title: Microstructure and mechanical properties of aluminium based nanocomposites strengthened with alumina and silicon carbide

authors: Gazawi, Amro Abdul-Karim

abstract: Al-Al₂O₃ and Al-4wt%Cu-SiC metal matrix nanocomposites were studied because these materials have a potential for offering good ductility, high strength, and high electrical and/or thermal conductivity, which make them ideal for engineering applications such as aerospace and automobile components. In order to achieve these goals the reinforcement phase needs to be in a particulate form, and the size of the particles needs to be small.
Samples of aluminium based nanocomposites were produced with different volume fractions, ranging from 2.5-10 vol.% of alumina (Al₂O₃) and silicon carbide (SiC) nanoparticles. High energy mechanical milling (HEMM) with various milling times ranging from 6-12 hours was used to produce these samples. Optical microscopy, XRD, SEM, TEM and microindentation were used to characterize the milled powder and bulk samples. Bulk solid Al-(2.5-10) vol. % Al₂O₃ and Al-4wt%Cu-(2.5-10) vol. %SiC nanocomposites samples were produced using different powder consolidation techniques such as powder compact forging and powder compact extrusion.
The microstructure of the composite powder/balls/granules produced was studied in details to understand the morphology, macrostructure and microstructural evolution during the HEMM and with changing volume percent of the reinforcements in the matrix. The nano SiC and Al₂O₃ were imbedded into the aluminium matrix due to the high forces and strains affecting particle surfaces during milling and the very small size of the reinforcement relative to the size of the Al particles. The average microhardness was increased with increasing volume fraction of reinforcement within the matrix. HEMM was used to fabricate Ultra-Fine Grained (UFG) and nanostructured Al- (2.5-10) vol. %Al₂O₃ composites with a dispersion of nano alumina within the matrix and Al-4wt%Cu- (2.5-10) vol%SiC with two different sizes of SiC in the micro and nano ranges.
A UFG structure in the Al and Al-(2.5-10)vol.% Al₂O₃ nanocomposites can be synthesized by a combination of high energy mechanical milling and severe plastic deformation used to consolidate the powder compacts into nearly fully dense forged discs and extruded bars. No significant microscopic yielding was found in the Al-2.5 and 10 vol. %Al₂O₃ composites produced by powder compact forging. However, Al-5vol. % Al₂O₃ showed plastic yielding of 8%, and the best fracture strength of 343 MPa. No significant microscopic yielding was noticed for the Al- 10 vol. %Al₂O₃ composite produced by powder compact extrusion. Al-2.5vol. % Al₂O₃ showed plastic yielding of ~1% with the highest tensile strength of 364 MPa while Al-5vol. % Al₂O₃ showed plastic yielding of 8% with a yield strength of 318 MPa.
The average microhardness of the extruded bars for Al-4wt%Cu-(2.5-10)vol.% SiC increased from 104 HV to 205 HV with increasing the volume fraction of SiC nanoparticles from 2.5 to 10%. The ultimate tensile strength increased from 168 MPa to 400 MPa with increasing volume fraction of SiC nanoparticles from 2.5 to 5% while the ductility dropped from 6.8% to 1.2 %. The fracture strength of the Al-4wt%Cu-micro-SiC was increased from 225 MPa for Al-4wt%Cu-2.5vol. %SiC to 412 MPa for Al-4wt%Cu-10vol. % SiC. The Al-4wt%Cu-2.5vol. %SiC forged disc did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol. %SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

text: Microstructure and mechanical properties of aluminium based nanocomposites strengthened with alumina and silicon carbide Al-Al₂O₃ and Al-4wt%Cu-SiC metal matrix nanocomposites were studied because these materials have a potential for offering good ductility, high strength, and high electrical and/or thermal conductivity, which make them ideal for engineering applications such as aerospace and automobile components. In order to achieve these goals the reinforcement phase needs to be in a particulate form, and the size of the particles needs to be small.
Samples of aluminium based nanocomposites were produced with different volume fractions, ranging from 2.5-10 vol.% of alumina (Al₂O₃) and silicon carbide (SiC) nanoparticles. High energy mechanical milling (HEMM) with various milling times ranging from 6-12 hours was used to produce these samples. Optical microscopy, XRD, SEM, TEM and microindentation were used to characterize the milled powder and bulk samples. Bulk solid Al-(2.5-10) vol. % Al₂O₃ and Al-4wt%Cu-(2.5-10) vol. %SiC nanocomposites samples were produced using different powder consolidation techniques such as powder compact forging and powder compact extrusion.
The microstructure of the composite powder/balls/granules produced was studied in details to understand the morphology, macrostructure and microstructural evolution during the HEMM and with changing volume percent of the reinforcements in the matrix. The nano SiC and Al₂O₃ were imbedded into the aluminium matrix due to the high forces and strains affecting particle surfaces during milling and the very small size of the reinforcement relative to the size of the Al particles. The average microhardness was increased with increasing volume fraction of reinforcement within the matrix. HEMM was used to fabricate Ultra-Fine Grained (UFG) and nanostructured Al- (2.5-10) vol. %Al₂O₃ composites with a dispersion of nano alumina within the matrix and Al-4wt%Cu- (2.5-10) vol%SiC with two different sizes of SiC in the micro and nano ranges.
A UFG structure in the Al and Al-(2.5-10)vol.% Al₂O₃ nanocomposites can be synthesized by a combination of high energy mechanical milling and severe plastic deformation used to consolidate the powder compacts into nearly fully dense forged discs and extruded bars. No significant microscopic yielding was found in the Al-2.5 and 10 vol. %Al₂O₃ composites produced by powder compact forging. However, Al-5vol. % Al₂O₃ showed plastic yielding of 8%, and the best fracture strength of 343 MPa. No significant microscopic yielding was noticed for the Al- 10 vol. %Al₂O₃ composite produced by powder compact extrusion. Al-2.5vol. % Al₂O₃ showed plastic yielding of ~1% with the highest tensile strength of 364 MPa while Al-5vol. % Al₂O₃ showed plastic yielding of 8% with a yield strength of 318 MPa.
The average microhardness of the extruded bars for Al-4wt%Cu-(2.5-10)vol.% SiC increased from 104 HV to 205 HV with increasing the volume fraction of SiC nanoparticles from 2.5 to 10%. The ultimate tensile strength increased from 168 MPa to 400 MPa with increasing volume fraction of SiC nanoparticles from 2.5 to 5% while the ductility dropped from 6.8% to 1.2 %. The fracture strength of the Al-4wt%Cu-micro-SiC was increased from 225 MPa for Al-4wt%Cu-2.5vol. %SiC to 412 MPa for Al-4wt%Cu-10vol. % SiC. The Al-4wt%Cu-2.5vol. %SiC forged disc did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol. %SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

year: 2014

title: Korean migrants' experiences and attitudes towards mental illness and mental health services in New Zealand

authors: Oh, Leah Minkyung

subjects: Korean

abstract: The process of migration is known to cause significant psychological distress. Korean migrants living in New Zealand are the focus of this study as the term “Asian” has been identified as over-simplyfying the diversity that exists across Asian groups. Furthermore, research in other Western countries on Korean migrants show that they underutilise mental health services when compared to other Asian groups. Semi-structured interviews were conducted with ten members from the local Korean community which explored their experiences and attitudes towards mental illness and mental health services in New Zealand. Through thematic analysis common themes and patterned responses were identified. Some identified themes were: Cultural barriers, language barriers and lack of information on mental health and mental health services. The most influential factor was found to be Korean cultural values being in conflict with the general understanding of mental illness and mental health services in New Zealand. The implications of this research will be to assist Korean migrants to access mental health services in times of need.

text: Korean migrants' experiences and attitudes towards mental illness and mental health services in New Zealand The process of migration is known to cause significant psychological distress. Korean migrants living in New Zealand are the focus of this study as the term “Asian” has been identified as over-simplyfying the diversity that exists across Asian groups. Furthermore, research in other Western countries on Korean migrants show that they underutilise mental health services when compared to other Asian groups. Semi-structured interviews were conducted with ten members from the local Korean community which explored their experiences and attitudes towards mental illness and mental health services in New Zealand. Through thematic analysis common themes and patterned responses were identified. Some identified themes were: Cultural barriers, language barriers and lack of information on mental health and mental health services. The most influential factor was found to be Korean cultural values being in conflict with the general understanding of mental illness and mental health services in New Zealand. The implications of this research will be to assist Korean migrants to access mental health services in times of need.

year: 2014

title: Rewi Mokena: youngest son of Mokena Hou

authors: Hart, Philip

abstract: The youngest child of Mokena Hou, Rewi Mokena moved from place to place when young, finally settling permanently at Te Aroha. Having received some education, he was fluent in English. Like the typical rangatira of the time, he acquired interests in several blocks of land, obtained income from these in the short term, but because of financial difficulties was brought before the court several times. 
His involvement in gold mining started in a small way in 1875. Five years later, he would assist Hone Werahiko to prospect Te Aroha – and to fend off inquisitive Pakeha. He invested in claims in all of the three areas where gold was found.
By the twentieth century, Rewi was the most important rangatira at Te Aroha, and had wider influence, assisting the King Movement to seek redress for lost land. From a young age he participated in Pakeha society, notably as a rugby player, and became a prominent Mormon. His complicated private life, including bigamy and a wife’s attempted suicide because of his adultery, did not lower his high standing in Maori society nor damage his popularity with Pakeha.

text: Rewi Mokena: youngest son of Mokena Hou The youngest child of Mokena Hou, Rewi Mokena moved from place to place when young, finally settling permanently at Te Aroha. Having received some education, he was fluent in English. Like the typical rangatira of the time, he acquired interests in several blocks of land, obtained income from these in the short term, but because of financial difficulties was brought before the court several times. 
His involvement in gold mining started in a small way in 1875. Five years later, he would assist Hone Werahiko to prospect Te Aroha – and to fend off inquisitive Pakeha. He invested in claims in all of the three areas where gold was found.
By the twentieth century, Rewi was the most important rangatira at Te Aroha, and had wider influence, assisting the King Movement to seek redress for lost land. From a young age he participated in Pakeha society, notably as a rugby player, and became a prominent Mormon. His complicated private life, including bigamy and a wife’s attempted suicide because of his adultery, did not lower his high standing in Maori society nor damage his popularity with Pakeha.

year: 2016