article, TiO2 reinforced Aluminum alloy (A356) composite was successfully fabricated by squeeze casting. Furthermore, the composite employed heat treatment was transformed to an intermetallic matrix composite by in-situ synthesis of Al2O3 reinforcement and TiAl3 matrix. According to the differential scanning calorimeter (DSC) analysis, it was found that there were two mechanisms in the chemical reaction between TiO2 and Al while the temperature was over the eutectic point of aluminum alloy (A356). One was alumina, and the other was TiAl3.Correspoundlly, the former was conducted by one dimensional diffusion control, but the latter was a first order reaction. For the oxidation test, the Al2O3/TiAl3 specimens were kept in oxygen atmosphere under 7000C ,8000C and 9000C respectively, the results illustrated that the rate of oxidation between initial state and final state was significantly different.Further observation showed that they were caused by a transformation from a transition state θ-Al2O3 to a stable state α-Al2O3. Alternatively, for the compressive strength under various temperatures, the results showed that the specimens of TiO2/Al composite at 4000C were lower than that at room temperature due to the matrix soften, from 525MPa reduced to 275MPa. On the contrary, the specimens of Al2O3/TiAl3 composite just slightly reduced to 500MPa from 550MPa, and hence possessed good performance at higher temperature.