Novel Co 20 Cr 15 Fe 26 Mn 17 Ni 22 ultra-fine grained high-entropy alloy

International audienceIn a non-equiatomic HEA from CoCrFeMnNi family, so-called A3S® alloy (austenitic superstainless steel), exceptional mechanical properties are observed. High yield strength (800 MPa) associated with significant elongation to fracture (35 %) and a stable austenitic paramagnetic structure (down to LN2 temperature) may be obtained in hot forged materials. Mechanical resistance (YS) of A3S is at least 200 MPa higher than that measured in equiatomic alloy (EA) of the same family. These properties come from a nanostructure, easily formed in the material after classical hot thermomechanical treatment (forging). Yet, mechanical resistance of A3S decreases strongly after a post-forging high temperature annealing: in this state, identical behaviors of A3S and EA are noticed. Effects of thermal conditions of forging and recrystallization annealing have been investigated in A3S. Only slight effect of temperature of forging (between 900 and 1100°C) has been shown. Surprising effects of recrystallization annealing have been found. Low temperature (up to 600°C for 48h) treatment leads to recrystallization with formation of fine (1 µm) grains. At higher temperatures (700-1100°C), recrystallization is blocked: only recovery followed by grain growth and formation of numerous twins is observed. Moreover, in this state, very high density of dislocations is conserved: they present ordered configurations with alignments in {111} planes. Formation of twins has major effect on mechanical behavior of both A3S and EA. Their absence stabilizes nanostructures and leads to high YS values while decrease of YS is accompanied by twins presence. Relative difficulty to form these defects in A3S (as compared to EA) is explained by high value of stacking fault energy, evaluated from TEM measurements of dislocations dissociation. Moreover, strong dependence of SFE on temperature has been shown: its lower value at high temperatures is in agreement with numerous twins observed

Recognition and support of children with speech, language and communication needs :

PhD ThesisThe thesis considers how early years and primary teachers support children with speech, language and communication needs and how mentors might then support student primary teachers in advancing their understanding of language development. The study discusses how, in the process, teachers might draw on and interact with their own knowledge, the constructed reality of their work place and the wider imperatives that shape their day-to-day practice. These three interconnecting themes of knowledge, policy and practice are examined by drawing on a variety of research methods including interview, questionnaire and desk-based research. The thesis proposes that the role of the teacher as a communicator needs to be placed much more in the foreground and is the central skill to be fostered as part of the very complex and demanding position held. Initial training and ongoing continuous professional learning should promote teachers’ identification and advancement of their own communication skills. Prioritising these skills is crucial so that teachers can first recognise and then support the communication development of pupils with speech, language and communication needs, and the elaboration of these skills in all pupils. The accompanying commentary uses two vehicles to reflect on the body of work presented: a structured analytic approach to analyse the papers presented and autoethnographic interviews to contextualise the author’s research journey as a teacher-educator whose professional background is speech and language therapy and teaching

Development of Photodegradable Polymeric Materials for Sustainable Composite Resins and Adhesives

This thesis will discuss the synthesis of photodegradable materials for use as composite resins and adhesives, where debonding or degradation can be triggered by irradiation with ultraviolet (UV) light. An ortho-nitrobenzyl (o-NB) containing diol was synthesised and reacted with phenyl isocyanate to form a urethane. Cleavage of the urethane linkage was observed after UV irradiation