Effects of Isothermal Heat Treatment on Mechanical Properties of U-2Nb Alloy

The phase transformation of U-2Nb alloy under isothermal condition and the mechanical properties corresponding to the morphological changes were studied within 450-635 degrees C. By applying the optical microscope, scanning electron microscope techniques, and tensile and compression tests, the relationship between the structure and properties was discussed. The results show that the alloy has two distinct microstructure features during isothermal heat treatment from 550 degrees C to 635 degrees C, The main factor affecting the strength and plasticity is the lamellar spacing of the dual-phase in the range of 550 similar to 635 degrees C. which is mainly determined by the formation temperature. The higher the temperature, the greater the lamellar spacing, the lower the strength, and the higher the plasticity. The isothermal holding time is positively correlated to the lamellar spacing. The best general properties obtained in this study are elongation of 22%, reduction area of 27.4%, tensile strength of 875 MPa and yield strength of 410 MPa. Quenching and annealing techniques were applied for samples treated at the temperature within 450 similar to 500 degrees C. The main factors influencing the mechanical properties within this temperature range are speculated to be the texture of the acicular martensite and the distribution or size of the granular structure. All samples with quenching+annealing treatment show strength higher than 1000 MPa, but with low plasticity. Elongation and reduction of area are within 5%. The annealing temperature affects the strength much more than plasticity. The plasticity improves slightly by extending the annealing time.