D.G. Leo Prakash

2D Quantitative Characterization of Microstructural Inhomogeneities in the Pressure Die Cast AZ91 Magnesium Alloy

Abstract Inclusions, shrinkage pores and gas pores are the major processing defects of pressure die cast AZ91 magnesium alloy. These inhomogeneities influence the mechanical properties of the material. Hence, quantitative characterization of size and arrangement of inclusions, shrinkage and gas microporosity is expected to be useful to understand the processing-property-microstructure correlation. In the present work an image analysis procedure has been explained to separately quantify the above inhomogeneities. The important parameters of image processing like montage creation, magnification selection and shrinkage pore separation are explained. The inclusions, shrinkage and gas micropores were separated by the above procedure and size, nearest neighbor distance distributions of these inhomogeneities were obtained in order to characterize the material.

Influence of Sn on Deformation Mechanisms During Room Temperature Compression of Binary Zr–Sn Alloys

Role of Sn on the deformation mechanisms of Zr was investigated using in situ neutron diffraction and complementary electron microscopy techniques. Binary Zr-Sn alloys having fully recrystallized microstructure and typical rolling texture were subjected to in situ loading and diffraction experiments along the rolling direction of the sample. Significant twinning activity was observed and the twins were observed to be {101 ̅2}〈101 ̅1〉 type tensile twins. Critical stress for the twin nucleation and the extent of twinning were found to be strongly influenced by the Sn content. Critical plastic strain for the nucleation of twining, however, was observed to be weakly dependent on the Sn content. Results indicate significant plastic slip activity to be a necessary condition for the onset of twinning. http://mc04.manuscriptcentral.com/astm-stp STP: Selected Technical Papers

Influence of Quenchant Hydrodynamics and Boiling Phase Incipient Temperature Shifts on Residual Stress Formation

Quench heat treatments are used in metallurgical applications to alter material mechanical properties such as hardness and strength. Although these conventional heat treatments have been used for many decades, specific influences of material properties and heat transfer conditions during quenching are not very well understood. In particular, predictions based on steady-state boiling heat transfer coefficients disagree with observations, leading to the use of average uniform heat transfer coefficient applied over entire component surfaces as a rule of thumb, with adjustments made for particular processes and components. This paper investigates the effects of multiphase boiling heat transfer and transitional nucleate boiling regimes on the final residual stress states within components. The results of this study show that correct representation of heat transfer conditions provides significant improvements over the current quench modeling techniques, ultimately allowing production of engineering components with superior mechanical properties, reduced distortion, and well-controlled beneficial residual stress states.

The Effect of Aluminium on Deformation and Twinning in Alpha Titanium: The 45° Case

The deformation behaviour of binary Ti-Al model alloys has been observed in respect to nucleation, propagation and growth of twins, specifically the interaction of slip and {1 0 -1 2} tensile twins. The area fraction of twins increases by trend from Ti-0Al to Ti-4Al but significantly reduces to Ti-6Al. The lattice strain evolution during compression was measured using in-situ neutron diffraction and decreases from Ti-0Al to Ti-4Al but increases to Ti-6Al. The twin activity in hcp Ti behaves as expected from fcc materials until 4 wt.% Al concentration, but it is believed that short or long range ordering reduces the twin activity in Ti-6Al.

A study of residual elastic strain distribution in an AZ91 Mg alloy bar loaded in four point bending

This paper presents a study of the residual strain field within a high pressure die cast (HPDC) AZ91 Mg alloy bar subjected to four point bending. The technique employed for this purpose is high energy synchrotron X-ray diffraction. Strain scanning using polychromatic X-ray beam allows the collection of multiple peak diffraction patterns and monitoring of small peak shifts as a function of beam position. These shifts allow collective interpretation in terms of the equivalent macroscopic residual elastic strain. Residual elastic strain distributions were studied in the sections subjected to pure bending and also in sections of contact between the sample and the rollers. These experimental results are compared with the predictions from a finite element analysis of contact and deformation. Good agreement is found between the modelled and measured results. It is hoped that these results help improved understanding of complex deformation behaviour of thin-walled HPDC AZ91 components and provide useful background information for lifing assessment of such structures.

In Situ Observation on the Influence of ß Grain Growth on Texture Evolution during Phase Transformation in Ti-6A-4V

In the present study, in situ phase transformation experiments have been carried out using neutron diffraction to monitor the texture evolution during the α→ß→α phase transformation in Ti-6Al-4V with and without 0.4% yttrium additions. The aim of adding yttrium was to control ß grain growth above the transus ß by grain boundary pinning. In the present case, strengthening of the ß texture, occurring during ß grain coarsening resulted in strengthening of particular ß texture components, which increases the likelihood of α texture modification by selective growth of α variants on the common (110) ß grain boundaries into unoccupied large β grains.

Quantitative Characterization of Pore Arrangement in Pore Bands in Pressure Die Cast AZ91 Magnesium Alloy by Image Processing

Microporosity is the major processing defect in pressure die cast AZ91 magnesium alloy. There is a big difference in the arrangement of pores in different regions of the castings. The present work explains the pore arrangement in pore bands and other regions. Quantification and characterization of pores in pore bands is expected to be useful to understand the process-propertymicrostructure correlation. A computational microstructural (image) analyzing technique has been developed by a programming language to quantify and analyze the micropores in pore bands. The pore band regions and the rest were separated and quantified. In addition, image analyzing technique was used to measure the clustering tendency of porosity in pore bands and it was compared with other regions.