Effect Of Cr Element And Super Gravity Field On Microstructure And Properties Of AlNiCr Alloy

In this paper,supergravity solidification technique was used.Al-Ni-Cr alloy with different Cr content was prepared by solidification under different gravity fields.The effects of supergravity and cr elements on the solidification microstructure and properties of the alloy were analyzed and discussed.Al-Ni-Cr alloy is obtained by adding different Cr content under normal gravity.The solidification structure of Al-Ni-Cr alloy was found to be composed of primary??Al?crystals and Al-Al₃Ni eutectic structure.The solidified structure of alloy is obviously refined after adding Cr.when the content of Cr is 0.2at.%,?-Al is obviously refine and the average grain size is 30.8?m.The average grain size of Al₃Ni reach the optimum value,when the content of Cr is 0.3at.%.The average diameter and spacing were0.13?m and 0.19?m,respectively.With the increasing of Cr content,the microhardness of the alloy increase.When the content of Cr is 0.5at.%,it reach the optimum value of51.2 HV,which increases 32.2%.AlNi_2.5Cr_0.3 alloy is obtained under different supergravity fields.The results show that the solidification microstructure of AlNi_2.5Cr_0.3 alloy can be divided into two parts,the main part in the intermediate region is the Al-Al₃Ni eutectic organization,accounting for more than 80%.The second is??Al?primary crystals and Al-Al₃Ni eutectic structure in the surface region,accounting for less than 20%.The grains could be obviously refined under super-gravity field.The diameter of?-Al reaches the minimum value of 10.13?m under the gravity coefficient G=3000g,and the diameter and spacing of Al₃Ni reaches the minimum value of 72 and 92 nm,under the gravity coefficient G=2000g,respectively.Under the super-gravity field,the hardness of alloy in the core is greater than the surface.The highest average hardness is 60.8 HV in the middle part.Al-Ni-Cr Alloy is obtained by adding different content of Cr under the gravity coefficient G=2000g.The results show that the microstructure refinement effect of al-ni-Cr alloy was the best within 0.2⁰.3at.%.When the atomic fraction of Cr is 0.2%,the grain size reaches nanometer level.The diameter of rod is only 69nm and the spacing is reduced to 88nm.When the atomic fraction of Cr is 0.3%,the average grain of primary??Al?is refined and the size is 13.67?m.The yield strength of AlNi_2.5Cr_0.2 alloy is134MPa and its elongation is about 33%.In addition,Al-Ni-Cr alloy changed from ductile fracture to brittle fracture by element of Cr.The fracture paths of the alloy can be inferred as intergranular fracture and transgranular fracture.