Creep and Superplasticity: Evolution and Rationalization

Abstract

Detailed studies on the creep behavior of materials are of scientific and practical significance. From a scientific point of view, data obtained from such studies are critical to the characterization of creep behavior in terms of deformation mechanisms. From a practical point of view, information inferred from such studies is useful because of its relevance to many design considerations. Over the past several decades, much progress has been made in rationalizing the creep behavior of metals and solid‐solution alloys. Such progress is extended to understanding the creep behavior of new classes of materials such as powder metallurgy (PM) Al alloys, discontinuous SiC composites, superplastic alloys, and high‐entropy alloys (HEAs). Progress in micrograin superplasticity (1 μm < d < 10 μm, where d is the grain size) has been applied to the emergence of high strain rate (HSR) superplasticity using ultrafine‐grained alloys (0.3 μm < d < 1 μm). The concept of creep is utilized to develop a deformation mechanism for nanocrystalline (nc) materials (d < 100 nm). Using the details of this mechanism, it is possible (1) to explain why the behavior of nc material is not superplastic and 2) to predict a transition from superplastic behavior to nc behavior.

Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy

“…According to the constitutive equation for superplasticity, a decrease in grain size is essential to achieve superplasticity at a high-strain rate 4,5,9,10 . Besides, Grain Boundary Sliding (GBS), the predominant deformation mechanism found in superplastic behavior, is predominantly observed in materials with small grains and high-angle grain boundaries 11,12 . More importantly, retention of Ultra-Fine Grains (UFGs) or nanoscale grains without significant grain growth at elevated temperatures is essential to accommodate GBS and GBS-induced cavitation through diffusion or dislocation motion 11,13,14 .…”

“…Besides, Grain Boundary Sliding (GBS), the predominant deformation mechanism found in superplastic behavior, is predominantly observed in materials with small grains and high-angle grain boundaries 11,12 . More importantly, retention of Ultra-Fine Grains (UFGs) or nanoscale grains without significant grain growth at elevated temperatures is essential to accommodate GBS and GBS-induced cavitation through diffusion or dislocation motion 11,13,14 . The representative CoCrFeMnNi HEA with a single Face-Centered Cubic (FCC) structure exhibited a reasonable superplastic elongation of 570% at elevated temperature 15 .…”

Recent Progress in Polyhydroxyalkanoates‐Based Copolymers for Biomedical Applications

“…Poly( -caprolactone)/PHB copolymer: Poly( -caprolactone) (PCL) has a high degree of crystallinity, a slow rate of degradation, and significant viscoelastic and rheological properties. [45] It is often utilized for a biodegradable polymer plasticizer as a result of its linear structure. It has been found that due to the presence of the segment PCL, the fracture growth rate, ductility, and mechanical processability of the composite can be significantly improved, and overall strengthening and toughening can be achieved.…”

Friction stir processing to improve grain refinement and superplasticity of Al-Mg-Mn-Cr alloy

“…Grain boundary sliding is the key superplastic deformation mechanism that accommodated by dislocation and diffusional creep, and grain rotation [1]- [5] . Thus, for a good superplastic properties fine-grained structure and movable high angle grain boundaries are required [6]- [10] . Grain refinement improves superplasticity, strain rates and elongations increase that favor formability [11]- [13] .…”