Preparation And Properties Of Cu-Gd₂O₃ Gradient Composite Materials

Using the high melting point and stable chemical properties of rare earth oxides,a novel copper-based gradient composite was designed and fabricated.The rare earth oxide Gd₂O₃ could refine the grain of the material,improve the mechanical properties,and has characteristics of electronic conduction and anti-electrical ablation.It was excellent for copper-based dispersion strengthening phase of functionally graded materials（FGMs）.In this paper,the Gd₂O₃ reinforced copper-based FGMs were fabricated by the principle of powder metallurgy,combining with cold isostatic pressing,vacuum pressureless sintering and hot rolling.A multi-layer coaxial powder filling method was used to realize a spatially graded structure,in which the pure Cu functional layer was located on the outermost layer,the functional layer with the highest Gd₂O₃ content was located in the core,and the transitional layer was located between two functional layers,constituting a three-layer gradient.The effects of cold pressing pressure,rolling temperature and other process parameters on the properties of the gradient composites had been studied,and the gradients of the composition in the materials had been optimized.In addition,some analysis methods were used to analyze the microstructure and interface of the FGMs,discussed the strengthening and deformation mechanism of the FGMs.The results indicated that the optimal preparation process of Cu-Gd₂O₃ FGMs was:the cold isostatic pressing was 200MPa and the rolling temperature was 800^oC,and after each pass of rolling,the sample was kept at 800^oC and the next rolling was performed.At this time,the preferred composition gradient was 0-3-6.The three-point bending test strength was 509MPa,bending strain was 59%.The conductivity of the pure Cu layer was93%IACS,and the 6wt%Gd₂O₃/Cu layer was 76%IACS.The metallurgical bonding between the graded layers of the material was well,the pure copper layer was randomly oriented twins,and the Gd₂O₃/Cu gradient layer was a fine grained equiaxed crystal,Gd₂O₃ was added to form a network.Because of a semi-coherent/incoherent relationship,the interface between Gd₂O₃ and Cu was well-bonded.Annealing can release the work hardening stress,reduce the dislocation density,resulting in a decrease in material strength and plasticity.Rolling deformation began in the particle rearrangement,a certain degree of plastic deformation,gradually eliminated the discontinuous voids,and finally approached the complete plastic deformation.With the increase of the rolling reduction,voids and microcracks shrank and disappeared,the grain boundary interface kept enhancing,and the material was denser.The fracture was changed from a fractured neck to a transcrystalline fracture.The main strengthening mechanisms of Cu-Gd₂O₃ FGMs were load transfer strengthening,thermal mismatch strengthening,Orowan strengthening and Hall-Patch strengthening.Among them,the thermal mismatch strengthening has a significant effect on the material strength.The deviation between the calculated results and the experimental data might be effected by the presence of in-situ Gd₂O₃ size,plus Gd₂O₃ agglomeration,voids and other defects and grain statistical errors.