The Ageing Behavior And Mechanical Properties Of CuAgZr Alloy For Combustion Chamber Liner In Rocket Engine

Copper and copper-based alloys with heat treatment are widely used in aerospace engineering because of their excellent strength and electrical conductivities, outstanding resistance to high temperature low cycle fatigue properties. With the developments of our space project, high temperature, high pressure, high temperature low-cycle fatigue properties required for combustion chamber liner in rocket engine. Current materials used in rocket engine such as Cu Zr alloy not suitable for the developments of our space project. A better material is needed.Compared to the Cu Zr alloy, Cu Ag Zr alloy has better mechanical properties at evaluating temperature, it is a valuable material in space filed. The heat treatment process of the Cu Ag Zr alloy is closely related to the microstructure and the mechanical properties. The current work was designed to investigate the differential heat treatment process, the ageing behavior and mechanical properties by XRD, DTA, OM, SEM, TEM, tensile test and hardness test.The experimental results show that there are α-Cu matrix and the eutectic phase consist of β-Ag and m phase in the hot squeezed Cu Ag Zr alloy. The banded morphology second phases along the grain boundaries were distributed in a certain direction. With the solution temperature and solution time increasing, the morphology of the second phase from band to network and spheroidal. Then, the second phases were dissolved in the matrix. Moreover, the grain size increased. The optimal solution temperature of 940 oC and solution time of 10 h was founded. When the solution temperature from over 940 oC, the Cu Ag Zr alloy is overrunning.Based on the TEM observation, it is found that the different precipitates during the aging process. The precipitation sequence in the same age time: spheroidal Ag preciptates→rod-shaped Ag precipitates→plate-shaped Cu Zr precipitates→Zr-rich precipitates. The precipitation sequence in the same age temperature: spheroidal Ag preciptates→rod shaped Ag precipitates→plate-shaped Zr-rich precipitates.The evolution of nano-size Ag precipitates in the nucleation and growth process: At the early stage of ageing, first the spherical Ag precipitates are preferentially heterogeneous nucleation of individual dislocations. With the ageing temperature increased and ageing time prolonged, the spherical Ag precipitates increased and growth rapidly. When the size of the spherical Ag precipitates is over critical size, then some Ag precipitates of the precipitates grow as rods along a <011> or <011?> direction on a {100} plane,the morphology of the Ag precipitates becomes rod-shaped to spherical. When the elongated precipitates reach a critical size, the new precipitate, then chooses <011> or <01> direction to grow in. When the ageing temperature increased and ageing time prolonged further, Ostwald Ripening be bappening.The room temperature tensile results show that the strength of the Cu Ag Zr alloy increased with the solution temperature. when the solution temperature reaches the melt point of the second phase, the mechanical properties decline significantly. The alloy with solution treatment have good duclility.The hardness test results and the room temperature tensile results show that the hardness, the yield strength and the ultimate tensile strength increase monotonously when the ageing time is prolonged for the Cu Ag Zr alloy aged at 350 oC. When the ageing temperature over 400 oC, the hardness, the yield strength and the ultimate tensile strength increased at first and then decreased, the elongation decline monotonously with the ageing time is prolonged. The hardness and strength increased at first and then decreased with the ageing temperature at the same ageing time. The time of showing ageing-peak is shortened rapidly when increasing the aging temperature. When the ageing temperature over 700 oC, the hardness is lower than that before aging.