Tailoring thermal expansion coefficient from positive through zero to negative in the compositional crossover alloy Ti₅₀(Pd₄₀Cr₁₀) by uniaxial tensile stress

The precision control of thermal expansion is of fundamental interest and desirable for applications that require materials to retain their shape at different temperatures. In the present study, we propose that the thermal expansion coefficient can be tuned by uniaxial external stress for a single material embedded with nanoclusters, if the formation, growth or alignment of the nanoclusters depends on the external stress. We demonstrate the idea in a prototype alloy (Ti₅₀(Pd₄₀Cr₁₀)) located at the compositional crossover region between martensite and strain glass in the temperature-composition phase diagram of Ti₅₀(Pd_50−xCr_x). Its thermal expansion coefficient varies linearly from positive, through zero to negative values with increasing uniaxial tensile stress within 200 K ~ 300 K. The phase field simulations show that the volume fraction of nanoscale martensite variant favored by the external stress increases with stress, producing extra strain and compensating for the contraction of the austenite matrix on cooling. The degree of compensation leads to different thermal expansion coefficients. Such a tunable thermal expansion behavior occurs only in the crossover compositions between martensite and strain glass, providing a design recipe for searching new systems with similar behavior.