Study On Interface Reaction Of Cu-Al-Ni Ternary System

Interface reaction for heterogeneous materials is a prevalent phenomenon in materials science. And it is a key factor influencing the final product quality in many processes, such as materials joining, powder metallurgy, mechanical alloying and composite materials. Therefore, studies of interface reaction are important both in theory and practice. The ternary Cu-Al-Ni diffusion couples were prepared by mechanical method .The heat treatments of diffusion couples were carried out under different conditions. The interface diffusion layers were researched by means of color metallograph, microhardness and SEM. The results show that a continuous solid solution is formed at the Cu-Ni interface of diffusion couples. The interfaces of the continuous solid solutions are blurry and have different colors. The higher the annealing temperature, the more obvious the color difference is. For Al-Cu and Al-Ni interfaces, phenomena of interface reactions are different under different heat treatment conditions. According to the different characteristics interface reaction can be divided into three stages: low temperature, transition, high temperature. At 500℃for 25-125h and at 520℃for 25-100h, interface diffusion layers are narrow. Sublayer structure of Al-Cu interfaces is Cu/Cu4Al3/CuAl2/Al. And sublayer structure of Al-Ni interfaces is Ni/Ni2Al3/Al. At 520℃for 125h and at 530℃for 25-50h, solid solution Al(Cu) at the Al-Cu interface produces liquid phase at eutectic temperature. As a result diffusion layers expand to aluminum rapidly. Sublayer structure of Al-Cu interfaces is Cu/CuAl/CuAl2/Al+CuAl2/Al. At the Al-Ni interface a concentration gradient is formed because nickel dissolves into the liquid aluminum. Intermetallic compounds produce at higher concentrations. Sublayer structure of Al-Ni interfaces is Ni/Ni2Al3/NiAl3/Al. At 540-600℃for different annealing time, Al matrix is consumed completely and a reaction zone is formed. At 550℃eutectic structure CuAl2+Al appears in the reaction zone. On the other hand, intermetallic compounds appear at higher concentrations and in Cu matrix. Sublayer structure of Al-Cu interfaces is Cu/Cu3Al2/Cu4Al3/ CuAl/CuAl2/CuAl2+Al. Al-Ni interface still includes two sublayers. Sublayer structure of Al-Ni interfaces is Ni/Ni2Al3/NiAl3/CuAl2+Al. At 600℃CuAl2 fills with the reaction zone and CuAl grows dendritically to the reaction zone. There are six sublayers between Cu matrix and the reaction zone. Sublayer structure of Al-Cu interfaces is Cu/Cu3Al/Cu9Al4/Cu3Al2/ Cu5Al3/Cu4Al3/CuAl/CuAl2+CuAl. Sublayer structure of Al-Ni interfaces is Ni/Ni2Al3/NiAl3/ CuAl2+CuAl. The valence electron structures of the matrix of diffusion couples and intermetallic compounds are calculated according to the empirical electron theory in solid and molecules. The experimental phenomena and properties of diffusion layers are analysed qualitatively according to calculation results.