New Ti-alloy with negative and zero thermal expansion coefficients

Most materials expand upon heating due to the anharmonicity of the atomic potential energy. This thermal expansion is one of the intrinsic properties of any material which is very difficult to be controlled. Recently, a negative thermal expansion factor was introduced to those Ti-alloys with high elastic softening when cold deformed. This negative thermal expansion factor is changeable in these types of alloys depending on the alloy composition, degree of cold deformation, and thermal history of the alloy. This change gives a lot of room to control the coefficient of thermal expansion (CTE) of those Ti-alloys to turn from positive though zero to negative values and vice versa. In this paper, the appearance of the NTE factor is discussed and the possible methods to control the final thermal expansion coefficient to achieve a zero thermal expansion coefficient are presented. The unique thermal expansion behavior of the alloys will locate them as an excellent candidate in sensing apparatus and other precious equipments.