title: Mechanical properties and fracture behaviour of nanostructured and ultrafine structured TiAl Alloys synthesised by mechanical milling of powders and hot isostatic pressing

authors: Zhang, Deliang

subjects: fracture behaviour

abstract: Bulk nanostructured (grain sizes in the range of 50-200nm) and ultrafine structured (grain sizes in the range of 100-500nm) γ-TiAl based alloys with compositions Ti-47Al (in at%) and Ti–45Al–2Cr–2Nb–1B–0.5Ta (in at%), respectively, have been produced using a combination of high energy mechanical milling of mixtures of elemental powders and hot isostatic pressing at 800 and 1000oC respectively, and the microstructures of the samples have been characterised. At room temperature, the HIPed samples fractured prematurely at tensile stresses in the range of 200-300MPa and showed no ductility, very likely due to the relative high oxygen content (0.6wt%) in the samples and very low tolerance of TiAl based alloys on dissolved oxygen. At 800oC, the HIPed samples showed a yield strength in the range of 55-70MPa, a tensile strength in the range of 60-80MPa, a large amount of elongation to fracturing around 100% and clear strain softening. Examination of the fractured tensile test specimens at room temperature and 800oC showed that the level of the consolidation was fairly high, but the HIPed samples do contain a small fraction of interparticle boundaries with weak atomic bonding. The fracture of the HIPed samples in tensile testing at room temperature and 800oC, respectively, is predominately intergranular, and the large amount of plastic deformation prior to fracture at 800oC is achieved mainly through grain boundary sliding in conjunction with dislocation gliding, in agreement with the deformation mechanisms of nanostructured and ultrafine structured alloys generally agreed by researchers.

text: Mechanical properties and fracture behaviour of nanostructured and ultrafine structured TiAl Alloys synthesised by mechanical milling of powders and hot isostatic pressing Bulk nanostructured (grain sizes in the range of 50-200nm) and ultrafine structured (grain sizes in the range of 100-500nm) γ-TiAl based alloys with compositions Ti-47Al (in at%) and Ti–45Al–2Cr–2Nb–1B–0.5Ta (in at%), respectively, have been produced using a combination of high energy mechanical milling of mixtures of elemental powders and hot isostatic pressing at 800 and 1000oC respectively, and the microstructures of the samples have been characterised. At room temperature, the HIPed samples fractured prematurely at tensile stresses in the range of 200-300MPa and showed no ductility, very likely due to the relative high oxygen content (0.6wt%) in the samples and very low tolerance of TiAl based alloys on dissolved oxygen. At 800oC, the HIPed samples showed a yield strength in the range of 55-70MPa, a tensile strength in the range of 60-80MPa, a large amount of elongation to fracturing around 100% and clear strain softening. Examination of the fractured tensile test specimens at room temperature and 800oC showed that the level of the consolidation was fairly high, but the HIPed samples do contain a small fraction of interparticle boundaries with weak atomic bonding. The fracture of the HIPed samples in tensile testing at room temperature and 800oC, respectively, is predominately intergranular, and the large amount of plastic deformation prior to fracture at 800oC is achieved mainly through grain boundary sliding in conjunction with dislocation gliding, in agreement with the deformation mechanisms of nanostructured and ultrafine structured alloys generally agreed by researchers.

year: 2011

title: Towards an integrated refinement environment for formal program development

authors: Reeves, Steve

subjects: computer science

abstract: One of the main hurdles to the general adoption of formal program development techniques is a lack of tools to support their use in combination with more traditional development techniques. This paper describes an integrated environment for software development which embodies the aim of formal program development. Multiple levels of refinement of each specification are supported, with associated proof obligations, each of which can be viewed at various levels of detail throughout the development process. All of these formal views are kept consistent with each other and with more traditional design and implementation views. This allows software developers to specify, design, refine, prove, implement and document their software within a single integrated environment.

text: Towards an integrated refinement environment for formal program development One of the main hurdles to the general adoption of formal program development techniques is a lack of tools to support their use in combination with more traditional development techniques. This paper describes an integrated environment for software development which embodies the aim of formal program development. Multiple levels of refinement of each specification are supported, with associated proof obligations, each of which can be viewed at various levels of detail throughout the development process. All of these formal views are kept consistent with each other and with more traditional design and implementation views. This allows software developers to specify, design, refine, prove, implement and document their software within a single integrated environment.

year: 1995-08

title: Ko te Korokoro o te Parata: Ko tātou tonu

authors: Higgins, Rawinia

subjects: Whakaora reo

abstract: I roto i ngā kaupapa whakaora i te reo Māori kei te waipukehia tātou e te reo Pākehā. Ahakoa he aha te kaupapa kei te mate tonu te reo Māori, ā kāore anō tātou kia kite kei hea te ara tika hei karo atu i te korokoro o te parata. Kāore hoki tātou e titiro me pēhea e whakarekareka ai te reo ki te huhua o ngā Māori, tuatahi; tuarua ki te motu whānui. Ko te āhua nei ko tātou tonu kei te patu i tō tātou reo. He tere nō tātou ki te whakahāwea i ngā tūmomo kaupapa whakaora reo Māori. Kei ngā ngutu noa iho te mate nui ki te reo Māori. Ka ara mai he kaupapa whakaora reo, arā kē te tokomaha o ngā tāngata e patu ana i taua kaupapa. Ahakoa ko wai, kāore tētahi kaupapa e noho tapu ana. Katoa kei te tātāhia e tātou tonu. Nō reira, me aha? Me tuku kia mate? Me pēhea te patu i te korokoro o te parata mehemea ko tātou tonu taua taniwha?

text: Ko te Korokoro o te Parata: Ko tātou tonu I roto i ngā kaupapa whakaora i te reo Māori kei te waipukehia tātou e te reo Pākehā. Ahakoa he aha te kaupapa kei te mate tonu te reo Māori, ā kāore anō tātou kia kite kei hea te ara tika hei karo atu i te korokoro o te parata. Kāore hoki tātou e titiro me pēhea e whakarekareka ai te reo ki te huhua o ngā Māori, tuatahi; tuarua ki te motu whānui. Ko te āhua nei ko tātou tonu kei te patu i tō tātou reo. He tere nō tātou ki te whakahāwea i ngā tūmomo kaupapa whakaora reo Māori. Kei ngā ngutu noa iho te mate nui ki te reo Māori. Ka ara mai he kaupapa whakaora reo, arā kē te tokomaha o ngā tāngata e patu ana i taua kaupapa. Ahakoa ko wai, kāore tētahi kaupapa e noho tapu ana. Katoa kei te tātāhia e tātou tonu. Nō reira, me aha? Me tuku kia mate? Me pēhea te patu i te korokoro o te parata mehemea ko tātou tonu taua taniwha?

year: 2011-04