Preparation And Properties Of B-based B-Gd-TM (TM=Fe,Co,Ni) Amorphous Alloys

Amorphous alloys have excellent mechanical,physical and chemical properties due to their unique short-range ordered structure with the absence of long-term periodicity.Till now,thousands of amorphous alloys have been developed,and most of them are metal-based alloys based on metallic elements such as Pd,Mg,La,Zr,Cu,etc.There are very few amorphous alloys based on non-metallic or metalloid elements except the reported Si-and Ge-based amorphous alloys.The strength,hardness,and thermal stability of the two metalloid-based amorphous alloys are significantly higher than the Al-based amorphous alloys in the same alloy system;they also have extremely high electrical resistance comparable to semiconductors,which is much higher than that of the metal-based amorphous alloys.However,the Si-based amorphous alloys have a low structural stability and a strong tendency of phase separation,and their amorphous forming ability（AFA）is poor.Therefore,it is of significance to develop a new type of metalloid-based amorphous alloys with high stability,and to study the formation mechanism,functional properties,and the correlation between the chemical composition and properties,which can not only fill the gap in the amorphous alloy system,but also broaden the research and application fields of the amorphous alloys.The metalloid B element can effectively improve the AFA of the amorphous alloys,especially for the transition-metal-based alloys;compared with other metalloid elements,the B content forming the amorphous phase with the transitional elements is very high.The B content in the binary Fe-B amorphous alloys is as high as 35 at.%,and that in the amorphous Co-B and Ni-B alloys is even more than 40 at.%.Additions of large-diameter rare earth and/or pre-transition metal elements into the Fe-B,Co-B and Ni-B alloys might help improve the AFA,increase the B content for the amorphous formation,and develop B-based amorphous alloys.In this paper,the rare earth element Gd was added into the B-TM（TM=Fe,Co,Ni）alloys,and the effects of B and Gd contents and TM element types on the formation and thermal stability of the B-Gd-TM amorphous alloy were systematically studied,and the B-based amorphous alloy were successfully prepared.Then,the Vickers hardness（H_v）,electrical resistivity（ρ）and crystallization behavior of the B-based amorphous alloys were investigated,and the property differences between the B-and metal-based amorphous alloys were discussed.The main research results are as follows:1.Melt-spun B_xGd₁₀Ni_90-x alloys can form a fully amorphous phase when B content ranges from 20 to 40 at.%.The onset temperature of crystallization（T_x）,H_v andρall gradually increase with the rise of B content,and the T_x,H_v andρof the amorphous alloys are 822-903 K,789-1122 and 158-288μΩcm,respectively.2.Melt-spun B_xGd₁₀Co_90-x alloys can form amorphous alloys with a B content ranging from 20 at.%to 50 at.%,and the T_x,H_v andρincrease with enriching of the B content.The T_x,H_v andρof the B-based B₅₀Gd₁₀Co₄₀ amorphous alloy are 1061 K,1540 and 428μΩcm,respectively,which are much higher than those of 886 K,932 and 226μΩcm,respectively,for a B₂₀Gd₁₀Co₇₀ amorphous alloy.The crystallization process of the B₅₀Gd₁₀Co₄₀ amorphous alloy is amorphous→amorphous+Gd B₆+Co B+Co₂Gd B₂→Gd B₆+Co B+Co₂Gd B₂+Co₇Gd₂.3.The B content range of B_xGd₁₀Fe_90-x amorphous alloys is broadened to 10-50 at.%,and the T_x,H_v andρare gradually increasing with the increase of the B content.The T_x,H_v andρof a B-based B₅₀Gd₁₀Fe₄₀ amorphous alloy are 1152 K,1581 and 326μΩcm,respectively.The apparent activation energies for nucleation and growth of the B₅₀Gd₁₀Fe₄₀ amorphous alloy are672 and 751 k J/mol,respectively,which are much higher than those of 381 and 232 k J/mol for a B₂₀Gd₁₀Fe₇₀ amorphous alloy.The crystallization process of the B₅₀Gd₁₀Fe₄₀amorphous alloy is amorphous→amorphous+Fe B+Fe₃Gd→Fe B+Fe₃Gd+B₄Fe Gd.4.Melt-spun B-based B-Gd-Co/Fe alloys can form amorphous alloys in the composition ranges of B₅₀Gd_5-10Co_40-45 and B₅₀Gd_10-15Fe_35-40,while the melt-spun B-based B-Gd-Ni ribbons can not form the fully amorphous phase.The amorphous alloys can be obtained by substitution of Fe and Co in B₅₀Gd₁₀Fe_40-xCo_x（x=0-40）alloys.Adding 2.5 at.%Ta into the B₅₀Gd₁₀Co₄₀alloy can also obtain the B-based amorphous alloy,and the T_x and H_v are increased to 1098 K and 1603,respectively,while theρis reduced to 353μΩcm compared with the amorphous B50Gd10Co40.5.The B-based B-Gd-TM-（Ta）amorphous alloys possess very high thermal stability,hardness,and resistivity,whose T_x,H_v andρare 949-1155 K,1370-1647,and 286-511μΩcm,respectively.Theρvalues of the B-based alloys are much higher than that of the metal-based amorphous alloys.