Oxidation Behavior of NiTi-Al Based Alloy with Nb and Mo Additions

Abstract

Abstract. Oxidation behavior of a Ni-45Ti-5Al-2Nb-1Mo (composition in at %) alloy was studied in comparison with the Ni-45Ti-5Al alloy by X-ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic oxidation tests. The results show that the microstructure of Ni-45Ti-5Al-2Nb-1Mo alloy is composed of NiTi matrix, Ti 2 Ni and (Nb, Ti) solid solution phases. By 2 at% Nb and 1 at% Mo addition, the Ni-45Ti-5Al-2Nb-1Mo alloy shows excellent oxidation resistance. The mass gain of Ni-45Ti-5Al-2Nb-1Mo alloy after 100 h exposure at 800 °C is 2.29 mg/cm 2 , which is much lower than that of Ni-45Ti-5Al alloy. This is mainly resulted from the doping effect of Nb and Mo in TiO 2 and the formation of a continuous Al 2 O 3 layer by Nb and Mo addition.The oxide scale of the present alloy is with multi-layer structure in order of TiO2 layer/ Al2O3 + NiAl2O4 mixture layer/ TiO2 layer/ Nb-rich TiO2 layer/ Ni3Ti layer from outside. IntroductionOrder intermetallic alloys based on aluminides have been developed as high temperature structural materials for decades [1]. Recent investigations indicate that NiTi-Al based intermetallic alloys have the potential to use as high temperature structural materials for aerospace applications because of their low density, high strength at high temperature and good corrosion resistance. The addition of small amount of Al (no more than 8 at%) into NiTi alloy can dramatically improve the strength especially at high temperature [2][3]. Alloying is an effective method to improve the mechanical properties of NiTiAl based alloys. Many elements, such as Mo, Nb, Hf, Zr, B and RE, have been added to strengthen the NiTi-Al alloys [4][5][6][7]. It has been reported that a Nb-and Mo modified Ni-45Ti-5Al-2Nb-1Mo (at%) alloy is expected to become a potential high-temperature structural material with strength of 650 MPa at 650 °C and 350 MPa at 800 °C [8][9].Actual applications in the aerospace industry require the alloys to be considered in a variety of high-temperature environments. The oxidation behaviors of ternary NiTi-Al alloys at temperatures between 600 °C and 800 °C have been systemically studied, which found that NiTi-Al alloys shows poor oxidation resistance with the mass gain more than 20 mg/cm 2 after exposure in air at 800 °C for 100h. By adding little quaternary element Nb (3 at%), the oxidation resistance of NiTi-Al alloys can be notably improved [10][11].However, so for the studies on the oxidation behavior of NiTi-Al based alloys are limited, especially the knowledge of NiTi-Al based alloy simultaneously modified by two or more alloying elements are still lack. Therefore, in this paper, the isothermal oxidation behavior of Nb-and Mocontaining Ni-45Ti-5Al-2Nb-1Mo alloy is studied and discussed in detail.

Optimization of TiC Content during Fabrication and Mechanical Properties of Ni-Ti-Al/TiC Composites Using Mixture Designs

“…To improve the mechanical properties at high temperature, Ni-45Ti-5Al-2Nb-1Mo alloy was prepared by adding a small amount of at% [7]. In addition, studies have been conducted to improve the compressive strength at room temperature by preparing (Ti, Al) 2 Ni and (Zr, Ti, Al) 2 Ni solid phase by adding 8 at% of Zr [8], and numerous studies have investigated methods to improve high-temperature properties [3,9,10]. …”