Ultrasonic shot peening (USP) is an effective method for modifying the surface layers of metals and alloys, improving their physical and mechanical properties, in particular, wear resistance and fatigue strength. This paper examines the effect of the size of reinforcing particles of the AlCuFe intermetallic compound on the structure and wear of the surface layers of an aluminum composite subjected to USP.
The use of AlCuFe particles of different sizes allows us to evaluate their role in the formation of the hardened layer. Small particles are usually more evenly distributed in the matrix and contribute to the creation of a more homogeneous structure after ultrasonic hardening. Large particles, on the contrary, can act as stress concentrators and lead to the formation of microcracks.
To modify the surface layers of aluminum samples, quasicrystalline (QC) AlCuFe particles of two types are used: large (c-QC), obtained by spraying and having an average size of about 25 μm, and small (f-QC), formed by grinding and characterized by a size of 0.3–0.5 μm.
In this paper, we investigate the effect of QC particles of different dispersion on the microstructural features and wear resistance of composite layers formed near the aluminum surface. X-ray diffraction, transmission and scanning electron microscopy are used to study the relationship between the microstructure of reinforced aluminum layers and their behavior under sliding friction. It is found that composites reinforced with both types of QC particles demonstrate an increase in wear resistance by almost two times compared to annealed aluminum. This effect is due to a combination of several factors: (i) high hardness and wear resistance of QC reinforcement (most pronounced for c-QC); (ii) the presence of a strong interphase connection of uniformly distributed reinforcing QC particles; (iii) a fine-grained structure of the aluminum matrix (in the case of f-QC) or an increased density of dislocations organized into small dislocation cells (in the case of c-QC), which corresponds to an increase in the volume fraction of grain boundaries/dense dislocation walls.
Studies of the microstructure of surface layers have shown that ultrasonic doping results in grain refinement of the aluminum matrix and the formation of a nanostructured layer. The presence of reinforcing AlCuFe particles prevents grain growth during deformation, facilitating further structure refinement. At the same time, the particle size has a significant effect on the degree of grinding and homogeneity of the structure. Analysis of the wear resistance of composites after ultrasonic doping revealed that samples with small AlCuFe particles demonstrate higher wear resistance compared to samples reinforced with large particles. This is due to a more uniform stress distribution and the absence of concentrators that contribute to the development of wear.
Thus, the size of the reinforcing AlCuFe particles has a significant impact on the structure and wear resistance of the surface layers of aluminum composites after ultrasonic blasting. Optimization of the particle size allows creating materials with improved performance characteristics.
Author: BN Mordyuk, MO Iefimov, KE Grinkevych, AV Sameljuk, MI Danylenko
Institute: G. V. Kurdyumov Institute of Metal Physics, Academician Vernadsky Boulevard, 36, UA-03680, Kyiv, Ukraine, Fraunhofer Institute for Materials Science, Krzyzhanovsky St., 3, UA-03142, Kyiv, Ukraine