Invar Properties in Ti-Alloys Achieved Through Alloy Design and Thermomechanical Treatments

Invar non-ferromagnetic Ti-alloys with zero thermal expansion coefficients are designed by optimizing both the alloy composition and the thermomechanical treatment. The thermal expansion coefficient is controlled in those alloys which exhibit high elastic softening, since unique microstructures tend to be formed in them by cold deformation. The strains and stresses stored in the alloys by cold deformation are released to some extent in the course of the subsequent heating treatment, which leads to either a negative, positive or zero thermal expansion coefficient, depending on the conditions of cold deformation and heat treatment. Such unique thermal expansion behavior is fully reversible in a certain temperature range.