Feedback, Iterative Processing and Academic Trust - Teacher Education Students\u27 Perceptions of Assessment Feedback

Abstract: Feedback and reflective processes play an important role in learning with both teachers and students required to play active roles. The importance of feedback processes and practices takes on an added dimension in the field of teacher education as the assessment and feedback processes are also professional practices that students themselves will be enacting in their professional roles. To this end, feedback provides opportunities for students to develop their own professional assessment literacy but also draws attention to the role of the teacher-education lecturer or assessor and the roles and relationships involved. This article reports on a research study which investigated teacher education students’ perceptions of assessment feedback and how they used it. Drawing upon a sociocultural framing, findings highlight the importance of different mediating means including rules, roles and relationships, the practice of iterative processing and the importance of ‘academic trust’

The role of ultrasonic treatment in refining the as-cast grain structure during the solidification of an Al-2Cu alloy

The effect of Ultrasonic Treatment (UT) over selected temperature ranges during cooling and solidification of an Al-2Cu alloy melt on the grain structure and cooling behaviour of the alloy has been investigated using a molybdenum sonotrode introduced without preheating. UT was applied over various temperature ranges before, during and after the nucleation of primary aluminium grains. It was found that ultrasonic grain refinement was achieved only when UT was applied from more than 20 °C above the liquidus temperature until below the liquidus temperature after nucleation has occurred. Applying UT from 40 °C or 60 °C above the liquidus to just above the liquidus brings the melt to a condition that favours nucleation, survival of the nucleated grains and their subsequent transport throughout the melt. Continuing to apply UT beyond the liquidus for a short time enhances both nucleation and convection thereby ensuring the formation of a fine, uniform equiaxed grain size throughout the casting. The lack of grain refinement when UT was applied from 20 °C above the liquidus temperature or from temperatures below the liquidus temperature is attributed to the formation of a strong solidified layer on the sonotrode which hinders the effective transmission of ultrasonic irradiation into the liquid metal. The application of a preheated sonotrode showed that formation of a solid layer can be prevented by preheating the sonotrode to 285 °C. Thus, an appropriate amount of superheat of the liquid metal or sufficient preheating of the sonotrode is necessary for ultrasonic grain refinement when a sonotrode is introduced into the melt

In Situ Synchrotron Radiation Study of TiH2-6Al-4V and Ti-6Al-4V: Accelerated Alloying and Phase Transformation, and Formation of an Oxygen-Enriched Ti4Fe2O Phase in TiH2-6Al-4V

In situ heating, synchrotron radiation X-ray diffraction has been used to study the alloying and phase transformation behavior of TiH2-6Al-4V and Ti-6Al-4V alloys. Accelerated alloying and phase transformation were observed in the powder compact of the TiH2-6Al-4V alloy subjected to a high heating rate. In addition, an oxygen-stabilized Ti4Fe2O phase, which is present as sub-micron or nanoscaled particles, has been identified in the TiH2-6Al-4V alloy. The implications of these experimental findings have been discussed in terms of alloying, improved densification and oxygen scavenging in titanium and titanium alloys

Response of aluminium honeycomb sandwich panels subjected to foam projectile impact - an experimental study

Aluminium honeycomb sandwich panels have potential applications as a protective mechanism that can be used to prevent failure of an important structure subjected to impact loading. Therefore it is important to fully understand the resistance of the sandwich panels subjected to impact loading conditions. The main objective of this work was to study the resistance of sandwich panels with different aluminium honeycomb cores, air sandwich panels (no core between the two face sheets) and monolithic plates of equivalent mass subjected to impact from foam projectiles. The deformation and the elastic spring-back of the honeycomb sandwich panels and the monolithic plates have been compared and discussed. The resistance of the panels and plates has been quantified by their back-face deflection with respect to the projectile impulse. Five different types of aluminium honeycombs have been used as the core material. The front-face sheet and the back-face sheet of the honeycomb sandwich panels are made of aluminium plate with 1 mm thickness. Cylindrical ALPORAS aluminium foams with a relative density between 9% and 11% are employed as the metal foam projectiles. They are fired at several hundred metres per second towards the centre of the panels and plates using a gas gun. The deflection histories of the back-face have been measured using a laser displacement sensor. From the deflection histories, the maximum deflection and the final deflection of the back-face can be distinguished. Deformation modes and failure modes of the individual component have been observed and classified into several categories. Moreover, the deflections of the honeycomb sandwich panels have been compared with deflections from air sandwich panels. It is found that the honeycomb sandwich panels outperform both the air sandwich panels and the monolithic plates within an impulse range of 2.25 kNsm(-2) similar to 4.70 kNsm(-2). Outside this operational range, the advantages associated with employing the honeycomb sandwich panels as a protective structure upon impact of foam projectiles diminishes. (C) 2014 Elsevier Ltd. All rights reserved

Grain refinement of wire arc additively manufactured titanium by the addition of silicon

This study demonstrates that silicon additions are effective in refining the microstructure of additive layer manufactured (ALM) titanium components. The addition of up to 0.75 wt% silicon to commercially pure titanium manufactured by wire arc ALM results in a significant reduction of the prior-β grain size. It is observed that silicon also reduces the width of the columnar grains and allows for the nucleation of some equiaxed grains through the development of constitutional supercooling and growth restriction. The grain size of the ALM components is compared to a casting process and it is found that the as-deposited microstructure produced during ALM exhibits larger average grain sizes. Using the Interdependence model for predicting grain size, it was determined that the population of nucleant particles that naturally occur in titanium, has comparable potency (i.e. ability to activate at a similar undercooling) regardless of the processing method, however, the ALM process contains fewer, sufficiently potent, nucleant particles than for the casting process due to the effect of subsequent cycles of remelting and heating

Tool life and wear mechanisms in laser assisted milling Ti-6Al-4V

Thermally assisted machining processes are gaining popularity among researchers and engineers as a method for improving the machinability of difficult-to-cut materials such as titanium. The process of artificially introducing heat to the cutting zone is reported to have many benefits; however, it remains unclear whether the process offers any tool life improvements during milling Ti–6Al–4V when compared to conventional milling processes. This paper compares the tool life during laser assisted milling, dry milling, milling with flood emulsion, milling with minimum quantity lubrication (MQL) and a hybrid laser+MQL process. It is found that conventional coolants offer superior tool life at the standard cutting speeds recommended by the tooling manufacturer, but at higher speeds the coolant deteriorates tool life due to thermal shock/fatigue. Despite this, laser assisted machining performed poorly and exacerbated thermally related tool wear mechanisms such as adhesion, diffusion and attrition. Hybrid laser+MQL substantially improved tool life by suppressing the thermal wear processes while also preventing thermal fatigue on the cutting tool

Development of a non intrusive heat transfer coefficient gauge and its application to high pressure die casting

This paper presents a design for a robust sensor suitable for determining heat flow and heat transfer coefficient in high pressure die casting.A design methodology for the sensor is presented, together with the conclusions of this analysis.A sensor has been manufactured to these principles and some typical results from its operation are introduced

Sensitivity of Ti-6Al-4V components to oxidation during out of chamber Wire + Arc Additive Manufacturing

Reactive metals including titanium readily oxidise and should be protected from the atmosphere during Additive Manufacturing processes. This work explores the sensitivity of Ti-6Al-4V components to oxidation contamination during out of chamber Wire + Arc Additive Manufacturing when using inert gas trailing shields. Five Ti-6Al-4V components were produced with varying argon trailing shield configurations that range from ideal inert gas shielding (resulting in no surface contamination) through to very poor inert gas shielding that results in substantial surface oxidation. Despite significant changes in the degree of surface oxide contamination between each component, the overall increase in oxygen concentration in the bulk alloys was minimal and had negligible influence on the tensile strength and ductility

Grain refinement of an Al-2 wt%Cu Alloy by Al3Ti1B master alloy and ultrasonic treatment

Both inoculation by AlTiB master alloys and Ultrasonic Treatment (UT) are effective methods of refining the grain size of aluminium alloys. The present study investigates the influence of UT on the grain refinement of an Al-2 wt% Cu alloy with a range of Al3Ti1B master alloy additions. When the alloy contains the smallest amount of added master alloy, UT caused significant additional grain refinement compared with that provided by the master alloy only. However, the influence of UT on grain size reduces with increasing addition of the master alloy. Plotting the grain size data versus the inverse of the growth restriction factor (Q) reveals that the application of UT causes both an increase in the number of potentially active nuclei and a decrease in the size of the nucleation free zone due to a reduction in the temperature gradient throughout the melt. Both these factors promote the formation of a fine equiaxed grain structure

Porous Titanium Scaffolds Fabricated by Metal Injection Moulding for Biomedical Applications

Biocompatible titanium scaffolds with up to 40% interconnected porosity were manufactured through the metal injection moulding process and the space holder technique. The mechanical properties of the manufactured scaffold showed a high level of compatibility with those of the cortical human bone. Sintering at 1250 °C produced scaffolds with 36% porosity and more than 90% interconnected pores, a compressive yield stress of 220 MPa and a Young's modulus of 7.80 GPa, all suitable for bone tissue engineering. Increasing the sintering temperature to 1300 °C increased the Young's modulus to 22.0 GPa due to reduced porosity, while reducing the sintering temperature to 1150 °C lowered the yield stress to 120 MPa, indicative of insufficient sintering. Electrochemical studies revealed that samples sintered at 1150 °C have a higher corrosion rate compared with those at a sintering temperature of 1250 °C. Overall, it was concluded that sintering at 1250 °C yielded the most desirable results