Effect of cooling rate on microstructure and tensile properties of Zr-3.1Nb alloy

Abstract

In order to improve the mechanical properties of Zr-3.1Nb alloy, the effects of different cooling rates on the tensile properties of the alloy were studied by controlled heat treatment. And the change of phase composition and micromorphology of the alloy samples at various cooling rates were analyzed by X-ray diffractometer, optical microscopy, scanning electron microscopy-energy dispersive spectrometer and transmission electron microscopy. The results show that with increasing cooling rate, the yield strength and tensile strength of the samples increase from 382, 426 MPa to 535, 617 MPa, respectively. There are many slip systems in FC-2 sample, which contains the high content of β phase, leading to the better elongation of 21.15%.The fracture mode of all samples is plastic fracture, and the plasticity deteriorates with increasing cooling rate. The three groups of samples in furnace cooling process all contain α and β phases, and the β phase is reticular, while the α phase is equiaxed. The ω phase is newly precipitated in air cooling sample, and the morphology of α phase could be divided into block and lath. The β phase in water cooling sample disappears and transforms into many lath α′ martensite. Due to the higher cooling rate, the distribution of α phase tends to be dispersed, and the grain size decreases from 3.56 μm in FC-1 sample to 1.74 μm in water cooling sample.

Keywords

• metallic material
• zr alloy
• cooling rate
• phase transformation
• tensile property