Thermal and mechanical processes alter the microstructure of materials, which determines their mechanical properties. This makes reliable microstructural analysis important to the design and manufacture of components. However, the analysis of complex microstructures, such as Ti6Al4V, is difficult and typically requires expert materials scientists to manually identify and measure microstructural features. This process is often slow, labour intensive and suffers from poor repeatability. This paper overcomes these challenges by proposing a new set of automated techniques for 2D microstructural analysis. Digital image processing algorithms are developed to isolate individual microstructural features, such as grains and alpha lath colonies. A segmentation of the image is produced, where regions represent grains and colonies, from which morphological features such as; grain size, volume fraction of globular alpha grains and alpha colony size can be measured. The proposed measurement techniques are shown to obtain similar results to existing manual methods while drastically improving speed and repeatability. The benefits of the proposed approach when measuring complex microstructures are demonstrated by comparing it with existing analysis software. Using a few parameter changes, the proposed techniques are effective on a variety of microstructure types and both SEM and optical microscopy image

Severe plastic deformation (SPD) of titanium creates an ultrafine-grained (UFG) microstructure which results in significantly enhanced mechanical properties, including increasing the high cycle fatigue strength. This work addresses the challenge of maintaining the high level of properties as SPD processing techniques are evolved from methods suitable for producing laboratory scale samples to methods suitable for commercial scale production of titanium semi-products. Various ways to optimize the strength and fatigue endurance limit in longlength Grade 4 titanium rod processed by equal channel angular pressing (ECAP) with subsequent thermal mechanical treatments are considered in this paper. Lowtemperature annealing of rods is found to increase the fatigue limit, simultaneously enhancing UFG titanium strength and ductility. The UFG structure in titanium provides an optimum combination of properties when its microstructure includes mostly equiaxed grains with highangle boundaries, the volume fraction of which is no less than 50%.

This work is related to the enhancement of the fatigue properties in ultrafine-grained Ti alloys produced by severe plastic deformation techniques. To process commercially pure Ti Grade 4 and Ti-6Al-4V alloys, combined severe plastic deformation techniques that include equal channel angular pressing and additional thermal and deformation treatments were used. As a result we could produce ultrafine-grained Ti materials with a similar grain size of less than 300–400 nm but different in their shape and grain boundary structure (both low- and high-angle, equilibrium and non-equilibrium grain boundaries). It is shown that tailoring grain boundaries by severe plastic deformation techniques makes it possible to considerably enhance the strength of Ti materials while preserving high ductility. In turn, ultrafine-grained materials with enhanced strength and ductility demonstrate superior fatigue endurance and life.

No abstract

Incremental equal channel angular pressing (I-ECAP) is a severe plastic deformation process used to refine grain size of metals, which allows processing very long billets. As described in the current article, an AZ31B magnesium alloy was processed for the first time by three different routes of I-ECAP, namely, A, B C , and C, at 523 K (250°C). The structure of the material was homogenized and refined to~5 microns of the average grain size, irrespective of the route used. Mechanical properties of the I-ECAPed samples in tension and compression were investigated. Strong influence of the processing route on yield and fracture behavior of the material was established. It was found that texture controls the mechanical properties of AZ31B magnesium alloy subjected to I-ECAP. SEM and OM techniques were used to obtain microstructural images of the I-ECAPed samples subjected to tension and compression. Increased ductility after I-ECAP was attributed to twinning suppression and facilitation of slip on basal plane. Shear bands were revealed in the samples processed by I-ECAP and subjected to tension. Tensioncompression yield stress asymmetry in the samples tested along extrusion direction was suppressed in the material processed by routes B C and C. This effect was attributed to textural development and microstructural homogenization. Twinning activities in fine-and coarsegrained samples have also been studied.

No abstract

Abstract. An AZ31B wrought magnesium alloy was processed by incremental equal channel angular pressing (I-ECAP) using routes A and B C . Despite the fact that the measured grain size for both routes was very similar, the mechanical properties were different. Tensile strength was improved using route A comparing to route B C , without ductility loss, while tension-compression anisotropy observed for route A was significantly suppressed when using route B C . Moreover, billet shape evolution resulting from subsequent passes of I-ECAP was studied. Significant distortion after processing using route B C and no occurrence of such effect for route A were observed. Results of a finite element analysis showed that nonuniform strain rate sensitivity might be responsible for different billet shapes. The conclusion is drawn that processing route has a strong influence on the billet shape and mechanical properties when processing magnesium alloys by I-ECAP.

Abstract. Titanium is a material that exhibits many desirable properties including a very high strength to weight ratio and corrosive resistance. However, the specific properties of any components depend upon the microstructure of the material, which varies by the manufacturing process. This means it is often necessary to analyse the microstructure when designing new processes or performing quality assurance on manufactured parts. For Ti6Al4V, grain size analysis is typically performed manually by expert material scientists as the complicated microstructure of the material means that, to the authors knowledge, no existing software reliably identifies the grain boundaries. This manual process is time consuming and offers low repeatability due to human error and subjectivity. In this paper, we propose a new, automated method to segment microstructural images of a Ti6Al4V alloy into its constituent grains and produce measurements. The results of applying this technique are evaluated by comparing the measurements obtained by different analysis methods. By using measurements from a complete manual segmentation as a benchmark we explore the reliability of the current manual estimations of grain size and contrast this with improvements offered by our approach.