Al based layered in situ metal-matrix composites fabricated by constrained high pressure torsion

Abstract

Severe plastic deformation is often used to obtain an ultrafine-grained structure in metals and alloys, and this direction in metal processing continues to develop actively. At the same time, severe deformation also makes it possible to perform interfusion of different metals for the synthesis of ultrafine-grained and nanocrystalline materials with heterogeneous structure that determines their unique set of properties. Primarily, pure metal powders were used as starting components, and the method was called mechanical alloying. In recent years, a new approach has been developed, consisting in solid-phase connection of thin disks by means of shear deformation on Bridgman anvils, and the resulting composite materials were called hybrid composites. This paper presents the results of a study of hybrid composites based on Al processed by severe plastic deformation. Bulk hybrid composites Al-Cu, Al-Nb, Al-Mg, Al-Ti were fabricated in one step by shear deformation under high pressure. All obtained composites were monolithic with a heterogeneous structure consisting of a plastic aluminum matrix and harder inclusions of second metals and intermetallic particles. Varying the annealing temperature allows processing composites with different fractions of intermetallic particles. Analysis of microstructure, phase composition and properties has led to several unusual results. Using the Al-Cu composite as an example, a significant decrease in the activation energy for the growth of intermetallic particles during annealing was shown. In Al-Nb composite, it was revealed that the formation of a small amount of the intermetallic phase Al3Nb occurs at room temperature, while the equilibrium temperature of formation of this phase is above 600°C. Analysis of the tensile properties of Al-Cu composites showed a significant increase in the strength compared to the initial components. The results obtained are discussed and explained in terms of the contribution of various factors to the strengthening and softening of the composite material.