Peiman Shahbeigi Roodposhti

Microstructural approach to equal channel angular processing of commercially pure titanium—A review

Abstract A review on severe plastic deformation (SPD) technique of equal channel angular pressing (ECAP) process of commercially pure titanium (CP-Ti) alloys was presented with a major emphasize on the influence of ECAP parameters that include channel and curvature angles, processing route, temperature of operation, pressing speed, internal heating, number of pass through the die and back pressure. Various ECAP characteristics such as microstructure, strain inhomogeneity and mechanical properties are considered to achieve the maximum homogeneity, equilibrium grain refinement and mechanical improvement of CP-Ti. Investigations show that a pressing speed of 1–3 mm/s at 450 °C with route BC along with channel and curvature angles of 90°and 20° respectively with backpressure can lead to the most homogeneous ultrafine microstructure.

Dislocation Density Evolution During Creep of AZ31 Mg Alloy: A Study by X-ray Diffraction Line Profile Analysis

X-ray diffraction line profile analysis technique was employed to investigate the dislocation density evolution during high temperature creep of Mg-3Al-1Zn alloy. The microstrains within the domain and dislocation density were calculated by the simplified Williamson–Hall and Williamson–Smallman methods. Further analysis on the possible dynamic recrystallization (DRX) and dynamic recovery (DRV) shows a relation between the number of dynamically recrystallized grains and the dislocation density. At constant temperature, higher stresses lead to more DRX and an enhancement on the dislocation density; whereas, at lower stresses the DRV is dominant leading to decrease in the dislocation density.

Effects of Microstructure and Processing Methods on Creep Behavior of AZ91 Magnesium Alloy

This review sheds light on the creep properties of AZ91 magnesium alloys with a major emphasis on the influence of microstructure on the creep resistance and underlying creep deformation mechanism based on stress exponent and activation energy. Effects of processing routes such as steel mold casting, die casting, and thixoforming are considered. Roles of a wide range of additional alloying elements such as Si, Sb, Bi, Ca, Sn, REs, and combined addition of them on the microstructure modification were investigated. The reaction between these elements and the Mg or Al in the matrix develops some thermally stable intermetallic phases which improves the creep resistance at elevated temperatures, however does not influence the creep mechanism.

A Review of the Influence of Production Methods and Intermetallic Phases on the Creep Properties of AZ91

A review on the creep properties of AZ91 magnesium alloys is presented with a major emphasis on the influence of production methods that include steel mold casting, die casting and Thixoforming. Various creep characteristics such as the stress exponent and activation energy along with their resistance to creep for the alloys produced via different methods are compared. Role of intermetallic phases resulting from various alloying additions such as Si, Sb, Bi, Ca and rare earth elements on different creep mechanisms (grain boundary sliding and dislocation glide/climb) are also evaluated.

Fracture Behavior and Grain Boundary Sliding During High-Temperature Low-Stress Deformation of AZ31 Magnesium Alloy

Low-stress high-temperature tensile-creep behavior of AZ31 Mg alloy was investigated to characterize microstructure evolution, uncover dominant creep mechanism and find a correlation with common creep models. The stress exponent, inverse grain size exponent and activation energy value were evaluated. Cavity nucleation from stress concentration sites, types of fracture surfaces and microstructural evidence of grain migrations were observed in crept samples that are indicative of Rachinger mechanism of grain boundary sliding (GBS). Experimental data reveal a reasonable correlation with Langdon’s model. Further analysis on fracture behavior of this alloy in a wider range of stresses show that they follow Monkman-Grant model in predicting the fracture time.

Creep Deformation Mechanisms and Related Microstucture Development of AZ31 Magnesium Alloy

Because of ever increasing demanded of Magnesium alloys in various industries, high temperature deformation of Mg-Al-Zn alloys (AZ31) at constant stress (i.e. creep) were studied at a wide range of stresses and temperatures to characterize underlying deformation mechanism and dynamic recrystallization (DRX) Various microstructures (e.g. grain growth & DRX) are noted during steady-state creep mechanisms such as grain boundary sliding (GBS), dislocation glide creep (DGC) and dislocation climb creep (DCC). Although a combination of DRX and grain growth is characteristic of low stacking fault energy materials like Mg alloys at elevated temperatures, observation reveals grain growth at low strain-rates (GBS region) along with dynamic recovery (DRV) mechanism. Scanning Electron Microscopic (SEM) characterization of the fracture surface reveals more inter-granular fracture for large grains (i.e. GBS region with DRV process) and more dimple shape fracture for small grains (i.e. DGC & DCC region with DRX).