| Two-phase Cr/Nb Cr2 alloy is a kind of very protential materials for Advanced high temperature structural application. Based on the previous research achievements,the two-phase Cr/Nb Cr2 alloy with the composition of(Cr-12Nb)-4.4Ni was prepared by mechanical alloying and hot pressing. The high temperature mechanical property was studied by compression experiment. The effect of alloying on high temperature mechanical properties was studied. Then, based on the BP artificial neural network,the material constitutive relation models of two-phase Cr/Nb Cr2 alloy were constructed, Finally,the high temperature compression deformation mechanism of two kinds of alloy was studied. The main results were as follows:When the compression deformation is carried out at 900 ℃ and 1000℃, the stress-strain curves of(Cr-12Nb)-4.4Ni alloy is strain softening model which is closely related to the strain rate and temperature. The softening degree of two-phase Cr/Nb Cr2 is obviously with lower deformation temperature and higher strain rate. However, the stress-strain curve shows approximately state flow model when the compression deformation temperature increases to 1200℃.Compared with the two-phase Cr/Nb Cr2 alloy with the composition of Cr-12 Nb, the high temperature strength of two-phase Cr/Nb Cr2 alloy can be effectively improved by adding right amount of nickel element under the higher strain rate condition( =0.1s-1,0.01s-1).When strain rate is 0.1s-1, the high temperature compression strength of two-phase Cr/Nb Cr2,which was compressed at 800℃,1000℃and 1200℃,.increases 23.5%,14.2% and 154.3%,respectively. At the same time,the yield strength increases 22.8%, 33.6% and 22.8%,respectively. When strain rate is 0.01s-1, the high temperature compression strength of(Cr-12Nb)-4.4 Ni alloy increases 20.2%,3.9% and 3.9%, respectively after compressed at 800 ℃,1000 ℃and 1200 ℃. Meanwhile, the yield strength increased 27.3%, 36.3% and 27.3%, respectively. However, the compression strength and yield strength show no obvious change when the strain rates drops to 0.001s-1. The results show that Ni can effectively improve the high temperature mechanical properties of two-phase Cr/Nb Cr2 alloy under medium-high strain rate. Furthermore, the Arrhenius equation is used to calculate the activation energy of the two-phase Cr/Nb Cr2 alloy when the strain is 0.4.The results show that Ni can effectively reduce the deformation activation energy of two-phase Cr/Nb Cr2 alloy.Based on the BP artificial neural network, the material constitutive models of two kinds of two-phase Cr/Nb Cr2 alloy(Cr-12 Nb and(Cr-12Nb)-4.4Ni) have been constructed. The prediction results show that the constitutive models can effectively predict work hardening and dynamic softening phenomenon of two-phase Cr/Nb Cr2 alloy during the hot deformation and has a high capacity in precision and prediction.Though the analysis of compression deformation microstructure, it shows that matrix phase softening degree of unalloying Cr/Nb Cr2 alloy increases with deformation temperature and the main deformation mechanism of the matrix is dislocation slip. At the same time, the dislocation configuration is more obviously in the matrix phase with the increase of strain rate. This phenomenon shows that the deformation mechanism of matrix phase is also dominated by dislocation motion. While, the deformation degree of hard Laves phase is small during in the process of deformation, the tissue of twinning is increased with the decline of the deformation temperature or increase of the strain rate. And the deformation mechanism of hard Laves phase is dominated by the twin deformation. Compared with unalloying Cr/Nb Cr2 alloy, Ni element is mainly distributed in the Nb Cr2 grains. And it can promote the dislocation multiplication, improve the resistance of the deformation in the two-phase Cr/Nb Cr2 alloy grains internal and improve the high temperature plastic of hard Laves phase grains, effectively. Overall, Ni element ultimately improve the high-temperature compressive performance of Cr/Nb Cr2 alloy. |
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