As-Cast Microstructure and Mechanical Properties of Sub-Rapid Solidification-Processed Cu-Cr-Nb Alloy AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23110008

Chinese Library Classification Number:TF77

Citation Information:

High-strength and excellent-conductivity copper alloys are widely used in the field of rocket engine combustion chamber materials due to their excellent physical and mechanical properties. Among them，the Cu-Cr-Nb alloy is a kind of precipitation-strengthened copper alloy，such the strengthening effect attributes to the intermetallic compound Cr₂Nb. The alloy not only has good high-temperature stability，but also has advantages such as high temperature oxidation resistance，high strength at room temperature and high temperature，at the same time，it has the ability to resist creep and thermal corrosion，and has become a fourth-generation rocket engine combustion chamber wall material. Since Cr and Nb have infinite solubility in liquid copper but low solubility in solid copper，when Cu-Cr-Nb alloys are prepared by conventional casting metallurgical process，the incipient Cr₂Nb phase is preferentially generated during solidification，and the Cr₂Nb phase in the alloys prepared by conventional casting is coarse and cannot be removed by subsequent processing. In this paper，Cu-Cr-Nb alloys with different Cr and Nb contents （Cu-8Cr-4Nb，Cu-4Cr-2Nb，Cu-2Cr-1Nb，Cu-1Cr-0.5Nb，and Cu-0.8Cr-0.4Nb） were prepared by vacuum induction melting and water-cooled copper mold casting，and the effects of alloy composition on the as-cast microstructure and mechanical properties under sub-rapid solidification conditions was investigated. The principle of designing the composition of Cu-Cr-Nb alloy was that the atomic ratio of Cr to Nb was 2∶1. The ratio of 2∶1 fits the molecular composition of Cr₂Nb，too much Cr，Nb elements would cause elemental segregation，the formation of large-size Cr₂Nb，had formed hard inclusions，resulting in fracture. Sub-rapid solidification was a solidification process between near-equilibrium low-rate growth and away-from-equilibrium rapid growth with a cooling rate in the range of 10~1×10³ K·s⁻¹，which was a method of solidification that allows the alloy to grow at a faster growth rate at a larger supercooling degree. At higher cooling rates，the alloy solidified rapidly from the liquid state to form a supersaturated solid solution. This supersaturated solid solution was aged to obtain finer，more dispersed particles of the precipitated phase. The results showed that the microstructure of the cast Cu-Cr-Nb system alloy consisted mainly of α-Cu matrix，high melting point intermetallic compound Cr₂Nb and nonequilibrium Cu-Cr eutectic phase. As Cr and Nb content decreased，the primary Cr₂Nb phase in the alloy showed a uniform diffuse distribution，the morphology evolved from coarse rod-like to granular，the average size decreased from 13.3 to 3.9 μm，the area fraction decreased from 15.8% to 1.3%，and the eutectic phase gradually disappeared. Cu-8Cr-4Nb alloy contained a large amount of the large-size intermetallic compound Cr₂Nb. Its pinning on the grain boundaries played a hindering role to the dislocation motion during the deformation process，effectively hindering the dislocation motion within the crystal and pinning effect on the grain boundaries，leading to brittle fracture of the material，and the strength of its alloys was enhanced while the electrical conductivity and plasticity are minimized. As the number and size of primary Cr₂Nb phases decreased，the strength of the alloy tended to decrease，while plasticity and electrical conductivity gradually increased，and the fracture mechanism changed from brittle fracture to plastic fracture. Cr₂Nb strengthening phase was the main load-bearing phase of Cu-Cr-Nb system alloys，and the improvement of mechanical properties such as tensile strength and yield strength of the alloys mainly relied on the diffuse reinforcing effect of Cr₂Nb phase. In a comprehensive analysis，the best composition of Cu-Cr-Nb alloy prepared by sub-rapid solidification was Cu-1Cr-0.5Nb，when the tensile strength，yield strength and elongation reached the optimum of 225 MPa，110 MPa and 37.5%，respectively，and the electrical conductivity was 48.16%IACS.