Effect Of Element B On Microstructure Evolution And Properties Of CrFeCoNiTi_x High Entropy Alloys

Since the definition of high-entropy alloy was proposed in 2004,it has provided new ideas for the research of alloys by scholars from all over the world.High-entropy alloys have a lot of research space in composition design and performance enhancement because of its four unique effects.High entropy alloys have excellent mechanical properties,high temperature thermal stability,excellent magnetic properties,hydrogen storage and fatigue resistance.These properties make high-entropy alloys not only widely used in life,but also play a huge role in the industrial and military fields.In this paper,elements B were added on the basis of CrFeCoNiTi_xwith excellent mechanical properties in the composition design of high-entropy alloy.High entropy alloy blocks were obtained by mechanical alloying and SPS sintering.The influence of B element content on the microstructure and element distribution of CrFeCoNiTi_xhigh-entropy alloy was studied by OM,XRD,SEM,EDS and other characterization methods.The effect of B element content on the comprehensive room temperature mechanical properties of CrFeCoNiTi_xhigh-entropy alloy was studied by Vickers hardness test and compression performance test.The addition of B element will make the B element highly dissolved in the CrFeCoNiTi_0.6high-entropy alloy first.The alloy structure is dominated by the FCC phase structure,as well as the BCC phase and the Tetragonal structure phase with lower content.When the B content continues to increase,the B element reaches the solid solution limit in the solid solution and precipitates long and needle-like B-containing compounds in the interdendritic region of the alloy.The number of B-containing compounds gradually increased,the size gradually became larger,and the morphology changed from dendritic and needle-like to dendritic.Among them,B,Fe,and Cr are enriched in the second phase,Co,Fe,and Ni elements are enriched in the dendrite region,and Fe and Cr elements are gradually segregating into the second phase.The mechanical properties of the alloy were improved by the solid solution strengthening and the second phase precipitation.But the precipitation of a large amount of boride will affect the plasticity of the alloy.The CrFeCoNiTi_0.6B_0.1high-entropy alloy has the best mechanical properties among the six alloys with different B content,with a Vickers hardness of 207.3HV and a compressive strength of 813.9MPa.The microstructure and properties of CrFeCoNiTi_xB_0.05high entropy alloy were studied by changing Ti content.The structure of the CrFeCoNiTi_xB_0.05high-entropy alloy is dominated by the FCC structure phase,and the?phase B2 phase is also present in the alloy with a low content.As the Ti content increases,the precipitation of the?phase in the alloy is suppressed,and the alloy is promoted to form a new second phase Fe₂Ti.The content of Fe,Co,Ni,and Cr in the crystal grains is relatively high,and the content of Ti element at the grain boundaries is relatively high,and the segregation is serious.Fe and Ti are mainly distributed in this granular second phase The increase in Ti content promotes the improvement of the mechanical properties of the alloy.CrFeCoNiTi_1.0B_0.05Vickers hardness was the highest at416.54MPa,and CrFeCoNiTi_0.8B_0.05high-entropy alloy had the highest compression strength at 586.3MPa.The addition of Ti element promotes the formation of the second phase in the alloy,and the granular second phase will improve the mechanical properties of the alloy to a certain extent.At the same time,the increase of Ti element content will increase the crystal plane spacing of the alloy,lattice distortion will improve the mechanical properties of the alloy,but the addition of a large number of Ti elements will lead to more defects in the alloy and reduce the performance of the alloy.