title: Tribological properties of thermally sprayed TiAl-Al₂O₃ composite coating

authors: Salman, Asma Siddiq

subjects: engineering

abstract: The use of thermal spray coatings provides protection to the surfaces operating in severe environments. The main goal of the current work is to investigate the possibility of using a high velocity oxy fuel (HVOF) thermally sprayed wear resistant TiAl/Al2O3 coating on tool steel (H13) which is used for making dies for aluminium high pressure die casting. A feedstock of TiAl/Al2O3 composite powder was produced from a mixture of Al and TiO2 powders by high energy mechanical milling, followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxy-fuel (HVOF) technique onto H13 steel substrates to produce a composite coating. The present study describes and compares the tribological properties such as friction and sliding wear rate of the coating both at room and high temperature (700°C). The results showed that the composite coating has lower wear rate at high temperature (700°C) than the uncoated H13 sample. At Room temperature without using lubricant there is no much significant difference between the wear rate of the coated and uncoated samples. The experimental results showed that the composite coating has great potential for high temperature application due to its lower wear rate at high temperature in comparison with the uncoated sample at the same temperature. The composite coating was characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses the wear resistance performance of the coatings at room and high temperatures.

text: Tribological properties of thermally sprayed TiAl-Al₂O₃ composite coating The use of thermal spray coatings provides protection to the surfaces operating in severe environments. The main goal of the current work is to investigate the possibility of using a high velocity oxy fuel (HVOF) thermally sprayed wear resistant TiAl/Al2O3 coating on tool steel (H13) which is used for making dies for aluminium high pressure die casting. A feedstock of TiAl/Al2O3 composite powder was produced from a mixture of Al and TiO2 powders by high energy mechanical milling, followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxy-fuel (HVOF) technique onto H13 steel substrates to produce a composite coating. The present study describes and compares the tribological properties such as friction and sliding wear rate of the coating both at room and high temperature (700°C). The results showed that the composite coating has lower wear rate at high temperature (700°C) than the uncoated H13 sample. At Room temperature without using lubricant there is no much significant difference between the wear rate of the coated and uncoated samples. The experimental results showed that the composite coating has great potential for high temperature application due to its lower wear rate at high temperature in comparison with the uncoated sample at the same temperature. The composite coating was characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses the wear resistance performance of the coatings at room and high temperatures.

year: 2009

title: Characterisation and modelling of loudspeaker cone resonance

authors: Taberner, Andrew James

abstract: Loudspeaker cone resonance (“cone break-up”) is a fundamental cause of ripple in the electrical impedance and sound pressure responses of electrodynamic loudspeakers. In this thesis, the dependence of the characteristics of loudspeaker cone resonances on the material properties and thickness profile of the cone is extensively determined by creating 2D and 3D finite element models of a 6½-inch polypropylene-cone loudspeaker. Techniques for adjusting the resonant characteristics of loudspeaker cones by varying the material properties and thickness profile of the cone are explored and summarised.

The effect of cutting narrow slots through the surface of a loudspeaker cone is determined using 3D finite element modelling techniques, and cone slots are shown to have a large influence on the characteristics of the loudspeaker cone. A slotted loudspeaker cone with desirable impedance and sound pressure response characteristics is modelled and constructed. The measured response of the slotted loudspeaker is demonstrated to be a significant improvement over the characteristics of an unslotted loudspeaker.

text: Characterisation and modelling of loudspeaker cone resonance Loudspeaker cone resonance (“cone break-up”) is a fundamental cause of ripple in the electrical impedance and sound pressure responses of electrodynamic loudspeakers. In this thesis, the dependence of the characteristics of loudspeaker cone resonances on the material properties and thickness profile of the cone is extensively determined by creating 2D and 3D finite element models of a 6½-inch polypropylene-cone loudspeaker. Techniques for adjusting the resonant characteristics of loudspeaker cones by varying the material properties and thickness profile of the cone are explored and summarised.

The effect of cutting narrow slots through the surface of a loudspeaker cone is determined using 3D finite element modelling techniques, and cone slots are shown to have a large influence on the characteristics of the loudspeaker cone. A slotted loudspeaker cone with desirable impedance and sound pressure response characteristics is modelled and constructed. The measured response of the slotted loudspeaker is demonstrated to be a significant improvement over the characteristics of an unslotted loudspeaker.

year: 1998

title: Understanding ‘higher’ Māori fertility in a ‘low’ fertility context: Does cultural identity make a difference?

authors: Rarere, Moana

subjects: Maori fertility

abstract: The Māori fertility transition brought an end to decades of very high fertility rates, and a convergence towards long-term fertility levels similar to Pākehā/New Zealand European women. However, important differences endure. The Māori total fertility rate (TFR) remains above replacement level, and Māori women have children earlier and over a longer period. All of this has and still is occurring in a society that facilitates and favours low fertility and small family sizes. Using births data and cultural identity markers in the New Zealand Census, this paper explores the influence of culture as a contributing factor to higher fertility outcomes amongst Māori women in a low-fertility society.

text: Understanding ‘higher’ Māori fertility in a ‘low’ fertility context: Does cultural identity make a difference? The Māori fertility transition brought an end to decades of very high fertility rates, and a convergence towards long-term fertility levels similar to Pākehā/New Zealand European women. However, important differences endure. The Māori total fertility rate (TFR) remains above replacement level, and Māori women have children earlier and over a longer period. All of this has and still is occurring in a society that facilitates and favours low fertility and small family sizes. Using births data and cultural identity markers in the New Zealand Census, this paper explores the influence of culture as a contributing factor to higher fertility outcomes amongst Māori women in a low-fertility society.

year: 2018