Effect Of The Morphology Of The Second Phase On The Thermal Conductivity And Melting Point Of Cu-Ni-Nb Alloy

Cu-Ni-Nb alloy has a high melting point and a proper thermal conductivity, which has broad application prospects in the field of heat exchange materials. The second phase distribution of Cu-Ni-Nb alloy significantly affects the properties of melting point and thermal conductivity of the alloy. Based on the copper alloy and related phase diagram, Cu-Ni-Nb alloy was prepared by vacuum arc melting process. The morphology of the second phase of Cu-Ni-Nb alloy under cast and heat treatment was studied systematically. The effect of the morphology of the second phase on the thermal conductivity and melting point of the alloy was studied. The main conclusions are as follows.(1) The second phase morphology of cast Cu-Ni-Nb alloy is mainly existed as the following three kinds, lamellar, spherical(rod-shaped), short rod. The concentration of Nb element in the second phase of the solid liquid interface is relatively large with the increase of Nb element. The α phase growth rate of the alloy is faster than that of the second phase when the mass fraction of the as cast alloy Ni element is 20wt%, 30wt%,so that the second phase is separated into the sieve mesh. The second phase morphology has a tendency to shift from lamellar to spherical(rod-shaped).(2) The cast Cu-Ni-Nb alloy matrix is α phase. The most of the second phase of the cast Cu-Ni-Nb alloy is composed of NbNi3 phase. The second phase of Cu-30Ni-10 Nb alloy is composed of a spherical NbNi3 phase and a small amount of granular γ-Nb phase. The second phase of Cu-40Ni-5Nb alloy is composed of a small amount of granular α-Ni phase and a short rod-shaped NbNi3 phase. The second phase of Cu-40Ni-10 Nb alloy is composed of Ni8 Nb phase and short rod-shaped α-Ni phase.(3) The weakening degree of matrix metal bond energy of alloy by second phase of spherical(rod) shape is stronger than second phase of lamellar shape of alloy.Therefore, When the mass fraction of the Ni element is the same, the greater the degree of the solute elements in the alloy matrix dissolved in the second phase with the decrease of Ni/Nb mass ratio, resulting in the melting point of the second phase of the lamellar morphology of the alloy is higher than that of the spherical(rod like) shape of the second phase alloy.(4) The difference of the second phase morphology of the cast alloy leads to the difference of the solute elements in the alloy matrix dissolved in the second phase. Thediffusion rate of the solid solution atoms increases with the increase of the degree of solute elements in the alloy matrix dissolved in the second phase, so the matrix grain size of the alloy is increased, and the thermal conductivity of the alloy increases correspondingly.(5) After solution and aging treatment, the second phase of Cu-30Ni-5Nb alloy are lamellar, snow floc, irregular shape. As the aging temperature increases to 650℃,the part of the second phase in Cu-30Ni-5Nb alloy is grown up to the irregular block shape and the second phase volume fraction increases to 33.53%.(6) The optimum solution aging treatment process parameters of Cu-30Ni-5Nb alloy are as follows. Solution temperature is 900℃, solid solution time is 2h by water cooling. Aging temperature is 650℃, aging time is 6h by air cooling. The melting point of that alloy is 1156.19℃. Its thermal conductivity is 40.1W/m·K, which is higher27.59% compared to cast Cu-30Ni-5Nb alloy.