Temperature and strain-rate sensitivity parameters: Analysis of the deformed metal matrix composite A359/SiC/20p

Abstract

In hot deformation of metals, the choice of process parameters such as temperature, stress, strain, strain rate, microstructure evolution and plastic stability affects product quality in terms of final shape and mechanical properties. The constitutive relationships among deformation parameters, derived from data of mechanical tests, are used to model manufacturing processes and to produce behavior maps, which are a useful representation of the stress-temperature domains for certain deformation mechanisms. Frost and Ashby [1] analyzed in normalized stress vs. homologous-temperature maps the deformation mechanisms occurring in creep of metals. Raj studied fracture behavior in pure aluminum and dilute alloys, identifying in strain-rate vs temperature maps safe areas of restoration and dangerous areas, where products are liable to be damaged because of adiabatic heating, cavity formation at hard particles and wedge-crack nucleation at grain-boundary triple junctions [2]. Raj’s maps do not however describe the hot behavior of commercial alloys and complex materials like metal matrix composites, which may easily undergo plastic instabilities [3]. Processing maps, generated by combining power-dissipation and stability maps, are considered a useful tool to describe the flow, the fracture behavior and microstructure of complex materials [4]. They show the path of metal-microstructure evolution within stable and unstable regions under various combinations of applied-temperature (T ), strain (e) and strain rate (e) conditions. The approach is based on the dynamic material model, DMM, which assumes that during hot deformation the workpiece is an energy dissipator, through plastic work, by means of dynamic restoration and precipitation, non-homogeneous deformation, plastic instability and damage mechanisms such as cavitation and cracking [5]. The manner of dissipation is related to the values of flow-stress sensitivity to both temperature, s [6] and strain rate, m [7, 8]. The sensitivity parameters, Equations 1 and 2, and the criteria for workpiece plastic stability, Equations 3–6, are defined as follows [9]: